National Instruments SCXI-1125 User Manual
TM
SCXI
SCXI-1125 User Manual
SCXI-1125 User Manual
April 2008
372425B-01
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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,
P0.<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 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.
monospace bold Bold text in this font denotes the messages and responses that the computer
automatically prints to the screen. This font also emphasizes lines of code
that are different from the other examples.
monospace italic
Italic text in this font denotes text that is a placeholder for a word or value
that you must supply.
Contents
Chapter 1
About the SCXI-1125
What You Need to Get Started ......................................................................................1-1
National Instruments Documentation ............................................................................1-2
Installing Application Software, NI-DAQ, and the DAQ Device .................................1-4
Installing the SCXI-1125 Module into the SCXI Chassis...............................1-4
Connecting the SCXI-1125 in an SCXI Chassis
to an E/M Series DAQ Device for Multiplexed Scanning ...........................1-4
Connecting the SCXI-1125 in a PXI/SCXI Combination Chassis
to an E/M Series DAQ Device for Multiplexed Scanning ...........................1-4
Connecting the SCXI-1125 to a n E/M Series DAQ Device
for Parallel Scanning ....................................................................................1-5
Verifying the SCXI-1125 Installation in Software ........................................................1-5
Installing SCXI Using NI-DAQmx in Software .............................................1-5
Manually Adding Modules in NI-DAQmx .....................................................1-6
Installing SCXI Using Traditional NI-DAQ (Legacy) in Software ................1-6
Manually Adding Modules in Traditional NI-DAQ (Legacy) ........................1-6
Verifying and Self-Testing the Installation .....................................................1-6
Troubleshooting the Self-Test Verification ...................................................................1-7
Troubleshooting in NI-DAQmx ......................................................................1-7
Chapter 2
Connecting Signals
AC and DC Voltage Connections..................................................................................2-1
Ground-Referenced Signal ..............................................................................2-2
Floating Signal.................................................................................................2-3
AC-Coupling ...................................................................................................2-4
Pin Assignments ............................................................................................................2-5
Temperature Sensor Connection .....................................................................2-7
Rear Signal Connector.....................................................................................2-7
© National Instruments Corporation v SCXI-1125 User Manual
Contents
Chapter 3
Configuring and Testing
SCXI-1125 Software-Configurable Settings .................................................................3-1
Common Software-Configurable Settings ...................................................... 3-1
Filter Bandwidth ............................................................................... 3-1
Gain/Input Range.............................................................................. 3-1
Connecting the SCXI-1125 in an SCXI Chassis
to an E/M Series DAQ Device for Multiplexed Scanning........................... 3-2
Connecting the SCXI-1125 in a PXI/SCXI Combination Chassis
to an E/M Series DAQ Device for Multiplexed Scanning........................... 3-2
Configurable Settings in MAX...................................................................................... 3-2
NI-DAQmx ..................................................................................................... 3-3
Creating a Voltage Global Channel or Task..................................... 3-3
Traditional NI-DAQ (Legacy) ........................................................................ 3-4
Configuring Module Property Pages
in Traditional NI-DAQ (Legacy)................................................... 3-5
Creating a Virtual Channel ............................................................... 3-6
Verifying the Signal ...................................................................................................... 3-6
Verifying the Signal in NI-DAQmx Using a Task or Global Channel........... 3-6
Verifying the Signal in Traditional NI-DAQ (Legacy) .................................. 3-7
Verifying the Signal Using Channel Strings .................................... 3-7
Verifying the Signal Using Virtual Channel .................................... 3-8
Chapter 4
Theory of Operation
Gain ............................................................................................................................... 4-1
Filter Bandwidth and Cutoff Frequency ........................................................................ 4-2
Operating in Multiplexed Mode .................................................................................... 4-2
Multiplexed Hardware Operation Theory....................................................... 4-3
Operating in Parallel Mode ........................................................................................... 4-3
Theory of Parallel Hardware Operation.......................................................... 4-4
Chapter 5
Using the SCXI-1125
Temperature Measurements Using Thermocouples...................................................... 5-1
Making High-Voltage Measurements ........................................................................... 5-4
Developing Your Application in NI-DAQmx............................................................... 5-5
Typical Program Flowchart ............................................................................ 5-5
General Discussion of Typical Flowchart....................................................... 5-7
Creating a Task Using DAQ Assistant or Programmatically ........... 5-7
Adjusting Timing and Triggering..................................................... 5-7
SCXI-1125 User Manual vi ni.com
Contents
Configuring Channel Properties........................................................5-8
Acquiring, Analyzing, and Presenting ..............................................5-9
