NI PXI-4220 User manual

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PXI
NI PXI-4220 User Manual
NI PXI-4220 User Manual
May 2005
373530B-01
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Warranty
The NI PXI-4220 is 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
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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,
DIO<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 icon is marked on the
product, refer to the Read Me First: Safety and Radio-Frequency
Interference document, shipped with the product, for 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. This font 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, and code excerpts.
monospace italic Italic text in this font denotes text that is a placeholder for a word or value
that you must supply.
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©National Instruments Corporation v NI PXI-4220 User Manual
Contents
Chapter 1
About the NI PXI-4220
What You Need to Get Started ......................................................................................1-2
National Instruments Documentation ............................................................................1-3
Installing the Application Software, NI-DAQ, and the DAQ Device ...........................1-3
Installing the NI PXI-4220 ............................................................................................1-4
LED Pattern Descriptions ..............................................................................................1-4
Chapter 2
Connecting Signals
Connecting Bridge Sensor Signals to the NI PXI-4220 ................................................2-1
Quarter-Bridge Type I .....................................................................................2-4
Quarter-Bridge Type II....................................................................................2-6
Half-Bridge Type I ..........................................................................................2-7
Half-Bridge Type II.........................................................................................2-8
Full-Bridge Type I...........................................................................................2-9
Full-Bridge Type II..........................................................................................2-10
Full-Bridge Type III ........................................................................................2-11
Remote Sense ..................................................................................................2-12
Chapter 3
Configuring and Testing
Verifying and Self-Testing Using Device Test Panels ..................................................3-1
NI PXI-4220 Software-Configurable Settings...............................................................3-2
Common Software-Configurable Settings ......................................................3-2
Bridge Configuration and Completion..............................................3-2
Excitation Level ................................................................................3-2
Filter ..................................................................................................3-3
Gain/Input Range ..............................................................................3-3
Offset Null Compensation Potentiometers .......................................3-3
Shunt Calibration Switches...............................................................3-4
Simultaneous Sample and Hold ........................................................3-4
Configurable Settings in MAX ......................................................................................3-4
NI-DAQmx......................................................................................................3-5
Creating a Strain Global Channel or Task ........................................3-6
Creating a Custom Voltage with
Excitation Global Channel or Task ................................................3-7
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Contents
NI PXI-4220 User Manual vi ni.com
Verifying the Signal ...................................................................................................... 3-8
Verifying the Signal in NI-DAQmx Using a Task or Global Channel........... 3-8
Chapter 4
Theory of Operation
Strain Gauge Theory...................................................................................................... 4-1
Wheatstone Bridges ........................................................................................ 4-1
Strain Gauges .................................................................................................. 4-2
Acronyms, Formulas, and Variable Definitions ............................................. 4-2
Software Scaling and Equations ..................................................................... 4-3
Quarter-Bridge Type I..................................................................................... 4-4
Quarter-Bridge Type II ................................................................................... 4-6
Half-Bridge Type I.......................................................................................... 4-8
Half-Bridge Type II ........................................................................................ 4-10
Full-Bridge Type I .......................................................................................... 4-12
Full-Bridge Type II ......................................................................................... 4-14
Full-Bridge Type III........................................................................................ 4-16
NI PXI-4220 Theory of Operation ................................................................................ 4-18
Bridge Configuration and Completion............................................................ 4-21
Excitation ........................................................................................................ 4-21
Remote Sense ................................................................................... 4-22
Gain/Input Range ............................................................................................ 4-24
