National Instruments Computer Hardware 1141 User Manual

TM  
SCXI  
SCXI-1141/1142/1143 User Manual  
SCXI-1141/1142/1143 User Manual  
May 2007  
371748E-01  
 
   
Important Information  
Warranty  
The SCXI-1141, SCXI-1142, and SCXI-1143 modules are warranted against defects in materials and workmanship for a period of one year  
from the date of shipment, as evidenced by receipts or other documentation. National Instruments will, at its option, repair or replace equipment  
that proves to be defective during the warranty period. This warranty includes parts and labor.  
The media on which you receive National Instruments software are warranted not to fail to execute programming instructions, due to defects in  
materials and workmanship, for a period of 90 days from date of shipment, as evidenced by receipts or other documentation. National Instruments  
will, at its option, repair or replace software media that do not execute programming instructions if National Instruments receives notice of such defects  
during the warranty period. National Instruments does not warrant that the operation of the software shall be uninterrupted or error free.  
A Return Material Authorization (RMA) number must be obtained from the factory and clearly marked on the outside of the package before any  
equipment will be accepted for warranty work. National Instruments will pay the shipping costs of returning to the owner parts which are covered by  
warranty.  
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the event that technical or typographical errors exist, National Instruments reserves the right to make changes to subsequent editions of this document  
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For patents covering National Instruments products, refer to the appropriate location: Help»Patents in your software, the patents.txtfile  
on your CD, or ni.com/patents.  
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Conventions  
The following conventions are used in this manual:  
<>  
Angle brackets that contain numbers separated by an ellipsis represent  
a range of values associated with a bit or signal name—for example,  
AO <3..0>.  
»
The » symbol leads you through nested menu items and dialog box options  
to a final action. The sequence File»Page Setup»Options directs you to  
pull down the File menu, select the Page Setup item, and select Options  
from the last dialog box.  
This icon denotes a note, which alerts you to important information.  
This icon denotes a caution, which advises you of precautions to take to  
avoid injury, data loss, or a system crash. When this symbol is marked on a  
product, refer to the Read Me First: Safety and Radio-Frequency  
Interference document for information about precautions to take.  
When symbol is marked on a product, it denotes a warning advising you to  
take precautions to avoid electrical shock.  
When symbol is marked on a product, it denotes a component that may be  
hot. Touching this component may result in bodily injury.  
bold  
Bold text denotes items that you must select or click in the software, such  
as menu items and dialog box options. Bold text also denotes parameter  
names.  
italic  
Italic text denotes variables, emphasis, a cross-reference, or an introduction  
to a key concept. Italic text also denotes text that is a placeholder for a word  
or value that you must supply.  
monospace  
Text in this font denotes text or characters that you should enter from the  
keyboard, sections of code, programming examples, and syntax examples.  
This font is also used for the proper names of disk drives, paths, directories,  
programs, subprograms, subroutines, device names, functions, operations,  
variables, filenames, and extensions.  
 
 
Chapter 1  
a PXI/SCXI Combination Chassis................................................................1-4  
Installing the Terminal Block ........................................................................................1-4  
Installing SCXI Chassis and Modules in Software .........................................1-5  
Chapter 2  
Front Connector Signal Descriptions ..............................................................2-3  
Analog Input Channels......................................................................2-3  
Rear Signal Connector...................................................................................................2-7  
Chapter 3  
Auto-Zero..........................................................................................3-2  
Configurable Settings in MAX......................................................................................3-2  
NI-DAQmx......................................................................................................3-3  
Creating a Global Channel or Task...................................................3-3  
Verifying the Signal.......................................................................................................3-4  
Verifying the Signal in NI-DAQmx Using a Task or Global Channel ...........3-4  
© National Instruments Corporation  
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SCXI-1141/1142/1143 User Manual  
 
