Operating instructions

3 Design and principle of
operation
The electropneumatic Ex d positioner is
mounted on pneumatic control valves. It is
used to assign the valve stem position (con
-
trolled variable x) to the control signal (ref
-
erence variable w). The electric control sig
-
nal received from a control system is com
-
pared to the travel or rotational angle of the
control valve, and a signal pressure (output
variable y) is produced for the pneumatic
actuator.
The positioner basically consists of an elec
-
trical travel sensor system (2), an analog i/p
converter (6) with downstream air capacity
booster (7) and the electronic unit with a
microcontroller (5).
In case of a system deviation, the actuator is
either vented or filled with more air. The sig
-
nal pressure supplied to the actuator can be
limited to 1.4 bar, 2.4 bar or 3.7 bar by
8 EB 8387-3 EN
Design and principle of operation
%
S
mm
%
mm
w
x
G
PD
Serial
Interface
16
22
20
13
23
BE
4
21
17
FSK
5
19
3
6
7
8
1
w
9
x
y
Fig. 2 · Functional diagram
1 Control valve
2 Travel sensor
3 PD controller
4 A/D converter
5 Microcontroller
6 i/p converter
7 Air capacity booster
8 Pressure regulator
9 Flow regulator
13* Analog position
transmitter
16 LCD
17* Control of forced venting
19 D/A converter
20 Serial interface (SSP)
21* HART
®
modulation
22 Rotary pushbutton
23* Binary input
* Optional
Ex d enclosure