National Instruments Network Card NI 9237 User Manual

OPERATING INSTRUCTIONS AND SPECIFICATIONS  
NI 9237  
4-Channel, 24-Bit Half/Full-Bridge Analog Input Module  
Français Deutsch  
ni.com/manuals  
 
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.  
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.  
© National Instruments Corp.  
3
NI 9237 Operating Instructions and Specifications  
 
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.  
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. If you are using the NI 9237 in Gas Group IIC hazardous  
locations or in ambient temperatures of –40 °C Ta 70 °C, you  
must use the device in an NI chassis that has been evaluated as  
EEx nC IIC T4, Ex nA IIC T4, or Ex nL IIC T4 equipment.  
NI 9237 Operating Instructions and Specifications  
4
ni.com  
 
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.  
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 and exit through opposing  
enclosure walls.  
© National Instruments Corp.  
5
NI 9237 Operating Instructions and Specifications  
 
Connecting the NI 9237  
The NI 9237 has four RJ-50 receptacles that provide connections  
for four half or full bridges.  
Ch0 – Ch3  
1
2
SC  
AI+  
AI–  
RS+  
RS–  
EX+  
EX–  
T+  
3
Ch 0  
Ch 1  
Ch 2  
Ch 3  
4
5
6
7
8
9
T–  
SC  
10  
EX+  
EX–  
EX+  
EX–  
Figure 1. NI 9237 Pin Assignments  
NI 9237 Operating Instructions and Specifications  
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When you connect a half bridge to the NI 9237, you must connect  
the AI+, EX–, and RS– signals, but you do not connect the AI–  
signal. When you connect a full bridge, you must connect the AI+,  
AI–, EX–, and RS– signals. Refer to Figure 2 for an illustration of  
how to connect half and full bridges to the NI 9237.  
Note You can use a quarter bridge with the NI 9237 if  
you add a resistor externally to create a half bridge. You  
also can use a quarter bridge with the NI 9237 if you use  
the NI 9944 or NI 9945 Quarter Bridge Completion  
Accessory. Visit ni.com and search for the NI 9944 and  
NI 9945 Quarter Bridge Completion Accessories for  
more information about these accessories and how to  
purchase them.  
Note National Instruments does not recommend using  
an RJ-45 cable 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 and Specifications  
 
The NI 9237 has a four-terminal external excitation voltage source  
connector. You can use the EX+ and EX– terminals on the  
connector to connect one external excitation voltage source to the  
module. You can use the additional EX+ and EX– terminals on the  
connector to wire multiple NI 9237 modules together in a daisy  
chain.  
Note When you insert or remove a new sensor from the  
NI 9237, slight changes in the excitation voltages can  
cause a mismatch between the internal half-bridge  
completion resistors and the half-bridge sensors, which  
results in a change in the measurement offsets.  
National Instruments recommends performing bridge  
calibrations of quarter- or half-bridge sensors after  
connecting all sensors to the NI 9237 and after removing  
or attaching any additional sensor. Visit ni.com/info  
and enter the info code rdw9237 for more information  
about changes in voltage offsets in the NI 9237.  
NI 9237 Operating Instructions and Specifications  
8
ni.com  
 
RS+  
EX+  
AI+  
AI–  
EX–  
RS–  
SC  
SC  
T+  
TEDS  
T–  
NI 9237  
Figure 2. Connecting a Half or Full Bridge to the NI 9237  
© National Instruments Corp.  
9
NI 9237 Operating Instructions and Specifications  
 
 
Each channel on the NI 9237 has an independent 24-bit ADC  
and an input amplifier that enable you to sample signals from all  
four channels simultaneously.  
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 Specifications section  
for more information about the common-mode rejection  
ratio (CMRR).  
You also can connect floating signals to the NI 9237. If you  
connect floating signals to the NI 9237, National Instruments  
recommends connecting the EX– signal to the earth ground or  
shield for better noise rejection.  
The NI 9237 also includes filters to prevent aliasing. The filters  
on the NI 9237 filter according to the data rate. Refer to the  
Understanding NI 9237 Filtering section for more information  
about filtering.  
NI 9237 Operating Instructions and Specifications  
10  
ni.com  
 
