Burkert Type 8693 - Manual (Page 24)

24
Description of system
8. Type 8693
pOsiTiOner WiTh prOcess cOnTrOller
If the positioner is operated with process controller Type 8693, the aforementioned position control becomes the
subordinate auxiliary control circuit; this results in a cascade control. The process controller in the main control
circuit of the positioner 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 measuring system records
the current position ( POS) of the pneumatic actuator. The position controller compares this actual position value
with the set-point value ( CMD), which is determined by the process controller. In case of a control deviation (Xd1),
a pulse-width modulated voltage signal is sent to the control system as a manipulated variable. If there is a positive
control difference in single-acting actuators, the air inlet valve is controlled via output B1. If the control difference is
negative, the bleed valve is controlled via output E1. 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 measuring
Position
controller
CMD Xd1
B1
E1
P
K
Z1
POS
position control circuit
+ -
Process variable
Process
position
control
circuit
Transmitter
Process controller
Process set-point
value
SP Xd2 CMD
Valve
opening
Z2
PV
+
-
Figure 6: Signal flow plan of process controller
english
Type 8692, 8693