Contents  
Chapter 4  
Using the External Clock Input....................................................................... 4-14  
DC-Correction Circuitry and Overload Recovery .......................................... 4-15  
Rear Connector Analog Outputs ................................................................................... 4-16  
Chapter 5  
Using a NI-DAQmx Channel Property Node in LabVIEW............. 5-9  
Specifying Channel Strings in NI-DAQmx .................................................... 5-10  
Programmable NI-DAQmx Properties ............................................. 5-12  
Calibration..................................................................................................................... 5-13  
External Calibration ........................................................................................ 5-13  
Specifications  
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Contents  
Appendix B  
Common Questions  
Glossary  
Index  
Figures  
Figure 2-4.  
Figure 2-5.  
Ground Offset AC-Coupled Signal Connection....................................2-6  
Floating AC-Coupled Signal Connection..............................................2-6  
Figure 4-1.  
Figure 4-2.  
SCXI-1141/1142/1143 Module Block Diagram ...................................4-2  
Ideal and Real Lowpass Filter Transfer Function Characteristics ........4-5  
Module Filters .......................................................................................4-7  
Typical Passband Responses of the SCXI-1141/1142/1143 Module....4-8  
Figure 4-5.  
Figure 5-1.  
Typical Program Flowchart for Voltage Measurement Channels.........5-2  
Figure A-1. SCXI-1141/1142/1143 Dimensions ......................................................A-5  
Figure B-1. Removing the SCXI-1141/1142/1143 Module .....................................B-2  
© National Instruments Corporation  
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Contents  
Tables  
Table 1-1.  
Accessories Available for the SCXI-1141/1142/1143.......................... 1-4  
Table 2-1.  
Table 2-2.  
Front Signal Pin Assignments............................................................... 2-2  
Rear Signal Pin Assignments................................................................ 2-8  
Table 5-4.  
Table 5-5.  
Table 5-6.  
NI-DAQmx Current Measurement Properties...................................... 5-6  
Programming a Task in LabVIEW ...................................................... 5-8  
Table A-1.  
Table C-1.  
Settling Time with Respect to Cutoff Frequency ................................. A-3  
Digital SIgnals on the SCXI-1141/1142/1143...................................... C-2  
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1
About the SCXI-1141/1142/1143  
This chapter describes the SCXI-1141/1142/1143 module, and explains  
how to install and remove the hardware and software.  
The SCXI-1141/1142/1143 module has eight lowpass filters and  
eight differential-input amplifiers. The SCXI-1141 has elliptic filters;  
the SCXI-1142, Bessel filters; and the SCXI-1143, Butterworth filters.  
You can use the SCXI-1141/1142/1143 module for lowpass filtering and  
antialiasing applications as well as for general-purpose signal amplification  
and filtering. The SCXI-1141/1142/1143 module works with National  
Instruments E/M Series DAQ devices. You can use one DAQ device to  
control several SCXI-1141/1142/1143 modules, in combination with other  
SCXI modules in a chassis. Each SCXI-1141/1142/1143 module can  
multiplex its channels into a single channel of the DAQ device, although  
separate outputs are also available. You can multiplex the output of several  
SCXI-1141/1142/1143 modules into a single channel, thus greatly  
increasing the number of analog input signals that the DAQ device can  
digitize.  
The SCXI-1304 shielded terminal block has screw terminals for easily  
connecting signals to the SCXI-1141/1142/1143 module and is the terminal  
block recommended for use with this module.  
Refer to Appendix A, Specifications, for detailed SCXI-1141/1142/1143  
module specifications.  
© National Instruments Corporation  
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Chapter 1  
About the SCXI-1141/1142/1143  
What You Need to Get Started  
To set up and use the SCXI-1141/1142/1143 module, you need the  
following:  
Hardware  
SCXI-1141/1142/1143 module  
One of the following terminal blocks:  
SCXI-1304  
SCXI-1305  
An SCXI chassis or PXI/SCXI combination chassis  
One of the following:  
E/M Series DAQ device  
SCXI-1600  
A computer if using an SCXI chassis  
Cabling, cable adapter, and sensors as required for your  
application  
Software  
NI-DAQ  
One of the following software packages:  
LabVIEW  
Measurement Studio  
LabWindows/CVI™  
Documentation  
Read Me First: Safety and Radio-Frequency Interference  
DAQ Getting Started Guide  
SCXI Quick Start Guide  
SCXI-1141/1142/1143 User Manual  
Terminal block installation guide for your application  
Documentation for your software  
You can download NI documents from ni.com/manuals. To download  
the latest version of NI-DAQmx visit ni.comand click Drivers and  
Updates. In the Product Line drop-down menu locate Multifunction  
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Chapter 1  
About the SCXI-1141/1142/1143  
DAQ. Select the appropriate information for your application in the  
remaining drop-down menus and click Go.  
National Instruments Documentation  
The SCXI-1141/1142/1143 User Manual is one piece of the documentation  
set for data acquisition (DAQ) systems. You could have any of several  
types of manuals depending on the hardware and software in the system.  
Use the manuals you have as follows:  
SCXI chassis or PXI/SCXI combination chassis manual—Read this  
manual for maintenance information on the chassis and for installation  
instructions.  
The DAQ Getting Started Guide—This document has information on  
installing NI-DAQ and the E/M Series DAQ device. Install these  
before you install the SCXI module.  
The SCXI Quick Start Guide—This document contains a quick  
overview for setting up an SCXI chassis, installing SCXI modules and  
terminal blocks, and attaching sensors. It also describes setting up the  
SCXI system in MAX.  
The SCXI hardware user manuals—Read these manuals next  
for detailed information about signal connections and module  
configuration. They also explain, in greater detail, how the module  
works and contain application hints.  
Accessory installation guides or manuals—Read the terminal block  
and cable assembly installation guides. They explain how to physically  
connect the relevant pieces of the system. Consult these guides when  
you are making the connections.  
The E/M Series DAQ device documentation—This documentation has  
detailed information about the E/M Series DAQ device that plugs into  
or is connected to the computer. Use this documentation for hardware  
installation and configuration instructions, specification information  
about the E/M Series DAQ device, and application hints.  
Software documentation—You may have both application software  
and NI-DAQ software documentation. NI application software  
includes LabVIEW, LabWindows/CVI, and Measurement Studio.  
After you set up the hardware system, use either your application  
software documentation or the NI-DAQ documentation to help you  
write your application. If you have a large, complex system, it is  
worthwhile to look through the software documentation before you  
configure the hardware.  
© National Instruments Corporation  
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Chapter 1  
About the SCXI-1141/1142/1143  
The following help file for software information:  
Start»Programs»National Instruments»NI-DAQ»  
NI-DAQmx Help  
Installing Application Software, NI-DAQmx, and the  
DAQ Device  
Refer to the DAQ Getting Started Guide packaged with the NI-DAQmx  
software to install your application software, NI-DAQmx driver software,  
and the E/M Series DAQ device to which you will connect the  
SCXI-1141/1142/1143. NI-DAQ 8.3 or later is recommended to configure  
and program the SCXI-1141/1142/1143 module.  
Note Refer to the Read Me First: Radio-Frequency Interference document before  
removing equipment covers or connecting or disconnecting any signal wires.  
Installing the SCXI-1141/1142/1143 into an SCXI Chassis or a PXI/SCXI  
Combination Chassis  
Refer to the SCXI Quick Start Guide to install the SCXI-1141/1142/1143  
module.  
Installing the Terminal Block  
Table 1-1 shows the supported SCXI-1141/1142/1143 terminal blocks.  
Refer to the SCXI Quick Start Guide and the terminal block installation  
guide for more information about the terminal block.  
Table 1-1. Accessories Available for the SCXI-1141/1142/1143  
Accessory  
Description  
SCXI-1304  
Screw terminal block—Mounts on the front of the SCXI-1141/1142/1143 module.  
It includes AC coupling circuitry and ground referencing through a 100 KΩ bias  
resistor on each channel.  
SCXI-1305  
BNC terminal block—Mounts on the front of the SCXI-1141/1142/1143 module.  
It is functionally equivalent to the SCXI-1304 terminal block.  
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Chapter 1  
About the SCXI-1141/1142/1143  
Verifying the SCXI-1141/1142/1143 Installation in  
Software  
Refer to the SCXI Quick Start Guide for information on verifying the SCXI  
installation.  
Installing SCXI Chassis and Modules in Software  
Refer to the SCXI Quick Start Guide for information on installing chassis  
and modules using NI-DAQmx in software.  
Troubleshooting the Self-Test Verification  
If the self-test verification did not verify the chassis configuration,  
complete the steps in this section to troubleshoot the SCXI configuration.  
Troubleshooting in NI-DAQmx  
If you get a Verify SCXI Chassis message box showing the SCXI  
chassis model number, Chassis ID: x, and one or more messages  
stating Slot Number: x Configuration has module: SCXI-XXXX  
or 1141/1142/1143, hardware in chassis is: Empty, take the  
following troubleshooting actions:  
Make sure the SCXI chassis is powered on.  
Make sure all SCXI modules are properly installed in the chassis.  
Refer to the SCXI Quick Start Guide for proper installation  
instructions.  
Make sure the cable between the SCXI chassis and E/M Series  
DAQ device is properly connected.  
Inspect the cable connectors for bent pins.  
Make sure you are using the correct NI cable assembly.  
Test the E/M Series DAQ device to verify it is working properly.  
Refer to the E/M Series DAQ device help file for more  
information.  
© National Instruments Corporation  
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Chapter 1  
About the SCXI-1141/1142/1143  
If you get a Verify SCXI Chassis message box showing the SCXI  
chassis model number, Chassis ID: x, and the message Slot  
Number: x Configuration has module: SCXI-XXXX or  
1141/1142/1143, hardware in chassis is: SCXI-YYYY,  
1141/1142/1143, or Empty, complete the following troubleshooting  
steps to correct the error.  
1. Expand NI-DAQmx Devices.  
2. Right-click the SCXI chassis and click Properties to load the  
chassis configurator.  
3. Under the Modules tab, ensure that the cabled module is listed in  
the correct slot.  
4. If the cabled module is not listed in the correct slot, complete the  
following troubleshooting steps:  
a. If the cabled module is not listed in the correct slot and the  
slot is empty, click the drop-down listbox next to the correct  
slot and select the cabled module. Configure the cabled  
module following the steps listed in the SCXI Quick Start  
Guide. Click OK.  
b. If another module is displayed where the cabled module  
should be, click the drop-down listbox next to the correct slot  
and select the cabled module. A message box opens asking  
you to confirm the module replacement. Click OK. Configure  
the cabled module following the steps listed in the SCXI  
Quick Start Guide. Click OK.  
If you have more than one kind of SCXI module in the SCXI chassis,  
ensure that you have the highest priority SCXI module cabled to the  
E/M Series DAQ device. Refer to the SCXI Quick Start Guide to find  
out which SCXI module in the chassis should be cabled to the  
E/M Series DAQ device.  
After checking the preceding items, return to the Troubleshooting the  
Self-Test Verification section and retest the SCXI chassis.  
If these measures do not successfully configure the SCXI system, contact  
NI. Refer to the Technical Support Information document for contact  
information.  
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2
Connecting Signals  
This chapter describes input and output signal connections to the  
SCXI-1141/1142/1143 module through the front and rear signal  
connectors.  
Caution Connections that exceed any of the maximum ratings of input or output signals  
on the SCXI-1141/1142/1143 module can damage the SCXI-1141/1142/1143 module, the  
SCXIbus, any connected DAQ device, and the computer with which the DAQ device is  
used. NI is not liable for any damage resulting from such signal connections.  
Front Connector  
Table 2-1 shows the pin assignments for the SCXI-1141/1142/1143  
module front connector.  
© National Instruments Corporation  
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Chapter 2  
Connecting Signals  
Table 2-1. Front Signal Pin Assignments  
Front Connector Diagram  
Pin Number  
Column A  
AI 0 +  
NC  
Column B  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
Column C  
AI 0 –  
NC  
32  
31  
30  
29  
28  
27  
26  
25  
24  
23  
22  
21  
20  
19  
18  
17  
16  
15  
14  
13  
12  
11  
10  
9
Column  
A
B
C
AI 1 +  
NC  
AI 1 –  
NC  
32  
31  
30  
29  
28  
27  
26  
25  
24  
23  
22  
21  
20  
19  
18  
17  
16  
15  
14  
13  
12  
11  
10  
9
A GND  
NC  
A GND  
NC  
AI 2 +  
NC  
AI 2 –  
NC  
AI 3 +  
NC  
AI 3 –  
NC  
A GND  
NC  
A GND  
NC  
AI 4 +  
NC  
AI 4 –  
NC  
AI 5 +  
NC  
AI 5 –  
NC  
A GND  
NC  
A GND  
NC  
AI 6 +  
NC  
AI 6 –  
NC  
AI 7 +  
NC  
AI 7 –  
NC  
NC  
NC  
8
7
NC  
NC  
6
8
RSVD  
NC  
RSVD  
NC  
5
7
4
6
RSVD  
NC  
RSVD  
NC  
3
5
2
1
4
RSVD  
NC  
EXT CLK  
NC  
NC means no connection.  
RSVD means reserved.  
2
D GND  
NC  
OUT CLK  
NC  
1
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Chapter 2  
Connecting Signals  
Front Connector Signal Descriptions  
Pins  
Signal Names  
Description  
A32, A30, A26, A24,  
A20, A18, A14, A12  
AI+<0..7+>  
Positive input channels—these pins connect to the  
noninverting inputs of the instrumentation amplifier  
of each channel.  
C32, C30, C26, C24,  
C20, C18, C14, C12  
AI–<0..7–>  
Negative input channels—these pins connect to the  
inverting inputs of the instrumentation amplifier of  
each channel.  
A28, A22, A16, C28,  
C22, C16  
A GND  
D GND  
Analog ground—these pins connect to the module  
analog ground.  
A2, C8  
Digital ground—these pins connect to the module  
digital ground.  
A8, A6, A4, C8  
C4  
RSVD  
Reserved—do not connect any signals to these pins.  
EXT CLK  
External clock—you can use this signal to set the  
filter cutoff frequency.  
C2  
OUT CLK  
Output clock—this signal has a frequency that is  
proportional to the cutoff frequency. You can use this  
signal to externally control the cutoff frequency.  
Note: All other pins are not connected.  
Analog Input Channels  
The SCXI-1141/1142/1143 module instrumentation amplifiers can reject  
any common-mode voltage within their common-mode input range caused  
by ground-potential differences between the signal source and the module.  
In addition, the amplifiers can reject common-mode noise pickup in the  
leads connecting the signal sources to the SCXI-1141/1142/1143 module.  
However, you should take care to minimize noise pickup. The  
common-mode rejection of the instrumentation amplifiers decreases  
significantly at high frequencies. The amplifiers do not reject  
normal-mode noise.  
The maximum differential input voltage range of the  
SCXI-1141/1142/1143 module instrumentation amplifiers is a function of  
the gain of the amplifiers, G, and is equal to 5 V/G. The common-mode  
input range of the SCXI-1141/1142/1143 module, however, is not a  
function of gain—the differential input amplifier rejects common-mode  
signals as long as the signal at both inputs is within 5 V of the module  
© National Instruments Corporation  
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Chapter 2  
Connecting Signals  
analog ground. The inputs are protected against maximum input voltages  
of up to 15 V powered off and 30 V powered on.  
Caution Exceeding the differential or common-mode input voltage limits distorts input  
signals. Exceeding the maximum common-mode input voltage rating can damage the  
SCXI-1141/1142/1143 module, the SCXIbus, and the DAQ device. NI is not liable for any  
damage resulting from such signal connections.  
All eight channels have fully differential inputs, so you can  
ground-reference the signals you measure. If the signals connected to the  
differential amplified inputs are not ground referenced, connect a 100 kΩ  
resistor from the negative input to ground to provide a DC path for the input  
bias currents. If you do not do this, the bias currents of the instrumentation  
amplifiers of the nonreferenced channels charge up stray capacitances,  
resulting in uncontrollable drift and possible saturation.  
Note The recommended SCXI-1304 or SCXI-1305 terminal block has all necessary  
circuitry for AC or DC coupling and for floating or ground-referenced signals. The  
SCXI-1304 AC/DC Coupling Terminal Block Installation Guide and SCXI-1305 AC/DC  
Coupling BNC Terminal Block Installation Guide have instructions for signal connection.  
Figures 2-2 through 2-5 provide supplemental information on connecting signals to the  
SCXI-1141/1142/1143 module.  
Figure 2-1 illustrates how to connect a ground-referenced signal source to  
an SCXI-1141/1142/1143 module channel.  
IN+  
IN–  
SCXI-1141/1142/1143  
Figure 2-1. Ground-Referenced Signal Connection  
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Chapter 2  
Connecting Signals  
Figure 2-2 illustrates how to connect a non-referenced (floating) signal  
source to an SCXI channel.  
IN+  
IN–  
100 kΩ  
SCXI-1141/1142/1143  
A GND  
A
Figure 2-2. Floating Signal Connection  
For AC-coupled signals, connect an external resistor from the AC-coupled  
input channel to ground. This provides a DC path for the amplifier input  
bias current. Typical resistor values range from 100 kΩ to 10 MΩ. This  
solution, although necessary, lowers the input impedance of the channel  
and introduces an additional DC offset voltage proportional to the product  
of the input bias current and the resistor value used. Using a 1 MΩ resistor  
results in 200 µV of offset, which is insignificant in most applications.  
However, if you use larger-valued bias resistors, significant input offset can  
result. Lower-valued bias resistors increase loading of the source, which  
can result in gain error.  
Figures 2-3 through 2-5 illustrate how to connect AC-coupled signals.  
1µF  
IN+  
1MΩ  
IN–  
SCXI-1141/1142/1143  
Figure 2-3. Ground-Referenced AC-Coupled Signal Connection  
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Connecting Signals  
1 µF  
IN+  
IN–  
1 MΩ  
1 µF  
1 MΩ  
SCXI-1141/1142/1143  
A GND  
A
Figure 2-4. Ground Offset AC-Coupled Signal Connection  
1 µF  
IN+  
1 MΩ  
IN–  
100 kΩ  
SCXI-1141/1142/1143  
A GND  
A
Figure 2-5. Floating AC-Coupled Signal Connection  
Digital Input and Output  
You can use the EXT CLK input pin on the front connector of the  
SCXI-1141/1142/1143 module to control filter cutoff frequency for special  
purposes. The clock should be a TTL-logic-level or CMOS-logic-level  
square wave, with a frequency of less than 2.5 MHz that is 100 times the  
desired cutoff frequency. The absolute maximum input voltage for the  
EXT CLK pin is 5.5 V with respect to D GND; the minimum input voltage  
is –0.5 V.  
The OUT CLK pin on the front connector is a CMOS-logic-level output  
clock, which you can configure to have a frequency that is proportional to  
See Chapter 4, Theory of Operation, for more details on using these  
two signals.  
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Chapter 2  
Connecting Signals  
Rear Signal Connector  
Note If you use the SCXI-1141/1142/1143 module with a National Instruments DAQ  
device and SCXI cable assembly, you do not need to read the remainder of this chapter.  
If you also use the SCXI-1180 feedthrough panel, the SCXI-1343 rear screw-terminal  
adapter, or the SCXI-1351 one-slot cable extender with the SCXI-1141/1142/1143  
module, you should read this section.  
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Table 2-2 shows the pin assignments for the SCXI-1141/1142/1143 module  
rear signal connector. Pins without signal labels are not connected.  
Table 2-2. Rear Signal Pin Assignments  
Rear Connector Diagram  
Signal Name  
NC  
Pin Number  
Pin Number  
Signal Name  
NC  
1
2
AI 0 +  
AI 1 +  
AI 2 +  
AI 3 +  
AI 4 +  
AI 5 +  
AI 6 +  
AI 7 +  
NC  
3
4
AI 0 –  
A GND  
A GND  
A GND  
A GND  
A GND  
A GND  
A GND  
NC  
5
6
1
3
5
7
9
2
4
7
8
6
9
10  
12  
14  
16  
18  
20  
22  
24  
26  
28  
30  
32  
34  
36  
38  
40  
42  
44  
46  
48  
50  
8
10  
11  
13  
15  
17  
19  
21  
23  
25  
27  
29  
31  
33  
35  
37  
39  
41  
43  
45  
47  
49  
11 12  
13 14  
15 16  
17 18  
19 20  
21 22  
23 24  
25 26  
27 28  
29 30  
31 32  
33 34  
35 36  
37 38  
39 40  
41 42  
43 44  
45 46  
47 48  
49 50  
NC  
NC  
NC  
DIG GND  
SER DAT OUT  
NC  
SER DAT IN  
DAQ D*/A  
SLOT 0 SEL*  
NC  
NC  
NC  
DIG GND  
NC  
NC  
SCAN CLK  
NC  
SER CLK  
NC  
NC  
NC  
NC  
RSVD  
NC  
NC  
NC  
NC means no connection.  
RSVD means reserved.  
NC  
NC  
NC  
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In parallel output mode, channel 0 is selected at the output multiplexer and  
is connected to AI 0. The seven other channels are directly connected to  
AI 1 through AI 7, respectively, on the rear connector.  
In multiplexed mode, the AI 0 signal pair is used for sending all eight  
channels of the SCXI-1141/1142/1143, and analog signals from other  
modules, to the connected E/M Series DAQ device. If the module is cabled  
directly to the DAQ device, the other analog channels of the DAQ device  
are unavailable for general-purpose analog input because they are  
connected to the SCXI-1141/1142/1143 amplifier outputs. This means that  
connecting an SCXI-1180 module to the 50-pin breakout connector of the  
SCXI-1349, or other cable adapter assembly, may cause interference and  
incorrect measurements when the DAQ device is cabled to the  
SCXI-1141/1142/1143.  
The communication signals between the DAQ device and the SCXI system  
are listed in Table 2-3. If the DAQ device is connected to the  
SCXI-1141/1142/1143, these digital lines are unavailable for  
general-purpose digital I/O.  
Table 2-3. SCXI-1141/1142/1143 Rear Communication Signals  
NI-DAQmx  
SCXI Signal  
Device Signal  
Name  
Pin  
Name  
Direction  
Description  
5, 7, 9,  
11,13,  
15, 17  
AI <1..7>  
N/A  
Output  
Analog outputs—these pins are the  
outputs of channels 1 through 7,  
regardless of the scanning mode.  
6, 8,  
10,12,  
14,16,  
18  
A GND  
DIG GND  
SER DAT IN  
AI GND  
Analog ground—these pins connect  
to the module analog ground. They  
are used as the reference points for  
AI 1 + through AI 7 +.  
24,  
33  
D GND  
P0.0  
Digital ground—these pins supply  
the reference for E/M Series DAQ  
device digital signals and connect to  
the module digital ground.  
25  
Input  
Serial data in—this signal taps into  
the SCXIbus MOSI line to send  
serial input data to a module or  
Slot 0.  
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Table 2-3. SCXI-1141/1142/1143 Rear Communication Signals (Continued)  
NI-DAQmx  
Device Signal  
Name  
SCXI Signal  
Name  
Pin  
Direction  
Description  
26  
SER DAT OUT  
P0.4  
Output  
Serial data out—this signal taps into  
the SCXIbus MISO line to accept  
serial output data from a module.  
27  
DAQ D*/A  
P0.1  
Input  
Board data/address line—this signal  
taps into the SCXIbus D*/A line to  
indicate to the module whether the  
incoming serial stream is data or  
address information.  
29  
36  
SLOT 0 SEL*  
SCAN CLK  
P0.2  
Input  
Input  
Slot 0 select—this signal taps into  
the SCXIbus INTR* line to indicate  
whether the information on MOSI is  
being sent to a module or Slot 0.  
AI HOLD,  
AI HOLD COMP  
Scan clock—a rising edge indicates  
to the scanned SCXI module that the  
E/M Series DAQ device has taken a  
sample and causes the module to  
advance channels.  
37  
43  
SER CLK  
RSVD  
EXT STROBE*  
RSVD  
Input  
Input  
Serial clock—this signal taps into  
the SCXIbus SPI CLK line to clock  
the data on the MOSI and MISO  
lines.  
Reserved.  
Notes: All other pins are not connected.  
An * means the signal is asserted low.  
The signals on the rear signal connector are classified as analog output,  
digital I/O, or timing I/O signals.  
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Chapter 2  
Connecting Signals  
Analog Output Signal Connections  
Pins 3 through 17 of the rear signal connector are analog output signal pins.  
Pin 3 is the main output, and pin 4 is its reference signal. All eight channels  
are multiplexed onto this output when the module is software-configured  
for multiplexed scanning mode. In parallel scanning mode, the output of  
pin 3 is the output of one selected channel. Channel 0 is the power-up and  
reset default. When scanning multiple modules, you can also connect this  
output to the SCXIbus analog bus and the analog bus will drive this output.  
Pins 5, 7, 9, 11, 13, 15, and 17 are direct outputs from channels 1 through 7,  
respectively. In parallel mode, all eight channels are available  
simultaneously at the rear connector. Pins 6, 8, 10, 12, 14, 16, and 18 are  
the reference signals for outputs 1 through 7.  
Caution The SCXI-1141/1142/1143 module analog outputs are not overvoltage protected,  
although they are short-circuit protected. Applying external voltage to these outputs can  
result in damage to the SCXI-1141/1142/1143 module. NI is not liable for any damage  
resulting from such signal connections.  
Digital I/O Signal Connections  
Pins 24 through 27, 29, 33, 36, 37, and 43 constitute the digital I/O lines  
of the rear signal connector. Each of these pins is in one of three  
categories—digital input signals, digital output signals, and timing signals.  
Pins 24 and 33 are the digital ground reference for all of the DAQ device  
digital signals and are tied to the module digital ground.  
The digital input signals are pins 25, 27, 29, and 37. Each digital line  
emulates an SCXIbus communication signal as follows:  
Pin 25 is SER DAT IN and is equivalent to the SCXIbus MOSI serial  
data input line.  
Pin 27 is DAQ D*/A and is equivalent to the SCXIbus D*/A line.  
Pin 27 indicates to the module whether the incoming serial stream on  
SER DAT IN is data (DAQ D*/A = 0) or address (DAQ D*/A = 1)  
information.  
Pin 29 is SLOT 0 SEL* and is equivalent to the SCXIbus INTR* line.  
Pin 29 indicates whether the data on the SER DAT IN line is being sent  
to Slot 0 (SLOT 0 SEL* = 0) or to a module (SLOT 0 SEL* = 1).  
Pin 37 is SER CLK and is equivalent to the SCXIbus SPI CLK line.  
Pin 37 is used to clock the serial data on the SER DAT IN line into the  
module registers.  
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Chapter 2  
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The digital output signal is pin 26. Pin 26 is SER DAT OUT and is  
equivalent to the SCXIbus MISO serial data output line.  
The digital I/O signals of the SCXI-1141/1142/1143 module correspond  
to the digital I/O lines of an E/M Series DAQ device. Table 2-4 lists the  
equivalencies.  
Table 2-4. SCXIbus to SCXI-1141/1142/1143 Module Rear Signal Connector  
to DAQ Device Pin Equivalencies  
SCXI-1141/1142/1143  
Rear Signal Connector  
E/M Series  
DAQ Device  
SCXIbus Line  
MOSI  
SER DAT IN  
DAQ D*/A  
DIO0  
DIO1  
D*/A  
INTR*  
SLOT 0 SEL*  
SER CLK  
DIO2  
SPI CLK  
MISO  
EXT STROBE*  
DIO4  
SER DAT OUT  
Note: An * means the signal is asserted low.  
The digital timing signals are pins 36 and 43:  
Pin 36 is SCAN CLK, the signal used as a clock for the  
SCXI-1141/1142/1143 module multiplexer counter. The DAQ device  
pulses this signal at the end of each conversion if the module is in  
multiplexed mode.  
Pin 43 is a reserved digital input.  
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3
Configuring and Testing  
This chapter discusses configuring the SCXI-1141/1142/1143 in MAX  
using NI-DAQmx, creating and testing a virtual channel, global channel,  
and/or task.  
Notes NI recommends that you have NI-DAQmx 8.3 or later installed.  
Refer to the SCXI Quick Start Guide if you have not already configured the chassis.  
SCXI-1141/1142/1143 Software-Configurable Settings  
This section describes how to set the gain/input signal range and how to  
configure your software for compatible sensor types. It also describes how  
to perform configuration of these settings for the SCXI-1141/1142/1143 in  
NI-DAQmx. For more information on the relationship between the settings  
and the measurements and how to configure settings in your application,  
Common Software-Configurable Settings  
This section describes the most frequently used software-configurable  
settings for the SCXI-1141/1142/1143. Refer to Chapter 4, Theory of  
Operation, for a complete list of software-configurable settings.  
Gain/input range is a software-configurable setting that allows you to  
choose the appropriate amplification to fully utilize the range of the  
E/M Series DAQ device. In most applications NI-DAQ chooses and sets  
the gain for you determined by the input range. This feature is described in  
Chapter 4, Theory of Operation. Otherwise, you should determine the  
appropriate gain using the input signal voltage range and the full-scale  
limits of the SCXI-1141/1142/1143 output. You can select a gain of 1, 2, 5,  
10, 20, 50, or 100 on a per channel basis.  
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Chapter 3  
Configuring and Testing  
The front end of the SCXI-1141/1142/1143 includes a software  
configurable switch that allows you to programmatically connect the input  
channels of the SCXI-1141/1142/1143 to either the front connector or  
internal ground. Refer to Table 5-1, NI-DAQmx Voltage Measurement  
Properties, for details about the available input coupling modes supported  
by the SCXI-1141/1142/1143.  
Auto-Zero  
Setting the Auto-zero mode to Once improves the accuracy of  
the measurement. With auto-zero enabled, the inputs of the  
SCXI-1141/1142/1143 are internally grounded. The driver makes a  
measurement when the task begins and then subtracts the measured offset  
from all future measurements.  
Although the DAQ driver does wait a certain amount of time for the signal  
to settle, it may not be long enough if the filter is set to very low cutoff  
frequency. This is especially true if the voltage ever goes out of range and  
the amplifier becomes saturated. You can manually zero out the offset by  
comparing the ground coupled value of a channel to its DC coupled value,  
then subtracting that offset from future measurements. This allows you to  
