8-Channel, 24-Bit Quarter-Bridge Analog Input
Module
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This document describes how to use the National Instruments 9235
and National Instruments 9236 and includes specifications and
terminal assignments. In this document, the NI 9235 and NI 9236
are referred to inclusively as the NI 9235/9236. 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
and enter
cseriesdoc for information about C Series
ni.com/info
documentation.
Note The safety guidelines and specifications in this
document are specific to the NI 9235/9236. 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. Visit
ni.com/info and enter cseriesdoc for information
about C Series documentation.
NI 9235/9236 2ni.com
Safety Guidelines
Operate the NI 9235/9236 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 9235/9236 is suitable for use in Class I, Division 2, Groups
A, B, C, D, T4 hazardous locations; Class I, Zone 2,
AEx nA IIC T4, and Ex nA IIC T4 hazardous locations; and
nonhazardous locations only. Follow these guidelines if you are
installing the NI 9235/9236 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 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 limit:
Capacitance .......................... 0.2 μF max
Special Conditions for Hazardous Locations Use in Europe
This equipment has been evaluated as Ex nA IIC T4 equipment
under DEMKO Certificate No. 07 ATEX 0626664X. Each module
is marked II 3G and is suitable for use in Zone 2 hazardous
locations. If you are using the NI 9235/9236 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 9235/9236 4ni.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.
Yo u can connect a quarter-bridge sensor to each channel. Each
channel has an EXC terminal that provides the excitation voltage
stimulus, an AI terminal that measures the bridge voltage, and an
RC terminal that provides the quarter-bridge completion. Refer to
Figure 2 for an illustration of how to connect quarter-bridge
sensors to the NI 9235/9236.
EXC*
AI**
RC*
NI 9235/9236
* For best system accuracy, set up the connections to EXC and RC with
equal lengths of an identical wire type and gauge.
** For best system accuracy, set up the connection to AI directly at the
sensor instead of shorting AI to RC directly at the terminals.
Figure 2. Quarter-Bridge Connections for the NI 9235/9236
Use a flathead screwdriver with a blade smaller than 2.3 × 1.0 mm
(0.09 × 0.04 in.) to connect wires to the detachable spring-terminal
connector. Insert the screwdriver into a spring clamp activation slot
and press a wire into the corresponding connector terminal, then
remove the screwdriver to clamp the wire into the terminal. Refer
to the Specifications section for more information about
spring-terminal wiring.
Figure 3. Connecting Wires to the NI 9235/9236 Connector
NI 9235/9236 8ni.com
Wiring for High-Vibration Applications
If an application is subject to high vibration, National Instruments
recommends that you use the NI 9965 backshell kit to protect the
connections. Refer to Figure 4 for an illustration of the NI 9965
connector backshell.
The NI 9235/9236 is isolated from earth ground. However, the
individual channels are not isolated from each other. The EXC
terminals all connect internally to a common excitation supply.
Yo u must connect each EXC terminal to only one gage to maintain
the channel-to-channel crosstalk performance of the module.
Each channel on the NI 9235/9236 has an independent 24-bit ADC
and input amplifier that enables you to sample signals from all
eight channels simultaneously. Refer to Figures 5 and 6 for
illustrations of the input circuitry for one channel of the
NI 9235/9236.
NI 9235/9236 10ni.com
EXC
AI
RC
120 Ω
Bridge
Completion
Resistor
50 kΩ
Resistor
Shunt
+
–
Filtered
Differential
Amplifier
ADC
+
–
Excitation
2.0 V
Bridge
NI 9235
Figure 5. Input Circuitry for One Channel of the NI 9235
Figure 6. Input Circuitry for One Channel of the NI 9236
The NI 9235/9236 also includes filters to prevent aliasing. The
filters on the NI 9235/9236 filter according to the sampling rate.
Refer to the Understanding NI 9235/9236 Filtering section for
more information about filtering.
NI 9235/9236 12ni.com
Quarter-bridge measurements are inherently sensitive to accuracy
degradation due to the lead resistance of wiring from the sensor to
the measurement device. For a given change in the gage resistance,
the total effective resistance changes slightly less. Accordingly, the
measured mV/V reading is less than its true value. However, you
can use shunt calibration to quantify the lead wire desensitization,
and can then design the software application to correct subsequent
readings for this gain error. The gain error caused by a lead wire
equals R
, where RL is the lead wire resistance, and RG is the
L/RG
quarter-bridge completion resistance.
Shunt Calibration
The NI 9235/9236 shunt calibration circuitry consists of a
precision resistor and a software-controlled switch, connected
across the internal quarter-bridge completion resistor. Refer to the
software help for information about enabling the shunt calibration
switch for the NI 9235/9236. Each input channel has a unique
shunt calibration resistor that can operate independently, as shown
in Figures 5 and 6.
Shunt calibration simulates strain input by changing the resistance
of an arm in the bridge by a known amount. By shunting, or
connecting, a large resistor across one arm of the bridge, a specific
change occurs in the bridge voltage ratio. With the connected
sensor in a stable, typically unloaded, state, you can measure the
output of the bridge before and after the shunt calibration. You can
compare the measured reading change to the shunt calibration
output value to verify system setup or compensate for
quarter-bridge lead wire desensitization error. Refer to the
Specifications section for the shunt calibration output value. Visit
ni.com/info and enter lwcomp for information about lead wire
compensation.
