21
Process controller Type 8793
Type 8792, 8793 REV.2
8
PROCESS CONTROLLER TYPE 8793
In the case of process controller Type 8793 the position control mentioned in chapter “7” becomes the sub-
ordinate 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 position actual value with the
set-point value (
CMD
) which is specified by the process controller. If there is a control difference (Xd1), the
actuator is aerated and de-aerated via the actuating 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
Actuating
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
Summary of Contents for 8792
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