Mitsubishi Electric MELSEC iQ-R Series Programming Manual page 598

■Operation details of step response method
The manipulated value is output in step form to the actual plant, and each constant is determined according to the maximum
slope and equivalent dead time.
The following operations are automatically performed. The generated value is saved in P, I, and D areas of the tag data.
Manipulated
variable MV
Process variable
PV
Equivalent dead time L
(seconds)
• Constants calculation with ZN method (Ziegler-Nichols' step response method)
The P/PI/PID control type is determined by I and D values of the tag data before auto tuning.
Condition
Integral time (I) Derivative time
(D)
I = 0 D = 0
(Integral time )
I > 0 D = 0
I > 0 D > 0
Ex.
Auto tuning is executed when the tag data before auto tuning are I > 0 and D = 0.
(For I > 0 and D = 0, the PI control calculates constants.)
Item
Step manipulated variable
Equivalent dead time L
Equivalent time constant T
The variation width of process variable Y
Maximum slope R
Proportional gain (P)
=
R×L
Integral time (I) = 3.33L = 3.33  8 = 26.6 seconds, derivative time (D) = 0 second
APPX
596
Appendix 3 Related Functions of Process
Maximum slope R
(R = Y/T)
Equivalent time constant T (seconds)
Control type
P control
PI control
PID control
Step manipulated variable
0.9
×
100
Step manipulated variable
t
Change range of process variable Y
(Obtained by the division by the
process variable span)
t
Constant
Proportional gain (P)
Step manipulated variable
1.0
×
R×L
100
0.9 Step manipulated variable
×
R×L 100
Step manipulated variable
1.2
×
R×L 100
Value
20%
8 seconds
16 seconds
0.25
0.25 / 16 = 0.016
0.9
20
= × = 1.4
0.016×8 100
Integral time (I) Derivative time
(seconds) (D) (seconds)
0 0
(Integral time )
3.33L 0
2L 0.5L