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OPERATING INSTRUCTIONS
NI 9237
4-Channel, 24-Bit Half/Full-Bridge Analog Input Module
ni.com/manualsja .)
(For a Japanese language version, go to
These operating instructions describe how to use the National
Instruments 9237 module. For information about installing, configuring, and programming the system, refer to the system documentation. Visit ni.com/info
and enter the info code rdsoftwareversion
to determine which software you need for the modules you are using.
Note
The safety guidelines and specifications in this document are specific to the NI 9237. The other components in the system might not meet the same safety ratings and specifications. Refer to the documentation for each component in the system to determine the safety ratings and specifications for the entire system.
Safety Guidelines
Operate the NI 9237 only as described in these operating instructions.
Hot Surface
This icon denotes that the component may be hot. Touching this component may result in bodily injury.
NI 9237 Operating Instructions 2 ni.com
Safety Guidelines for Hazardous Locations
The NI 9237 is suitable for use in Class I, Division 2, Groups A, B,
C, D, T4 hazardous locations; Class I, Zone 2, AEx nC IIC T4 and
Ex nC IIC T4 hazardous locations; and nonhazardous locations only. Follow these guidelines if you are installing the NI 9237 in a potentially explosive environment. Not following these guidelines may result in serious injury or death.
Caution
Do not disconnect I/O-side wires or connectors unless power has been switched off or the area is known to be nonhazardous.
Caution
Do not remove modules unless power has been switched off or the area is known to be nonhazardous.
Caution
Substitution of components may impair suitability for Class I, Division 2.
Caution
For Zone 2 applications, install the system in an enclosure rated to at least IP 54 as defined by IEC 60529 and EN 60529.
© National Instruments Corp.
3 NI 9237 Operating Instructions
Caution
For Zone 2 applications, connected signals must be within the following limits:
Capacitance .......................... 0.2
μF max
Inductance ............................ 80 mH max
Special Conditions for Hazardous Locations Use in Europe
This equipment has been evaluated as EEx nC IIC T4 equipment under DEMKO Certificate No. 03 ATEX 0324020X. Each module is marked II 3G and is suitable for use in Zone 2 hazardous locations.
Special Conditions for Marine Applications
Some modules are Lloyd’s Register (LR) Type Approved for marine applications. To verify Lloyd’s Register certification, visit ni.com/certification
and search for the LR certificate, or look for the Lloyd’s Register mark on the module.
NI 9237 Operating Instructions 4 ni.com
Caution
To meet radio frequency emission requirements for marine applications, use shielded cables and install the system in a metal enclosure. Suppression ferrites must be installed on power supply inputs near power entries to modules and controllers. Power supply and module cables must be separated on opposite sides of the enclosure and must enter/exit through opposing enclosure walls.
Wiring the NI 9237
The NI 9237 has four RJ-50 receptacles that provide connections
for four half or full bridges. Table 1 lists the signal names of the
terminals for each connector, and shows the correlation between the pin numbers of the RJ-50 10-position/10-conductor (10p10c) modular plug and the NI 9237 receptacle. The NI 9237 also has a four-position connector you can use to connect an external
excitation voltage source to the module. Table 1 lists the
connections between an external excitation voltage source and the NI 9237.
© National Instruments Corp.
5 NI 9237 Operating Instructions
.
Table 1. Channel Signal Names
RJ-50 (10p10c) Modular Plug and
Receptacle Pin Numbers
RJ-50
Pin
1
2
3
4
5
6
7
8
9
RJ-45
Pin
—
1
2
3
4
5
6
7
8
Signal
Name
SC
AI +
AI –
RS +
RS –
EX +
EX –
T +
T –
10 — SC
* These signals are shared by all four RJ-50 connectors on the NI 9237.
Signal
Description
Shunt calibration
Positive input signal
Negative input signal
Positive remote sense signal
Negative remote sense signal
Positive excitation signal*
Negative excitation signal*
TEDS DATA
TEDS Return*
Shunt calibration
NI 9237 Operating Instructions 6 ni.com
Note
National Instruments does not recommend using an RJ-45 with the NI 9237 because it can physically damage pins 1 and 10 on the device, and thus permanently disable shunt calibration no matter what connector you use.
