Differential Pressure Transmitter

Differential pressure transmitter is one of pneumatic transmitter types. Pneumatic transmitter uses high-pressure air as the medium. The air pressure is generated by compressor. The air is supplied to the transmitter with pressure approximately 20 Psi.  The next step, transmitter issue standard signal with pressure 3-15 Psi.

Pneumatic transmitter types are often used for measurement is Differential Pressure Transmitter as show in Figure 1 below.

Figure 1: Differential Pressure Transmitter

In differential pressure transmitter, the pressure of fluid that will be measured is connected on two sides of transmitter; high pressure side and low pressure side, where both sides are mounted in area between diaphragm capsules. The side that has low pressure will flow on the right side of diaphragm capsule. At high pressure side, fluid flows greater than fluid at low pressure side, so the push force of diaphragm from left side to right side of diaphragm will be greater.

The change force of diaphragm is then channeled through flexible bar to move the force bar, where the bar rotates counter-clockwise. Seal diaphragm acts as a fulcrum and as a result, cavity between nozzle and flapper becomes smaller. So air will normally come out from nozzle cavity. Nozzle gap must be limited so that the pressure generated by nozzle transmitter will increase and the output will get reinforcement from pneumatic amplifier.

Part of the output is used as feed back bellows which is modified in the form of reinforcement. The reinforcement of differential pressure transmitter is used by range bar  and use range wheel as a fulcrum. By making changes to the flapper position will reduce pressure transmitter. The end result is difference pressure between before diaphragm and after diaphragm will occur. Gap between flapper and nozzle transmitter that has been reduced will increase the output and stabilize it, by this way both pressure will be balanced.