Wiring TEDS Channels  
Ensure that neither the TEDS data (T+) nor the TEDS return (T–)  
signal is tied in common to any AI signals on the NI 9237. The  
NI 9237 connects all the T– signals together internally. Visit  
ni.com/info and enter the info code rdteds for more  
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 half- and  
full-bridge sensors.  
Long wire and small gauge wire have greater resistance, which can  
result in gain error. The resistance in the wires that connect the  
excitation voltage to the bridge causes a voltage drop, which is a  
source of gain error. The NI 9237 includes remote sensing to  
compensate for this gain error. Connect remote sense wires to the  
points where the excitation voltage wires connect to the bridge  
© National Instruments Corp.  
11 NI 9237 Operating Instructions and Specifications  
 
circuit. Refer to Figure 3 for an illustration of how to connect  
remote sense wires to the NI 9237.  
RS+  
R
lead  
EX+  
R
R
R
R
bridge  
bridge  
bridge  
AI+  
AI–  
bridge  
R
EX–  
RS–  
lead  
NI 9237  
Figure 3. Connecting Remote Sense Wires to the NI 9237  
NI 9237 Operating Instructions and Specifications  
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The actual bridge excitation voltage is smaller than the voltage at  
the EX+ and EX– leads. If you do not use remote sensing of the  
actual bridge voltage, the resulting gain error is:  
Rlead  
-----------------  
for half-bridge sensors and  
Rbridge  
2 Rlead  
-------------------  
Rbridge  
for full-bridge sensors.  
If you connect the remote sense signals directly to the bridge  
resistors, the NI 9237 senses the actual bridge voltage 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. Remote sensing corrects for resistances from the EX pins  
on the NI 9237 to the sensor, and shunt calibration corrects for  
these errors and for errors caused by wire resistance within an arm  
of the bridge. Shunt calibration is most useful with quarter-bridge  
© National Instruments Corp.  
13 NI 9237 Operating Instructions and Specifications  
 
sensors 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  
resistor and a software-controlled switch. Refer to the software  
help for information about enabling the shunt calibration switch for  
the NI 9237.  
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. You can then measure  
the output of the bridge and compare it to the expected voltage  
value. You can use the results to correct gain errors in the entire  
measurement path, or to simply verify general operation to gain  
confidence in the setup.  
Use a stable signal, which is typically the unloaded state of the  
sensor, first with the shunt calibration switch off and then again  
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.  
NI 9237 Operating Instructions and Specifications  
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Excitation Voltages  
Although the sensor industry does not recognize a single standard  
excitation voltage level, excitation voltage levels of between  
2.5 Vand 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 total power.  
2
Vex  
R
---------  
The power consumed by a single bridge is  
resistance of the bridge.  
where R is the total  
For a quarter or half bridge, R is equal to two times the resistance  
of each element. For a full bridge, R is equal to the resistance of  
each element.  
© National Instruments Corp.  
15 NI 9237 Operating Instructions and Specifications  
 
The 150 mW limit allows you to power half and full 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 that causes more than 150 mW to  
dissipate across all the bridges, use the EX+ and EX– terminals on  
the external excitation voltage connector to connect an external  
excitation source to the NI 9237.  
Understanding NI 9237 Filtering  
The NI 9237 uses a combination of analog and digital filtering to  
provide an accurate representation of in-band 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 quantified  
primarily by passband flatness and phase nonlinearity. All signals  
that appear in the alias-free bandwidth are either unaliased signals  
NI 9237 Operating Instructions and Specifications  
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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 respect to  
frequency is called the passband flatness. The digital 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 the data rate. Figure 4 shows typical  
passband flatness for the NI 9237.  
© National Instruments Corp.  
17 NI 9237 Operating Instructions and Specifications  
 
