Control System

Fisher 546 I/P electro-pneumatic transducer

What is I/P converter?

I/P converter is a device that converts the current signal into a pneumatic signal. For the current signal in the range 4-20mA, a corresponding pneumatic signal in the range 3-15psi is formed. I to P converters use flapper nozzle mechanism.

Working mechanism:

The heart of this mechanism is a ferrous beam, located between the poles of a permanent magnet assembly, and centred within an electromagnet coil (solenoid). The current passing through the electromagnet coil imparts magnetic poles to the ends of the beam.

The coil is wrapped around the beam, by the right-hand tells us that the beam will magnetize with the right-hand side being “North” and the left-hand side being “South.” This electromagnetic polarity interacts with the permanent-magnetic poles to torque the beam clockwise around its pivot point (fulcrum), pushing the right-hand side down toward the nozzle.

The beam is levelled by two forces, the spring tension and the bellow pressure, bellow is feed with compressed air pressure. Thus the current applied to the coil governs the movement of the pivot beam.

Any movement of the beam towards the nozzle will increase the back pressure which is then fed to the balancing bellows at the other end of the beam. That bellow provides a restoring force to the beam to return it (nearly) to its original position.

The purpose of the pneumatic relay is to provide a modest pressure gain to raise the nozzle backpressure to standard levels. Depending on the back pressure the relay controlls the output signal in range 3-15psi or can done to 6-30psi according to purpose.


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