Chapter 5 Relay Ladder Logic Programming 123
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Integral controller
For smooth and stabilize the system once the EV value and is change drastically, integral control can delay the
react of the system and shrink control loop variation.
EV and time automatically adjust variable ΔPI.
Integral controller characteristic: reduce variation, delay reaction time.
Differential controller
System react is depends by PV value then convert to variable ΔPI and control the output result.
ΔPI will change depend on the value of PV. Process time is reduced via differential controller.
Differential control characteristic: reduce vibration, increase stability accelerate process time.
The features of PID control: fast, stable and accurate
Description of K
P
, T
I
, T
D
as show below:
The PID function control variable Kp, Ti and Td:
Increase Kp value to has a fast response time and reduce deviation quickly and the large Kp value will
eventually affect the stability of the system or even unstable.
Once the variation is occurred and integral loop start to process, a small Ti setting value has a greater integral result
and vice versa.
Differential control has a fast react feature, greater differential time Td setting is able to increase the system
response, and minimal the variation but the large differential time settings will un-stabilize the system easily.
Although the large Td setting value could reduce response time, user should setting differential time Td value
properly to prevent a system become a ultra sensitive controller.
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