Function blocks
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MN05013005E
217
• DC01ED to DC32ED: Activate the differential component;
• DC01SE to DC32SE: Activate the manual manipulated
variable
Memory requirement of the PID controller
The PID controller function block requires 96 bytes of memory
plus 4 bytes per constant on the function block input.
Function of the PID controller function block
The PID controller works on the basis of the PID algorithm.
According to this, the manipulated variable Y(t) is the result of
the calculation of the proportional component, an integral
component and a differential component.
Equation of PID controller:
Y(
t
) = Y
P
(
t
) + Y
I
(
t
) + Y
D
(
t
)
Y(
t
)= calculated manipulated variable with scan time
t
Y
P
(
t
)= Value of the proportional component of the manipulated
variable with scan time
t
Y
I
(
t
)= Value of the integral component of the manipulated variable
with scan time
t
Y
D
(
t
)= Value of the differential component of the manipulated
variable with scan time
t
J
The PID controller must be enabled so that it can work. Coil
DC..EN is active. If coil DC..EN is not active, the entire PID
controller is deactivated and reset. The manipulated
variable is set to zero.
The corresponding coils for the P, I and D components must
be active.
Example: If only coils DC..EP and DC..EI are activated, the
controller operates as a PI controller.
J
The device calculates the manipulated variable every time
the scan time T
c
has elapsed. If the scan time is zero, the
manipulated variable is calculated every cycle.