Answer / sumith

PID control valves works on 4-20 ma ,plc gives 4-20 ma to
pid valve according to the difference between setpoint and
actual value (for e.g s.p temp = 90 degc actual = 30
degc)now plc will give 20ma to pid valve for temp to reach
the setpoint.pid valve should have continous air supply.
to calibrate pid valve there is span and zero adjustment.

pid tuning is done in plc not in valve.pid tuning in plc is
trial and error type tuning.
we have to some values in P and I and D and check whether it
is reaching the setpoint smoothly

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Why 4ma - 20ma signal used in instrumentation??

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