control the time allowed for the signals to settle.  
Configurable Settings in MAX  
Note If you are not using an NI ADE, using an NI ADE prior to version 8.3, or are using  
an unlicensed copy of an NI ADE, additional dialog boxes from the NI License Manager  
appear allowing you to create a task or global channel in unlicensed mode. These messages  
continue to appear until you install version 8.3 or later of an NI ADE.  
This section describes where you can access each software-configurable  
setting in MAX. The location of the settings varies depending on the  
version of NI-DAQmx you use. Refer to the DAQ Getting Started Guide  
and the SCXI Quick Start Guide for more information on installing and  
configuring the hardware. You can use DAQ Assistant to graphically  
configure common measurement tasks, channels, or scales.  
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Chapter 3  
Configuring and Testing  
NI-DAQmx  
Using NI-DAQmx, you can configure software settings, such as sensor  
type and gain/input signal range, in the following ways:  
Task or global channel in MAX  
Functions in your application  
Note All software-configurable settings are not configurable both ways. This section only  
discusses settings in MAX. Refer to Chapter 4, Theory of Operation, for information about  
using functions in your application.  
Depending on the terminal block in use, you can use the  
SCXI-1141/1142/1143 module to make the following types of  
measurements:  
Voltage input  
Thermocouple  
RTD  
Thermistors  
Current input  
Creating a Global Channel or Task  
To create a new voltage, temperature, or current input NI-DAQmx global  
task or channel, complete the following steps:  
1. Double-click Measurement & Automation on the desktop.  
2. Right-click Data Neighborhood and select Create New.  
3. Select NI-DAQmx Task or NI-DAQmx Global Channel, and  
click Next.  
4. Select Analog Input.  
5. Select one of the following:  
Voltage  
Temperature and then select one of the following:  
Iex Thermistor  
RTD  
Thermocouple  
Vex Thermistor  
Current  
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Chapter 3  
Configuring and Testing  
6. If you are creating a task, you can select a range of channels by holding  
down the <Shift> key while selecting the channels. You can select  
multiple individual channels by holding down the <Ctrl> key while  
selecting channels. If you are creating a channel, you can only select  
one channel. Click Next.  
7. Name the task or channel and click Finish.  
8. Select the channel(s) you want to configure. You can select a range  
of channels by holding down the <Shift> key while selecting the  
channels. You can select multiple individual channels by holding down  
the <Ctrl> key while selecting channels.  
Note If you want to add channels of various measurement types to the same task, click  
the Add Channels button to select the measurement type for the additional channels.  
9. Enter the specific values for your application in the Settings tab.  
Context help information for each setting is provided on the right  
side of the screen. Configure the input signal range using either  
NI-DAQmx Task or NI-DAQmx Global Channel. When you set the  
minimum and maximum range of NI-DAQmx Task or NI-DAQmx  
Global Channel, the driver selects the best gain for the measurement.  
You also can set it through your application.  
10. If you are creating a task and want to set timing or triggering controls,  
enter the values in the Task Timing and Task Triggering tabs.  
11. Click Device and select Auto Zero mode if desired.  
Verifying the Signal  
This section describes how to take measurements using test panels in order  
to verify signal, and configuring and installing a system in NI-DAQmx.  
Verifying the Signal in NI-DAQmx Using a Task or Global Channel  
You can verify the signals on the SCXI-1141/1142/1143 using NI-DAQmx  
by completing the following steps:  
1. Expand Data Neighborhood.  
2. Expand NI-DAQmx Tasks.  
3. Click the task you created in the Creating a Global Channel or Task  
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Configuring and Testing  
4. Select the channel(s) you want to verify. You can select a block of  
channels by holding down the <Shift> key or multiple channels by  
holding down the <Ctrl> key. Click OK.  
5. Enter the appropriate information on the Settings and Device tab.  
6. Click the Test button.  
7. Click the Start button.  
8. After you have completed verifying the channels, click the Stop  
button.  
You have now verified the SCXI-1141/1142/1143 configuration and signal  
connection.  
Note For more information on how to further configure the SCXI-1141/1142/1143, or  
how to use LabVIEW to configure the module and take measurements, refer to Chapter 4,  
Theory of Operation.  
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4
Theory of Operation  
This chapter contains an overview of the SCXI-1141/1142/1143 module  
and explains the operation of each functional unit of the module.  
The SCXI-1141/1142/1143 module has eight software-controlled input  
channels that amplify and filter signals. Each channel has an output range  
of 5 V and has an input amplifier with gains of 1, 2, 5, 10, 20, 50, and 100.  
You can independently set each amplifier gain. The analog inputs are  
overvoltage protected. The SCXI-1141/1142/1143 module filters are  
lowpass, 8th-order elliptic, Bessel, and Butterworth filters respectively that  
can have a cutoff frequency from 10 Hz to 25 kHz. All eight filters have the  
same cutoff frequency. The outputs of all eight channels are available at the  
rear connector.  
The major components of the SCXI-1141/1142/1143 module are as  
follows:  
Digital control and calibration circuitry  
Input amplifiers  
Lowpass filters  
Power-Up State  
When the SCXI-1141/1142/1143 module is powered up or reset through  
software or the SCXI chassis reset button, the following states are defined:  
The gain of each amplifier is set to 1.  
Channel 0 is selected as the OUTPUT signal and the module defaults  
to multiplexed mode.  
All filters are placed in bypass mode.  
The external clock input is disabled.  
The cutoff frequency of the filters and the output clock frequency are not  
defined at power-up.  
The block diagram in Figure 4-1 illustrates the key functional components  
of the SCXI-1141/1142/1143 module.  
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Chapter 4  
Theory of Operation  
AI 0+  
+
Filter  
Bypass  
Instrumentation  
Filter  
Amplifier  
AI 0–  
AI 0  
AI 0  
Analog  
Switch  
Analog  
Switch  
AI 7  
AI 7+  
AI 7–  
+
Filter  
Bypass  
AI 7  
Instrumentation  
Amplifier  
Filter  
External Clock  
Digital  
Interface  
and Control  
Output Clock  
Digital Control Bus  
Calibration  
EEPROM  
Internal  
16-Pin Analog  
Input Connector  
SCXIbus Connector  
Figure 4-1. SCXI-1141/1142/1143 Module Block Diagram  
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Chapter 4  
Theory of Operation  
Digital Control Circuitry  
The digital control circuitry contains a Module ID (identification) register,  
a configuration register for the module, a gain register, and an EEPROM  
for storing gain-calibration constants.  
The Module ID register contains 20 (hex) for the SCXI-1141 module,  
35 (hex) for the SCXI-1142 module, and 34 (hex) for the SCXI-1143  
module. You can read this module ID over the SCXIbus to determine the  
type of module that is in a particular slot.  
Use the configuration register to select channels and configure the  
SCXI-1141/1142/1143 module for scanning, calibration, and control  
The gain register sets the gain of each amplifier.  
The frequency dividers control the filter cutoff frequency and the output  
clock frequency. For more information see the Using the External Clock  
Input section.  
The EEPROM stores the calibration constants for each gain for all eight  
channels. Information in the EEPROM is retained when the module is  
power off. The SCXI-1141/1142/1143 module has calibration constants  
already stored in the EEPROM. You can modify these constants for your  
set of operating conditions. One set of constants is reserved and cannot be  
modified except at the factory, which ensures that you do not accidentally  
erase the default calibration constants. For more information on the  
EEPROM and calibration, see Chapter 5, Using the SCXI-1141/1142/1143  
Module.  
Input Amplifiers  
The amplifiers provide gain to the differential signal between the inputs  
while rejecting common-mode noise voltages. The available gains are 1, 2,  
5, 10, 20, 50, and 100. The output range of the amplifiers is 5 V. Select  
the gain to prevent the output signals from reaching 5 V, or distortion  
occurs.  
The input amplifiers are fully differential amplifiers with input protection  
and calibration circuitry. The inputs are protected against input voltages up  
to 15 V powered off and 30 V powered on.  
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Theory of Operation  
In general, to provide optimum measurement resolution and noise  
rejection, you can select as high a gain as will not cause the output to exceed  
this limit. However, total harmonic distortion (THD) increases at higher  
output levels, especially at higher input frequencies. If THD is of  
significant concern in a given application, a lower gain (one or two steps  
lower) may be more appropriate.  
Correcting Gain and Offset Errors  
The input amplifiers have intrinsic errors in their gains and in their DC  
offsets. To compensate for the gain errors, calibration constants are stored  
in the EEPROM for each gain and for each channel. These constants  
contain the adjustment factors used to correct for the gain errors. If you are  
using NI software, these constants are read automatically from the  
EEPROM and the appropriate correction factor is applied when the raw  
data is scaled to a voltage.  
Gain errors are determined and calibration constants are loaded into the  
EEPROM at the factory. However, gain errors drift with temperature  
changes. You can add an additional set or subset of calibration constants to  
the EEPROM to optimize performance under a specific set of conditions.  
Details of this procedure are given in Chapter 5, Using the  
SCXI-1141/1142/1143 Module.  
To account for offset errors, you can configure the module to send a 0 V  
differential signal through the amplifiers. The signal at the output  
represents the DC offset error and should be read and subtracted from all  
subsequent readings. Before reading this offset error on a channel, either set  
the filter to bypass mode or allow it to settle for several seconds. Average  
several readings to minimize noise errors. This procedure is called  
calibration.  
Because the offset voltage changes with each gain, you should perform a  
new calibration each time the gain is changed. Offset errors also drift with  
changes in temperature, so you should update the offset correction  
periodically. Measurements made during the warm-up period of the module  
(approximately 20 minutes) and chassis are most susceptible to drifting  
offset errors.  
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Lowpass Filters  
The SCXI-1141/1142/1143 module filters are 8th-order elliptic, Bessel,  
and Butterworth lowpass filters, respectively. These filters are a hybrid of  
a switched-capacitor and a continuous-time architecture, thus providing  
good cutoff frequency control while avoiding the sampling errors found in  
conventional switched-capacitor designs. To better acquaint you with these  
filters, this section describes what the filters do and presents examples of  
how to use them on the SCXI-1141/1142/1143 module.  
Filter Theory  
Filters are generally grouped into one of five classifications—lowpass,  
highpass, bandpass, bandstop, and all-pass. These classifications refer  
to the frequency range (the passband) of signals that the filter is intended  
to pass from the input to the output without attenuation. Because the  
SCXI-1141/1142/1143 modules use a lowpass filter, this discussion is  
limited to lowpass filters.  
The ideal lowpass filter does not attenuate any input signal frequency  
components in the passband, which is defined as all frequencies below the  
cutoff frequency. The ideal lowpass filter completely attenuates all signal  
components in the stopband, which includes all frequencies above the  
cutoff frequency. The ideal lowpass filter also has a phase shift that is linear  
with respect to frequency. This linear phase property means that signal  
components of all frequencies are delayed by a constant time independent  
of frequency, thereby preserving the overall shape of the signal.  
In practice, real filters can only approximate the characteristics of an ideal  
filter. Figure 4-2 compares the attenuation of a real filter and an ideal filter.  
Passband  
Passband  
Transition  
Region  
Gain  
Gain  
Stopband  
Stopband  
fc  
Frequency  
b. Real  
fc  
Frequency  
a. Ideal  
Figure 4-2. Ideal and Real Lowpass Filter Transfer Function Characteristics  
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Theory of Operation  
As Figure 4-2b shows, a real filter has ripple (an uneven variation in  
attenuation versus frequency) in the passband, a transition region between  
the passband and the stopband, and a stopband with finite attenuation and  
ripple.  
In addition, real filters have some nonlinearity in their phase response. This  
causes signal components at higher frequencies to be delayed by longer  
times than signal components at lower frequencies, resulting in an overall  
shape distortion of the signal. You can observe this when a square wave or  
step input is sent through a lowpass filter. An ideal filter simply smooths the  
edges of the input signal, whereas a real filter causes some ringing in the  
total signal because the higher-frequency components of the signal are  
delayed. Figure 4-3 shows examples of these responses to a step input.  
Volts  
Volts  
Volts  
Time  
Time  
Time  
c. Real Filter Response  
a. Input Signal  
b. Ideal Filter Response  
Figure 4-3. Real and Ideal Filter Responses to a Step Input Signal  
Performance of the SCXI-1141/1142/1143 Module Filters  
The SCXI-1141/1142/1143 module is elliptic, Bessel, and Butterworth  
filters, respectively. Each filter design optimizes a particular set of  
characteristics. Therefore, selecting the appropriate module depends on  
the application.  
Magnitude Response  
The magnitude response is the amplitude of the output at a given frequency.  
The typical magnitude response of the SCXI-1141/1142/1143 module  
filters is shown in Figures 4-4 and 4-5. Figure 4-4 shows the full magnitude  
response and Figure 4-5 shows the ripple in the passband. Both graphs are  
plotted with the frequency axis normalized to the cutoff frequency value  
of 1.  
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As Figure 4-4 shows, the SCXI-1141/1142/1143 module provides 80 dB  
attenuation above 1.5 times the cutoff frequency for the SCXI-1141  
module, six times for the SCXI-1142 module, and 3.2 times for the  
SCXI-1143 module. The SCXI-1141, which incorporates an elliptic filter,  
is designed to provide maximum attenuation immediately above the cutoff  
frequency. Therefore, it is the ideal choice for applications in which you  
must remove signals very near the cutoff frequency.  
50  
0
Elliptic (1141)  
Bessel (1142)  
–50  
Butterworth (1143)  
–80 dB Intersection  
–80  
–100  
–150  
–200  
1 x 10–3  
0.01  
0.1  
1
10  
Frequency (Normalized)  
Figure 4-4. Typical Magnitude Response of the SCXI-1141/1142/1143 Module Filters  
Figure 4-5 compares the magnitude response of the SCXI-1141/1142/1143  
modules within the passband. The passband magnitude response begins to  
drop off immediately for the SCXI-1142 module. The SCXI-1141 performs  
much better than the SCXI-1142 in the passband, but it still exhibits about  
0.1 dB of ripple in magnitude in the passband. The SCXI-1143 module  
Butterworth filter is designed for maximum flatness in the passband and is  
nearly perfectly flat in most of the passband. For this reason the SCXI-1143  
module filter is the ideal choice for applications where flatness in the  
passband is critical.  
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0.5  
0
–0.5  
–1  
Elliptic (1141)  
Bessel (1142)  
–1.5  
–2  
Butterworth (1143)  
–2.5  
–3  
–3.5  
0
0.2  
0.4  
0.6  
0.8  
1
Frequency (Normalized)  
Figure 4-5. Typical Passband Responses of the SCXI-1141/1142/1143 Module  
Phase Response  
Figures 4-6 through 4-8 illustrate the phase response characteristics of the  
SCXI-1141/1142/1143 module filters. Figure 4-6 shows the phase shift as  
a function of frequency (normalized so that the cutoff frequency = 1). In an  
ideal filter, this would be a linear relationship. Figure 4-7 shows the  
deviation of the actual phase response from an ideal (linear) response.  
Generally, phase response is described in terms of the differential  
nonlinearity, or group delay. Group delay is defined as the negative  
derivative of the phase shift with respect to the frequency. In the ideal filter,  
group delay is a constant.  
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0
–200  
–400  
–600  
–800  
Elliptic (1141)  
Bessel (1142)  
Butterworth (1143)  
0
1
1.5  
2
Frequency (Normalized)  
Figure 4-6. Phase Response Characteristics of the SCXI-1141/1142/1143  
Module Filters  
Figure 4-7 shows the advantages of the SCXI-1142 Bessel filter. The  
Bessel filter is designed for constant group delay at the expense of passband  
gain and stopband rolloff. As a result, the SCXI-1142 Bessel filter is the  
best choice when the phase information of a signal is important or a signal  
must maintain a constant delay regardless of its frequency components.  
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Theory of Operation  
300  
200  
100  
0
Elliptic (1141)  
Bessel (1142)  
Butterworth (1143)  
–100  
0
0.5  
1
1.5  
2
Frequency (Normalized)  
Figure 4-7. Phase Error of the SCXI-1141/1142/1143 Module  
The most common effect of phase nonlinearity is ringing in response to a  
step input. As Figure 4-8 shows, the SCXI-1141 elliptic filter exhibits the  
overshoot or ringing. The SCXI-1143 module Butterworth filter has a step  
response that is a compromise between the SCXI-1141 module and the  
SCXI-1142 module. The SCXI-1143 module filter has an overshoot, but it  
has less ringing than the SCXI-1141. You should consider the step response  
if the intended application is sensitive to overshoot or ringing. See  
Table A-1, Settling Time with Respect to Cutoff Frequency, for detailed  
settling specifications. Additionally, use care when selecting gain settings  
to assure that the input signal plus any overshoot voltage result in an output  
signal within the 5 V range of the SCXI-1141/1142/1143 module.  
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1.4  
1.2  
1
Elliptic (1141)  
0.8  
0.6  
0.4  
0.2  
0
Bessel (1142)  
Butterworth (1143)  
0
2
4
6
8
10  
Time (Seconds)  
Figure 4-8. Unit Step Response of the SCXI-1141/1142/1143 Module  
Setting the Cutoff Frequency  
The cutoff frequencies of the filters in the SCXI-1141/1142/1143 module  
are set internally by dividing a base frequency of 100 kHz by an integer.  
You can determine the allowable cutoff frequencies for the  
SCXI-1141/1142/1143 module as follows:  
100  
n
--------  
fc =  
kHz  
where n is an integer 4 and fc 10 Hz. In other words, fc = {25, 20, 16.7,  
14.3, 12.5, ..., 0.01} kHz.  
If you are using NI software, the software automatically chooses a divisor,  
n, that best matches the cutoff frequency you specify and returns the actual  
cutoff frequency chosen.  
The correct cutoff frequency depends on the application. If phase  
nonlinearity, ringing, passband ripple, or aliasing is a concern in the  
application, you may need to set the cutoff frequency several times higher  
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Theory of Operation  
than the signal frequency range of interest. At frequencies much lower than  
the cutoff frequency, passband ripple and phase nonlinearity are much less  
noticeable. If you use the filter to prevent aliasing, you must set the cutoff  
frequency no higher than one-third of the frequency at which that channel  
is being sampled for the SCXI-1141 module, one-twelfth of the frequency  
for the SCXI-1142 module, or one-sixth of the frequency for the  
SCXI-1143 module.  
Using the SCXI-1141/1142/1143 Module as an Antialiasing Filter  
Aliasing, a phenomenon of sampled data acquisition systems, causes a  
high-frequency signal component to take on the identity of a low-frequency  
signal. Figure 4-9 shows an example of aliasing.  
1
–1  
0
2
4
6
8
10  
Input Signal  
Sampled Point  
Reconstructed Signal  
Figure 4-9. Aliasing of an Input Signal with a Frequency 0.8 Times the Sample Rate  
The solid line depicts a high-frequency signal being sampled at the  
indicated points. However, when these points are connected to reconstruct  
the waveform, as shown by the dotted line, the signal appears to have a  
lower frequency. Any signal frequency with a frequency component greater  
than one-half of the sample rate is aliased and incorrectly analyzed as  
having a frequency below one-half of the sample rate. This limiting  
frequency of one-half the sample rate is known as the Nyquist frequency.  
To prevent aliasing, you must remove all signal components with  
frequencies greater than the Nyquist frequency before sampling an input  
signaled. After an unfiltered signal is sampled and aliasing has occurred,  
it is impossible to accurately reconstruct the original signal. The  
SCXI-1141/1142/1143 module removes these high-frequency signals  
before they reach a DAQ device and cause aliasing.  
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Because the SCXI-1141 module stopband begins at 1.5 times the cutoff  
frequency, the Nyquist frequency should be at least 1.5 times the cutoff  
frequency. Thus, the rate at which the DAQ device samples a channel  
should be at least three times the filter cutoff frequency to acquire  
meaningful data.  
The stopband for the SCXI-1142 module begins at six times the cutoff  
frequency, so you should sample it at a rate of 12 times the cutoff frequency  
to acquire meaningful data.  
The stopband for the SCXI-1143 module begins at 3.2 times the cutoff  
frequency, so you should sample it at a rate of 6.4 times the cutoff  
frequency to acquire meaningful data.  
For example, if a DAQ device is scanning all eight channels of the  
SCXI-1141 at a rate of 120,000 channels/s, the sample rate for each of  
the eight channels is:  
120,000  
------------------ = 15,000 S/s  
8
and the cutoff frequency for the filters should be set no higher than:  
15,000  
--------------- = 5,000 Hz  
3
Using this stopband, the filter attenuates the input signal by 80 dB or more.  
This is enough attenuation to prevent aliasing on DAQ systems with 12 bits  
of precision or less. On systems with more than 12 bits of precision or  
systems with extremely high amounts of out-of-passband noise, higher  
sampling rates or lower cutoff frequencies are necessary to prevent aliasing.  
You can set the filter cutoff frequency closer to the sampling rate with the  
consequence of having some aliasing. If you can tolerate aliasing in the  
transition band, you can reduce the sampling rate to 2.6 times the cutoff  
frequency for the SCXI-1141 module, five times the cutoff frequency for  
the SCXI-1142 module, and 3.5 times the cutoff frequency for the  
SCXI-1143 module.  
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Chapter 4  
Theory of Operation  
Using the External Clock Input  
You can set the cutoff frequencies of filters in the SCXI-1141/1142/1143  
module by using the external clock input in applications that require  
external control of the cutoff frequency or that require finer resolution than  
the module provides internally. The cutoff frequency for each filter using  
the external clock as a base is:  
fext/(100 × n)  
where fext is the frequency of the external clock and n is an integer you  
select such that 2 n 216.  
When the frequency of the external clock changes, the cutoff frequency  
changes proportionally.  
An external clock can control the SCXI-1141/1142/1143 module filters  
because they use a switched-capacitor architecture, which uses analog  
sampling. However, this technique is also susceptible to aliasing in much  
the same way as the digital sampling of a DAQ device (with a Nyquist  
frequency of one-half the external clock frequency). Analog sampling also  
creates high-frequency images of the signal because the output waveform  
has a staircase shape.  
The SCXI-1141/1142/1143 module prevents these errors by using sets of  
prefilters and postfilters that do not sample the signal. A different set of  
prefilters and postfilters is used for each of 12 ranges of input frequencies.  
The prefilters reduce signals that can alias into a lower frequency by at least  
40 dB, and the postfilters reconstruct the output waveform, reducing  
high-frequency images to at least –80 dB.  
NI software automatically chooses the correct set of prefilters and  
postfilters when you specify a cutoff frequency. However, when the  
external clock input is used to set the cutoff frequency of a filter, you must  
still supply an approximate cutoff frequency so that the software can  
determine the appropriate set of prefilters and postfilters.  
Table 4-1 gives the ranges of cutoff frequencies that the prefilters and  
postfilters use.  
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Table 4-1. Cutoff Frequency Ranges for the SCXI-1141/1142/1143 Module  
Prefilters and Postfilters  
Range  
Cutoff Frequencies  
10–25 kHz  
A
B
C
D
E
F
4.3–10 kHz  
1.9–4.4 kHz  
1.5–3.4 kHz  
700 Hz–1.8 kHz  
300–700 Hz  
130–300 Hz  
100–225 Hz  
49–110 Hz  
G
H
I
J
21–49 Hz  
K
L
15–21 Hz  
10–15 Hz  
For best results, the cutoff frequency of a particular filter should remain  
within this range. If the cutoff frequency goes above this range, the  
prefilters and postfilters interfere with signals in the passband, causing  
additional attenuation near the cutoff frequency. If the cutoff frequency  
goes below this range, the level of protection from aliasing within the filter  
and from imaging in the output decreases.  
DC-Correction Circuitry and Overload Recovery  
The SCXI-1141/1142/1143 module incorporates circuitry that corrects for  
the DC gain and offset errors of the filters, leaving only the errors of the  
amplifiers. However, this correction circuitry takes approximately 15 s to  
completely respond to changes in these errors due to overload conditions  
(caused by driving the output signal outside of the 5 V range) and upon  
power-up (no data should be taken during the first 15 s). Overload  
conditions result whenever the input signal exceeds 5 V/gain. You must  
use a gain setting that prevents the maximum input signal from exceeding  
this limit, or the DC-correction circuitry will take 15 s to recover from  
overloads.  
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Theory of Operation  
Filter Bypass Mode  
You can bypass the filter of any channel through software control, thus  
making the unfiltered signal available at the output. The input amplifiers  
are not bypassed.  
You can use the filter bypass to examine the effect that the filter has on the  
input signal. Using this mode, you can examine an input signal without the  
added effects of passband ripple and phase nonlinearities.  
At power-up and at reset, all the channels of the SCXI-1141/1142/1143  
module default to the filter bypass mode.  
Rear Connector Analog Outputs  
The connector signals A OUT<1..7> and A GND are the outputs of  
channels 1 through 7. You can configure the OUTPUT and OUTPUT REF  
signals as any channel (0 through 7) of the SCXI-1141/1142/1143 module  
or as the output of a channel passed along the SCXIbus from any other  
module in the chassis. Thus, the SCXI-1141/1142/1143 modules can  
present its outputs in both parallel and multiplexed modes.  
Multiplexed Mode (Recommended)  
In multiplexed mode, the output signals for channels 1 through 7 are sent  
to the rear signal connector but are usually ignored. All samples from the  
module are from the OUTPUT signal of the rear signal connector,  
which you can configure as the output of any channel of the  
SCXI-1141/1142/1143 module or as the output of any other module in  
multiplexed mode that is sending its output onto the SCXIbus. You can also  
configure the SCXI-1141/1142/1143 module to send any one of its outputs  
to the SCXIbus. Thus, in multiplexed mode only, one module in a chassis  
needs to be connected to a DAQ device. You can pass signals from the  
other modules to the DAQ device through the SCXIbus.  
Multiplexed mode is also useful for performing scanning operations with  
the SCXI-1141/1142/1143 module. E/M Series devices support scanning.  
The SCXI chassis is programmed with a module scan list that dynamically  
controls which module sends its output to the SCXIbus during a scan. You  
can specify this list to scan the modules in any order, with an arbitrary  
number of channels for each module entry in the list. However, you must  
scan the channels on the SCXI-1141/1142/1143 module in consecutive,  
ascending order. After channel 7 is scanned, the module wraps back to  
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channel 0 and continues. You can program the SCXI-1141/1142/1143  
module to start scans with any channel.  
Parallel Mode  
When the OUTPUT signal is configured as the rear connector output of  
channel 0, the rear signal connector simultaneously carries each of the rear  
connector outputs of the SCXI-1141/1142/1143 module channels on a  
different pin, and the module is in parallel mode. In this mode, you can use  
an SCXI-1180 feedthrough panel to make each of the outputs available at  
the front of the chassis. A DAQ device cabled to an SCXI-1141/1142/1143  
module in parallel mode reads a separate output signal from the module on  
each of its analog inputs. You cannot multiplex the parallel outputs of a  
module onto the SCXIbus. Only a DAQ device directly cabled to the  
module has access to the outputs.  
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5
Using the SCXI-1141/1142/1143  
Module  
This chapter makes suggestions for developing your application and  
provides basic information regarding calibration.  
Developing Your Application in NI-DAQmx  
Note If you are not using an NI ADE, using an NI ADE prior to version 8.3, or are using  
an unlicensed copy of an NI ADE, additional dialog boxes from the NI License Manager  
appear allowing you to create a task or global channel in unlicensed mode. These messages  
continue to appear until you install version 8.3 or later of an NI ADE.  
This section describes how to configure and use NI-DAQmx to control the  
SCXI-1141/1142/1143 in LabVIEW, LabWindows/CVI, and Measurement  
Studio. These ADEs provide greater flexibility and access to more settings  
than MAX, but you can use ADEs in conjunction with MAX to quickly  
create a customized application.  
Typical Program Flowchart  
Figure 5-1 shows a typical program voltage measurement flowchart for  
creating a task to configure channels, take a measurement, analyze the data,  
