Appendix 3 Determining Three Pid Constants - Mitsubishi Electric MELSEC iQ-R Series Programming Manual

Appendix 3
The auto tuning function of PID operation instructions is performed in two methods: limit cycle method and step response
method.
Overview of limit cycle method
This section describes the limit cycle method that is a method to determine the amplitude (a) and vibration period (, 
the input values, and calculate the proportional gain (K
expression of "Operation characteristics and three constants".
■Limit cycle method
This method determines three PID constants by measuring the variations of input values while two-position control (output by
switching between the output upper limit (ULV) and output lower limit (LLV) according to the deviation) is performed.
■Operation characteristics (reverse action example)
After the end of tuning cycle, the output lower limit (LLV) is retained for the manipulated value (MV) during 
to the normal PID control occurs.

can be determined by (50+K
W
= -50 to 32717 [%]; If an abnormal range is specified, operation is performed assuming 
(Setting range K
W
MV
ULV
LLV
Input value
SV+SHPV
SV
SV-SHPV
ULV: Output upper limit value
LLV: Output lower limit value
SV: Set value
t: Time
SHPV: PV value threshold (hysteresis) width
■Operation characteristics and three constants
Control method
Proportional control (P action)
only
PI control (PI action)
PID control (PID action)
APPX
2056

Appendix 3 Determining Three PID Constants

Determining Three PID Constants
)/100  (-
), and the wait setting parameter (K
W on
Proportional gain (K ) [%]
P
1
(ULV-LLV) × 100
a
0.9
(ULV-LLV) × 100
a
1.2
(ULV-LLV) × 100
a
), integral time (T ), and derivative time (T
P I
τ
τ
on
τ τ τ
0 1 2
Integral time (T ) [100ms]
I

τ
⎞ ⎞
on
τ
⎟ ⎟
33 × on 1 -
τ
⎠ ⎠
τ
⎞ ⎞
on
τ ⎟ ⎟
20 × on 1 -
τ
⎠ ⎠
) according to the following
D
W
) can be set in parameter (s3)+28.
W
W
t
τ
w
t
Derivative time (T


τ
⎞
τ ⎟
50 × on 1 -
⎠
) of
on
, and a transition
= 0.)
a
) [10ms]
D
⎞
on
⎟
τ
⎠