21
Typ EP 501
Description of System
9.
PROCESS CONTROLLER TYPE EP 501 C
In the case of process controller Type EP 501 C the position control mentioned in Chapter “8” becomes the subor-
dinate auxiliary control circuit; this results in a cascade control. The process controller in the main control circuit of
Type EP 501 C has a PID function. The process set-point value (
SP
) is specified as set-point value and compared
with the actual value (
PV
) of the process variable to be controlled. The position sensor records the current position
(
POS
) of the pneumatic actuator. The positioner compares this actual position value with the set-point value (
CMD
),
which is determined by the process controller. If there is a control difference (Xd1), the actuator is aerated and
deaerated via the control system. In this way the position of the actuator is changed until control difference is 0. Z2
represents a disturbance variable.
Valve opening
Continuous
valve
Control system
Solenoid valves
Position sensor
Positioner
CMD
Xd1
B1
E1
P
K
Z1
POS
Position control circuit
+ -
Process variable
Process
Transmitter
Process
controller
Process set-
point value
SP
Xd2
CMD
Valve
opening
Z2
PV
+
-
Position
control
circuit
Figure 5:
Signal flow plan of process controller
english