present the data, stop the measurement, and clear the task.  
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No  
Yes  
Create Task Using  
DAQ Assistant?  
Create a Task  
Programmatically  
Create Task in  
DAQ Assistant  
or MAX  
Yes  
Create Channel  
Create Another  
Channel?  
No  
Hardware  
Timing/Triggering?  
No  
No  
Further Configure  
Channels?  
Yes  
Adjust Timing Settings  
Yes  
Configure Channels  
Yes  
Analyze Data?  
No  
Process  
Data  
Start Measurement  
Read Measurement  
Yes  
Display Data?  
No  
Graphical  
Display Tools  
Yes  
Continue Sampling?  
No  
Stop Measurement  
Clear Task  
Figure 5-1. Typical Program Flowchart for Voltage Measurement Channels  
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General Discussion of Typical Flowchart  
The following sections briefly discuss some considerations for a few of the  
steps in Figure 5-1. These sections are meant to give an overview of some  
of the options and features available when programming with NI-DAQmx.  
Creating a Task Using DAQ Assistant or  
Programmatically  
When creating an application, you must first decide whether to create the  
appropriate task using the DAQ Assistant or programmatically in the ADE.  
Developing your application using DAQ Assistant gives you the ability to  
configure most settings such as measurement type, selection of channels,  
excitation voltage, signal input limits, task timing, and task triggering. You  
can access the DAQ Assistant through MAX or your NI ADE. Choosing to  
use the DAQ Assistant can simplify the development of your application.  
NI recommends creating tasks using the DAQ Assistant for ease of use,  
when using a sensor that requires complex scaling, or when many  
properties differ between channels in the same task.  
If you are using an ADE other than an NI ADE, or if you want to explicitly  
create and configure a task for a certain type of acquisition, you can  
programmatically create the task from your ADE using functions or VIs.  
If you create a task using the DAQ Assistant, you can still further configure  
the individual properties of the task programmatically with functions  
or property nodes in your ADE. NI recommends creating a task  
programmatically if you need explicit control of programmatically  
adjustable properties of the DAQ system.  
Programmatically adjusting properties for a task created in the DAQ  
Assistant overrides the original, or default, settings only for that session.  
The changes are not saved to the task configuration. The next time you load  
the task, the task uses the settings originally configured in the DAQ  
Assistant.  
Adjusting Timing and Triggering  
There are several timing properties that you can configure through the  
DAQ Assistant or programmatically using function calls or property nodes.  
If you create a task in the DAQ Assistant, you can still modify the timing  
properties of the task programmatically in your application.  
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When programmatically adjusting timing settings, you can set the task to  
acquire continuously, acquire a buffer of samples, or acquire one point at a  
time. For continuous acquisition, you must use a while loop around the  
acquisition components even if you configured the task for continuous  
acquisition using MAX or the DAQ Assistant. For continuous and buffered  
acquisitions, you can set the acquisition rate and the number of samples to  
read in the DAQ Assistant or programmatically in your application. By  
default, the clock settings are automatically set by an internal clock based  
on the requested sample rate. You also can select advanced features such as  
clock settings that specify an external clock source, internal routing of the  
clock source, or select the active edge of the clock signal.  
Configuring Channel Properties  
All ADEs used to configure the SCXI-1141/1142/1143 access an  
underlying set of NI-DAQmx properties. Table 5-1 shows some of these  
properties. You can use Table 5-1 to determine what kind of properties you  
need to set to configure the module for your application. For a complete list  
of NI-DAQmx properties, refer to your ADE help file.  
Note You cannot adjust some properties while a task is running. For these properties,  
you must stop the task, make the adjustment, and re-start the application. Tables 5-1  
through 5-4 assume all properties are configured before the task is started.  
Table 5-1. NI-DAQmx Voltage Measurement Properties  
Property  
Short Name  
AI.Max  
Description  
Analog Input»Maximum Value  
Analog Input»Minimum Value  
Specifies the maximum value  
you expect to measure. The  
SCXI-1141/1142/1143 gain and  
E/M Series DAQ device range  
are computed automatically  
from this value.  
AI.Min  
Specifies the minimum value  
you expect to measure. The  
SCXI-1141/1142/1143 gain and  
E/M Series DAQ device range  
are computed automatically  
from this value.  
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Table 5-1. NI-DAQmx Voltage Measurement Properties (Continued)  
Property Short Name Description  
AI.Gain  
Analog Input»General  
Properties»Advanced»Gain  
and Offset»Gain Value  
Specifies a gain factor to apply  
to the signal conditioning  
portion of the channel. The  
SCXI-1141/1142/1143 supports  
1, 2, 5, 10, 20, 50, or 100.  
Analog Input»General  
Properties»Advanced»High  
Accuracy Settings»Auto Zero  
Mode  
AI.AutoZeroMode  
AI.Coupling  
Specifies when to measure  
ground. NI-DAQmx subtracts  
the measured ground voltage  
from every sample.  
Analog Input»General  
Properties»Advanced»Input  
Configuration»Coupling  
Specifies the input coupling  
of the channel. The  
SCXI-1141/1142/1143 supports  
DC and GND coupling.  
Analog Input»General  
Properties»Filter»Analog  
Lowpass»Cutoff Frequency  
AI. LowPass.CutoffFreq Specifies the lowpass cutoff  
frequency  
Table 5-2. NI-DAQmx Thermocouple Measurement Properties  
Property  
Short Name  
Description  
Analog Input»Temperature» AI.Thrmcpl.Type  
Thermocouple»Type  
Specifies the type of thermocouple  
connected to the channel.  
Analog Input»Temperature» AI.Thrmcpl.ScaleType Specifies the method or equation form  
Thermocouple»ScaleType  
that the thermocouple scale uses.  
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Table 5-3. NI-DAQmx RTD Measurement Properties  
Property  
Short Name  
Description  
Analog Input»Temperature»  
RTD»Type  
AI.RTD.Type  
Specifies the type of RTD  
connected to the channel.  
Analog Input»Temperature»  
RTD»R0  
AI.RTD.R0  
Specifies the resistance in ohms of  
the sensor at 0 °C.  
Analog Input»Temperature»  
RTD»Custom»A, B, C  
AI.RTD.A  
AI.RTD.B  
AI.RTD.C  
Specifies the A, B, or C constant of  
the Callendar-Van Dusen equation  
when using a custom RTD type.  
Analog Input»General Properties» AI.Resistance.Cfg  
Signal Conditioning»Resistance  
Configuration  
Specifies the resistance  
configuration for the channel, such  
as 2-wire, 3-wire, or 4-wire.  
Table 5-4. NI-DAQmx Thermistor Measurement Properties  
Property  
Short Name  
Description  
Analog Input»Temperature»  
Thermistor»R1  
AI.Thrmistr.R1  
Specifies the resistance in ohms of  
the sensor at 0 °C.  
Analog Input»Temperature»  
Thermistor»Custom»A, B, C  
AI.Thrmistr.A  
AI.Thrmistr.B  
AI.Thrmistr.C  
Specifies the A, B, or C constant  
of the Steinhart-Hart thermistor  
equation, which NI-DAQmx uses to  
scale thermistors.  
Table 5-5. NI-DAQmx Current Measurement Properties  
Property  
Short Name  
Description  
Analog Input»General Properties» AI.CurrentShunt.Loc  
Signal Conditioning»Current  
Shunt Resistors»Location  
Specifies whether the  
shunt resistance location is  
internal or external.  
Analog Input»General Properties» AI.CurrentShunt.Resistance Specifies the resistance, in  
Signal Conditioning»Current  
Shunt Resistor»Value  
ohms, of the external shunt  
resistance.  
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Note This is not a complete list of NI-DAQmx properties and does not include every  
property you may need to configure your application. It is a representative sample of  
important properties to configure for voltage measurements. For a complete list of  
NI-DAQmx properties and more information about NI-DAQmx properties, refer to your  
ADE help file.  
Acquiring, Analyzing, and Presenting  
After configuring the task and channels, you can start the acquisition, read  
measurements, analyze the data returned, and display it according to the  
needs of your application. Typical methods of analysis include digital  
filtering, averaging data, performing harmonic analysis, applying a custom  
scale, or adjusting measurements mathematically.  
NI provides powerful analysis toolsets for each NI ADE to help you  
perform advanced analysis on the data without requiring you to have a  
programming background. After you acquire the data and perform any  
required analysis, it is useful to display the data in a graphical form or log  
it to a file. NI ADEs provide easy-to-use tools for graphical display, such as  
charts, graphs, slide controls, and gauge indicators. NI ADEs have tools  
that allow you to easily save the data to files such as spread sheets for easy  
viewing, ASCII files for universality, or binary files for smaller file sizes.  
Completing the Application  
After you have completed the measurement, analysis, and presentation of  
the data, it is important to stop and clear the task. This releases any memory  
used by the task and frees up the DAQ hardware for use in another task.  
Note In LabVIEW, tasks are automatically cleared.  
Developing an Application Using LabVIEW  
This section describes in more detail the steps shown in the typical program  
flowchart in Figure 5-1, such as how to create a task in LabVIEW and  
configure the channels of the SCXI-1141/1142/1143. If you need more  
information or for further instructions, select Help»VI, Function, &  
How-To Help from the LabVIEW menu bar.  
Note Except where otherwise stated, the VIs in Table 5-6 are located on the Functions»  
All Functions»NI Measurements»DAQmx - Data Acquisition subpalette and  
accompanying subpalettes in LabVIEW.  
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Table 5-6. Programming a Task in LabVIEW  
Flowchart Step  
VI or Program Step  
Create Task in DAQ Assistant  
Create a DAQmx Task Name Controllocated on the  
Controls»All Controls»I/O»DAQmx Name Controls  
subpalette, right-click it, and select New Task (DAQ  
Assistant).  
Create a Task  
Programmatically  
(optional)  
DAQmx Create Task.vilocated on the Functions»  
All Functions»NI Measurements»DAQmx - Data  
Acquisition»DAQmx Advanced Task Options  
subpalette—This VI is optional if you created and configured  
the task using the DAQ Assistant. However, if you use it in  
LabVIEW, any changes you make to the task are not saved to a  
task in MAX.  
Create Virtual Channel(s)  
DAQMX Create Virtual Channel.vilocated on the  
Functions»All Functions»NI Measurements»DAQmx - Data  
Acquisition subpalette—Use this VI to add virtual channels to  
the task. Select the type of virtual channel based on the  
measurement you plan to perform.  
Adjust Timing Settings  
(optional)  
DAQmx Timing.vi(Sample Clock by default)—This VI is  
Assistant. Any timing settings modified with this VI are not  
saved in the DAQ Assistant. They are only available for the  
present session.  
Configure Channels  
(optional)  
NI-DAQmx Channel Property Node, refer to the Using a  
NI-DAQmx Channel Property Node in LabVIEW section for  
more information. This step is optional if you created and fully  
configured the channels using the DAQ Assistant. Any channel  
modifications made with a channel property node are not saved  
in the task in the DAQ Assistant. They are only available for the  
present session.  
Start Measurement  
Read Measurement  
Analyze Data  
DAQmx Start Task.vi  
DAQmx Read.vi  
Some examples of data analysis include filtering, scaling,  
harmonic analysis, or level checking. Some data analysis tools  
are located on the Functions»Signal Analysis subpalette and on  
the Functions»All Functions»Analyze subpalette.  
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Table 5-6. Programming a Task in LabVIEW (Continued)  
Flowchart Step  
Display Data  
VI or Program Step  
You can use graphical tools such as charts, gauges, and graphs  
to display the data. Some display tools are located on the  
Controls»All Controls»Numeric»Numeric Indicator  
subpalette and Controls»All Controls»Graph subpalette.  
Continue Sampling  
For continuous sampling, use a While Loop. If you are using  
hardware timing, you also need to set the DAQmx Timing.vi  
sample mode to Continuous Samples. To do this, right-click the  
terminal of the DAQmx Timing.vilabeled sample mode and  
click Create»Constant. Click the box that opens on the block  
diagram and select Continuous Samples.  
Stop Measurement  
Clear Task  
DAQmx Stop Task.vi(This VI is optional, clearing the task  
automatically stops the task.)  
DAQmx Clear Task.vi  
Using a NI-DAQmx Channel Property Node in  
LabVIEW  
You can use property nodes in LabVIEW to manually configure the  
channels. To create a LabVIEW property node, complete the following  
steps:  
1. Launch LabVIEW.  
2. Create the property node in a new VI or in an existing VI.  
3. Open the block diagram view.  
4. From the Functions toolbox, select All Functions»NI  
Measurements»DAQmx - Data Acquisition, and select DAQmx  
Channel Property Node.  
5. The ActiveChans property is displayed by default. This allows you to  
specify exactly what channel(s) you want to configure. If you want to  
configure several channels with different properties, separate the lists  
of properties with another Active Channels box and assign the  
appropriate channel to each list of properties.  
Note If you do not use Active Channels, the properties are set on all of the channels in  
the task.  
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6. Right-click ActiveChans, and select Add Element. Left-click the new  
ActiveChans box. Navigate through the menus, and select the  
property you wish to define.  
7. Change the property to read or write to either get the property or write  
a new value. Right-click the property, go to Change To, and select  
Write, Read, or Default Value.  
8. After you have added the property to the property node, right-click the  
terminal to change the attributes of the property, add a control,  
constant, or indicator.  
9. To add another property to the property node, right-click an existing  
property and left-click Add Element. To change the new property,  
left-click it and select the property you wish to define.  
Note Refer to the LabVIEW Help for information about property nodes and specific  
NI-DAQmx properties.  
Specifying Channel Strings in NI-DAQmx  
Use the channel input of DAQmx Create Channel to specify the  
SCXI-1141/1142/1143 channels. The input control/constant has a  
pull-down menu showing all available external channels. The strings take  
one of the following forms:  
single device identifier/channel number—for example SC1Mod1/ch0  
multiple, noncontinuous channels—for example SC1Mod1/ch0,  
SC1Mod1/ch4.  
multiple continuous channels—for example SC1Mod1/ch0:4  
(channels 0 through 4)  
When you have a task containing SCXI-1141/1142/1143 channels, you can  
set the properties of the channels programmatically using the DAQmx  
Channel Property Node.  
Text Based ADEs  
You can use text based ADEs such as LabWindows/CVI, Measurement  
Studio, Visual Basic 6, .NET, and C# to create code for using the  
SCXI-1141/1142/1143.  
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LabWindows/CVI  
LabWindows/CVI works with the DAQ Assistant in MAX to generate  
code for an voltage measurement task. You can then use the appropriate  
function call to modify the task. To create a configurable channel or task in  
LabWindows/CVI, complete the following steps:  
1. Launch LabWindows/CVI.  
2. Open a new or existing project.  
3. From the menu bar, select Tools»Create/Edit DAQmx Tasks.  
4. Choose Create New Task In MAX or Create New Task In Project  
to load the DAQ Assistant.  
5. The DAQ Assistant creates the code for the task based on the  
parameters you define in MAX and the device defaults. To change  
a property of the channel programmatically, use the  
DAQmxSetChanAttributefunction.  
Note Refer to the NI LabWindows/CVI Help for more information on creating NI-DAQmx  
tasks in LabWindows/CVI and NI-DAQmx property information.  
Measurement Studio (Visual Basic 6, .NET, and C#)  
When creating an voltage measurement task in Visual Basic 6, .NET and  
C#, follow the general programming flow in Figure 5-1. You can then use  
the appropriate function calls to modify the task. This example creates a  
new task and configures an NI-DAQmx voltage measurement channel on  
the SCXI-1141/1142/1143. You can use the same functions for Visual  
Basic 6, .NET and C#.  
The following text is a function prototype example:  
void AIChannelCollection.CreateVoltageChannel(  
System.String physicalChannelName,  
System.String nameToAssignChannel,  
System.Double minVal,  
System.Double maxVal);  
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To actually create and configure the channel, you would enter something  
resembling the following example code:  
Task myTask = new  
NationalInstruments.DAQmx.Task(“myTaskName”);  
MyTask.DAQmxCreateAIVoltageChan (  
“SC1Mod1/ai0”, // System.String physicalChannelName  
“Voltage0”, // System.String nameToAssignChannel  
-10.0, // System.Double minVal  
10.0); // System.Double maxVal  
// setting attributes after the channel is created  
AIChannel myChannel = myTask.AIChannels[“Voltage0”];  
myChannel.AutoZeroMode = kAutoZeroTypeOnce;  
Modify the example code above or the code from one of the shipping  
examples as needed to suit your application.  
Note You can create and configure the voltage measurement task in MAX and  
load it into your application with the function call  
NationalInstruments.DAQmx.DaqSystem.Local.LoadTask.  
Refer to the NI Measurement Studio Help for more information on creating NI-DAQmx  
tasks in LabWindows/CVI and NI-DAQmx property information.  
Programmable NI-DAQmx Properties  
All of the different ADEs that configure the SCXI-1141/1142/1143 access  
an underlying set of NI-DAQmx properties. Tables 5-1, 5-2, and 5-3  
provide a list of some of the properties that configure the  
SCXI-1141/1142/1143. You can use this list to determine what kind of  
properties you need to set to configure the device for your application. For  
a complete list of NI-DAQmx properties, refer to your ADE help file.  
Note Tables 5-1, 5-2, and 5-3 are not complete lists of NI-DAQmx properties and  
do not include every property you may need to configure voltage measurements. It is a  
representative sample of important properties to configure voltage measurements. For a  
complete list of NI-DAQmx properties and more information on NI-DAQmx properties,  
refer to your ADE help file.  
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Chapter 5  
Using the SCXI-1141/1142/1143 Module  
Calibration  
The SCXI-1141/1142/1143 is shipped with a calibration certificate and is  
calibrated at the factory to the specifications described in Appendix A,  
Specifications. Calibration constants are stored inside the calibration  
EEPROM and provide software correction values your application  
development software uses to correct the measurements for both offset and  
gain errors in the module.  
External Calibration  
If you have an accurate calibrator and DMM, you can externally calibrate  
the SCXI-1141/1142/1143 gain and offset constants using NI-DAQmx  
functions.  
Most external calibration documents for SCXI modules are available to  
download from ni.com/calibrationby clicking Manual Calibration  
Procedures. For external calibration of modules not listed there, Basic  
Calibration Service or Detailed Calibration Service is recommended.  
You can get information about both of these calibration services from  
ni.com/calibration. NI recommends performing an external  
calibration once a year.  
© National Instruments Corporation  
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A
Specifications  
This appendix lists the specifications for the SCXI-1141/1142/1143  
module. These specifications are typical at 25 °C unless otherwise noted.  
Amplifier Characteristics  
Number of channels ............................... 8 differential  
Output signal range ................................ 5 V  
Channel gains (software-selectable) ...... 1, 2, 5, 10, 20, 50, 100  
Input overvoltage protection  
Powered on ..................................... 30 V  
Powered off..................................... 15 V  
Input coupling ........................................ DC (AC available with  
SCXI-1304 or SCXI-1305  
terminal block)  
Input impedance  
Powered on ..................................... 10 GΩ in parallel with 40 pF  
Powered off..................................... 2.4 kΩ  
Input bias current ................................... 450 pA  
Input bias current  
temperature coefficient .......................... 0.8 pA/°C  
Input offset current................................. 250 pA  
Common-mode rejection ratio ............... 60 dB (G = 1)  
© National Instruments Corporation  
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Appendix A  
Specifications  
DC gain error.......................................... 0.6% before calibration,  
0.02% after calibration1  
9.5  
Gain  
DC input offset ....................................... 10 + ----------- mV max  
Filter Characteristics  
Filter type  
SCXI-1141 module..........................8th-order elliptic  
SCXI-1142 module..........................8th-order Bessel  
SCXI-1143 module..........................8th-order Butterworth  
Filter architecture....................................Switched capacitor with prefilters  
and postfilters  
Rolloff rate..............................................135 dB/octave  
Cutoff frequency (fc) range.....................10 Hz to 25 kHz  
Cutoff choices (software-selectable) ......Divided from 100 kHz or external  
clock (for example, 25 kHz,  
20 kHz, 16.7 kHz, 14.3 kHz,  
or from external)  
Passband ripple  
(SCXI-1141 module only)......................0.2 dB, DC to fc  
Phase matching  
(SCXI-1142 only)...................................3° max error at fc  
Stopband attenuation  
SCXI-1141module...........................80 dB at 1.5 × fc  
SCXI-1142 module..........................80 dB at 6 × fc  
SCXI-1143 module..........................80 dB at 3.2 × fc  
Prefilter aliasing rejection.......................> 80 dB below 99 × fc  
> 40 dB above 99 × fc  
Sampled image + clock feedthrough ......<–75 dB  
1
SCXI-1141/1142/1143 module factory calibration conditions: Vin(–) = 0 V, Vin(+) = fullscale  
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Appendix A  
Specifications  
Bandwidth and response time  
Table A-1. Settling Time with Respect to Cutoff Frequency  
Step Response Settling Time in ms  
(Full-Scale Input Step)  
Module  
Bandwidth  
10  
1%  
5250  
103  
0.1%  
10805  
4500  
887  
0.024%  
SCXI-1141  
14585  
7380  
100  
1000  
25000  
10  
10  
4090  
0.575  
3595  
4480  
815  
0.97  
2600  
SCXI-1142  
SCXI-1143  
9335  
8085  
5965  
250  
13960  
11365  
9590  
100  
1000  
25000  
10  
19.55  
5000  
547  
3174  
10676  
8140  
6207  
1399  
13514  
11567  
10419  
4838  
100  
1000  
25000  
270  
73  
System Noise  
THD  
1 kHz............................................... –70 dB  
0–25 kHz ........................................ –60 dB  
Input noise.............................................. 30 nV × fc  
Output noise ........................................... 500 µVrms  
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Appendix A  
Specifications  
Stability  
DC gain temperature coefficient.............20 ppm/°C  
32  
Gain  
Input offset drift...................................... 20 + ----------- µV/°C typ  
100  
Gain  
60 + ----------- µV/°C max  
AC gain temperature coefficient.............280 ppm/°C  
Digital Input/Output  
EXT CLK pin input voltage  
with respect to DIG GND.......................5.5 V max  
–0.5 V min  
Absolute maximum voltage input  
rating with respect to DIG GND.............–0.5 to 5.5 V  
Digital input referenced to DIG GND  
VIH, input logic high voltage ...........2 V min  
VIL, input logic low voltage.............0.8 V max  
Digital output referenced to DIG GND  
V
V
OH, output logic high voltage........3.7 V min at 4 mA  
OL, output logic low voltage .........0.4 V max at 4 mA  
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Appendix A  
Specifications  
Physical  
3.0 cm  
(1.2 in.)  
17.2 cm  
(6.8 in.)  
18.8 cm  
(7.4 in.)  
Figure A-1. SCXI-1141/1142/1143 Dimensions  
Weight  
SCXI-1141 and SCXI-1143............ 623 g (22.0 oz)  
SCXI-1142...................................... 676 g (22.8 oz)  
I/O connectors  
Rear connector ................................ 50-pin male ribbon-cable  
Front connector............................... 96-pin DIN C male  
(screw-terminal adapters available)  
Maximum Working Voltage  
Maximum working voltage refers to the signal voltage plus the  
common-mode voltage.  
Channel-to-earth..................................... 5 V, Measurement Category I  
Channel-to-channel ................................ 10 V, Measurement Category I  
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Appendix A  
Specifications  
Environmental  
Operating temperature ............................0 to 50 °C  
Storage temperature................................–20 to 70 °C  
Humidity.................................................10 to 90% RH, noncondensing  
Maximum altitude...................................2,000 m  
Pollution Degree (indoor use only) ........2  
Safety  
This product is designed to meet the requirements of the following  
standards of safety for electrical equipment for measurement, control,  
and laboratory use:  
IEC 61010-1, EN-61010-1  
UL 61010-1, CSA 61010-1  
Note For UL and other safety certifications, refer to the product label or visit  
ni.com/certification, search by model number or product line, and click the  
appropriate link in the Certification column.  
Electromagnetic Compatibility  
This product is designed to meet the requirements of the following  
standards of EMC for electrical equipment for measurement, control,  
and laboratory use:  
EN 61326 EMC requirements; Minimum Immunity  
EN 55011 Emissions; Group 1, Class A  
CE, C-Tick, ICES, and FCC Part 15 Emissions; Class A  
Note For EMC compliance, operate this device according to product documentation.  
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Appendix A  
Specifications  
CE Compliance  
This product meets the essential requirements of applicable European  
Directives, as amended for CE marking, as follows:  
73/23/EEC; Low-Voltage Directive (safety)  
89/336/EEC; Electromagnetic Compatibility Directive (EMC)  
Note Refer to the Declaration of Conformity (DoC) for this product for any additional  
regulatory compliance information. To obtain the DoC for this product, visit  
ni.com/certification, search by model number or product line, and click the  
appropriate link in the Certification column.  
Waste Electrical and Electronic Equipment (WEEE)  
EU Customers At the end of their life cycle, all products must be sent to a WEEE recycling  
center. For more information about WEEE recycling centers and National Instruments  
WEEE initiatives, visit ni.com/environment/weee.htm.  
© National Instruments Corporation  
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B
Removing the  
SCXI-1141/1142/1143 Module  
This appendix describes how to remove the SCXI-1141/1142/1143 module  
from an SCXI chassis and from MAX.  
Removing the SCXI-1141/1142/1143 Module from MAX  
To remove a module from MAX, complete the following steps after  
launching MAX:  
1. Expand Devices and Interfaces to display the list of installed devices  
and interfaces.  
2. Expand NI-DAQmx Devices to display the chassis.  
3. Expand the appropriate chassis to display the installed modules.  
4. Right-click the module or chassis you want to delete and click Delete.  
5. You are presented with a confirmation window. Click Yes to continue  
deleting the module or chassis or No to cancel this action.  
Note Deleting the SCXI chassis deletes all modules in the chassis. All configuration  
information for these modules is also deleted.  
The SCXI chassis and/or SCXI module(s) should now be removed from the  
list of installed devices in MAX.  
Removing the SCXI-1141/1142/1143 Module from an  
SCXI Chassis  
Consult the documentation for the chassis and accessories for additional  
instructions and precautions. To remove the SCXI-1141/1142/1143 module  
from a chassis, complete the following steps while referring to Figure B-1:  
1. Power off the chassis. Do not remove the SCXI-1141/1142/1143  
module from a chassis that is powered on.  
© National Instruments Corporation  
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Appendix B  
Removing the SCXI-1141/1142/1143 Module  
2. If the SCXI-1141/1142/1143 is the module cabled to the E/M Series  
DAQ device, disconnect the cable.  
3. Remove any terminal block that connects to the  
SCXI-1141/1142/1143.  
4. Rotate the thumbscrews that secure the SCXI-1141/1142/1143 to the  
chassis counterclockwise until they are loose, but do not completely  
remove the thumbscrews.  
5. Remove the SCXI-1141/1142/1143 by pulling steadily on both  
thumbscrews until the module slides completely out.  
6
5
1
®
4
S
C
X
I
1
1
0
0
2
3
1
2
Cable  
SCXI Module Thumbscrews  
3
4
SCXI-1141/1142/1143 Module  
Terminal Block  
5
6
SCXI Chassis Power Switch  
SCXI Chassis  
Figure B-1. Removing the SCXI-1141/1142/1143 Module  
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C
Common Questions  
This appendix lists common questions related to the use of the  
SCXI-1141/1142/1143.  
Which version of NI-DAQ works with the SCXI-1141/1142/1143, and  
how do I get the most current version of NI-DAQmx?  
click Drivers and Updates. In the Product Line drop-down menu locate  
Multifunction DAQ. Select the appropriate information for your  
application in the remaining drop-down menus and click Go.  
I have gone over the Verifying the SCXI-1141/1142/1143 Installation in  
Software section of Chapter 1, About the SCXI-1141/1142/1143, yet I still  
cannot correctly test and verify that my SCXI-1141/1142/1143 is  
working. What should I do now?  
Unfortunately, there is always the chance that one or more components in  
the system are not operating correctly. You may have to call or email a  
technical support representative. The technical support representative often  
suggests additional troubleshooting measures. If requesting technical  
support by phone, have the system nearby so you can try these measures  
immediately. NI contact information is listed in the Technical Support  
Information document.  
In NI-DAQmx, can I use channels of different measurement types in  
the same task?  
Yes, you can set up the channels programmatically or through the DAQ  
Assistant.  
Will MAX allow me to configure two SCXI-1141/1142/1143 modules  
that are in the same chassis, in multiplexed mode, with two different  
E/M Series DAQ devices?  
No.  
© National Instruments Corporation  
C-1  
SCXI-1141/1142/1143 User Manual  
 
