Burkert Type 8694 - Manual (Page 16)

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Systemdescription
5.5. Type 8694 positioner (position controller)
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 definable as standard signal. In case
of a control deviation (Xd1), a pulse-width modulated voltage signal is sent to the control system as a manipu-
lated 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. Z1 represents a disturbance variable.
Valve opening
Control valve Control system
Solenoid valves
Position measuring system
Position
controller Position
set-point
value
CMD Xd1
B1
E1
P
K
Z1
POS
Position control
circuit
+ -
Figure 4: Signal flow plan of position controller
5.5.1. Schematic representation of the position control Type 8694
4 ... 20 mA 1)
0 ... 20 mA
CHARACT SPLTRNG 2)
DIR.CMD
CUTOFF X.TIME 2)
X.CONTROL
DBND
POS
CMD
INP
POS
CMD
DIR.ACT 2) X.LIMIT 2)
1)
Default setting
2)
Can only be activated with communications software
Figure 5: Schematic representation of position control
English
Type 8694