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OPERATING INSTRUCTIONS AND SPECIFICATIONS
NI 9235/9236
8-Channel, 24-Bit Quarter-Bridge Analog Input
Module
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ni.com/manuals
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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 ni.com/info and enter
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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 in
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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 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
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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
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EXC0 1 13 EXC1 AI0 2 14 AI1 RC0 3 15 RC1 EXC2 4 16 EXC3 AI2 5 17 AI3 RC2 6 18 RC3 EXC4 7 19 EXC5 AI4 8 20 AI5 RC4 9 21 RC5 EXC6 10 22 EXC7 AI6 11 23 AI7 RC6 12 24 RC7 Connecting the NI 9235/9236 The NI 9235/9236 has a 24-terminal detachable spring-terminal connector that provides connections for 8 analog input channels. Figure 1. NI 9235/9236 Terminal Assignments NI 9235/9236 6 ni.com
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You 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 gau
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Connecting Wires to the NI 9235/9236 Connector 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
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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. Figure 4. NI 9965 Connector Backshell © National Instruments Corp. 9 NI 9235/9236
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NI 9235/9236 Circuitry 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. You 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. Re
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EXC AI 2.0 V + + ADC Bridge – – Excitation Filtered RC Differential Amplifier 120 Ω 50 kΩ Bridge Shunt Completion Resistor Resistor NI 9235 Figure 5. Input Circuitry for One Channel of the NI 9235 © National Instruments Corp. 11 NI 9235/9236
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EXC AI 3.3 V + + ADC Bridge – – Excitation Filtered RC Differential Amplifier 350 Ω 100 kΩ Bridge Shunt Completion Resistor Resistor NI 9236 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 12 ni.com
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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
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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 o
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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 passba
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0.025 0.000 –0.025 –0.050 0 1 2 3 4 5 Frequency (kHz) Figure 7. Typical Passband Response for the NI 9235/9236 NI 9235/9236 16 ni.com Gain (dB)
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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 fr
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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
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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
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Specifications 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 max NI 9236.......................................350 Ω, 10 ppm/°C max ADC resolution.................................24 bits