Filter ................................................................................................................ 4-25
Offset Null Compensation .............................................................................. 4-26
Shunt Calibration ............................................................................................ 4-27
Simultaneous Sample and Hold ...................................................................... 4-28
Maximum Acquisition Rate.............................................................. 4-30
Measurement Considerations.......................................................................... 4-30
Differential Signals........................................................................... 4-30
Common-Mode Rejection Ratio....................................................... 4-30
Effective CMR.................................................................................. 4-31
Timing and Control Functional Overview ...................................................... 4-31
Programmable Function Inputs....................................................................... 4-32
Device and PXI Clocks ................................................................................... 4-33
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Contents
©National Instruments Corporation vii NI PXI-4220 User Manual
Chapter 5
Developing Your Application
Developing Your Application in NI-DAQmx ...............................................................5-1
Typical Program Flow.....................................................................................5-1
General Discussion of Typical Flow Chart .....................................................5-3
Creating a Task Using DAQ Assistant or Programmatically ...........5-3
Adjusting Timing and Triggering .....................................................5-4
Configuring Channel Properties........................................................5-4
Perform Offset Null Compensation ..................................................5-6
Perform Shunt Calibration ................................................................5-7
Acquiring, Analyzing, and Presenting ..............................................5-7
Completing the Application ..............................................................5-8
Developing an Application Using LabVIEW..................................................5-8
Using a DAQmx Channel Property Node in LabVIEW ...................5-10
Synchronization and Triggering ......................................................................5-12
Synchronizing the NI PXI-4220......................................................................5-12
Synchronizing the NI PXI-4220 Using LabVIEW ...........................5-14
Other Application Documentation and Material ...........................................................5-15
Calibrating the NI PXI-4220..........................................................................................5-16
Calibrating the NI PXI-4220 ...........................................................................5-16
Internal Calibration Procedure ..........................................................5-16
External Device Calibration..............................................................5-17
Calibrating the System ....................................................................................5-17
Offset Null Compensation ................................................................5-17
Shunt Calibration ..............................................................................5-17
Appendix A
Specifications
Appendix B
Timing Signal Information
Appendix C
Removing the NI PXI-4220
Appendix D
Common Questions
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Contents
NI PXI-4220 User Manual viii ni.com
Glossary
Index
Figures
Figure 2-1. NI PXI-4220 Front Label...................................................................... 2-2
Figure 2-2. PXI-4220 Front Connector and General Circuit Diagram.................... 2-3
Figure 2-3. Socketed Resistor Locations ................................................................. 2-4
Figure 2-4. Quarter-Bridge I Circuit Diagram......................................................... 2-5
Figure 2-5. Quarter-Bridge II Circuit Diagram ....................................................... 2-6
Figure 2-6. Half-Bridge Type I Circuit Diagram..................................................... 2-7
Figure 2-7. Half-Bridge Type II Circuit Diagram ................................................... 2-8
Figure 2-8. Full-Bridge Type I Circuit Diagram ..................................................... 2-9
Figure 2-9. Full-Bridge Type II Circuit Diagram.................................................... 2-10
Figure 2-10. Full-Bridge Type III Circuit Diagram................................................... 2-11
Figure 2-11. Remote Sense Circuit Diagram............................................................. 2-12
Figure 4-1. Basic Wheatstone Bridge Circuit Diagram........................................... 4-1
Figure 4-2. Quarter-Bridge Type I Measuring Axial and Bending Strain............... 4-4
Figure 4-3. Quarter-Bridge Type I Circuit Diagram ............................................... 4-4
Figure 4-4. Quarter-Bridge Type II Measuring Axial and Bending Strain ............. 4-6
Figure 4-5. Quarter-Bridge Type II Circuit Diagram .............................................. 4-7
Figure 4-6. Half-Bridge Type I Measuring Axial and Bending Strain.................... 4-8
Figure 4-7. Half-Bridge Type I Circuit Diagram..................................................... 4-9
Figure 4-8. Half-Bridge Type II Rejecting Axial and
Measuring Bending Strain .................................................................... 4-10
Figure 4-9. Half-Bridge Type II Circuit Diagram ................................................... 4-11
Figure 4-10. Full-Bridge Type I Rejecting Axial and Measuring Bending Strain .... 4-12
Figure 4-11. Full-Bridge Type I Circuit Diagram ..................................................... 4-13
Figure 4-12. Full-Bridge Type II Rejecting Axial and Measuring Bending Strain... 4-14
Figure 4-13. Full-Bridge Type II Circuit Diagram .................................................... 4-15
Figure 4-14. Full-Bridge Type III Measuring Axial and
