Burkert Type 8696 - Manual (Page 17)

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Systemdescription
5.6. Type 8696 positioner
The position measuring system records the current position ( POS) of the pneumatic actuator. The positioner com-
pares this actual position value with the set-point value ( CMD), which is definable as norm signal. 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. 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 5: Signal flow plan of positioner
5.6.1. Schematic representation of the position control Type 8696
4 ... 20 mA 2)
0 ... 20 mA
CHARACT SPLTRNG 3)
DIR.CMD CUTOFF X.TIME 3)
X.CONTROL
DBND
POS
CMD
INP
POS
CMD
DIR.ACT 3) X.LIMIT 3)
2)
Default setting
3)
can only be activated with communications software
Figure 6: Schematic representation of the position control
english
Type 8696