Pid Operation Block Diagram And Operation Expressions - Mitsubishi Electric MELSEC-Q series Programming Manual

PID operation block diagram and operation expressions

PID operation block diagram
The PID operation block diagram for incomplete derivative is shown below.
Operation expressions
The operation expressions for PID control using PID control instructions are indicated below.
Name
Process value Forward
differentiation operation
Incomplete
derivative
Reverse
operation
*1 PV is calculated using the following expression.
fn
Therefore, it is the same as the PV (process value) of the input data as long as the filter coefficient is not set for the input data.
Process Value after Filtering PV
PV : Process value of the present sampling cycle
n
: Filter coefficient
PV : Process value of the preceding sampling cycle (after filtering)
fn-1
PV is stored in the I/O data area. ( Page 51 I/O Data)
fn
Operation Expressions
+ (PV
= PV - PV )
fn n fn-1 n
Meanings of Symbols
EV : Deviation in the present sampling cycle
n
EV : Deviation in the preceding sampling cycle
n-1
SV: Set value
PV : Process value of the present sampling cycle (after
fn
filtering)
PV : Process value of the preceding sampling cycle
fn-1
(after filtering)
PV : Process value of the sampling cycle two cycles
fn-2
before (after filtering)
MV: Output change value
MV : Present manipulation value
n
D : Present derivative term
n
D : Derivative term of the preceding sampling cycle
n-1
K : Proportional constant
P
T : Sampling cycle
S
T : Integral constant
I
T : Derivative constant
D
K : Derivative gain
D
3 PID CONTROL SPECIFICATIONS
3.1 PID Control by incomplete derivative
3
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