0.025  
0.000  
–0.025  
–0.050  
0
0.1  
0.2  
0.3  
0.4  
0.5  
Frequency/Data Rate  
Figure 4. Typical Passband Flatness for the NI 9237  
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  
NI 9237 Operating Instructions and Specifications  
18  
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rate. The stopband rejection is the minimum amount of attenuation  
applied by the filter to all signals with frequencies within the  
stopband.  
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.  
Understanding NI 9237 Data Rates  
The frequency of a master timebase (fM) controls the data rate (fs)  
of the NI 9237. The NI 9237 includes an internal master timebase  
with a frequency of 12.8 MHz, but the module also can accept an  
external master timebase or export its own master timebase. To  
synchronize the data rate of an NI 9237 with other modules that use  
master timebases to control sampling, all of the modules must  
share a single master timebase source. Refer to the software help  
for information about configuring the master timebase source for  
the NI 9237. Visit ni.com/info and enter cseriesdoc for  
information about C Series documentation.  
© National Instruments Corp.  
19 NI 9237 Operating Instructions and Specifications  
 
 
The following equation provides the available data rates of the  
NI 9237:  
f
÷ 256  
n
--M------------------  
fs =  
where n is any integer from 1 to 31.  
However, the data rate must remain within the appropriate data rate  
range. Refer to the Specifications section for more information  
about the data rate range. When using the internal master timebase  
of 12.8 MHz, the result is data rates of 50 kS/s, 25 kS/s, 16.67 kS/s,  
and so on down to 1.613 kS/s, depending on the value of n. When  
using an external timebase with a frequency other than 12.8 MHz,  
the NI 9237 has a different set of data rates.  
Note The cRIO-9151 R Series Expansion chassis does  
not support sharing timebases between modules.  
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 manual for information about  
NI 9237 Operating Instructions and Specifications  
20  
ni.com  
 
support for sleep mode. If the chassis supports sleep mode, refer to  
the software help for information about enabling sleep mode. Visit  
ni.com/info and enter cseriesdoc for information about  
C Series documentation.  
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  
in normal mode. Refer to the Specifications section for more  
information about power consumption and thermal dissipation.  
Specifications  
The following specifications are typical for the range –40 to 70 °C  
unless otherwise noted.  
Input Characteristics  
Number of channels..........................4 analog input channels  
Bridge completion  
Half and Full...............................Internal  
Quarter........................................External  
ADC resolution.................................24 bits  
© National Instruments Corp.  
21 NI 9237 Operating Instructions and Specifications  
 
 
Type of ADC.....................................Delta-Sigma (with analog  
prefiltering)  
Sampling mode.................................Simultaneous  
Internal master timebase (fM)  
Frequency...................................12.8 MHz  
Accuracy..................................... 100 ppm max  
Data rate range (fs) using internal master timebase  
Minimum....................................1.613 kS/s  
Maximum ...................................50 kS/s  
Data rate range (fs) using external master timebase  
Minimum....................................390.625 S/s  
Maximum ...................................51.3 kS/s  
f
÷ 256  
n
--M------------------  
1
Data rates (fs)...................................  
, n = 1, 2, …, 31  
Typical input range ........................... 25 mV/V  
Scaling coefficient ............................2.9802 nV/V per LSB  
1
The data rate must remain within the appropriate data rate range. Refer to the  
Understanding NI 9237 Data Rates section for more information.  
NI 9237 Operating Instructions and Specifications  
22  
ni.com  
 
Overvoltage protection  
between any two pins........................ 30 V  
Accuracy  
Percent of  
Range**  
(Gain Error) (Offset Error)  
Percent of  
Reading  
Measurement Conditions*  
Calibrated typ (25 °C, 5 °C)  
Calibrated max (–40 to 70 °C)  
Uncalibrated typ (25 °C, 5 °C)  
Uncalibrated max (40 to 70 °C)  
0.05%  
0.20%  
0.20%  
0.60%  
0.05%  
0.25%  
0.1%  
0.35%  
* Before offset null or shunt calibration.  
** Range equals 25 mV/V.  
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  
© National Instruments Corp.  
23 NI 9237 Operating Instructions and Specifications  
 
