6. Function blocks
6.1 Manufacturer function blocks
6.1.4 Open-loop and closed-loop function blocks
6.1.4.1 DC - PID controller
General
easyE4 The base devices provide 32 PID controller function blocks
DC01...DC32.
Operating principle
A closed-loop control circuit with a PID controller consists of the following com-
ponents:
l Setpoint (reference variable),
l Actual value (controlled variable),
l System deviation = (setpoint–actual value),
l PID controller,
l Control system (e.g. PTn system),
l Disturbance variables.
The PID controller operates on the basis of the equation 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.
PID controller equation:
Y(t) = YP(t) + YI(t) + YD(t)
Y(t)=
calculated manipulated variable with scan time t
YP(t)=
Value of the proportional component of the manip-
ulated variable with scan time t
YI(t) =
Value of the integral component of the manipulated
variable with scan time t
YD(t)=
Value of the differential component of the manip-
ulated variable with scan time t
Proportional component
The proportional component YP is the product of the gain (Kp) and the control difference
(e). The control difference is the difference between the setpoint (Xs) and the actual
value (Xi) at a specified scan time. The equation used by the device for the proportional
component is as follows:
272
easyE4 11/18 MN050009 EN www.eaton.com
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