Mitsubishi Electronics MELSEC-F

/FX

3UC

PLC User's Manual - Analog Control Edition

PID Instruction (FNC 88)

M-21

4 Auto-Tuning

4.2 Step Response Method

-4AD-PNK

-ADP

-4AD-TC

-ADP

PID Instruction

(FNC 88)

4.2 Step Response Method

4.2.1 Parameters to be set by auto-tuning (step response method)

4.2.2 Auto-tuning procedure

1Transferring the output value for auto-tuning to the output value

Set the output value for auto-tuning to the maximum available output value multiplied by 0.5 to 1 for

the output equipment.

2Setting the parameter , target value (SV), etc. that cannot be set in auto-

tuning according to the system

Note that auto-tuning may not be executed normally if the cautions described below are not fol-

lowed

1. Set items

2. Cautions on setting

1) Difference between the target value (SV) and the measured value (PV)

If the difference between the target value (SV) and the measured value (PV) is less than 150 when auto-

tuning is started, auto-tuning is not executed normally.

Accordingly, if the difference is less than 150, set the target value for auto-tuning.

Set the target value again when auto-tuning is completed.

2) Sampling time (TS)

Make sure the sampling time is set for auto-tuning to 1 second (1000 ms) or more.

It is recommended that the sampling time is set to that it is considerably longer than the output change

cycle.

3Setting to ON bit 4 of +1 (operation setting ACT) to start auto-tuning

When the variation from the measured value at the start of auto-tuning to the target value reaches

1/3 or more, auto-tuning is completed. And bit 4 of +1 (operation setting ACT) is

automatically set to OFF.

1. Important point

Start auto-tuning while the system is stable.

If the system is unstable when auto-tuning is started, auto-tuning may not be executed normally.

Parameter Setting position Parameter Setting position

Operation setting (ACT) +1, bit 0 (operation direction) Integral time (TI)+4

Proportional gain (KP)+3 Differential time (TD)+6

Set item and parameter Remarks

Target value (SV) The difference from the measured value (PV) should be 150 or more.

(For the details, refer to "2. Cautions on setting" below.)

Sampling time (TS) 1,000 ms or more (For the details, refer to "2. Cautions on setting" below.)

Input filter (α)+2

Differential gain (KD)+5 When setting the input filter, set the differential gain to "0" usually.

Others Set other items, as necessary.

Set item Setting in PID instruction

Target value (SV) Make sure that the difference from the measured value is 150 or

more when auto-tuning is started.