© National Instruments Corp.
7 NI 9237 Operating Instructions
3
2
4
1
1 EX–
2 EX+
3 EX+
4 EX–
Figure 1. Four-Position External Excitation Voltage Source Connector
NI 9237 Operating Instructions 8 ni.com
Connecting Sensors to the NI 9237
Refer to Figure 2 for an illustration of how to connect full and half
bridges to the NI 9237.
RS +
EX +
AI +
AI –*
2
1
TEDS
EX –
SC
SC
T +
RS –
T –
*
When you connect a half bridge to the NI 9237, the AI– signal is not connected.
1 The dotted line indicates that the full bridge is optional while the half bridge is required.
2 These four signals are the only signals that must be connected.
Figure 2. Half- and Full-Bridge Connections
© National Instruments Corp.
9 NI 9237 Operating Instructions
Note
You can use a quarter bridge with the NI 9237 if you either add a resistor externally to create a half bridge or use the NI 9944 or NI 9945 Quarter Bridge Completion
Accessory. Visit ni.com
and search for the NI 9944 and/or NI 9945 Quarter Bridge Completion Accessories for more information about these accessories and how to purchase them.
Wiring TEDS Channels
Ensure that neither the TEDS data (T+) nor the TEDS return (T–) is tied in common to any AI signals on the NI 9237. Visit ni.com/ info
and enter the info code rdteds
for information about TEDS sensors.
NI 9237 Connection Options
Wiring resistance can create errors in bridge circuits. The NI 9237 provides two mechanisms to correct for these errors: remote sensing and shunt calibration.
Remote Sensing
Remote sensing continuously and automatically corrects for errors in excitation leads, and generally is most appropriate for full- and half-bridge sensors.
NI 9237 Operating Instructions 10 ni.com
Long wire and smaller gauge wire has greater resistance, which can result in gain error. The voltage drop caused by resistance in the wires connecting the excitation voltage to the bridge is a source of gain error.
The NI 9237 includes remote sensing to compensate for this error.
Remote sense wires are connected to the point where the excitation voltage wires connect to the bridge circuit.
Figure 3 shows a diagram of how the NI 9237 uses remote sensing.
R bridge
AI +
R bridge
R lead
R bridge
AI –
R bridge
R lead
RS +
EX +
EX –
RS –
Figure 3. Remote Sense Error Compensation
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11 NI 9237 Operating Instructions
As shown in Figure 3, the actual bridge excitation voltage is
smaller than the voltage at the EX+ and EX– leads. If remote sensing of the actual bridge voltage is not used, the resulting gain error is
2R
le ad
-----------------
R bridge
for full-bridge sensors, and
-----------------
R
R le ad bridge
for half-bridge sensors.
If the remote sense (RS) signals are connected directly to the bridge resistors, the NI 9237 senses the actual bridge voltage sense and eliminates the gain errors caused by the resistance of the EX+ and EX– leads.
Shunt Calibration
Shunt calibration can correct for errors from the resistance of both the excitation wiring and wiring in the individual resistors of the bridge. Shunt calibration is most useful with quarter-bridge sensors
NI 9237 Operating Instructions 12 ni.com
because there may be significant resistance in the wiring to the active resistor in the bridge.
The NI 9237 shunt calibration circuitry consists of a precision
100 k
Ω resistor and a software-controlled switch. You can leave the shunt calibration terminals connected to the sensor, and then apply or remove the shunt calibration resistance in software.
While remote sensing corrects for resistances from the EX terminals on the NI 9237 to the sensor, shunt calibration corrects for these errors and for errors caused by wire resistance within an arm of the bridge.
Shunt calibration involves simulating the input of strain by changing the resistance of an arm in the bridge by some known amount. This is accomplished by shunting, or connecting, a large resistor of known value across one arm of the bridge, creating a known strain-induced change in resistance. The output of the bridge can then be measured and compared to the expected voltage value. The results are used to correct gain errors in the entire measurement path, or to simply verify general operation to gain confidence in the setup.
