Mitsubishi Electric MELSEC iQ-R Series - Page 2059

APPX
Appendix 3 Determining Three PID Constants
2057
A
Overview of step response method
This section describes the step response method that is used to determine the optimum value of three PID constants
(proportional gain (K
P
), integral time (T
I
), and derivative time (T
D
)).
■Step response method
This method determines the three PID constants according to the operation characteristics (maximum ramp (R), dead time
(L)) that can be determined from input changes by providing the control system with stepwise output of 0100%
*1
.
*1 Stepwise output can also be determined by 075% or 050%.
■Operation characteristics
■Operation characteristics and three constants
MV: Manipulated value
L: Dead time
R: Maximum ramp
t: Time
Control method Proportional gain (K
P
) [%] Integral time (T
I
) [100ms] Derivative time (T
D
) [10ms]
Proportional control (P action)
only

PI control (PI action) 33L 
PID control (PID action) 20L 50L
0%
100%
MV MV
t
t (s)
R
L 1 (s)
Rate of change
in input value
RL
1
× MV × 100
RL
0.9
× MV × 100
RL
1.2
× MV × 100