Instrumentation

Working principle of pressure transmitter

In this lesson, we will study the working principle of a pressure transmitter.

The Pressure Transmitter Works on Variable Capacitance  Principle. A variable capacitance pressure transducer has a capacitive plate bonded to one side of the diaphragm and another capacitive plate bonded to an unpressurized surface in close proximity to the diaphragm. A change in pressure will widen or narrow the gap between the two plates which varies the capacitance.

When Pressure is applied on Pressure Transmitter it is Applied on the Diaphragm of Pressure  Transmitter, When Pressure Changes variation in Diaphragm Occurs. This variation Causes variation in Silicon Oil Filled in the Transmitter. Displacement of sensing diaphragm is proportional to differential pressure. The position of the sensing diaphragm is detected by capacitor plates on both sides of the sensing diaphragm.

This variation Causes Variation in the Capacitance Due to Capacitance Variation Current Varies means 4-20 m amp varies.

The Capacitance is Given by the Equation:

C= KS(N-1)/d

  • C: Capacitance
  • K: dielectric constant of the material between the plates
  • S: Area of one side of one plate
  • N: Number of plates
  • d: distance between two adjacent plates.

A capacitance transducer operates on the principle that the physical property to be sensed changes on of the variables in the above equation (usually the distance d) which then changes the capacitance C.

Capacitive Transducer

Answer:  The capacitive transducer or sensor is nothing but the capacitor with variable capacitance. The capacitive transducer comprises two parallel metal plates that are separated by the material such as silicon oil, which is called as the dielectric material. In the typical capacitor, the distance between the two plates is fixed, but in variable capacitance transducers, the distance between the two plates is variable.

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