Burkert Type 8793 - Manual (Page 23)

23
Description of System
9. PROCESS CONTROLLER TYPE 8793
In the case of process controller Type 8793 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 8793 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
Types 8792, 8793