National Instruments NI 9237E Series User manual

OPERATING INSTRUCTIONS AND SPECIFICATIONS
NI 9237E
4-Channel, 24-Bit Half/Full-Bridge Analog Input Module

NI 9237E Operating Instructions and Specifications 2 ni.com
This document describes how to use the National Instruments 9237E
and includes dimensions, pin assignments, and specifications for the
NI 9237E. In this document, the NI 9237E with RJ-50 connectors
and the NI 9237E with DSUB are referred to inclusively as the
NI 9237E. Visit ni.com/info and enter rdsoftwareversion to
determine which software you need for the modules you are using.
For information about installing, configuring, and programming the
system, refer to the system documentation. Visit ni.com/info and
enter cseriesdoc for information about C Series documentation.
Caution National Instruments makes no electromagnetic
compatibility (EMC) or CE marking compliance claims
for the NI 9237E. The end-product supplier is responsible
for conformity to any and all compliance requirements.
Caution The NI 9237E must be installed inside a suitable
enclosure prior to use. Hazardous voltages may be present.

© National Instruments Corp. 3 NI 9237E Operating Instructions and Specifications
NI 9237E Dimensions
The following figure shows the dimensions of the NI 9237E.
Figure 1. NI 9237E Dimensions in Millimeters (Inches)
73.4 (2.89)
0.0 (0.00)
26.7 (1.05) 58.4 (2.30) 66.0 (2.60)
0.0 (0.00)

NI 9237E Operating Instructions and Specifications 4 ni.com
Connecting the NI 9237E
The NI 9237E has four RJ-50 receptacles or a 37-pin DSUB
connector that provides connections for four half or full bridges,
and an external excitation voltage source.
Figure 2. NI 9237E with RJ-50 Pin Assignments
Ch 0
Ch 1
Ch 2
Ch 3
SC
AI+
AI–
RS+
RS–
EX+
EX–
T+
T–
SC
1
2
3
4
5
6
7
8
9
10
Ch0 – Ch3
EX+ EX+
EX– EX–

© National Instruments Corp. 5 NI 9237E Operating Instructions and Specifications
Figure 3. NI 9237E with DSUB Pin Assignments
1
2
3
4
5
6
7
8
9
10
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
RS0+
EX0+
AI0+
SC0+
RS1+
EX1+
AI1+
SC1+
T–
Vex+
RS2+
EX2+
AI2+
SC2+
RS3+
EX3+
AI3+
SC3+
T–
RS0–/SC0–
EX0–
AI0–
T0+
RS1–/SC1–
EX1–
AI1–
T1+
T–
Vex–
RS2–/SC2–
EX2–
AI2–
T2+
RS3–/SC3–
EX3–
AI3–
T3+

NI 9237E Operating Instructions and Specifications 6 ni.com
When you connect a half bridge to the NI 9237E, you must connect
the AI+, EX+ and EX–, and RS+ and RS– signals, but you do not
need to connect the AI– signal because it is connected internally.
When you connect a full bridge, you must connect the AI+ and
AI–, EX+ and EX–, and RS+ and RS– signals. Refer to Figure 4
for an illustration of how to connect half and full bridges to the
NI 9237E.
Note You can use a quarter bridge with the NI 9237E if
you add a resistor externally to create a half bridge. You
also can use a quarter bridge with the NI 9237E
with RJ-50 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 9237E with RJ-50 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 9237E Operating Instructions and Specifications
Note When you insert or remove a new sensor from the
NI 9237E, 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 9237E 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 9237E.

NI 9237E Operating Instructions and Specifications 8 ni.com
Figure 4. Connecting a Half or Full Bridge to the NI 9237E
1NI9237E with DSUB only 2NI9237E with RJ-50 only
EX+
EX–
SC
SC
RS+
RS–
RS– /SC–
T+
T–
AI–
AI+
TEDS
NI 9237E
1
2

© National Instruments Corp. 9 NI 9237E Operating Instructions and Specifications
Each channel on the NI 9237E has an independent 24-bit ADC
and an input amplifier that enable you to sample signals from all
four channels simultaneously.
The NI 9237E 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 9237E to a device that is biased at any voltage
within the NI 9237E 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 9237E. If you
connect floating signals to the NI 9237E, National Instruments
recommends connecting the EX– signal to the earth ground or
shield for better noise rejection.
The NI 9237E also includes filters to prevent aliasing. The filters
on the NI 9237E filter according to the data rate. Refer to the
Understanding NI 9237E Filtering section for more information
about filtering.

