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The resulting changes in capacitance can be measured and converted into an electrical The flexing alters the gap between the plates creating, in effect, a variable capacitor. To maximize the output of the sensor and to reduce sensitivity to errors.Ĭapacitive sensors generally feature two closely spaced, electrically-isolated metallic surfaces one of which acts as a diaphragm by slightly flexing under applied Generally, the strain gauges are connected to form a Wheatstone bridge circuit Of the strain gauges which is detected and converted into an electrical signal proportional to pressure. Increasing pressure results in changes in the resistivity Polysilicon thin film, bonded metal foil, thick film, or sputtered thin film-when mechanical strain (pressure) is applied. Piezoresistive sensors are based upon the piezoresistive effect which describes changes in the electrical resistivity of a semiconductor or metal -commonly silicon, Sensors detect that movement (the strain) and convert to a unit of pressure.Īmong force collector sensors, there are two types that we see most often: Or diaphragm to move in relation to the amount of pressure. Simply put, pressure applies force to a diaphragm or piston which causes the piston These electronic sensors employ a forceĬollector such as a diaphragm or piston to measure the strain caused by force applied over an area.

Though there are many sensing technologies available, most pressure sensors, transmitters, and transducers use force collector type sensors. The sensor measures theĭifference between two pressures, such as each side of a filter to measure pressure drop. It is equal to gauge pressureĭifferential pressure: Similar to gauge pressure although the reference point is another pressure point rather than ambient pressure. Sealed gauge sensors may use a fixed pressure different than ambient atmospheric temperature.Ībsolute pressure: The sensor is referenced against a perfect vacuum so it, therefore, includes the effects of atmospheric pressure. It is equal to absolute pressure minusĪmbient air pressure. Gauge pressure: The sensor is referenced against atmospheric pressure so it does not include the effects of that pressure. The type of pressure refers to the zero reference point of a measurement. There are also different types of pressure to consider. Other units of measure include kg/cm2, inH2O, mmHg, Pa, and many others. We will see PSI ( pounds per square inch) or bar. Pressure sensor is a catch-all term that includes both pressure transmitters as well as pressure transducers.Īs pressure is defined as force over a unit area, there are a number of ways to articulate pressure readings depending upon the unit of force and the unit of area. They are also sensitive to electromagnetic interference. Transducers areīetter for short runs as electrical resistance can cause errors on longer runs.

Pressure transducers are voltage output devices that, generally, have three or four wires to power the device as well as transmit the output signal. Transmitters are ideal for longs runs as wiring is simpler and cheaper and there is no significantĭegradation of the output signal with distance. They are often scaled from 4-20 mA although other ranges are available. Pressure transmitters are current output devices that, generally, have two or three wires that are used to both power the device as well as transmit the output Transducers are the class of instruments which convert applied pressure into a measurable electrical signal which can be used for display or to trigger a control function.Īlthough many users-and even some manufacturers- use the terms sensors, transmitters and transducers interchangeably, technically there are differences between them. Usually involving liquids and gases, pressure is a critical component of a diverse array of applications,īoth those that rely on accurate pressure control as well as those that derive other values (such as depth/level or flow) based upon pressure. Pressure is defined as the amount of force applied over a unit area.