Transmitters and Control Loops

Differential pressure or AP cell transmitters come in two basic designs pneumatic or electronic. Controllers are typically mounted between 400 feet (closed loop) and 1,000 feet (open loop) from the transmitter. The signal from an electronic transmitter is proportional to the difference in the high-and low-pressure legs. Standard output signals are 4 to 20 mA, 10 to 50 mA, and 1 to 5 volts (V). 

Flow Orifice plate, flow nozzle, AP cell (diaphragm) AP cell 

Pressure Flelix, spiral, bellows, bourdon tube, AP cell AP cell 

Temperature Capillary tubing, thermal resistance bulb Thermocouple, RTD 

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