Rejecting Bending Strain ...................................................................... 4-17
Figure 4-15. Full-Bridge Type III Circuit Diagram................................................... 4-17
Figure 4-16. Block Diagram of the NI PXI-4220...................................................... 4-19
Figure 4-17. Signal During Simultaneous Sample and Hold Sampling .................... 4-29
Figure 4-18. AI CONV CLK Signal Routing............................................................ 4-32
Figure 4-19. NI PXI-4220 PXI Trigger Bus Signal Connection ............................... 4-34
Figure 5-1. Typical Program Flowchart .................................................................. 5-2
Figure 5-2. LabVIEW Channel Property Node with Filtering Enabled at
10 kHz and SS/H Disabled ................................................................... 5-11
Figure 5-3. General Synchronizing Flowchart ........................................................ 5-13
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Contents
©National Instruments Corporation ix NI PXI-4220 User Manual
Figure B-1. Typical Posttriggered Sequence ............................................................B-2
Figure B-2. Typical Pretriggered Sequence..............................................................B-2
Figure B-3. AI START TRIG Input Signal Timing .................................................B-3
Figure B-4. AI START TRIG Output Signal Timing...............................................B-3
Figure B-5. AI REF TRIG Input Signal Timing.......................................................B-4
Figure B-6. AI REF TRIG Output Signal Timing....................................................B-5
Figure B-7. AI SAMP CLK Input Signal Timing ....................................................B-6
Figure B-8. AI SAMP CLK Output Signal Timing..................................................B-6
Figure B-9. AI CONV CLK Input Signal Timing ....................................................B-7
Figure B-10. AI CONV CLK Output Signal Timing .................................................B-8
Figure B-11. AI SAMPLE CLK TIMEBASE Signal Timing ....................................B-9
Figure B-12. AI HOLD COMPLETE Signal Timing.................................................B-10
Figure C-1. Injector/Ejector Handle Position Before Device Removal....................C-2
Tables
Table 3-1. Excitation Voltage for Configuration and Gauge Resistances..............3-3
Table 4-1. Strain-Gauge Configurations.................................................................4-2
Table 4-2. Control Codes for Coarse and Fine Null Potentiometers ......................4-26
Table 4-3. Maximum Sampling Rates ....................................................................4-30
Table 4-4. PXI Trigger Bus Timing Signals...........................................................4-35
Table 5-1. NI-DAQmx Properties ..........................................................................5-4
Table 5-2. Programming a Task in LabVIEW........................................................5-8
Table 5-3. Synchronizing the NI PXI-4220 Using LabVIEW................................5-14
Table A-1. Maximum Sampling Rates ....................................................................A-1
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©National Instruments Corporation 1-1 NI PXI-4220 User Manual
1
About the NI PXI-4220
This chapter provides an introduction to the NI PXI-4220 device and
its installation.
The NI PXI-4220 is part of the SC Series of data acquisition (DAQ) devices
with integrated signal conditioning. The SC Series reduces measurement
setup and configuration complexity by integrating signal conditioning and
DAQ on the same product.
The NI PXI-4220 is a full-featured dynamic strain device with
programmable bridge-sensor signal conditioning, programmable filter, and
programmable gain settings per channel ensuring maximum accuracy for
bridge sensors. The NI PXI-4220 features the National Instruments (NI)
programmable gain amplifier (PGA), an instrumentation-class amplifier that
guarantees fast settling times at all gain settings. The NI PXI-4220 also uses
the NI-DAQmx DAQ Assistant, specifically the
Strain Gage Calibration
wizard, to easily perform offset null compensation and shunt calibration.
The NI PXI-4220 is a two-channel module for interfacing to Wheatstone
bridge configurations. The NI PXI-4220 has the following features:
• Two differential analog input (AI) channels
• 16-bit resolution
• 333 kS/s single-channel sampling rate
• 66 kS/s per channel when simultaneously sampling
• Direct connectivity through two male D-Subminiature (D-SUB)
connectors
• Instrumentation amplifier per channel
• Simultaneous sample-and-hold (SS/H) capability using track-and-hold
(T/H) circuitry
• Synchronization with other DAQ devices through the PXI trigger bus
• 4-pole software programmable Butterworth filters with software
selectable filter settings of bypass (no filtering), 10 Hz, 100 Hz, 1 kHz,
and 10 kHz per channel
• Programmable voltage excitation with remote sense per channel
• Programmatic offset null compensation per channel
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Chapter 1 About the NI PXI-4220
NI PXI-4220 User Manual 1-2 ni.com
• Programmatic shunt calibration per channel
• Programmatic bridge completion per channel
• Programmable Function Input (PFI) pin for external timing, triggering,
and calibration.
You can configure most settings on a per-channel basis through software.
The NI PXI-4220 is configured using Measurement & Automation
Explorer (MAX) or through function calls to NI-DAQmx.
What You Need to Get Started
To set up and use the NI PXI-4220, you need the following:
❑Hardware
– NI PXI-4220 device
– PXI chassis
– Sensors as required by your application
❑Software
– NI-DAQ 7.0 or later
– One of the following:
•LabVIEW
• Measurement Studio
• LabWindows™/CVI™
• Refer to National Instruments»NI-DAQ»NI-DAQ
Read Me for supported text-based compilers
❑Documentation
– NI PXI-4220 User Manual
– DAQ Quick Start Guide
– Read Me First: Safety and Radio-Frequency Interference
– PXI chassis user manual
– Documentation for your software
❑Tools
– 1/8 in. flathead screwdriver
You can download NI documents from ni.com/manuals.