Channel-to-channel matching (calibrated)  
Input Signal  
Frequency  
(fin)  
Gain  
Maximum  
Phase  
Typical  
0.15%  
0.4%  
Maximum  
0 to 1 kHz  
0.3%  
1.1%  
0.125°/kHz · fin  
1 to 20 kHz  
Phase nonlinearity  
fin = 0 to 1 kHz............................<0.001°  
fin = 0 to 20 kHz.......................... 0.1°  
Input delay ........................................38.4/fs + 4.8 μs  
Passband  
Frequency...................................0.45 · fs  
Flatness.......................................0.1 dB max  
Stopband  
Frequency...................................0.55 · fs  
Rejection.....................................100 dB  
Alias-free bandwidth ........................0.45 · fs  
Oversample rate................................64 · fs  
NI 9237 Operating Instructions and Specifications  
24  
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Rejection at oversample rate1  
fs = 10 kS/s..................................60 dB @ 640 kHz  
fs = 50 kS/s..................................90 dB @ 3.2 MHz  
Common-mode voltage,  
all signals to earth ground................. 60 VDC  
CMRR  
Relative to earth ground2  
(fin = 0 to 60 Hz).........................140 dB  
Relative to EX–  
(fin = 0 to 1 kHz).........................85 dB  
SFDR (1 kHz, –60 dBFS).................106 dB  
Total Harmonic Distortion (THD)  
1 kHz, –20 dBFS ........................100 dB  
8 kHz, –20 dBFS ........................90 dB  
1
Rejection by analog prefilter of signal frequencies at oversample rate.  
2
Measured with a balanced cable. Shielded cables that are not twisted-pair may be  
significantly unbalanced. To improve the balance of shielded, twisted-pair cables,  
NI recommends twisting together the AI+/AIpair, the RS+/RSpair, and the  
EX+/EXpair.  
© National Instruments Corp.  
25 NI 9237 Operating Instructions and Specifications  
 
Input noise  
Density  
(nV/Vrms per  
Total,  
Total,  
fin = 0 to 25 kHz fin = 0 to 1 kHz  
Excitation  
Voltage  
(μV/Vrms  
1.3  
)
(nV/Vrms  
250  
)
1Hz )  
2.5 V  
3.3 V  
5 V  
8
6
4
2
1.0  
190  
0.6  
130  
10 V  
0.3  
65  
Excitation noise ................................0.1 mV/Vrms  
Crosstalk  
fin = 1 kHz...................................110 dB  
fin = 10 kHz.................................100 dB  
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  
NI 9237 Operating Instructions and Specifications  
26  
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Shunt calibration  
Resistance...................................100 kΩ  
Resistor accuracy  
25°C ..................................... 110 Ω  
–40 to 70°C.......................... 200 Ω  
MTBF ...............................................603,359 hours at 25 °C;  
Bellcore Issue 2, Method 1,  
Case 3, Limited Part Stress  
Method  
Note Contact NI for Bellcore MTBF specifications at  
other temperatures or for MIL-HDBK-217F  
specifications.  
Power Requirements  
Power consumption from chassis  
Active mode ...............................740 mW max  
Sleep mode .................................25 μW max  
Thermal dissipation (at 70 °C)  
Active mode ...............................740 mW max  
Sleep mode .................................25 μW max  
© National Instruments Corp.  
27 NI 9237 Operating Instructions and Specifications  
 
Physical Characteristics  
If you need to clean the module, wipe it with a dry towel.  
Weight...............................................152 g (5.4 oz)  
Safety  
Safety Voltages  
Connect only voltages that are within the following limits.  
Between any two pins....................... 30 V max  
Isolation  
Channel-to-channel ....................None  
Channel-to-earth ground  
Continuous...........................60 VDC, Measurement  
Category I  
Withstand .............................1,000 Vrms, 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  
NI 9237 Operating Instructions and Specifications  
28  
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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.  
Caution Do not connect the NI 9237 to signals or use for  
measurements within Measurement Categories II,  
III, or IV.  
Hazardous Locations  
U.S. (UL) ..........................................Class I, Division 2,  
Groups A, B, C, D, T4;  
Class I, Zone 2,  
AEx nC IIC T4  
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  
© National Instruments Corp.  
29 NI 9237 Operating Instructions and Specifications  
 
