17
System description
5.6
Type 8696 positioner
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
). In case of a control deviation (Xd1), a pulse-width
modulated voltage signal is sent to the pilot valve 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
Valve
Pilot valve
system
Position sensor
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
Position set-
point value
CHARACT
SPLTRNG
2)
DIR.CMD
2)
CUTOFF
X.TIME
2)
X.CONTROL
DBND
POS
CMD*
CMD
DIR.ACT
2)
X.LIMIT
2)
2) Can only be activated with communications software
Figure 6:
Schematic representation of the position control
english
Type 8696, REV.2
Summary of Contents for 8696
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