A stable signal, which is typically the unloaded state of the sensor, is used first with the shunt calibration switch off and then again
© National Instruments Corp.
13 NI 9237 Operating Instructions
with the switch on. The difference in these two measurements provides an indication of the gain errors from wiring resistances.
You can design the software application to correct subsequent readings for this gain error.
Excitation Voltages
Although the sensor industry does not recognize a single standard excitation voltage level, excitation voltage levels of between
2.5 V and 10 V are common. You can program the NI 9237 to supply 2.5 V, 3.3 V, 5 V, or 10 V of excitation voltage, and the module can provide up to 150 mW of excitation power. Unless you supply external excitation voltage, National Instruments recommends that you set the excitation voltage to a value that keeps the total power below 150 mW. The NI 9237 automatically reduces internal excitation voltages as needed to stay below
150 mW.
The power consumed by a single bridge is
V e x
---------
R
2 where R is the total resistance of the bridge.
NI 9237 Operating Instructions 14 ni.com
For a full bridge, R is equal to the resistance of each element. For a half or quarter bridge, R is equal to two times the resistance of each element.
The 150 mW limit allows you to power full and half bridges as follows:
• Four 350
Ω half bridges at 5.0 V
• Four 350
Ω full bridges at 3.3 V
• Four 120
Ω half bridges at 2.5 V
If you need an excitation voltage greater than 150 mW, use the four-position external excitation voltage connector to connect an
external excitation source to the NI 9237. Refer to Figure 1 for an
illustration and pinout description of the four-position external excitation voltage connector.
© National Instruments Corp.
15 NI 9237 Operating Instructions
NI 9237 Circuitry
The NI 9237 is isolated from earth ground. However, the individual channels are not isolated from each other. The EX+, EX–, and
T– signals are common among all channels. You can connect the
NI 9237 to a device that is biased at any voltage within the NI 9237 rejection range of earth ground. Refer to the
section for more information.
You also can connect floating signals to the NI 9237. If you connect floating signals to the NI 9237, National Instruments recommends you connect the EX– signal to the earth ground or shield for better noise rejection.
Each channel on the NI 9237 has an independent 24-bit ADC and input amplifier that enable you to sample signals from all four channels simultaneously.
The NI 9237 also includes filters to prevent aliasing. The filters on the NI 9237 filter according to the sampling rate.
NI 9237 Operating Instructions 16 ni.com
Understanding NI 9237 Filtering
The NI 9237 uses a combination of analog and digital filtering to provide an accurate representation of desirable signals while rejecting out-of-band signals. The filters discriminate between signals based on the frequency range, or bandwidth, of the signal.
The three important bandwidths to consider are the passband, the stopband, and the alias-free bandwidth.
The NI 9237 represents signals within the passband as accurately as possible, as quantified primarily by passband flatness and phase nonlinearity. The filters reject frequencies within the stopband as much as possible, as quantified by stopband rejection. All signals that appear in the alias-free bandwidth are either unaliased signals or signals that have been filtered by at least the amount of the stopband rejection.
Passband
The signals within the passband have frequency-dependent gain or attenuation. The small amount of variation in gain with frequency is called the passband flatness. The filters of the NI 9237 adjust the frequency range of the passband to match the data rate. Therefore, the amount of gain or attenuation at a given frequency depends on
© National Instruments Corp.
17 NI 9237 Operating Instructions
the data rate. Figure 4 shows typical passband flatness for a range
of data rates.
0.025
0.000
–0.025
–0.050
0 0.2
0.4
0.6
Frequency/Sample Rate (kHz)
0.8
Figure 4. Typical Passband Response
1
NI 9237 Operating Instructions 18 ni.com
Stopband
The filter significantly attenuates all signals above the stopband frequency. The primary goal of the filter is to prevent aliasing.
Therefore, the stopband frequency scales precisely with the data rate. The stopband rejection is the minimum amount of attenuation applied by the filter to all signals with frequencies that would be aliased into the alias-free bandwidth.
Alias-Free Bandwidth
Any signal that appears in the alias-free bandwidth of the NI 9237 is not an aliased artifact of signals at a higher frequency. The alias-free bandwidth is defined by the ability of the filter to reject frequencies above the stopband frequency and equals the data rate minus the stopband frequency.
