For referring to variable capacitive sensing technologies, four specific terms are commonly used: pressure transmitters, transducers, sensors, and switches. Capacitance is the detection and measurement of pressure by the change in voltage across a capacitor. The capacitance of sensing technology can be fixed or adjustable and varies dependent on the application. Capacitive sensing technology is highly precise, boasting accuracies of up to ± 0.07% of full scale. This pressure sensing technology is used for applications where a high degree of accuracy is crucial, such as engine test stands and pressure decay leak detection.
A pressure sensor is any device that measures pressure and converts it to an electrical signal. It's an all-encompassing term that can be used to describe pressure transducers, transmitters, and switches. Although sometimes the terms transmitter, transducer, and switch are used interchangeably when referring to pressure measuring devices, each is a distinct measurement tool. These devices are similar but not identical, so the terms are not synonymous.
Pressure Transducers and Transmitters
Pressure transducers and pressure transmitters are very similar. A pressure transducer is an electromechanical device for translating pressure values into voltages across a high-impedance load of 5,000 ohms or greater. On the other hand, a transmitter translates pressure values into currents—generally 4-20 mA—across a low-impedance load. Generally, transmitters are preferred when sending a signal over relatively long distances. However, neither transducers nor transmitters control pressure. These devices are solely for measuring pressure and communicating the output electronically or visually.
Unlike a transducer or transmitter that can translate all of the pressures in its range, a pressure switch triggers at a specific set pressure. That set pressure can be high or low to meet the needs of the application. Also, a switch can either engage or disengage a circuit.
What kind of sensor do I need?
Whether a transducer, transmitter, or switch would be used depends on the application. Switches are commonly found in vehicles to indicate low engine oil pressure and in gas compressors with an automatic shut-off mechanism. Transducers and transmitters provide significantly more data beyond if a specified value has been hit. They are useful in critical spaces and industrial applications requiring high precision, feedback for a control system, data for alarm conditions, and trending information.