Design And Principle Of Operation - Samson 3730-2 Mounting And Operating Instructions

Design and principle of operation

3 Design and principle of oper-
ation
The electropneumatic positioner is mounted
on pneumatic control valves and is used to
assign the valve position (controlled vari-
able x) to the control signal (set point w). The
electric signal from a controlling system is
compared to the travel or the rotational an-
gle of the control valve and a signal pressure
(output variable y) is produced for the actua-
tor.
The positioner consists of a travel sensor sys-
tem (2) proportional to resistance, an analog
20
Serial
Interface
4
w
24V DC
17
12
8
Fig. 1: Functional diagram
10
16
mm
%
S
5
19
w
PD
x
3
18
6
9
Q
7
i/p converter with a downstream air capaci-
ty booster (7) and the electronics with micro-
controller (5).
The positioner is fitted with three binary con-
tacts as standard: A fault alarm output indi-
cates a fault to the control room and two
configurable software limit switches are used
to indicate the end positions of the valve.
The valve position is transmitted as a either
an angle of rotation or travel to the pick-up
lever and to the travel sensor (2) and sup-
plied to an analog PD controller. An A/D
converter (4) transmits the position of the
valve to the microcontroller (5). The PD con-
22
13
A3
15
A2
14
A1
14
2
G
10
1
y
x
1 Control valve
BE
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
10 Volume restriction
11* Inductive limit switch
12* Solenoid valve
13* Analog position transmitter
11
14 Software limit switch alarm
1/2
15 Fault alarm output, alarm 3
G
16 Display
17* Actuation of solenoid valve
18* Electrical insulation
19 D/A converter
20 Communication interface
22 Binary input BE*
* Options
EB 8384-2 EN