Diagnosing incorrect readings from a pressure measurement system

My new pressure sensor system is giving unexpected readings. How can I determine if the problem is with the voltage output pressure sensor or my data acquisition (DAQ) system?

A systematic troubleshooting approach is the most effective way to isolate the source of error in an instrumentation loop. By separating the sensor from the rest of the system, you can determine if the fault lies with the measurement device or the signal processing hardware. Here is a step-by-step diagnostic guide based on industry best practices.

Verify System Basics:

• Power Supply: Ensure the voltage supplied to the sensor is within its specified operating range.
• Wiring: Double-check that the electrical connections are correct.

Isolate and Test the Sensor:

• Disconnect the sensor’s signal wire from your DAQ, PLC, or display.
• Using a calibrated digital voltmeter (DVM), measure the voltage directly across the sensor’s signal output. This provides a direct, unfiltered reading of the sensor’s output.

Perform a Bench Test with a Calibrated Source:

• Connect the sensor to a known, stable pressure source, such as a pressure calibrator or deadweight tester. This allows you to apply precise pressures and validate the sensor’s response.
• Create a data table, recording the sensor’s direct voltage output (from your DVM) at several pressure points across the measurement range (e.g., 0%, 25%, 50%, 75%, and 100% of full scale).

Compare Measured Data to Specifications:

• Calculate the ideal output for each pressure point.
• Factor in the sensor’s allowable tolerances. This includes the accuracy, and the specified zero & span offset range.
• If your DVM readings fall within the calculated range of ideal output plus/minus the combined tolerances, the sensor is performing correctly.

Investigate the Data Acquisition System:

• If the bench test confirms the sensor is healthy, the problem lies downstream in your signal processing chain.
• Input Range: Confirm your DAQ card or PLC analogue input is configured for the correct voltage range.
• Software Scaling: Check the scaling factors used in your software or PLC logic to convert the voltage reading back into a pressure value (e.g., bar, psi). Incorrect scaling is a very common source of error.

By following this process, you can confidently determine whether the issue originates from the voltage output pressure sensor or the instrumentation used to read it.

Related Help Guides

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• How to create a list of specification parameters for a pressure sensor
• Checking the LHR error of a 0-5 Vdc output pressure transducer
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• Reduce calibration costs of analogue pressure gauges

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