Completing the Application ..............................................................5-9
Developing an Application Using LabVIEW..................................................5-9
Using a DAQmx Channel Property Node in LabVIEW ...................5-11
Specifying Channel Strings in NI-DAQmx.....................................................5-12
Text Based ADEs..............................................................................5-14
Measurement Studio (Visual Basic, .NET, and C#)........................................5-14
Programmable NI-DAQmx Properties..............................................5-14
Developing Your Application in Traditional NI-DAQ (Legacy) ..................................5-15
Traditional NI-DAQ (Legacy) in LabVIEW...................................................5-16
Typical Program Flow ......................................................................5-17
Configure the SCXI-1125 Settings Using Traditional NI-DAQ
(Legacy) in LabVIEW ..................................................................................5-18
Configure, Start Acquisition, and Take Readings Using Traditional
NI-DAQ (Legacy) in LabVIEW...................................................................5-19
Convert Scaling Using Traditional NI-DAQ (Legacy) in LabVIEW .............5-20
Analyze and Display Using Traditional NI-DAQ (Legacy) in LabVIEW ...... 5-20
Traditional NI-DAQ (Legacy) in Text-Based ADEs ......................................5-21
Configuring System Settings Using Traditional NI-DAQ (Legacy) C API....5-21
Configure Module Settings Using Traditional NI-DAQ (Legacy) C API ...... 5-22
Perform Offset Null Compensation
Using Traditional NI-DAQ (Legacy) C API ................................................5-23
Perform Acquisition Using Traditional NI-DAQ (Legacy) C API .................5-23
Perform Scaling, Analysis, and Display..........................................................5-24
Using Software for Multiplexed Scanning ......................................................5-24
LabVIEW and the SCXI Channel String ..........................................5-25
LabVIEW and the Virtual Channel String ........................................5-26
Performing a Multiplexed Scan.......................................................................5-27
C and Low-Level DAQ Functions .................................................... 5-28
Using Software for Parallel Scanning .............................................................5-28
LabVIEW and Parallel Mode............................................................5-28
C and Parallel Mode..........................................................................5-29
Other Application Documentation and Material ...........................................................5-29
Traditional NI-DAQ (Legacy) CVI Examples ................................................5-29
Traditional NI-DAQ (Legacy) Measurement Studio Examples......................5-29
Calibration .....................................................................................................................5-30
Calibration Procedures ....................................................................................5-30
One-Point Offset Calibration ............................................................5-31
Two-Point Gain and Offset Calibration ............................................5-32
© National Instruments Corporation vii SCXI-1125 User Manual
Contents
Appendix A
Specifications
Appendix B
Using SCXI Channel Strings with Traditional NI-DAQ (Legacy) 7.0
or Later
Appendix C
Removing the SCXI-1125
Appendix D
Common Questions
Glossary
Index
Figures
Figure 2-1. Connecting a Ground-Referenced Signal ............................................. 2-2
Figure 2-2. Connecting a Floating Signal................................................................ 2-3
Figure 2-3. Connecting a Floating AC-Coupled Signal ..........................................2-4
Figure 2-4. Connecting a Ground-Referenced AC-Coupled Signal ........................ 2-4
Figure 4-1. SCXI-1125 Block Diagram................................................................... 4-1
Figure 5-1. Typical Program Flowchart .................................................................. 5-6
Figure 5-2. LabVIEW Channel Property Node with Lowpass Frequency
Set at 10 kHz on Channel SC1Mod1/ai0 .............................................. 5-12
Figure 5-3. Typical SCXI-1125 Program Flow
with Traditional NI-DAQ (Legacy) ...................................................... 5-17
Figure 5-4. Using the AI Parameter VI to Set Up the SCXI-1125 .......................... 5-19
Figure A-1. SCXI-1125 Dimensions ........................................................................ A-7
Figure C-1. Removing the SCXI-1125.....................................................................C-2
SCXI-1125 User Manual viii ni.com
Tables
Contents
Table 2-1. Front Signal Pin Assignments ..............................................................2-6
Table 2-2. Rear Signal Pin Assignments ................................................................2-8
Table 5-1. Extended Gain and Range Using the SCXI-1327 or SCXI-1313A....... 5-4
Table 5-2. Extended Gain and Range Using the TBX-1316 ..................................5-5
Table 5-3. NI-DAQmx Properties ..........................................................................5-8
Table 5-4. Programming a Task in LabVIEW........................................................5-10
Table 5-5. NI-DAQmx Properties ..........................................................................5-15
Table 5-6. Settings for Configuring the SCXI-1125
Through the AI Parameter.....................................................................5-18
Table 5-7. Configuration Functions........................................................................5-22
Table 5-8. NI-DAQ Functions Used to Configure SCXI-1125 ..............................5-23
Table 5-9. Gain Values and Input Limits ..............................................................5-31
Table A-1. Input Signal Range Versus Gain ...........................................................A-1
Table A-2. Terminal Block Maximum Voltages.....................................................A-8
Table D-1. Comparison of the SCXI-1125 with the SCXI-1120 ............................D-1
Table D-2. Digital Signals on the SCXI-1125.........................................................D-3
© National Instruments Corporation ix SCXI-1125 User Manual
About the SCXI-1125
This chapter introduces the SCXI-1125 module and explains how to install
the software and hardware.