Sleep Mode
This module supports a low-power sleep mode. Support for sleep mode at the system level depends on the chassis that the module is plugged into. Refer to the chassis documentation for information about support for sleep mode. You can enable sleep mode in software. Refer to the driver software documentation for more information.
© National Instruments Corp.
19 NI 9237 Operating Instructions
Typically, when a system is in sleep mode, you cannot communicate with the modules. In sleep mode, the system consumes minimal power and may dissipate less heat than it does
information about power consumption and thermal dissipation.
Binary Data
Some devices in the system return uncalibrated binary data. For these devices, you can apply calibration coefficients and convert the data to engineering units in software. Refer to the software documentation for information about converting data. Some devices, such as those that use NI-DAQmx software, return calibrated data by default. Refer to the software documentation for more information.
NI 9237 Operating Instructions 20 ni.com
Specifications
The following specifications are typical for the range –40 to 70 °C unless otherwise noted.
Input Characteristics
Number of channels.......................... 4
Bridge completion
Full and half ............................... Internal
Quarter........................................ External
ADC resolution................................. 24 bits
Type of ADC..................................... Delta-sigma (with analog prefiltering)
Sampling mode ................................. Simultaneous
Data rates (f
s
) ...................................
, n = 1, 2, ... 31.
n
Master timebase (internal)
Frequency ................................... 12.8 MHz
Accuracy
..................................... ± 100 ppm max
Nominal full-scale range
................... ± 25 mV/V
© National Instruments Corp.
21 NI 9237 Operating Instructions
Scaling coefficient ............................ 2.9802 nV/V per LSB
Overvoltage protection between any two terminals
............... ± 30 V
Accuracy
Error*
Calibrated max (–40 to 70 °C)
Calibrated typ (25 °C, ±5 °C)
Uncalibrated max (–40 to 70 °C)
Percent of
Reading
0.20%
0.05%
0.60%
Uncalibrated typ (25 °C, ±5 °C)
* Excluding offset null or shunt calibration.
† Range equals 25mV/V
0.20%
Percent of
Range†
0.25%
0.05%
0.35%
0.1%
Gain drift........................................... 10 ppm/°C max
Offset drift
2.5 V excitation .......................... 0.6
μV/V per °C
3.3 V excitation .......................... 0.5
μV/V per °C
5 V excitation ............................. 0.3
μV/V per °C
10 V excitation ........................... 0.2
μV/V per °C
NI 9237 Operating Instructions 22 ni.com
Channel-to-channel matching (calibrated)
Input Signal
Frequency
(f
in
)
Typical
Gain
Maximum
0 to 1 kHz
1 to 20 kHz
* f
in
is in kHz.
0.15%
0.4%
0.3%
1.1%
Phase nonlinearity
0 to 1 kHz
................................... < 0.001°
0 to 20 kHz
................................. ± 0.1°
Input delay ........................................ 4.8
μs + 38.4/f
s
Passband
Frequency ................................... 0.45 · f
s
Flatness....................................... 0.1 dB max
Stopband
Frequency ................................... 0.55 · f
s
Rejection..................................... 100 dB
Phase
Maximum
0.125°/kHz
·
f in
*
© National Instruments Corp.
23 NI 9237 Operating Instructions
Alias-free bandwidth ........................ 0.45 · f
s
Oversample rate ................................ 64 · f
s
Rejection at oversample rate
1
50 kS/s.................................. 90 dB @ 3.2 MHz
10 kS/s.................................. 60 dB @ 640 kHz
Common-mode voltage
All signals to earth ground
......... ± 60 VDC
Common-mode rejection ratio (CMRR)
Relative to earth ground
2
............ 140 dB @ 0 to 60 Hz
Relative to EX– .......................... 85 dB @ 0 to 1 kHz
1
Rejection by analog prefilter of signal frequencies at oversample rate.
2
Measured with a balanced cable. Shielded cables may be significantly unbalanced.
