2 Principle of operation
The electropneumatic positioner is attached to pneumatic control valves. It is used to assign the
valve position (controlled variable x) to the control signal (reference variable w). The input sig-
nal received from a control system is compared to the travel or rotational angle of the control
valve, and a pneumatic signal pressure (output variable y) is produced.
The positioner consists of a travel sensor system proportional to resistance, an analog i/p con-
verter with a downstream booster and the electronics unit with microcontroller.
When a deviation occurs, the actuator is pressurized or vented. If required, the changes in the
signal pressure can be slowed down by a volume restriction Q. The signal pressure supplied to
the actuator can be limited by software or on site to 1.4, 2.4 or 3.7 bar.
A constant air stream to the atmosphere is created by the flow regulator (9) with a fixed set
point. The air stream is used to purge the inside of the housing as well as to optimize the air ca-
pacity booster. The i/p module (6) is supplied with a constant upstream pressure by the pres-
sure regulator (8) to make it independent of the supply air pressure.
The positioner communicates and is powered using IEC 61158-2 transmission technology con-
forming to the F
OUNDATION™ fieldbus specification.
KH 8384-5 EN 7
Principle of operation
w
x
Q
%
S
mm
GG
PD
Serial
Interface
16
15
BE2
BE1
112
4
13
20
17 18
19
24V DC
5
3
12
6
7
8
10
1
14
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 module
7 Pneumatic booster
8 Pressure regulator
9 Flow regulator
10 Volume restriction
11* Inductive limit switch
12* Solenoid valve
13 IEC 61158-2
interface module
14 Binary input BE1
(passive)
15* Binary input BE2 (active)
16 LCD
17* Solenoid valve control
18 Galvanic isolation
19 D/A converter
20 Serial interface (SSP)
* Option
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