The SCXI-1125 is an eight-channel isolated analog input conditioning
module with programmable gain and filter settings on each channel and
is jumperless. Each channel has 12 programmable gain settings from
1 to 2000 and two programmable filter settings of either 4 Hz or 10 kHz.
Each channel has an external circuit for grounding the inputs that you can
use for offset calibration. An onboard EEPROM provides nonvolatile
storage of software correction constants for both gain and offset.
1
The SCXI-1125 provides up to 300 V
has an input range of up to 1000 VDC when using an appropriate attenuator
terminal block. The SCXI-1125 supports both multiplexed and parallel
output modes and includes a cold-junction compensation (CJC) channel
that you can scan in multiplexed mode.
What You Need to Get Started
To set up and use the SCXI-1125 module, you need the following:
❑ Hardware
– SCXI-1125 module
– One of the following terminal blocks:
• SCXI-1305
• SCXI-1313A
• SCXI-1320
• SCXI-1327
• SCXI-1328
• SCXI-1338
• TBX-1316
• TBX-1328
• TBX-1329
working isolation per channel and
rms
© National Instruments Corporation 1-1 SCXI-1125 User Manual
Chapter 1 About the SCXI-1125
Note For maximum allowable voltage for a particular terminal block refer to Table A-2,
Terminal Block Maximum Voltages.
– SCXI or PXI/SCXI combination chassis
– One of the following:
• E/M Series DAQ device
• SCXI-1600 module
– A computer if using an SCXI chassis
– Cabling, cable adapter, and sensors as required for your
application
❑ Software
– NI-DAQ 7.0 or later
– One of the following software packages:
•LabVIEW
™
• LabWindows
• Measurement Studio
/CVI
™
❑ Documentation
– Read Me First: Safety and Radio-Frequency Interference
– DAQ Getting Started Guide
– SCXI Quick Start Guide
– SCXI-1125 User Manual
– Documentation for your hardware
– Documentation for your software
National Instruments Documentation
The SCXI-1125 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 or PXI 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.
SCXI-1125 User Manual 1-2 ni.com
Chapter 1 About the SCXI-1125
• 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—If you are using accessory
products, 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. National Instruments (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.
• One or more of the following help files for software information:
– Start»Programs»National Instruments»NI-DAQ»
NI-DAQmx Help
– Start»Programs»National Instruments»NI-DAQ»
Traditional NI-DAQ User Manual
– Start»Programs»National Instruments»NI-DAQ»
Traditional NI-DAQ Function Reference Help
• NI application notes or tutorials—NI has additional material on
measurements available at
ni.com/support.
You can download NI documents from
the latest version of NI-DAQ, click Drivers and Updates at
© National Instruments Corporation 1-3 SCXI-1125 User Manual
ni.com/manuals. To download
ni.com.
Chapter 1 About the SCXI-1125
Installing Application Software, NI-DAQ, and the DAQ Device
Refer to the DAQ Getting Started Guide packaged with the NI-DAQ
software to install your application software, NI-DAQ driver software, and
the DAQ device to which you will connect the SCXI-1125. NI-DAQ 7.0 or
later is required to configure and program the SCXI-1125 module. If you
do not have NI-DAQ 7.0 or later, you can either contact a NI sales
representative to request it on a CD or download the latest NI-DAQ version
from
ni.com.
