Answer / waqas ali

A PID controller is composed of three components:
P - Proportional
I - Integral
D - Differential
It controls the overall response of a system. The "P" term
controls the gain of the system. The "I" term controls
error and "D" term controls the overshoot of the system.

Answer / www.islamqa.com

Actually we can make it simple:

# P:
it's a controller gain which modify the controller o/p
proportional to the error.

# I:
it's a controller gain which modify the controller o/p
proportional to the integral of the error.

# D:
it's a controller gain which modify the controller o/p
proportional to error rate of change.



We have 4 parameters in our control loop to focus on:
1 - the rise time: the period of time during which the pv
get 90% of the desired sp value
2 - max overshoot
3 - settling time: the period of time during which the pv
get the desired sp value and saturate.
4 - error/offset

we can get it clear from this pic:
http://controls.ame.nd.edu/ame437/S2003/hw1/specifications.j
pg

Now we will take a look about the effect of each controller
gain on these parameters:

# P gain:
decrease rise time
increase max.overshoot
increase settling time
decrease error (but not eliminate)


# I gain:

decrease rise time
increase max.overshoot
increase settling time
eliminate error.


# D gain:

no effect on rise time
decrease max.overshoot
decrease settling time
decrease error.

the previous is guidelines to be in background while
dealing with PID,but they are not sharp limits.

Regards,

Ahmed Sabry
Control and Instrumentation Engineer
GPC - General Petroleum Company
ahmedsabry.online@gmail.com
CELL.: 00 2 0121367310

Answer / ajith294

At first you should understand what is the controller.

A controller is the device in a closed loop, that compares the measured valve (actual valve) with the desired valve and calculate the out put manipulated variable. Then The time (T) responds is determined by P,I,D

P: manipulated variable our put is proportional to the system deviation. that means variable only present if there is any system deviation.

I: manipulated variable is continues to increase, the system deviation decreases. this process continuous until system deviation is zero.

D: Differential compound evaluate the speed of change of the system deviation.

so if using the PID controls, we can control the flow to our desired valve at a very short time.

Best Regards

Answer / basheeruddin

PID controller is use to correct the errors between measure value PV ( i.e process value ) and set piont (sp).

deference between DCS and PLC including date processing and architacture.

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