I'm encountering an issue in LabVIEW when trying to collect data from a pressure transducer (full bridge) through an NI 9237 module mounted on a cDAQ-9174.
My troubleshooting so far appears to suggest the NI 9237 module is not generating the internal excitation voltage. I'm looking for guidance to help identify if I have a wiring issue or a faulty component.
I am utilizing the same pressure transducer and wiring configuration characterized in this thread:
The waveform generated in LabVIEW shows a noisy signal fluctuating around -0.0018 units. No change in pressure to the circuit to which the transducer is attached is reflected in the waveform. The three other channels of the NI 9237 module show a flatline equal to -0.0125 units. When I switch the channel to which the transducer is connected, the noisy signal follows and the disconnected channel now reads the same flatline -0.0125.
The test VI is elementary to help troubleshoot this issue, with a single DAQAssistant going to a waveform graph inside a while loop.
The channel is configured for signal input max/min of 5m/-1m and Vex source internal 2.5 V in a Full Bridge I configuration.
Troubleshooting Steps Completed:
I've cycled through multiple transducers and also explored another generic version of the pressure transducer with similar issues.
I've wired the transducers up directly to the pin connector plugged into the 9237 module and also used a breadboard circuit to evaluate different combinations of pin wiring; and I've replaced wires and connectors too many times to count.
I've switched bays of the chassis in which the 9237 module is mounted and also tried different USB ports on the computer.
In LabVIEW, I've toggled settings of the Vex value from 2.5 to 10 V. I know the transducer is a full bridge.
I've read countless forums and all NI-authored support pages for strain gauges, NI 9237 module, etc.
The current gap in my findings is that I'm not reading any voltage from pins 6 and 7 on the 9237 module when the system is supposed to be generating an internal excitation signal. Whether I connect the multimeter to the open wires extending from the RJ50 adapter or to the jumper pins on the module itself, I do not get any reading (I've taken this measurement both with the transducer attached and removed). Am I correct to think that I should be reading the same internal excitation voltage specified in the DAQ configuration across pins 6 and 7?
Thank you in advance.
Solved! Go to Solution.
Much appreciation to the technical support team at NI for assisting in this process.
Unfortunately, the NI-9237 module is malfunctioning and it is confirmed the device should be producing an excitation voltage across pins 6 and 7. The module needs to be repaired or replaced.
Troubleshooting steps that were requested and explored by the NI support technician:
1. Review the wiring diagram showing how the sensor is connected to the module.
2. Review the datasheet for the sensor.
3. Attempt to check with an alternate NI-9237 module (none were available to me).
4. Configuring the DAQAssistant to utilize an external excitation voltage (this yielded a response from the sensor in my VI, but the sensitivity was too high).
5. Review the LabVIEW code to ensure correct programming.
The technician tested the excitation voltage on hardware he had in his lab and confirmed a voltage reading could be measured across pins 6 and 7. The technician explained that he configured the DAQ assistant in LabVIEW to run continuously with internal excitation values (2.5 V and 5 V), and both voltages could be measured across pins 6 and 7 of the NI-9949 accessory connected through an RJ50 to RJ50 cable to the NI-9237.
In my case, I didn't have the NI-9949 accessory available, but stripped the wires of a cutoff RJ50 cable and took a volt meter across the exposed wires of pins 6 and 7.
Unfortunately, this is not detectable with the MAX self-test programs and now a repair/replacement ticket is underway.