Note Refer to the Read Me First: Safety and Radio-Frequency Interference document
before removing equipment covers or connecting or disconnecting any signal wires.
Installing the SCXI-1125 Module into the SCXI Chassis
Refer to the SCXI Quick Start Guide to install your SCXI-1125 module.
Connecting the SCXI-1125 in an SCXI Chassis to an E/M Series DAQ Device for Multiplexed Scanning
Refer to the SCXI Quick Start Guide to install the cable adapter and connect
the SCXI modules to the DAQ device.
If you have already installed the appropriate software, refer to Chapter 3,
Configuring and Testing, to configure the SCXI-1125 module(s).
Connecting the SCXI-1125 in a PXI/SCXI Combination Chassis to an E/M Series DAQ Device for Multiplexed Scanning
Refer to the SCXI Quick Start Guide to connect the SCXI modules to the
DAQ device.
If you have already installed the appropriate software, refer to Chapter 3,
Configuring and Testing, to configure the SCXI-1125 module(s).
SCXI-1125 User Manual 1-4 ni.com
Chapter 1 About the SCXI-1125
Connecting the SCXI-1125 to a n E/M Series DAQ Device for Parallel Scanning
This configuration allows you to route all eight channels of the SCXI-1125
in parallel to eight input channels of the E/M Series DAQ device to which
it is connected. In this mode, you cannot directly access the CJC channel.
Use this mode if you require a higher scanning rate than an SCXI system in
multiplexed mode allows.
If you have not already installed all the modules, refer to the Installing the
SCXI-1125 Module into the SCXI Chassis section, then complete the
following steps:
1. Power off the SCXI chassis and the computer that contains the
E/M Series DAQ device.
2. Insert the cable adapter into the rear of the SCXI-1125 module that is
to be accessed in parallel mode by the E/M Series DAQ device. Refer
to the installation guide for the cable assembly for more information.
3. Connect the cable to the back of the cable adapter ensuring that the
cable fits securely.
4. Connect the other end of the cable to the E/M Series DAQ device that
you want to use to access the SCXI-1125 in parallel mode.
5. Connect additional SCXI-1125 modules intended for parallel mode
operation by repeating steps 2 through 4.
6. Check the installation, making sure the cable is securely fastened at
both ends.
7. Power on the SCXI chassis.
8. Power on the computer.
If you have already installed the appropriate software, you are ready to
configure the SCXI-1125 module(s) you installed for parallel mode
operation.
Verifying the SCXI-1125 Installation in Software
Refer to the SCXI Quick Start Guide for information on verifying the SCXI
installation.
Installing SCXI Using NI-DAQmx in Software
Refer to the SCXI Quick Start Guide for information on installing modules
using NI-DAQmx in software.
© National Instruments Corporation 1-5 SCXI-1125 User Manual
Chapter 1 About the SCXI-1125
Manually Adding Modules in NI-DAQmx
If you did not auto-detect the SCXI modules, you must manually add each
of the modules. Refer to the SCXI Quick Start Guide to manually add
modules.
Note NI recommends auto-detecting modules for the first time configuration of the
chassis.
Installing SCXI Using Traditional NI-DAQ (Legacy) in Software
Refer to the SCXI Quick Start Guide for information on installing modules
using Traditional NI-DAQ (Legacy) in software.
Manually Adding Modules in Traditional NI-DAQ (Legacy)
If you did not auto-detect the SCXI modules, you must manually add each
of the modules. Refer to the SCXI Quick Start Guide to manually add
modules.
Note NI recommends auto-detecting modules for the first time configuration of the
chassis.
Verifying and Self-Testing the Installation
The verification procedure for the SCXI chassis is the same for both
NI-DAQmx and Traditional NI-DAQ (Legacy). To test the successful
installation for the SCXI chassis, refer to the SCXI Quick Start Guide.
Verify that the chassis is powered on and correctly connected to an
E/M Series DAQ device.
After verifying and self-testing the installation, the SCXI system should
operate properly with your ADE software. If the test did not complete
successfully, refer to Chapter 3, Configuring and Testing, for
troubleshooting steps.
SCXI-1125 User Manual 1-6 ni.com
Chapter 1 About the SCXI-1125
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 1125, 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.
• 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 1125,
hardware in chassis is: SCXI-YYYY, 1125, or Empty, complete the
following troubleshooting steps to correct the error.
