Pakarab fertilizers limited multan
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- 3. Secondary conversion element
- Capacitive pressure transducers
- C = K A/d
| 2.4 Pressure transducers A device that converts the mechanical output of a pressure sensor to a standard electrical is the transducer. An electrical pressure transducer consists of three elements 1. Pressure sensing element: usually a bellow, diaphragm or bourdon tube. 2. Primary conversion element: Converts mechanical action of the pressure sensing element into an electrical signal, usually resistance or voltage. 3. Secondary conversion element: It produces a standard signal according to the needs of the control system. 41 Field Instrumentation GEN Rev) Potentiometric pressure transducers Potentiometer is a variable resistor. It is made by winding resistance wire around an insulated cylinder. A movable electrical contact (a wiper) slides along the cylinder, touching the wire atone point on each turn. The position of wiper determines how much resistance between the end of wire and the wiper. Disadvantage is that it generates discrete output i.e. the wiper does not move continuously along the wire. Potentiometric pressure transducers Capacitive pressure transducers It is based on the principle of capacitor. The transducer contains two metal plates. One plate, the stator, is stationary. The other plate is a flexible metal diaphragm that moves closer to the stator when the pressure rises. As the pressure changes, the diaphragm moves and changes the capacitance of the device. C = K A/d where, C = capacitance, K = Dielectric constant, A = Cross sectional area of plates, d = Distance between plates. The transducer is connected in an ac bridge circuit. Changes in the measured pressure cause changes in the capacitance of the capacitor and in the bridge circuit’s response. These changes cause changes in the voltage output of the bridge circuit. 42 Field Instrumentation GEN Rev) Response time of capacitance transducer is very fast, as ten milliseconds. Capacitive pressure transducers Download 3.37 Mb. Share with your friends:
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