Mitsubishi Electric MELSEC iQ-R Series Programming Manual page 195

• PID operations are conducted as follows.
Item
Deviation (DVn)
Output variation (MV)
Bn
Kp: Gain
Ti: Integral time
Td: Derivative time
Md: Derivative gain
CT: Control cycle
DVn: Deviation
DVn-1: Last deviation value
PVn: Process variable
PVn-1: Last process variable
PVn-2: Process variable before the last value
SVn: Engineering value conversion processing result
The integral term and derivative term are as follows under the following conditions.
Item Condition
Derivative When Td = 0
term
When the control mode is MAN
When the control mode is CMV
Integral When Ti = 0
term
When either of MH or ML error has occurred, MVP > MH and the
following expression is satisfied
CT
×DVn>0
Ti
When either of MH or ML error has occurred, MVP < ML and the
following expression is satisfied
CT
×DVn<0
Ti
Ti: Integral time
CT: Control cycle
DVn: Deviation
MH: Output high limit value
ML: Output low limit value
MVP: MV Internal operation value
Set an integral multiple of the execution cycle (T) as a control cycle (CT).
Set 0.0 or a value equal to or larger than the control cycle (CT) as an integral constant.
PID operations of this tag access FB are performed every control cycle (CT) (MV output).
In other execution cycles (T), the last value is held (MV = 0).
■Engineering value conversion
This function block converts the setting value (%) from the primary loop in the CAS or CSV mode into an engineering value.
RH-RL
SV= × Setting value (%) from the primary loop + RL
100
RH: Engineering value high limit, RL: Engineering value low limit, SV: Setting value
Direct action
DVn = PVn - SVn
CT
ΔMV = Kp × { (DV - DV ) +
n n-1
Ti
Proportional
Gain
The following shows a proportional term, integral term, and derivative term of MV.
■Proportional term
MV = Kp  (DVn - DVn-1)
■Integral term
CT
ΔMV=Kp× ×DVn
Ti
■Derivative term
MV = Kp  Bn
Md×Td
B =B + ×
n n-1
Md×CT+Td
CT×B
n-1
{(PV -2PV +PV )-
n n-1 n-2
Td
10.3 Velocity Type PID Control (Enable Tracking for primary loop) (M+P_PID_T)
Reverse action
DVn = SVn - PVn
× DV + B }
n n
Derivative
Integral (imperfect derivative)
B =B +
n n-1
Md×CT+Td
{-(PV
}
n
Processing
Bn = 0
CT
×DV =0
n
Ti
10 LOOP CONTROL OPERATION
Md×Td
×
CT×B
n-1
-2PV +PV )-
}
n-1 n-2
Td
10
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