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 pressure 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
