Mitsubishi Electric MELSEC iQ-R Series Programming Manual page 601

■Operation details of the limit cycle method
● Generation and measurement of the limit cycle waveform
In the AUTO TUNING mode, the PV limit cycle waveform is generated by performing the 2-position ON/OFF operation of MV
output three times.
The 2-position ON/OFF operation is performed under the following conditions.
Control operation First MV output
■PV  SV
Reverse action
(PN = 0) MV = Output high limit (AT2MVH)
■PV > SV
MV = Output low limit (AT2MVL)
■PV  SV
Direct action
(PN = 1) MV = Output low limit (AT2MVL)
■PV > SV
MV = Output high limit (AT2MVH)
The PV oscillation waveform data for the limit cycle method at the first 2-position ON/OFF operation is ignored. The oscillation
amplitude Xc and oscillation period Tc are measured by using the PV oscillation waveform data at the second and third 2-
position ON/OFF operations.
Auto tuning ends at the apex of the third PV oscillation waveform.
The setting value is calculated by using SVC (setting value (current)) at auto tuning start.
The hysteresis (AT2HS) functions as a minimum compensation value of the amplitude. Set it in advance according to the
control target so that the oscillation period and oscillation amplitude are measured properly.
Ex.
PV  SV (PN = 0)
SV
PV
MV
AT2MVH
AT2MVL
Auto
mode
(1) 1st 2-position operation
(2) 2nd 2-position operation
(3) 3rd 2-position operation
2-position ON/OFF operation
■PV  SV + Hysteresis (AT2HS)
MV = Output low limit (AT2MVL)
■PV  SV - Hysteresis (AT2HS)
MV = Output high limit (AT2MVH)
■PV  SV + Hysteresis (AT2HS)
MV = Output high limit (AT2MVH)
■PV  SV - Hysteresis (AT2HS)
MV = Output low limit (AT2MVL)
Oscillation period Tc
(1) (2) (3)
2d
(2-position output)
Auto tuning mode
Remarks
For operation images, refer to the
following examples.
The MV high limit and low limit values at
PN = 0 are reversely output.
Oscillation Hysteresis
amplitude Xc AT2HS
Hysteresis
Oscillation
AT2HS
amplitude Xc
Auto mode
Appendix 3 Related Functions of Process
A
APPX
599