Working of I/P Transducer

Introduction

• I/P Transducer accepts an electrical input signal and produces a proportional pneumatic output.In this session we are going to discuss about how I/P transducer works.

To know about I/P converter calibration

Principle of Operation

Electronic Circuit

• The input current signal i.e. 4-20 ma is received by the transducers electronic circuit and compared to the output pressure from the booster stage.
• A solid-state pressure sensor is part of the electronic circuit and monitors the booster stage output. The silicon-based sensor uses strain gauge thin film technology. The sensor’s pressure signal is fed to a simple internal control circuit.The transducer’s performance is decided by the sensor/circuit combination. Changes in output load (leaks), variations in supply pressure, or even component wear are sensed and corrected by the sensor/circuit combination.

Magnetic Actuator

• The electronic circuit controls the level of current flowing through the actuator coil, which is located in the pilot/actuator assembly. A change to the level of coil current is made by the electronic circuit when it senses a discrepancy between the pressure measured by the sensor and the pressure required by the input signal
• The actuator performs the task of converting electrical energy (current) to motion. It uses a , coaxial moving magnet design optimized for efficient operation and is highly damped at its mechanical resonance. A silicone rubber diaphragm protects its working magnetic gaps from contamination.

Pilot Stage

• The pilot stage contains two opposed fixed nozzles: the supply nozzle and the receiver nozzle. It also contains the deflector, which is the moving element. See figures below The supply nozzles connected to the supply air and provide a high-velocity air stream.

• The receiver nozzle  of I/P Transducer captures the air stream and converts it back to pressure. The receiver nozzle pressure is the output pressure of the pilot stage. To vary the pilot output pressure, the high-velocity stream is diverted away from the receiver nozzle by the deflector, which is a cylindrical; aerodynamic body located between the two nozzles.
• In response to a change in actuator coil current, the deflector is repositioned between the nozzles. There is a linear relationship between the coil current and the pilot stage output pressure. For direct action units, the power-off, or fail-safe, position of the top of the deflector is near the center of the stream and results in nearly zero pilot output pressure.
• As the coil is energized, the deflector is drawn out of the stream. For reverse action units, the power-off, or fail-safe, position of the deflector is completely out of the stream. The result is maximum pilot output pressure. As the coil is energized, the deflector moves into the stream, resulting in a decreased pilot output pressure.

Booster Stage

• The receiver nozzle pressure controls the booster stage.If the receiver nozzle pressure increases the transducer output will also increases.A decrease in the receiver nozzle pressure positions the valving in the booster stage to allow exhaust to occur, decreasing the output signal.