 
Appendix C  
Common Questions  
Can I configure the SCXI-1141/1142/1143 for use in parallel mode?  
You can configure the SCXI-1141/1142/1143 for parallel mode using  
either NI-DAQmx or Traditional NI-DAQ (Legacy). For more information,  
refer to Chapter 4, Theory of Operation.  
How can I get the most accurate measurements with the  
SCXI-1141/1142/1143?  
You can use the AutoZero functionality of the SCXI-1141/1142/1143 once  
at the beginning of a measurement to compensate for any offset and achieve  
the best accuracy. For more information about the AutoZero mode, refer to  
Chapter 3, Configuring and Testing.  
How do I cascade the SCXI-1141/1142/1143 with another module?  
For more information about cascading the SCXI-1141/1142/1143, refer to  
ni.com/infoand use info code exy7sh.  
Which digital lines are unavailable on the E/M Series DAQ device if it  
is cabled to an SCXI-1141/1142/1143 module?  
Table C-1 shows the digital lines used by the SCXI-1141/1142/1143 for  
communication and scanning. These lines are unavailable for  
general-purpose digital I/O if the SCXI-1141/1142/1143 is connected to  
the E/M Series DAQ device.  
Table C-1. Digital SIgnals on the SCXI-1141/1142/1143  
Traditional  
E/M Series  
DAQ Device  
Signal Name  
NI-DAQmx  
SCXI Signal  
Name  
NI-DAQ  
(Legacy) SCXI  
Signal Name  
50-Pin  
68-Pin  
Connector Connector Direction1  
DIO0  
P0.0  
SER DAT IN  
SER DAT OUT  
DAQ D*/A  
25  
26  
27  
29  
36  
52  
19  
17  
49  
46  
Output  
Input  
DIO4  
P0.4  
P0.1  
P0.2  
DIO1  
Output  
Output  
Output  
DIO2  
SLOT 0 SEL*  
SCAN CLK  
SCAN CLK  
AI HOLD  
COMP,  
EXT STROBE* EXT STROBE* SER CLK  
37  
45  
Input  
1 With respect to the E/M Series DAQ device.  
SCXI-1141/1142/1143 User Manual  
C-2  
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Appendix C  
Common Questions  
In LabVIEW, can I use different input limits for the same  
SCXI-1141/1142/1143 channel if I repeat the channel in the SCXI  
channel string array?  
No. The SCXI-1141/1142/1143 cannot dynamically change the gain  
settings during scanning. Therefore, group channels with similar input  
ranges together in the channel string array. Make sure that repeated  
channels in different indices of the channel string array have the same input  
limits in the corresponding input limits array.  
In LabVIEW, can I use a VI to change my SCXI-1141/1142/1143  
configuration settings?  
Yes. You can change the configuration settings in NI-DAQmx using  
NI-DAQmx Tasks. In Traditional NI-DAQ (Legacy) you can use the  
AI Parameter VI to change all the SCXI-1141/1142/1143 configuration  
settings. For more information, refer to Chapter 5, Using the  
SCXI-1141/1142/1143 Module.  
Some SCXI modules permit flexible scanning. Does the  
SCXI-1141/1142/1143 module permit flexible scanning?  
No. You must scan the channels on the SCXI-1141/1142/1143 module in  
consecutive, ascending order. However, you can start the scan with any  
channel.  
Are there any cabling restrictions when using an SCXI-1141/1142/1143  
module with a plug-in E/M Series DAQ device?  
Yes. If a chassis contains an SCXI-1520, SCXI-1530/1531, or SCXI-1140  
module, at least one of these modules must be the cabled module. A cabled  
module is the module connected directly to the E/M Series DAQ device.  
This ensures that a timing signal is available for use by all  
simultaneous-sampling SCXI modules in the chassis.  
What is the power-on state of the SCXI-1141/1142/1143 multiplexer,  
analog bus switches, and configuration settings?  
The multiplexer, analog bus switches, and configuration settings are not in  
a known state immediately after power on. All hardware settings are  
programmed automatically when beginning an acquisition in LabVIEW or  
a test panel in MAX.  
© National Instruments Corporation  
C-3  
SCXI-1141/1142/1143 User Manual  
 