NI 9237E 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 9237E. The
NI 9237E connects all the T– signals together internally. The
NI 9237E with DSUB has only three T– pins. To connect four
TEDS sensors to the NI 9237E with DSUB, wire the TEDS return
signals of two of the sensors to one of the T– pins. Visit
ni.com/info and enter the info code rdteds for more
information about TEDS sensors.
Connection Options to Correct for Resistance Errors
Wiring resistance can create errors in bridge circuits. The
NI 9237E 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

© National Instruments Corp. 11 NI 9237E Operating Instructions and Specifications
source of gain error. The NI 9237E 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
circuit. Refer to Figure 5 for an illustration of how to connect
remote sense wires to the NI 9237E.
Figure 5. Connecting Remote Sense Wires to the NI 9237E
EX+
EX–
RS+
RS–
Rbridge
Rlead
Rlead
Rbridge Rbridge
Rbridge
NI 9237E
AI–
AI+

NI 9237E Operating Instructions and Specifications 12 ni.com
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:
for half-bridge sensors and
for full-bridge sensors.
If you connect the remote sense signals directly to the bridge
resistors, the NI 9237E 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 9237E 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
Rlead
Rbridge
-----------------
2Rlead 
Rbridge
--------------------

© National Instruments Corp. 13 NI 9237E Operating Instructions and Specifications
sensors because there may be significant resistance in the wiring to
the active resistor in the bridge.
The NI 9237E 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 9237E. Visit ni.com/info and enter cseriesdoc for
information about C Series documentation.
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 9237E Operating Instructions and Specifications 14 ni.com
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 9237E 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 9237E automatically
reduces internal excitation voltages as needed to stay below
150 mW total power.
The power consumed by a single bridge is where Ris the total
resistance of the bridge.
For a quarter or half bridge, Ris equal to two times the resistance
of each element. For a full bridge, Ris equal to the resistance of
each element.
Vex
2
R
---------

© National Instruments Corp. 15 NI 9237E Operating Instructions and Specifications
The 150 mW limit allows you to power half and full bridges as
follows:
• Four 350 half bridges at 5.0 V
• Four 350 full bridges at 3.3 V
• Four 120 half bridges at 2.5 V
If you need an excitation voltage that causes more than 150 mW to
dissipate across all the bridges, connect an external excitation
voltage source to the NI 9237E. For the NI 9237E with DSUB, use
the two Vex pins to connect the external excitation source. For the
NI 9237E with RJ-50, use the two EX+ and EX– terminals on the
four-terminal external excitation voltage connector to connect one
external excitation source. You can use the additional EX+ and
EX– terminals on the connector to wire multiple NI 9237E
modules together in a daisy chain.

NI 9237E Operating Instructions and Specifications 16 ni.com
Understanding NI 9237E Filtering
The NI 9237E 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 9237E 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
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 9237E 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 6 shows typical
passband flatness for the NI 9237E.

© National Instruments Corp. 17 NI 9237E Operating Instructions and Specifications
Figure 6. Typical Passband Flatness for the NI 9237E
Frequency/Data Rate
0.50.4
0.025
0.000
–0.025
–0.050
0.30.20.10
Gain (dB)

NI 9237E Operating Instructions and Specifications 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 within the
stopband.
Alias-Free Bandwidth
Any signal that appears in the alias-free bandwidth of the NI 9237E
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 it is equal to the
data rate minus the stopband frequency.
Understanding NI 9237E Data Rates
The frequency of a master timebase (fM) controls the data rate (fs)
of the NI 9237E. The NI 9237E 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 9237E with other
modules that use master timebases to control sampling, all of the

© National Instruments Corp. 19 NI 9237E Operating Instructions and Specifications
modules must share a single master timebase source. Refer to the
software help for information about configuring the master
timebase source for the NI 9237E. Visit ni.com/info and enter
cseriesdoc for information about C Series documentation.
The following equation provides the available data rates of the
NI 9237E:
fs=
where nis 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 9237E has a different set of data rates.
Note The NI cRIO-9151 R Series Expansion chassis
does not support sharing timebases between modules.
fM256
n
---------------------

NI 9237E Operating Instructions and Specifications 20 ni.com
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
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.