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Chapter 1 About the NI PXI-4220
©National Instruments Corporation 1-3 NI PXI-4220 User Manual
National Instruments Documentation
The NI PXI-4220 User Manual is one piece of the documentation set
for your DAQ system. You could have any of several types of manuals,
depending on the hardware and software in your system. Use the manuals
you have as follows:
•DAQ Quick Start Guide—This document describes how to install
NI-DAQ devices and NI-DAQ. Install NI-DAQmx before you install
the PXI module.
• PXI chassis manual—Read this manual for maintenance information
on the chassis and for installation instructions.
• Software documentation—You may have both application software
and NI-DAQmx software documentation. NI application software
includes LabVIEW, Measurement Studio, and LabWindows/CVI.
After you set up the hardware system, use either your application
software documentation or the NI-DAQmx 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.
Installing the Application Software, NI-DAQ, and the
DAQ Device
Refer to the DAQ Quick Start Guide, packaged with the NI-DAQ software,
for instructions for installing your application software, NI-DAQ driver
software, and the DAQ device to which you will connect the NI PXI-4220.
NI-DAQ 7.0 or later is required to configure and program the NI PXI-4220
device. If you do not have NI-DAQ 7.0 or later, you can either contact an
NI sales representative to request it on a CD or download the it from
ni.com.
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Chapter 1 About the NI PXI-4220
NI PXI-4220 User Manual 1-4 ni.com
Installing the NI PXI-4220
Note Refer to the Read Me First: Radio-Frequency Interference document before
removing equipment covers or connecting or disconnecting any signal wires.
Refer to the DAQ Quick Start Guide to unpack, install, and configure the
NI PXI-4220 in a PXI chassis.
LED Pattern Descriptions
The following LEDs on the NI PXI-4220 front panel confirm the system is
functioning properly:
• The ACCESS LED is normally green and blinks yellow for a minimum
of 100 ms during the NI PXI-4220 configuration.
• The ACTIVE LED is normally green and blinks yellow for a minimum
of 100 ms during data acquisition.
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©National Instruments Corporation 2-1 NI PXI-4220 User Manual
2
Connecting Signals
This chapter describes how to connect Wheatstone bridge sensors to the
NI PXI-4220 in quarter-, half-, and full-bridge configurations, and for
remote sensing.
Connecting Bridge Sensor Signals to the NI PXI-4220
This section discusses how to connect the signals of supported strain-gauge
configuration types as well as full-bridge sensors such as load, force,
torque, and pressure sensors. It also discusses connecting leads for remote
sensing. Refer to Chapter 4, Theory of Operation, for a discussion of
strain-gauge concepts.
Caution Refer to the Read Me First: Safety and Radio-Frequency Interference document
before removing equipment covers or connecting/disconnecting any signal wires.
Figure 2-1 shows the NI PXI-4220 front label, including the location of the
D-SUB connectors and PFI0/CAL SMB connector.
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Chapter 2 Connecting Signals
NI PXI-4220 User Manual 2-2 ni.com
Figure 2-1. NI PXI-4220 Front Label
Construct a signal lead with an SMB connection to connect a timing or
triggering signal to the PFI0/CAL SMB connector.
Caution The PFI0/CAL SMB connector is for low-voltage timing and calibration signals
only. Voltages greater than ±10 V can damage the device.
Figure 2-2 shows the pin signal assignments for each of the NI PXI-4220
D-SUB connectors. Refer to Figure 2-2 when constructing D-SUB
connection leads to ensure the signal wires are routed correctly. In the
electrical connection diagram, each signal connection node is labeled with
a pin number to indicate which pin carries the signal.
2 Channel Bridge Input
ACCESS ACTIVE
AI 0
AI 1
PFI 0/
CAL
NI PXI-4220
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Chapter 2 Connecting Signals
©National Instruments Corporation 2-3 NI PXI-4220 User Manual
Figure 2-2. PXI-4220 Front Connector and General Circuit Diagram
Note Refer to Figure 2-3 for quarter-bridge and shunt cal completion resistor locations.
