Omron SYSMAC CP Series Instruction & Reference Manual page 297

Block Diagram for Target Value PID with Two Degrees of Freedom
When overshooting is prevented with simple PID control, stabilization of disturbances is slowed (1). If
stabilization of disturbances is speeded up, on the other hand, overshooting occurs and response
toward the target value is slowed (2).
When target-value PID control with two degrees of freedom is used, on the other hand, there is no
overshooting, and response toward the target value and stabilization of disturbances can both be
speeded up (3).
Set value
SV
(target value)
Measured
PV
value (PV)
(1)
(2)
Overshoot
PID Parameter Settings
Control data Item
C Set value (SV)
C+1 Proportional band
C+2 Tik
Integral Constant
C+3 Tdk
Derivative Constant
C+4 Sampling period (τ)
Bits 04 to 15 2-PID parameter (α)
of C+5
Bit 03 of C+5 Manipulated variable
output designation
Bit 01 of C+5 PID constant change
enable setting
CP1E CPU Unit Instructions Reference Manual(W483)
Target value filter
1 + (1 – λ) Ti · s
+
1 + Ti · s
–
Simple PID Control
As the target response is slowed,
the disturbance response worsens.
As the disturbance response is
slowed, the target response worsens.
Contents
The target value of the process being controlled.
The parameter for P action expressing the pro-
portional control range/total control range.
A constant expressing the strength of the integral
action. As this value increases, the integral
strength decreases.
A constant expressing the strength of the deriva-
tive action. As this value increases, the derivative
strength decreases.
Sets the period for executing the PID action.
The input filter coefficient. Normally use 0.65 (i.e.,
a setting of 000). The filter efficiency decreases
as the coefficient approaches 0.
Designates the manipulated variable output for
when the PV equals the SV.
The timing of enabling changes made to the pro-
portional band (P), integral constant (Tik), and
derivative constant (Tdk) for use in PID calcula-
tions.
Proportional + integral elements
+
Kp
Kp +
Ti · s
Preceding
derivative-type elements
Kp Td/s
1 + λ · Td · s
Feed-forward PID Control
(3)
Target response
Setting range
Binary data (of the same number of bits as
specified for the input range)
0001 to 270F hex (1 to 9999);
(0.1% to 999.9%, in units of 0.1%)
0001 to 1FFF hex (1 to 8191);
(9999 = Integral operation not executed)
(See note 1.)
0001 to 1FFF hex (1 to 8191);
(0000 = Derivative operation not executed)
(See note 1.)
0001 to 270F hex (1 to 9999);
(0.01 to 99.99 s, in units of 10 ms)
000 hex: α = 0.65
Setting from 100 to 163 hex means that the
value of the rightmost two digits is set from
α= 0.00 to α= 0.99. (See note 2.)
0: Output 0%
1: Output 50%
0: At start of PID instruction execution
1: At start of PID instruction execution
and each sampling period
2 Instructions
Manipulated variable
–
Kp:Proportional constant
Ti:Integral time
Td:Derivative time
s:Laplace operator
α:2-PID parameter
λ:Incomplete derivative coefficient
Disturbance response
Change with ON
input condition
Allowed
Can be changed
with input condi-
tion ON if bit 1 of
C+5 is 1.
Not allowed
Allowed
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