Appendix C  
Which accessories can I use to connect signals to the front of the  
SCXI-1141/1142/1143 module?  
For information regarding available accessories, refer to Chapter 1, About  
the SCXI-1141/1142/1143.  
How do I control the gain using LabVIEW?  
The gain of each SCXI-1141/1142/1143 channel is automatically set based  
on the channel limits used in setting up the acquisition. You usually use the  
LabVIEW DAQmx Create Channel VI to set the channel limits. If the  
channel limits are not explicitly set, the SCXI-1141/1142/1143 defaults to  
the gain setting entered when the module was configured using MAX. For  
more information, refer to Chapter 3, Configuring and Testing.  
How do I perform external triggering using the SCXI-1141/1142/1143?  
For analog triggering, use the data acquisition device analog triggering  
functionality through pin PFI 0. Verify that the E/M Series DAQ device  
supports analog triggering. For more information about analog triggering  
with the SCXI-1141/1142/1143, refer to ni.com/infoand use the info  
code rdahtu.  
For digital triggering, use the data acquisition device digital triggering  
functionality through pin PFI 0. All E/M Series DAQ devices support  
digital triggering. For more information about digital triggering with the  
SCXI-1141/1142/1143, refer to the DAQ device help file.  
SCXI-1141/1142/1143 User Manual  
C-4  
ni.com  
 
