WHAT IS THE Differance b/w on/off & pid control valve?
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Answer Posted / kavi
Both are used to control a process. The on/off valves are
actuated by simple digital signal ( may contain voltage of
24 vdc/ac to 220vac) from an on-off controller or from a
controller whose output is of "on-off PID". In the first
one when the process exceeds a set value ( increase or
decrease) the digital output goes to valve to operate a
solenoid whose air supply opens or closes the valve ( a
full close or open condition). If the controller is having
an on-off PID the digital signal going to the valve is the
output of PID block of the controller which is in the form
of pulse width modulated one. In this also the valve will
have only two states like fullopen or full-close. In the
so called PID valve, the valve can have any postion of
opening basing on the analog signal received from the
controller. We can say that the valve opens or closes
proportional to the analog signal from the controller. In
this the controller tuning ( setting the values of P, I D )
has to be done by the process operator or the concern
instrument engineer/technician.
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