1. Expand the list of NI-DAQmx devices by clicking the + next to
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
© National Instruments Corporation 1-7 SCXI-1125 User Manual
Chapter 1 About the SCXI-1125
module following the steps listed in the SCXI Quick Start
Guide. Click OK.
b. If another module appears where the cabled module should
be, click the drop-down listbox next to the correct slot and
select the cabled module. A message box appears 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.
• 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 Signal Conditioning Technical Support Information
document for contact information.
SCXI-1125 User Manual 1-8 ni.com
Connecting Signals
This chapter describes the input and output signals connections to the
SCXI-1125 module with the module front connector and the rear signal
connector. This chapter also includes specifications and connection
instructions for the signals on the SCXI-1125 module connectors.
Notes Refer to the Read Me First: Safety and Radio-Frequency Interference document
before removing equipment covers or connecting or disconnecting any signal wires.
For EMC compliance, operate this device with shielded cabling.
The isolated channels of the SCXI-1125 allow you to make precision
high-voltage measurements or low-voltage measurement of signals riding
on high common-mode voltages while protecting sensitive computer parts
and equipment connected to the module. The isolated amplifiers fulfill
two purposes on the SCXI-1125 module. First, they can convert a small
signal riding on a high common-mode voltage into a single-ended signal
with respect to the SCXI-1125 chassis ground. With this conversion, you
can extract the analog input signal from a high common-mode voltage
before sampling by the E/M Series DAQ device. Second, the isolation
amplifier amplifies and filters an input signal resulting in increased
measurement resolution and accuracy. The following sections explain how
to make signal connections to maximize the effectiveness of the
SCXI-1125 for conditioning analog signals.
2
AC and DC Voltage Connections
You can make input signal connections to the SCXI-1125 through the front
signal connector or through accessory terminal blocks. Chapter 1, About
the SCXI-1125, contains a list of SCXI-1125-compatible terminal blocks.
Terminal blocks have features such as screw-terminal connectivity, BNC
connectivity, cold-junction temperature measurement, and attenuation.
The pin assignment for the SCXI-1125 front signal connector is shown in
Table 2-1. The positive input terminal for each channel is in Column A and
the negative input terminal for each channel is in Column C. Input
connections to each channel are fully floating with respect to ground and
© National Instruments Corporation 2-1 SCXI-1125 User Manual
Chapter 2 Connecting Signals
completely isolated from other channels. You can operate with
common-mode voltage levels up to 300 V
Figures 2-1 through 2-4 show signal connection methods that give the
highest noise immunity.
Ground-Referenced Signal
When the negative input signal line is connected either directly or
indirectly to earth ground (usually at the transducer end), connect this line
to the negative input terminal, as shown in Figure 2-1. No ground
connection is made at the SCXI-1125. This situation includes cases where
a floating source can be riding on a high common-mode voltage that is
ground referenced.
rms
.
+
V
s
–
+
V
High
cm
CMV
–
+
I
Module
+
V
out
–
Figure 2-1. Connecting a Ground-Referenced Signal
SCXI-1125 User Manual 2-2 ni.com
Floating Signal
Chapter 2 Connecting Signals
In cases where both signal lines at the transducer end are floating and no
common-mode voltage exists, establish an earth connection at the
SCXI-1125 by connecting the negative input line to chassis ground in the
terminal block, as shown in Figure 2-2. This eliminates noise that can ride
on the floating signal. If the floating signal is not configured like
Figure 2-2, the noise can couple to the chassis ground through the amplifier
and exhibit a differential mode signal that can be amplified by the
amplifier. Connecting the signal to chassis ground breaks the isolation
barrier.
+
V
s
–
+
I
Module
Figure 2-2. Connecting a Floating Signal
+
V
out
–
© National Instruments Corporation 2-3 SCXI-1125 User Manual
Chapter 2 Connecting Signals
AC-Coupling
You can have an application where you wish to measure only AC voltages
and remove the DC component of a signal before amplification and
sampling. In such cases, you can connect a capacitor in series with one or
both input terminals of the SCXI-1125, as shown in Figures 2-3 and 2-4.
A resistor is connected across the input terminals of the channel to DC
reference the input stage of the SCXI-1125. You do not need to use a bias
resistor with any high-voltage terminal blocks, since the terminal blocks
already have a resistor between the input terminals, or with the SCXI-1305
BNC connectivity terminal block, since this terminal block already has an
AC-coupling option built in.