Shunt
Calibration
Switches
Half-Bridge
Completion
–
Pin 2 (P0+)
Pin 3 (RS0+)
Pin 6 (S0–)
Pin 1 (S0+)
Pin 7 (P0–)
Pin 5 (SCCOM)
Pin 4
(QTR/Shunt Cal A)
SCB0
Shunt Cal B
Shunt Cal A
Quarter-Bridge
Completion
Pin 8 (RS0–)
Pin 9
(QTR/Shunt Cal B)
+
–
+
A
B
R1
R2
–
+–Vex
2
–
++Vex
2
Channel 0
Channel 1
Signal– (S–)
Excitation– (P–)
Remote Sense– (RS–)
QTR/Shunt Cal B (QTR/SCB)
12345
6789
12345
6789
Signal+ (S+)
Excitation+ (P+)
Remote Sense+ (RS+)
Shunt Cal A (SCA)
Shunt Cal COM (SCCOM)
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Chapter 2 Connecting Signals
NI PXI-4220 User Manual 2-4 ni.com
Figure 2-3 shows the location of the socketed NI PXI-4220 resistors.
Figure 2-3. Socketed Resistor Locations
Quarter-Bridge Type I
This section provides information about connecting the quarter-bridge
strain-gauge configuration type I.
Figure 2-4 shows the quarter-bridge type I circuit wiring diagram. Refer to
the Quarter-Bridge Type I section of Chapter 4, Theory of Operation, for
more information.
Note If you have a two-wire strain-gauge element, connect the active element leads to
S+ (pin 1) and P+ (pin 2) and short S+ (pin 1) to QTR/SCB (pin 9) and SCA (pin 4).
1 R4 (Shunt Cal B CH 0)
2 R1 (Shunt Cal A CH 0)
3 R5 (Quarter-Bridge Completion CH0)
4 R2 (Quarter-Bridge Completion CH1)
5 R6 (Shunt Cal B CH 1)
6 R3 (Shunt Cal A CH 1)
PXI-9-PIN DSUB
3
4
1
2
5
6
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Chapter 2 Connecting Signals
©National Instruments Corporation 2-5 NI PXI-4220 User Manual
Figure 2-4. Quarter-Bridge I Circuit Diagram
The following symbols apply to the circuit diagram and equations:
•R
1and R2are half-bridge completion resistors.
•R
3is the quarter-bridge completion resistor (dummy resistor).
•R
4is the active element measuring tensile strain (+ε).
•VEX is the excitation voltage.
•RLis the lead resistance.
•VCH is the measured voltage.
•RSA is shunt calibration resistor A.
•RSB is shunt calibration resistor B.
This configuration uses the Shunt Cal A switch for shunt calibration.
Note The value of the quarter-bridge completion resistor (dummy resistor) must equal the
nominal resistance of the strain gauge. NI recommends using a 0.1% precision resistor.
If a less precise resistor is used, offset null compensation calibration is not as accurate.
Refer to the Offset Null Compensation section of Chapter 4, Theory of Operation, for more
information.
+
–
+
–
R
L
R
L
NI PXI-4220Transducer
R
1
R
2
R
4
R
3
V
CH
S+ (Pin 1)
P+ (Pin 2)
P– (Pin 7)
Shunt Cal B
R
L
SCCOM (Pin 5)
QTR/SCB (Pin 9)
V
EX
R
S
B
P+
QTR
P–
S–
Shunt Cal A
R
S
A
SCA (Pin 4)
Jumper not required
when using SCB.
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Chapter 2 Connecting Signals
NI PXI-4220 User Manual 2-6 ni.com
Quarter-Bridge Type II
This section provides information about connecting the quarter-bridge
strain-gauge configuration type II. Figure 2-5 shows the quarter-bridge
type II circuit wiring diagram. Refer to the Quarter-Bridge Type II section
of Chapter 4, Theory of Operation, for more information.
Figure 2-5. Quarter-Bridge II Circuit Diagram
The following symbols apply to the circuit diagram and equations:
•R
1and R2are half-bridge completion resistors.
•R
3is the quarter-bridge temperature-sensing element (dummy gauge).
•R
4is the active element measuring tensile strain (+ε).
•VEX is the excitation voltage.
•RLis the lead resistance.
•VCH is the voltage measured.
•RSis shunt calibration resistor A.
Note The quarter-bridge type II is often confused with the more commonly used
half-bridge type I. For more information, refer to the Quarter-Bridge Type II and
Half-Bridge Type I sections of Chapter 4, Theory of Operation.
+
–
+
–
R
L
R
L
NI PXI-4220Transducer
R1
R2
R4
R3
V
CH
Shunt
Cal A
R
L
R
S
V
EX
R
L
S+ (Pin 1)
P+ (Pin 2)
P– (Pin 7)
SCA (Pin 4)
SCCOM (Pin 5)
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