Mitsubishi Electric MELSEC iQ-R Series Programming Manual page 602

Ex.
PV > SV (PN = 0)
SV
PV
MV
AT2MVH
AT2MVL
(1) 1st 2-position operation
(2) 2nd 2-position operation
(3) 3rd 2-position operation
The oscillation amplitude Xc is calculated by measuring and averaging out plus side and minus side maximum values of |PV -
SV|.
The output range d is calculated by (AT2MVH - AT2MVL) / 2.
● Calculation of threshold sensitivity and threshold period
Threshold sensitivity (Ku) and threshold period (Tu) are calculated from the measurement result of auto tuning by the limit
cycle method.
2
Ku = 4d / ( (Xc - AT2HS2))
Tu = Tc
● Calculation of optimal PID constant
The optimal PID constant is calculated from threshold sensitivity (Ku) and threshold period (Tu).
Values of proportional gain (Kp), integral time (Ti), and derivative time (Td) are calculated by using the coefficients specified
for the control type (ATTYPE) shown below.
Control type Control operation Control type
Constant-value PI
control
PID
Follow-up PI
control
PID
Ku: Process threshold sensitivity, Tu: Process threshold period
■Fine tuning after auto tuning
Fine tuning of PID constants is the same as that for the step response method. ( Page 597 Fine tuning after auto tuning)
APPX
600
Appendix 3 Related Functions of Process
(1)
2d
(2-position output)
Auto Auto tuning mode
mode
(ATTYPE)
1
2
3
4
Oscillation period Tc
Oscillation
amplitude Xc
Oscillation
amplitude Xc
(2) (3)
Auto mode
Proportional gain Integral time
(Kp) (Ti)
0.45Ku 0.83Tu
0.6Ku 0.5Tu
0.3Ku 1.0Tu
0.45Ku 0.6Tu
Hysteresis
AT2HS
Hysteresis
AT2HS
Derivative time
(Td)
0
0.125Tu
0
0.1Tu
Empirical rule
Ziegler-Nichols'
method
CHR method