Caution
Connecting a signal source to chassis ground in Figures 2-2 and 2-3, breaks the
isolation barrier.
+
V
s
–
R
bias
+
I
Module
+
V
–
Figure 2-3. Connecting a Floating AC-Coupled Signal
+
R
–
+
–
bias
High
CMV
V
s
V
cm
+
I
Module
+
–
out
V
out
Figure 2-4. Connecting a Ground-Referenced AC-Coupled Signal
SCXI-1125 User Manual 2-4 ni.com
The value of the bias resistor should be between 100 kΩ and 1 MΩ . An
added DC offset voltage results, due to input bias current flowing through
the bias resistor. For example, with a 1 MΩ bias resistor and the specified
maximum input bias current of 1 nA, you have a maximum added input
offset voltage of ±1 mV in addition to the initial offset voltage.
Since only the AC signal is of interest when AC-coupling, you can choose
to remove the DC offset in software by using a simple highpass filter.
Caution Pins A2, A4, A8, C2, C4, C6, and C8 on the front signal connector are not isolated
and do not have the same protection circuitry as the positive and negative analog input pairs
discussed in the Floating Signal section. Hooking up external signals to these pins can
damage the SCXI-1125 module.
Pin Assignments
The front signal connector is a special 32-pin DIN C male front connector
used for connecting analog input signals, including the CJC, to the analog
circuitry of the SCXI-1125. This connection allows access to the eight
differential analog input signals. The positive terminal is AIx + and the
negative terminal AIx –. A missing pin exists between two consecutive
input channels to meet the UL spacing requirements for high voltage
signals. CJ TEMP is the signal connection used by the cold-junction
channel on the SCXI-1125. The signals on pins A6, A8, C6, and C8 are
reserved for serial communication. The +5 V signal and CHS GND signals
are used as the power supply and ground signals for the CJC sensor and
other circuitry on the terminal block. The pin assignments for the
SCXI-1125 front signal connection are shown in Table 2-1.
Chapter 2 Connecting Signals
Caution Do not make signal connections to pins A2, A4, A6, A8, C2, C4, C6, or C8 on the
front signal connector. Connecting external signals to these pins can damage the
SCXI-1125 Module.
© National Instruments Corporation 2-5 SCXI-1125 User Manual
Chapter 2 Connecting Signals
Table 2-1. Front Signal Pin Assignments
Front Connector Diagram Pin Number Column A Column B Column C
32 AI 0 + — AI 0 –
Column
A B C
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
NC means no connection
— means no pin
31 — — —
30 AI 1 + — AI 1 –
29 — — —
28 NC — NC
27 — — —
26 AI 2 + — AI 2 –
25 — — —
24 AI 3 + — AI 3 –
23 — — —
22 NC — NC
21 — — —
20 AI 4 + — AI 4 –
19 — — —
18 AI 5 + — AI 5 –
17 — — —
16 NC — NC
15 — — —
14 AI 6 + — AI 6 –
13 — — —
12 AI 7 + — AI 7 –
11 — — —
10 NC — NC
9 — — —
8 RSVD — RSVD
7 — — —
6 RSVD — RSVD
5 — — —
4 +5 V — CJ TEMP
3 — — —
2 CHS GND — RSVD
1 — — —
SCXI-1125 User Manual 2-6 ni.com
Temperature Sensor Connection
Pin C4 on the front signal connector is used to connect to a terminal block
temperature sensor. The temperature sensor channel is not isolated and is
referenced to the chassis ground. The connection is overvoltage protected
to ±25 VDC with power on and ±15 VDC with power off.
Rear Signal Connector
The rear signal connector is a 50-pin male ribbon cable connector used for
analog signal connectivity and communication between the
SCXI-1125 and the connected DAQ device. The rear signal connector
allows the DAQ device to access all eight differential analog output signals
from the SCXI-1125. The positive terminal of each analog output is
CH x + and the negative terminal CH x –. Grounding signals, AI GND
and OUT REF, provide reference signals needed in the various analog
referencing modes on the E/M Series DAQ device. In multiplexed mode,
the CH 0 signal pair is used for sending all eight channels of the
SCXI-1125, and other analog signals from other modules, to the connected
E/M Series DAQ device. If the module is directly connected to the E/M
Series DAQ device, the other analog channels of the E/M Series DAQ
device are still unavailable for general-purpose analog input because they
are still connected to the amplifier outputs of the SCXI-1125 in multiplexed
mode.
