Chapter 7 Usage of Various Functions

Relay response method.

PID parameters are obtained by On/Off operation during 1 cycle of PV variation.

PID parameters are obtained by amplitude and period of oscillation

The On/Off operation will be occur at the SV value.

SV

MV

Period

Amplitude

Process reaction curve method(PRC method).

PID parameters are obtained by step response of process.

It is useful fo r time 1st order time delay system expressed as following

KTse +1

Obtained parameters may not accurate if the process can’t approximated to 1st order system, In this case, use relay response method.Ls

4000

80% of SV

63% of SV

Time delay(L)

MV

Time constant(T)

7-30

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LG Electronics 120S user manual Tse +1