![]() When transducers are directly interfaced with digital data acquisition systems and are located at some distance from the data acquisition hardware, high output voltage signals are preferred. Pressure transmitters can send the pressure measurement of interest using an analog pneumatic (3-15 psig), analog electronic (4-20 mA dc), or digital electronic signal. A pressure transmitter is a standardized pressure measurement package consisting of three basic components: a pressure transducer, its power supply, and a signal conditioner/retransmitter that converts the transducer signal into a standardized output. A pressure transducer might combine the sensor element of a gauge with a mechanical-to-electrical or mechanical-to-pneumatic converter and a power supply. The term pressure gauge usually refers to a self-contained indicator that converts the detected process pressure into the mechanical motion of a pointer. Often, the terms pressure gauge, sensor, transducer, and transmitter are used interchangeably. When using SI units, it is proper to add "gauge" to the units used, such as "Pa gauge." When the measurement of the pressure is in absolute units, the reference is full vacuum and the abbreviation for "pounds per square inch absolute" is psia. Therefore, the pressure unit "pounds per square inch gauge" is abbreviated psig. In those parts of the world that continue to use English units, gauge pressure is indicated by adding a "g" to the units descriptor. "Gauge" pressure is defined relative to atmospheric conditions. ![]() In fact, one might consider the differential pressure transmitter the model for all pressure transducers. Many features of modern pressure transmitters have come from the differential pressure transducer. The detected pressure differential is related to flowing velocity and therefore to volumetric flow. Depending on the reference pressure used, they could indicate absolute, gauge, and differential pressure.ĭifferential pressure transducers often are used in flow measurement where they are designed for differential pressure measurement across a venturi, orifice, or other type of primary element. Therefore, manometers are usually found in the laboratory or used as local indicators. But manometers are large, cumbersome, and not well suited for integration into automatic control loops. Originally, these tubes were made of glass, and scales were added to them as needed. ![]() U-tube manometers were among the first pressure indicators. Mechanical methods for pressure measurement have been known for centuries. Pressure transducers can come in a number of shapes and sizes, but the majority of transducers have a cylinder-shaped center which houses the diaphragm and the measurement pressure chamber, a pressure port at one end which is typically a threaded, bolted, barbed fitted, or open, and on the other end a location for signal transmission. ![]() These include the industrial pressure transducer, the liquid pressure transducer, and the micro pressure transducer, among others. There are a ubiquitous number of pressure transducer designs available for use in any number of industrial or laboratory applications. ![]()
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