Chapter 2 Connecting Signals
The communication signals between the DAQ device and the SCXI system
are SER DAT IN, SER DAT OUT, DAQ D*/A, SLOT 0 SEL*, SER CLK,
and AI HOLD COMP, AI HOLD. The digital ground, D GND on pins 24
and 33, provides a separate ground reference for the communication
signals. SER DAT IN, SER DAT OUT, DAQ D*/A, SLOT 0 SEL*, and
SER CLK are the communication lines for programming the SCXI-1125.
The AI HOLD COMP, AI HOLD and SYNC signals are the signals
necessary for multiplexed mode scanning. If the E/M Series DAQ device is
connected to the SCXI-1125, these digital lines are unavailable for
general-purpose digital I/O. The rear signal pin assignments are shown in
Table 2-2.
© National Instruments Corporation 2-7 SCXI-1125 User Manual
Chapter 2 Connecting Signals
Rear Connector
Diagram
Table 2-2. Rear Signal Pin Assignments
Signal Name Pin Number Pin Number Signal Name
AI GND 1 2 AI GND
12
34
56
78
910
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 means no
connection
CH 0 + 3 4 CH 0 –
CH 1 + 5 6 CH 1–
CH 2 + 7 8 CH 2 –
CH 3 + 9 10 CH 3 –
CH 4 + 11 12 CH 4 –
CH 5 + 13 14 CH 5 –
CH 6 + 15 16 CH 6 –
CH 7 + 17 18 CH 7 –
OUT REF 19 20 NC
NC 21 22 NC
NC 23 24 D GND
SER DAT IN 25 26 SER DAT OUT
DAQ D*/A 27 28 NC
SLOT 0 SEL* 29 30 NC
NC 31 32 NC
D GND 33 34 NC
NC 35 36 AI HOLD COMP, AI HOLD
SER CLK 37 38 NC
NC 39 40 NC
NC 41 42 NC
NC 43 44 NC
NC 45 46 SYNC
NC 47 48 NC
NC 49 50 NC
SCXI-1125 User Manual 2-8 ni.com
Configuring and Testing
This chapter discusses configuring the SCXI-1125 in MAX for use with
either NI-DAQmx or Traditional NI-DAQ (Legacy), creating and testing a
virtual channel, global channel or task. For more information on the
relationship between the settings and the measurements and how to
configure settings in your application, refer to Chapter 4, Theory of
Operation.
SCXI-1125 Software-Configurable Settings
This section describes the common software configurable settings and how
to verify the signal using both NI-DAQmx and Traditional NI-DAQ
(Legacy).
Common Software-Configurable Settings
This section describes the most frequently used software-configurable
settings for the SCXI-1125. Refer to Chapter 4, Theory of Operation, for a
complete list of software-configurable settings.
3
Filter Bandwidth
Filter bandwidth is a software-configurable setting that allows you to select
a lowpass filter cutoff frequency. You can choose 4.0 Hz or 10 kHz.
Gain/Input Range
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.
© National Instruments Corporation 3-1 SCXI-1125 User Manual
Chapter 3 Configuring and Testing
Connecting the SCXI-1125 in an SCXI Chassis to an E/M Series DAQ Device for Multiplexed Scanning
Refer to the SCXI Quick Start Guide to install the cable adapter and connect
the SCXI modules to the DAQ device.
If you have already installed the appropriate software, refer to Chapter 3,
Configuring and Testing, to configure the SCXI-1125 module(s).
Connecting the SCXI-1125 in a PXI/SCXI Combination Chassis to an E/M Series DAQ Device for Multiplexed Scanning
Refer to the SCXI Quick Start Guide to connect the SCXI modules to the
DAQ device.
If you have already installed the appropriate software, refer to Chapter 3,
Configuring and Testing, to configure the SCXI-1125 module(s).
Configurable Settings in MAX
Note If you are not using an NI ADE, using an NI ADE prior to version 7.0, 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 7.0 or later of an NI ADE.
This section describes where users can access each software-configurable
setting for modification in MAX. The location of the settings varies
depending on the version of NI-DAQ you use. Refer to either the
NI-DAQmx section or the Traditional NI-DAQ (Legacy) section. You also
can refer to the DAQ Getting Started Guide and the SCXI Quick Start Guide
for more information on installing and configuring your hardware. You also
can use the DAQ Assistant to graphically configure common measurement
tasks, channels, or scales.
