Pressure sensors are used to monitor the pressure in liquid and gasseous applications and this information can be used to regulate the pressure or determine that the pressure is within limits Modern PLCs and variable frequency drives include PID modules that easily enable the pressure transducer to be used as part of a pressure regulation system.
The following criteria should be considered when selecting a pressure transducer:
- Separation: As the monitored medium may be corrosive, or high /low temperature, it is sometimes necessary to use an isolation barrier with the pressure transducer. This may be built into the sensor, or may be a separate component.
- Accuracy: The accuracy of the pressure transducer is very dependent on the requirements of the application. The calibration is affected by temperature and age.
- Range: transducers are available from vacuum to high pressure. Differential transducers measure the pressure difference between two inputs, absolute sensors measure the pressure relative to absolute zero, and guage sensors measure the pressure relative to the atmospheric pressure.
- Temperature: The pressure measurement can be temperature dependent. Temperature compensation can be built into the transducers to reduce the thermal effects. The operating temperature range is usually provided by the manufacturer. Large errors can occur outside of that range. Very low temperatures in water applications, can cause the water to freeze and damage the sensor.
- Vibration/shock effects: Vibration and shock are highly application-specific environmental issues. They should reviewed for fit with manufacturer’s specifications.
- Hydraulics: Applications measuring the pressure of hydraulic oils can be subjected to very high pressure transients. These can be smoothed by the use of hydraulic snubbers or pressure vessels.
- Outputs: transducer outputs are available in industry-standard, millivolt, voltage, or current signals. Digital outputs with communication capability are available as well. The passive 4-20 mA output is the simplest since it is a two-wire connection. A voltage output is a three wire connection and is more easy to wire incorrectly. 4-20 mA circuits are more noise immune that voltage circuits so should be used in preference to voltage outputs where there is electrical noise.
- Units: Pressure transducers can be scaled for most pressure measurement units. Common units are KPA, Bar and PSI.
- Connections: There are a wide range of connections and threads that can be used for pressure sensors.