Answer / krishna

proportion control function is to maintain constant offset
between set point and process variable .but it cannot remove
the offset. it makes the p.v to oscillate between high and
low limits.

There are two things required for calibrating control valve
1)pneumatic tester ( signal :0.2 to 1kg /cm2
)
2) air supply source according to design of valve.
initial for 0.2 kg.cm2 valve should be (open or close )
according to ATO ATC) )
THEN CHECK POSITION AT 25 50 75 100 % OF VALVE ACCORKING TO
SIGNAL TUNE WITH POSITIONER

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 / prashant

proportional function is take place an action to maintain
the pv proportionaly to error in p.v . but an offset error
is sustained , that will be reduced by integral funtional.


calbration of control valve :::
1. check the pneumatic pressure of regulator
2. give the 4-20 ma to check the strock of c/v
3. if storck is not achieving then adjusted by zero
& span adjustement

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