NI 9237 Operating Instructions 24 ni.com
Input noise
Excitation
Voltage
2.5 V
3.3 V
5 V
10 V
Density
(nV/V rms
per
1Hz
)
8
6
4
2
Total
(50 kS/S)
(
μV/V
rms
)
1.3
1.0
0.6
0.3
Spurious-free dynamic range (SFDR).................................... 106 dB,
(1KHz, –60 dBFS)
Total harmonic distortion (fundamental @ –20 dBFS)
1 kHz .......................................... 100 dB
8 kHz .......................................... 90 dB
Excitation noise ............................... 0.1 mV/V rms
0 to 1 kHz
(nV/V rms
)
250
190
130
65
© National Instruments Corp.
25 NI 9237 Operating Instructions
Crosstalk
1 kHz .......................................... 110 dB
10 kHz ........................................ 100 dB
Shunt calibration
Resistance................................... 100 k
Ω
Resistor accuracy
25°C
..................................... ± 110 Ω
–40 to 70°C
.......................... ± 200 Ω
Excitation
Internal voltage........................... 2.5 V, 3.3 V, 5.0 V, 10.0 V
Internal power............................. 150 mW max
External voltage.......................... 2 V to 10 V
MTBF ............................................... 603,359 hours at 25 °C;
Bellcore Issue 6, Method 1,
Case 3, Limited Part Stress
Method
NI 9237 Operating Instructions 26 ni.com
Note
Contact NI for Bellcore MTBF specifications at other temperatures or for MIL-HDBK-217F specifications. Visit ni.com/certification
and search for the module number or product line for more information about MTBF and other product certifications.
Power Requirements
Power consumption from chassis
Active mode ............................... 740 mW max
Sleep mode ................................. 25
μW max
Thermal dissipation
Active mode ............................... 740 mW max
Sleep mode ................................. 25
μW max
Physical Characteristics
If you need to clean the module, wipe it with a dry towel.
Weight ............................................... 152 g (5.4 oz)
© National Instruments Corp.
27 NI 9237 Operating Instructions
Safety
Safety Voltages
Connect only voltages that are within these limits.
Between any two terminals
............... ± 30 V max
Isolation
Channel-to-channel .................... No isolation between channels
Channel-to-earth ground
Continuous ........................... 60 VDC, Measurement
Category I
Withstand ............................. 1,000 V rms
, verified by a 5 s dielectric withstand test
Measurement Category I is for measurements performed on circuits not directly connected to the electrical distribution system referred to as MAINS voltage. MAINS is a hazardous live electrical supply system that powers equipment. This category is for measurements of voltages from specially protected secondary circuits. Such voltage measurements include signal levels, special equipment, limited-energy parts of equipment, circuits powered by regulated low-voltage sources, and electronics. Do not connect the
NI 9237 Operating Instructions 28 ni.com
NI 9237 to signals or use for measurements within Measurement
Categories II, III, or IV.
Safety Standards
The NI 9237 is designed to meet the requirements of the following standards of safety for electrical equipment for measurement, control, and laboratory use:
• EN 61010-1, IEC 61010-1
• UL 61010-1
• CAN/CSA-C22.2 No. 61010-1
Note
For UL and other safety certifications, refer to the product label or visit ni.com/certification
, search for the module number or product line, and click the appropriate link in the Certification column.
Hazardous Locations
U.S. (UL) .......................................... Class I, Division 2,
Groups A, B, C, D, T4;
Class I, Zone 2,
AEx nC IIC T4
© National Instruments Corp.
29 NI 9237 Operating Instructions
Canada (C-UL) ................................. Class I, Division 2,
Groups A, B, C, D, T4;
Class I, Zone 2,
Ex nC IIC T4
Europe (DEMKO)............................. EEx nC IIC T4
Environmental
National Instruments C Series modules are intended for indoor use only but may be used outdoors if installed in a suitable enclosure.
Refer to the installation instructions for the chassis you are using for more information about meeting these specifications.