Excitation Voltage
The NI 9235/9236 provides a constant excitation supply voltage to
each channel. The excitation supply provides sufficient output
current to power all eight channels at minimum resistance.
The excitation supply retains regulation even if one channel
experiences a gage short. If more than one channel has a gage
short, the excitation supply enters a current limit state and the
excitation voltage falls accordingly.
NI 9235/9236 14ni.com
Understanding NI 9235/9236 Filtering
The NI 9235/9236 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 9235/9236 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 9235/9236 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 7 shows typical
passband flatness for the 10 kS/s data rate.
Figure 7. Typical Passband Response for the NI 9235/9236
NI 9235/9236 16ni.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 9235/9236 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 9235/9236 Data Rates
The frequency of a master timebase (fM) controls the data rate (fs)
of the NI 9235/9236. The NI 9235/9236 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 9235/9236 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 9235/9236. Visit ni.com/info and
enter
cseriesdoc for information about C Series documentation.
The following equation provides the available data rates of the
NI 9235/9236:
f
256÷
M
=
f
---------------------
s
n
where n is any integer in the set {2; 4, 5, ..., 63}.
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 10 kS/s, 8.333 kS/s,
7.143 kS/s, and so on down to 794 S/s, depending on the value of
n. When using an external timebase with a frequency other than
12.8 MHz, the NI 9235/9236 has a different set of data rates.
Note The cRIO-9151 R Series Expansion chassis does
not support sharing timebases between modules.
NI 9235/9236 18ni.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
CSeriesdocumentation.
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.
The following specifications are typical for the range –40 to 70 °C
unless otherwise noted. The specifications are the same for the
NI 9235 and the NI 9236 unless otherwise noted.
Input Characteristics
Number of channels .......................... 8 analog input channels
Quarter-bridge completion
NI 9235....................................... 120 Ω, 10 ppm/°C
NI 9236....................................... 350 Ω, 10 ppm/°C
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.
Caution Do not connect the NI 9235/9236 to signals or
use for measurements within Measurement Categories II,
III, or IV.
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Safety Standards
This product is designed to meet 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 visit
ni.com/certification, search
by modu le 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 nA IIC T4
Canada (C-UL) ................................. Class I, Division 2,
Groups A, B, C, D, T4;
Class I, Zone 2,
Ex nA IIC T4
Europe (DEMKO)............................. Ex nA IIC T4
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
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
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Shock and Vibration
To meet these specifications, you must panel mount the system and
use the NI 9965 backshell to protect the connections.
Operating vibration
Random (IEC 60068-2-64)......... 5 g
, 10 to 500 Hz
rms
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
Electromagnetic Compatibility
This product is designed to meet the requirements of the following
standards of EMC for electrical equipment for measurement,
control, and laboratory use:
•EN 61326 EMC requirements; Industrial Immunity
•EN 55011 Emissions; Group 1, Class A
•CE, C-Tick, ICES, and FCC Part 15 Emissions; Class A
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 by module number or
product line, and click the appropriate link in the
Certification column.
Environmental Management
National Instruments is committed to designing and manufacturing
products in an environmentally responsible manner. NI recognizes
that eliminating certain hazardous substances from our products is
beneficial not only to the environment but also to NI customers.
NI 9235/9236 34ni.com
For additional environmental information, refer to the NI and the
⬉ᄤֵᙃѻક∵ᶧࠊㅵ⧚ࡲ⊩ ˄Ё
˅
Ёᅶ᠋
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.
Waste Electrical and Electronic Equipment (WEEE)
EU Customers At the end of their 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
Yo u can obtain the calibration certificate and information about
calibration services for the NI 9235/9236 at
calibration
.
ni.com/
Calibration interval ........................... 1 year
Where to Go for Support
The National Instruments Web site is your complete resource for
technical support. At
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 9235/9236 36ni.com
ni.com/support you have access to
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 43 662 457990-0,
Belgium 32 (0) 2 757 0020, Brazil 55 11 3262 3599,
Canada 800 433 3488, China 86 21 5050 9800,
Czech Republic 420 224 235 774, Denmark 45 45 76 26 00,
Finland 358 (0) 9 725 72511, France 01 57 66 24 24,
Germany 49 89 7413130, India 91 80 41190000,
Israel 972 3 6393737, Italy 39 02 41309277, Japan 0120-527196,
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 7 495 783 6851,
Singapore 1800 226 5886, Slovenia 386 3 425 42 00,
South Africa 27 0 11 805 8197, Spain 34 91 640 0085,
Sweden 46 (0) 8 587 895 00, Switzerland 41 56 2005151,
Taiwan 886 02 2377 2222, Thailand 662 278 6777,
Turkey 90 212 279 3031, United Kingdom 44 (0) 1635 523545
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For patents covering National Instruments products, refer to the appropriate location: Help»Patents in your software,
patents.txt file on your media, or ni.com/patents.