Glossary  
Symbol  
Prefix  
pico  
Value  
10–12  
10–9  
10– 6  
10–3  
103  
p
n
nano  
micro  
milli  
kilo  
μ
m
k
M
G
T
mega  
giga  
106  
109  
tera  
1012  
Symbols  
°
degrees  
>
<
greater than  
greater than or equal to  
less than  
less than or equal to  
negative of, or minus  
ohms  
Ω
%
percent  
plus or minus  
positive of, or plus  
+
© National Instruments Corporation  
G-1  
SCXI-1141/1142/1143 User Manual  
 
 
Glossary  
A
A
amperes  
A GND  
A OUT  
AC  
analog ground signal  
analog output signal  
alternating current  
ADE  
aliasing  
application development environment  
the consequence of sampling that causes signals with frequencies higher  
than half the sampling frequency to appear as lower frequency components  
B
bias current  
the small input current flowing into or out of the input terminals of an  
amplifier  
BNC  
a type of coaxial signal connector  
C
C
Celsius  
CMOS  
complementary metal-oxide semiconductor  
noise that is found on both inputs of a differential amplifier  
the frequency that defines the upper end of the passband of a lowpass filter  
common-mode noise  
cutoff frequency  
D
DAQ  
data acquisition  
DAQ D*/A  
dB  
data acquisition board data/address line signal  
decibels  
DC  
direct current  
SCXI-1141/1142/1143 User Manual  
G-2  
ni.com  
 
