I have a 10bar pressure transducer with a 4-20mA output which is showing a random variation across a span of 0.3mA (+/- 1.5mA) at a fixed pressure. This seems to me to be very large and it doesn’t seem related to electrical noise. What is the possible cause of this output fluctuation and what would you expect the variation to be for a pressure transducer with a high accuracy current output?
Even a low grade accuracy pressure transducer should produce a more stable output signal. The variation you are experiencing equates to a total variation of 0.375% FS which is not acceptable for most types of sensors. The pressure transducer maybe faulty if the variation is truly random, but first you will need to eliminate any application variations that might be causing the drift in output:
- Is there any correlation with temperature change? Even with high accuracy pressure transducers, the errors can be quite significant with changes in temperature. The actual variation can vary depending on the manufacturer and type of sensor.
- Is the power supply adequate? Running the sensor near the minimum supply voltage limit can sometimes lead to problems especially if there is additional load resistance in series with the sensor.
- Is there a nearby source of electrical interference? A 4-20mA output signal is a robust signal, but if the electronics inside the transducer are not adequately protected some of the active solid state components may be susceptible to interference, especially if the EMC levels are exceptionally high.
- Is the pressure really fixed? If the vessel / pipe is a sealed system, the pressure will vary with changes in volume or temperature, are there any moving parts or heat sources that could cause the pressure to fluctuate?
- Have you checked the wiring connections? Poor electrical contacts could lead to fluctuations in output signal.