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I am working on PID loops now a days and need to know the exact description of PID control.

From TOHO TTM-X04 temperature controller, i learnt about P and I, but still i can't understand about D (Differential). As you know that this temperature controller shows manipulated output in %.

Below are the observations i learnt about P and I,

Proportional band only check the difference between actual value and set value and decide how much output in percentage is required to reduce this difference.

Example:

If P=1%

Present Value = 80 deg C

Set Value = 100 deg C

Difference = 20 deg C

Manipulated Output = 80% (assume)

If P=2%

Present Value = 80 deg C

Set Value = 100 deg C

Difference = 20 deg C

Manipulated Output = 60% (assume)

Conclusion is that manipulated output reduces as we increase the value of P in %.

Integral band increases the output if the difference remains unchanged.

Example:

If P=2% and I=300 Seconds or 5 minutes.

At 0th second of control time:

Present Value = 80 deg C

Set Value = 100 deg C

Difference = 20 deg C

Manipulated Output = 60% (assume)

At 300th second of control time:

Present Value = 80 deg C

Set Value = 100 deg C

Difference = 20 deg C

Manipulated Output = 100% (assume)

Conclusion is that output increases gradually and becomes full 100% in 300 seconds if present value remains 80 deg C.

Kindly share information about differential, as i am still struggling in getting clear information about differential.

Thanks to all

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# Proportional, Integral and Derivative

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