Glossary  
DIG GND  
DIN  
digital ground signal  
Deutsche Industrie Norme (German Industrial Standard)  
digital multimeter  
DMM  
E
EEPROM  
electrically erasable programmable read-only memory  
external clock signal  
EXT CLK  
F
fc  
cutoff frequency  
Fext  
external frequency  
G
G
gain  
gain error  
the difference between the actual and intended gain of a system  
H
hex  
hexadecimal (base 16)  
hertz  
Hz  
I
I/O  
input/output  
inch  
in.  
INTR*  
interrupt signal  
© National Instruments Corporation  
G-3  
SCXI-1141/1142/1143 User Manual  
 
Glossary  
L
lowpass filter  
a filter that passes signals below a cutoff frequency while blocking signals  
above that frequency  
M
max  
maximum  
MB  
megabytes  
min  
minutes, or minimum  
MISO  
MOSI  
multiplex  
Master-In-Slave-Out signal  
Master-Out-Slave-In signal  
to route one of many input signals to a single output  
N
Nyquist frequency  
the frequency that a sampling system can accurately reproduce, which is  
half the sampling frequency  
O
offset error  
OUTPUT  
OUTPUT REF  
the output of a system with a zero volt input  
output signal  
output reference signal  
P
passband  
the range of input frequencies that are passed to the filter output without  
attenuation  
ppm  
parts per million  
SCXI-1141/1142/1143 User Manual  
G-4  
ni.com  
 
Glossary  
R
rms  
root mean square  
rolloff  
the ratio that a system attenuates signals in the stopband with respect to the  
passband, usually defined in decibels per octave  
RSVD  
reserved signal/bit  
seconds  
S
s
S/s  
samples per second—used to express the rate at which a DAQ device  
samples an analog signal  
sample  
sample rate  
scan  
an instantaneous measurement of a signal, normally using an  
analog-to-digital convertor in a DAQ device  
the number of samples a system takes over a given time period, usually  
expressed in samples per second  
a collection of samples, usually with each sample coming from a different  
input channel  
SCAN CLK  
SCXI  
scan clock signal  
Signal Conditioning eXtensions for Instrumentation  
SCXIbus  
located in the rear of an SCXI chassis, the SCXIbus is the backplane that  
connects modules in the same chassis to each other  
SER CLK  
serial clock signal  
SER DAT IN  
SER DAT OUT  
SLOT 0 SEL  
SPI CLK  
serial data in signal  
serial data out signal  
slot 0 select signal  
serial peripheral interface clock signal  
the portion of a frequency spectrum blocked by a filter  
stopband  
© National Instruments Corporation  
G-5  
SCXI-1141/1142/1143 User Manual  
 
Glossary  
T
THD  
total harmonic distortion  
transistor-transistor logic  
TTL  
V
V
volts  
VI  
Vrms  
virtual instrument (a LabVIEW program)  
volts, root mean square  
W
working voltage  
the highest voltage that should be applied to a product during normal use,  
normally well under the breakdown voltage for safety margin  
SCXI-1141/1142/1143 User Manual  
G-6  
ni.com  
 
Index  
analog output  
multiplexed mode, 4-16  
A
A GND signal  
parallel mode, 4-17  
signal connections, 2-11  
applications  
front connector (table), 2-3  
rear connector (table), 2-9  
A OUT signal (table), 2-9  
AC-coupled signal connections  
floating (figure), 2-6  
ground-offset (figure), 2-6  
ground-referenced (figure), 2-5  
adjusting timing and triggering, 5-3  
AI+<0..7+> signal (table), 2-3  
AI–<0..7–> signal (table), 2-3  
aliasing  
presenting, 5-7  
completing, 5-7  
LabVIEW, 5-7  
programmable properties, 5-12  
specifying channel strings, 5-10  
definition, 4-12  
example (figure), 4-12  
preventing, 4-12  
amplifiers  
gain and offset correction, 4-4  
instrumentation amplifiers, 2-3  
specifications, A-1  
bypassing filters, 4-16  
theory of operation, 4-3  
front connection  
calibration  
exceeding maximum voltage  
overview, 5-1  
CE compliance specifications, A-7  
block (note), 2-4  
signal connections (figure)  
floating, 2-5  
common software-configurable settings  
gain/input range, 3-1  
floating AC-coupled, 2-6  
ground-offset AC-coupled, 2-6  
ground-referenced, 2-4  
ground-referenced AC-coupled, 2-5  
configuration  
channel properties, 5-4  
removing modules from MAX, B-1  
SCXI-1141/1142/1143  
common software settings, 3-1  
© National Instruments Corporation  
I-1  
SCXI-1141/1142/1143 User Manual  
 
 
Index  
pin equivalencies (table), 2-12  
digital I/O specifications, A-4  
documentation  
conventions used in the manual, iv  
task, 3-3  
troubleshooting self-test verification, 1-5  
verifying signal, 3-4  
SCXI-1141/1142/1143, 1-2  
NI-DAQmx, 3-4  
configuration register, 4-3  
configuration settings, gain/input range, 3-1  
configuring channel properties, 5-4  
connectors  
E
EEPROM  
front signal connector  
specifications, A-6  
pin assignments (table), 2-2  
conventions used in the manual, iv  
creating a task  
environmental specifications, A-6  
EXT CLK signal  
DAQ Assistant, 5-3  
description (table), 2-3  
frequencies, 4-14  
current measurement properties (table), 5-6  
setting  
formula for determining  
frequencies, 4-11  
F
filter bypass mode, 4-16  
filter specifications, A-2  
filter theory  
using external clock input, 4-14  
See also lowpass filters  
classification of filters, 4-5  
step input response (figure), 4-6  
transfer functions (figure), 4-5  
floating signal connections (figure), 2-5  
front connector  
D
D GND signal (table), 2-3  
DAQ Assistant, creating a task, 5-3  
DAQ D*/A signal  
digital I/O connections, 2-11  
digital control circuitry, 4-3  
digital I/O signal connections  
front connector, 2-6  
analog input channels  
common-mode signal rejection, 2-3  
exceeding maximum voltage  
(caution), 2-4  
emulation of SCXIbus  
signal connections (figures), 2-4, 2-5,  
2-6  
communication signals, 2-11  
SCXI-1141/1142/1143 User Manual  
I-2  
ni.com  
 
signal descriptions (table), 2-3  
front signal connector  
functional overview of SCXI-1141. See theory  
of operation  
software, 1-2  
SCXI-11141/1142/1143, 5-11  
lowpass filters, 4-5  
G
DC-correction circuitry, 4-15  
external clock input, 4-14  
filter bypass mode, 4-16  
filter theory, 4-5  
gain and offset correction, 4-4  
gain register, 4-3  
gain/input range, configuration, 3-1  
ground-offset AC-coupled signal connection  
(figure), 2-6  
(figure), 2-4  
phase response, 4-8  
SCXI-1141/1142/1143 as antialiasing  
filter, 4-12  
AC-coupled (figure), 2-5  
setting cutoff frequency, 4-11  
specifications, A-2  
H
I
installation  
filters, 4-6  
typical magnitude response (figure), 4-7  
Measurement & Automation Explorer  
(MAX), B-1  
NI-DAQ, 1-4  
removing SCXI-1141/1142/1143 from  
SCXI chassis, B-1  
configurable settings, 3-2  
removing modules, B-1  
self-test verification  
troubleshooting, 1-5  
measurement properties, NI-DAQmx  
current (table), 5-6  
L
LabVIEW, 1-2  
developing an application, 5-7  
programming a task (table), 5-8  
RTD (table), 5-6  
thermistor (table), 5-6  
thermocouple (table), 5-5  
voltage (table), 5-4  
© National Instruments Corporation  
I-3  
SCXI-1141/1142/1143 User Manual  
 
Index  
Measurement Studio, 1-2  
creating code for using  
SCXI-11141/1142/1143, 5-11  
Module ID register, 4-3  
O
operation of SCXI-1141/1142/1143. See  
theory of operation  
overload recovery, lowpass filters, 4-15  
N
National Instruments documentation, 1-3  
NI-DAQ, 1-2  
installation, 1-4  
parallel mode, analog output, 4-17  
passband, lowpass filters, 4-5  
performance of SCXI-1141/1142/1143 filters  
magnitude response, 4-6  
phase response, 4-8  
phase response, SCXI-1141/1142/1143 filters  
phase error (figure), 4-9  
response characteristics (figure), 4-10  
unit step response (figure), 4-11  
physical specifications, A-5  
NI-DAQmx  
acquiring, analyzing, and  
front connector  
NI-DAQmx channel property  
signal description (table), 2-3  
front signal connector (table), 2-2  
rear signal connector  
program flowchart (figure), 5-2  
specifying channel strings, 5-10  
SCXIbus to SCXI-1141/1142/1143  
power-up state, 4-1  
thermocouple measurement properties  
(table), 5-5  
voltage measurement properties  
(table), 5-4  
R
rear signal connector  
analog output signal connections, 2-11  
digital I/O signal connections  
emulation of SCXIbus  
noise pickup, minimizing, 2-3  
Nyquist frequency, 4-12  
communication signals, 2-11  
SCXIbus to SCXI-1141/1142/1143  
pin equivalencies (table), 2-12  
SCXI-1141/1142/1143 User Manual  
I-4  
ni.com  
 
Index  
removing  
SCXI-1141/1142/1143 from SCXI  
chassis, B-1  
requirements for getting started, 1-2  
ripple, real filters, 4-6  
emulation by digital I/O signal lines, 2-11  
equivalencies (table), 2-12  
self-test verification, troubleshooting, 1-5  
RTD  
digital I/O connections, 2-11  
SER DAT IN signal  
digital I/O connections, 2-11  
digital I/O connections, 2-12  
S
safety specifications, A-6  
SCXI chassis  
exceeding maximum ratings  
(caution), 2-1  
front connector  
module, 1-4  
SCXI-1141/1142/1143  
calibration, 5-13  
analog input channels, 2-3  
front signal connector  
common software settings, 3-1  
configuration settings, 3-1  
dimensions (figure), A-5  
hardware, 1-2  
analog output signal  
connections, 2-11  
software, 1-2  
using  
digital I/O signal connections, 2-11  
signals  
verifying, 3-4  
code, 5-11  
See also configuration, installation  
software  
verifying, 1-5  
overview, 1-1  
LabVIEW, 1-2  
requirements for getting started, 1-2  
SCXI-1141/1142/1143 software installation,  
verifying, 1-5  
LabWindows/CVI, 1-2  
Measurement Studio, 1-2  
NI-DAQ, 1-2  
SCXI-1304 or SCXI-1305 terminal block  
(note), 2-4  
SCXI-1141/1142/1143, 1-2  
© National Instruments Corporation  
I-5  
SCXI-1141/1142/1143 User Manual  
 
Index  
specifications  
antialiasing filter, 4-12  
transfer function characteristics  
amplifier characteristics, A-1  
CD compliance, A-7  
digital I/O, A-4  
electromagnetic compatibility, A-6  
environmental characteristics, A-6  
physical, A-5  
power-up state, 4-1  
(table), 5-6  
safety, A-6  
stability, A-4  
thermocouple, measurement properties  
timing and triggering, adjusting, 5-3  
transfer functions of lowpass filters  
characteristics (figure), 4-5  
purpose, 4-5  
system noise, A-3  
NI-DAQmx, 5-10  
stability specifications, A-4  
step input response of lowpass filters  
(figure), 4-6  
troubleshooting  
NI-DAQmx, 1-5  
stopband, 4-5  
T
verifying  
SCXI-1141/1142/1143 software  
theory of operation  
block diagram, 4-2  
signal, 3-4  
digital control circuitry, 4-3  
input amplifiers, 4-3  
gain and offset correction, 4-4  
lowpass filters  
NI-DAQmx, 3-4  
troubleshooting, 1-5  
Visual Basic  
SCXI-1141/1142/1143, 5-10  
DC-correction circuitry, 4-15  
external clock input, 4-14  
filter theory, 4-5  
magnitude response, 4-6  
overload recovery, 4-15  
performance, 4-6  
W
Waste Electrical and Electronic Equipment  
(WEEE) specification, A-7  
phase response, 4-8  
SCXI-1141/1142/1143 User Manual  
I-6  
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