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9  PID CONTROL FUNCTION

9.7  Auto-Tuning

For acquiring satisfactory control results during PID control, it is necessary to obtain the optimal value of each constant 
(parameter) suitable for the control target. This paragraph explains the step response method to obtain three constants in the 
PID control (proportional gain (KP), integral time (TI) and differential time (TD)).
In this method, by giving stepped output from 0 to 100 % to the control system, three constants in the PID control are obtained 
from the operation characteristics (maximum ramp (R) and dead time (L)) and the input value variation. The stepped output 
may be obtained from 0 to 75% or from 0 to 50 %.

■Operation characteristics and three constants

■Operation characteristics

The parameters specified in the step response method are shown below.

 100 ms]

 10 ms]

Only proportional control (P 
operation)





PI control (PI operation)

33L



PID control (PID operation)

20L

50L

Operation setting (ACT)

(s3)+3: b0 (operation direction)

Proportional gain (KP)

(s3)+3

Integral time (TI)

(s3)+4

Differential time (TD)

(s3)+6

RL

1

Output value 

(MV)

×

×100

RL

0.9

Output value 

(MV)

×

×100

RL

1.2

Output value 

(MV)

×

×100

0 %

100 %

Output value (MV)

Output value (MV)

Time

Dead time (L) [s]

Time (s)

1 (s)

Maximum ramp (R)

Input value variation