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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
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A PLC is programmed to drive three motors A, B and C as follows : After running motor A for an hour, motor B should get ON and motor A should get OFF. And after running motor B for an hour, motor C should get ON and motor B should get OFF. And after running motor C for an hour, motor A should get ON and motor C should get OFF. (That is, a cyclic repetition with time period one hour) Now, the second condition is: If any motor gone faulty and is tripped, the consecutive motor should get ON and the faulty (tripped) motor should be eliminated from cyclic repetition. The remaining two motors should bear the cyclic repetition of one hour each. (For healthy motor take logic as high and for tripped motor take logic as low) Now, the third condition is: When motor A load(Amps) exceeds 60% of its rated load, motor B should get ON in parallel to motor A. And when both motors A & B are running in parallel, and if their load exceeds 60% of their rated load, motor C should also start in parallel to A & B. [Here the cyclic repetition is eliminated, until their loads become normal(40%)] [Take logic high(1) for load at 60% and logic low(0) for load at 40%] Now draw a flow chart or a ladder diagram to fulfill the above condition.