Safety Standards  
This product meets the requirements of the following standards of  
safety for electrical equipment for measurement, control, and  
laboratory use:  
IEC 61010-1, EN 61010-1  
UL 61010-1, CSA 61010-1  
Note For UL and other safety certifications, refer to the  
product label or the Online Product Certification section.  
Electromagnetic Compatibility  
This product meets the requirements of the following EMC  
standards for electrical equipment for measurement, control, and  
laboratory use:  
EN 61326 (IEC 61326): Class A emissions; Basic immunity  
EN 55011 (CISPR 11): Group 1, Class A emissions  
AS/NZS CISPR 11: Group 1, Class A emissions  
FCC 47 CFR Part 15B: Class A emissions  
ICES-001: Class A emissions  
NI 9237 Operating Instructions and Specifications  
30  
ni.com  
 
Note For the standards applied to assess the EMC of this  
product, refer to the Online Product Certification section.  
Note For EMC compliance, operate this device with  
shielded cabling.  
CE Compliance  
This product meets the essential requirements of applicable  
European Directives as follows:  
2006/95/EC; Low-Voltage Directive (safety)  
2004/108/EC; Electromagnetic Compatibility Directive  
(EMC)  
Online Product Certification  
Refer to the product Declaration of Conformity (DoC) for  
additional regulatory compliance information. To obtain product  
certifications and the DoC for this product, visit ni.com/  
certification, search by module number or product line, and  
click the appropriate link in the Certification column.  
© National Instruments Corp.  
31 NI 9237 Operating Instructions and Specifications  
 
 
Shock and Vibration  
To meet these specifications, you must panel mount the system.  
Operating vibration  
Random (IEC 60068-2-64).........5 grms, 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  
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 manual for the chassis you are using for more  
information about meeting these specifications.  
Operating temperature  
(IEC 60068-2-1, IEC 60068-2-2) .....40 to 70 °C  
Storage temperature  
(IEC 60068-2-1, IEC 60068-2-2) .....40 to 85 °C  
Ingress protection..............................IP 40  
NI 9237 Operating Instructions and Specifications  
32  
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Operating humidity  
(IEC 60068-2-56)..............................10 to 90% RH,  
noncondensing  
Storage humidity  
(IEC 60068-2-56)..............................5 to 95% RH,  
noncondensing  
Maximum altitude.............................2,000 m  
Pollution Degree (IEC 60664)..........2  
Environmental Management  
NI is committed to designing and manufacturing products in an  
environmentally responsible manner. NI recognizes that  
eliminating certain hazardous substances from our products is  
beneficial to the environment and to NI customers.  
For additional environmental information, refer to the NI and the  
Environment Web page at ni.com/environment. This page  
contains the environmental regulations and directives with which  
NI complies, as well as other environmental information not  
included in this document.  
© National Instruments Corp.  
33 NI 9237 Operating Instructions and Specifications  
 
Waste Electrical and Electronic Equipment (WEEE)  
EU Customers At the end of the life cycle, all products  
must be sent to a WEEE recycling center. For more  
information about WEEE recycling centers and National  
Instruments WEEE initiatives, visit ni.com/  
environment/weee.  
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ni.com/environment/rohs_chinaDŽ  
about China RoHS compliance, go to  
environment/rohs_china  
(For information  
ni.com/  
.)  
Calibration  
You can obtain the calibration certificate and information about  
calibration services for the NI 9237 at ni.com/calibration.  
Calibration interval ...........................1 year  
NI 9237 Operating Instructions and Specifications  
34  
ni.com  
 
Where to Go for Support  
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© National Instruments Corp.  
35 NI 9237 Operating Instructions and Specifications  
 
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© 2006–2008 National Instruments Corp. All rights reserved.  
374186C-01  
Aug08  
 

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