Operating temperature
(IEC60068-2-1, IEC 60068-2-2) ...... –40 to 70 °C
Storage temperature
(IEC60068-2-1, IEC 60068-2-2) ...... –40 to 85 °C
Ingress protection.............................. IP 40
Operating humidity
(IEC 60068-2-56).............................. 10 to 90% RH, noncondensing
NI 9237 Operating Instructions 30 ni.com
Storage humidity
(IEC 60068-2-56).............................. 5 to 95% RH, noncondensing
Maximum altitude............................. 2,000 m
Pollution Degree (IEC 60664) .......... 2
Shock and Vibration
To meet these specifications, you must panel mount the system.
Operating vibration
Random (IEC 60068-2-34)......... 5 g, 10 to 500 Hz
Sinusoidal (IEC 60068-2-6) ....... 5 g, 10 to 500 Hz
Operating shock
(IEC 60068-2-27).............................. 30 g, 11 ms half sine,
50 g, 3 ms half sine,
18 shocks at 6 orientations
© National Instruments Corp.
31 NI 9237 Operating Instructions
Electromagnetic Compatibility
Emissions.......................................... EN 55011 Class A at 10 m
FCC Part 15A above 1 GHz
Immunity........................................... Industrial levels per
EN 61326-1:1997 +
A2:2001, Table 1
EMC/EMI ......................................... CE, C-Tick, and FCC Part 15
(Class A) Compliant
Note
For EMC compliance, operate this device with double-shielded cabling.
CE Compliance
This product meets the essential requirements of applicable
European directives, as amended for CE marking, as follows:
Low-Voltage Directive (safety)......... 73/23/EEC
Electromagnetic Compatibility
Directive (EMC) ............................... 89/336/EEC
NI 9237 Operating Instructions 32 ni.com
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 for the module number or product line, and click the appropriate link in the
Certification column.
Calibration
You can obtain the calibration certificate for the NI 9237 at ni.com/calibration
.
Calibration interval ........................... 1 year
© National Instruments Corp.
33 NI 9237 Operating Instructions
Where to Go for Support
The National Instruments Web site is your complete resource for technical support. At ni.com/support
you have access to everything from troubleshooting and application development self-help resources to email and phone assistance from
NI Application Engineers.
National Instruments corporate headquarters is located at
11500 North Mopac Expressway, Austin, Texas, 78759-3504.
National Instruments also has offices located around the world to help address your support needs. For telephone support in the
United States, create your service request at ni.com/support and follow the calling instructions or dial 512 795 8248. For telephone support outside the United States, contact your local branch office:
Australia 1800 300 800, Austria 43 0 662 45 79 90 0,
Belgium 32 0 2 757 00 20, Brazil 55 11 3262 3599,
Canada 800 433 3488, China 86 21 6555 7838,
Czech Republic 420 224 235 774, Denmark 45 45 76 26 00,
Finland 385 0 9 725 725 11, France 33 0 1 48 14 24 24,
Germany 49 0 89 741 31 30, India 91 80 41190000,
Israel 972 0 3 6393737, Italy 39 02 413091,
NI 9237 Operating Instructions 34 ni.com
Japan 81 3 5472 2970, Korea 82 02 3451 3400,
Lebanon 961 0 1 33 28 28, Malaysia 1800 887710,
Mexico 01 800 010 0793, Netherlands 31 0 348 433 466,
New Zealand 0800 553 322, Norway 47 0 66 90 76 60,
Poland 48 22 3390150, Portugal 351 210 311 210,
Russia 7 095 783 68 51, Singapore 1800 226 5886,
Slovenia 386 3 425 4200, South Africa 27 0 11 805 8197,
Spain 34 91 640 0085, Sweden 46 0 8 587 895 00,
Switzerland 41 56 200 51 51, Taiwan 886 02 2377 2222,
Thailand 662 278 6777, United Kingdom 44 0 1635 523545
© National Instruments Corp.
35 NI 9237 Operating Instructions
National Instruments, NI, ni.com, and LabVIEW are trademarks of National Instruments Corporation. Refer to the
Terms of Use section on ni.com/legal
for more information about National Instruments trademarks. Other product and company names mentioned herein are trademarks or trade names of their respective companies.
For patents covering National Instruments products, refer to the appropriate location: Help»Patents in your software, the patents.txt
file on your CD, or ni.com/patents
.
© 2006 National Instruments Corp. All rights reserved.
374186B-01 Aug06
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