2-2
Principle of Operation
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Transducer Operation Schematic
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As shown in the above schematic, the operation of the I/P Converter is controlled by
applying a 4 to 20mA DC signal to the input which causes the internal circuit to generate a
voltage. A drive current is also supplied to the torque motor which represents the circuit
load to operate the overall system. If the level of the input signal increases, the current to
the torque motor [1] increases and the flapper [2] moves so as to cover the nozzle [3] and
raise the pressure in the pilot relay (pneumatic valve) nozzle back-pressure chamber [4].
The increased nozzle back-pressure causes a displacement in the diaphragm assembly [5]
in the pilot relay, opening the port’s [6] inlet valve seat [7]. This increases the output air
pressure from the pilot relay. The output air pressure is also applied to the solid state
sensor [8] and converted into an electrical signal proportional to the pressure. This
electrical signal is then returned to the control circuit where it is used as a feedback signal.
The control circuit compares the sensor signal against the input signal to control the output
air pressure to match the input signal.
2－2