SCXI-1125 User Manual 3-2 ni.com
NI-DAQmx
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 on
using functions in your application.
Chapter 3 Configuring and Testing
In NI-DAQmx, you can configure software settings such as filter
bandwidth and gain/input signal range in the following ways:
• Task or global channel in MAX
• Functions in your application
These sections describe settings that you can change in MAX and where
they are located.
• Filter bandwidth—configure the Device tab using either NI-DAQmx
Task or NI-DAQmx Global Channel. You also can set the value
through your application.
• Input signal range—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.
• Modes of operation—configure only using chassis installation in
software. Refer to Chapter 1, About the SCXI-1125, for more
information on chassis installation. The default setting in NI-DAQmx
is multiplexed.
• Terminal block attenuation—for terminal blocks with manually
adjustable attenuation such as the SCXI-1327, you must configure the
attenuator in the chassis configurator. Refer to the SCXI Quick Start
Guide for more information.
Note Refer to Chapter 4, Theory of Operation, for information on configuring the settings
for your application using Traditional NI-DAQ (Legacy).
Creating a Voltage Global Channel or Task
To create a new 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.
© National Instruments Corporation 3-3 SCXI-1125 User Manual
Chapter 3 Configuring and Testing
4. Select Analog Input.
5. Select Voltage.
6. If you are creating a task, you can select a range of channels by holding
7. Name the task or channel and click Finish.
8. In the box labelled Channel List, select the channel(s) you want to
9. Enter the specific values for your application in the Settings tab.
10. Click the Device tab and select the autozero mode and lowpass filter
11. If you are creating a task and want to set timing or triggering controls,
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.
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.
Context help information for each setting is provided on the right side
of the screen. Refer to Chapter 3, Configuring and Testing, for more
information.
cutoff frequency.
enter the values in the Task Timing and Task Triggering tabs.
Traditional NI-DAQ (Legacy)
In Traditional NI-DAQ (Legacy), you can configure software settings, such
as configuration, voltage excitation level, filter bandwidth, gain/input
signal range, and calibration settings in the following three ways:
• module property pages in MAX
• virtual channels properties in MAX
• functions in your ADE
Note All software-configurable settings are not configurable in all three ways. This
section only discusses settings in MAX. Refer to Chapter 4, Theory of Operation, for
information on using functions in your application.
Most of these settings are available in module properties and/or using
virtual channels:
• Filter bandwidth—configure only using module properties. You also
can set bandwidth through your application. The default filter
bandwidth level for Traditional NI-DAQ (Legacy) is 4 Hz.
SCXI-1125 User Manual 3-4 ni.com
Chapter 3 Configuring and Testing
• Gain/input signal range—configure gain using module properties.
When you set the minimum and maximum range of the virtual
channel, the driver selects the best gain. The default gain setting
for Traditional NI-DAQ (Legacy) is 1000.
• Terminal block gain—this setting is only configurable if you selected
a terminal block that supports adjustable attenuation.
• Modes of operation—configure only using module properties. The
default setting in Traditional NI-DAQ (Legacy) is multiplexed mode.
Note Refer to Chapter 4, Theory of Operation, for information on configuring the settings
for your application using Traditional NI-DAQ (Legacy).
Configuring Module Property Pages in Traditional NI-DAQ (Legacy)
1. Right-click the SCXI-1125 module you want to configure and select
Properties. Click General.
2. If the module you are configuring is connected to an E Series DAQ
device, select that device by using Connected to. If you want this
E Series DAQ device to control the chassis, confirm there is a check in
the This device will control the chassis checkbox. If the module you
are configuring is not connected to an E Series DAQ device, select
None.
3. Click the Channel tab. Select the appropriate gain and filter for each
channel. If you want to configure all the channels at the same time,
select the Channel drop-down menu, scroll to the bottom, and select
All Channels. Refer to the SCXI-1125 Software-Configurable Settings
section for a detailed description of each setting. Click Apply.
4. Click Accessory. Select the accessory you connected to the module. If
the accessory has a configurable gain, select the desired gain. When
configuration is complete, click OK.
The Traditional NI-DAQ (Legacy) chassis and SCXI-1125 should now be
configured properly. If you need to change the module configuration,
right-click the module and repeat steps 1 through 4. Test the system
following the steps in the Troubleshooting the Self-Test Verification
section of Chapter 1, About the SCXI-1125.
© National Instruments Corporation 3-5 SCXI-1125 User Manual
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