Samson 3730-1 - Page 15

EB 8384-1 EN 15
Design and principle of operation
3 Design and principle of oper-
ation
Î RefertoFig.1
The electropneumatic positioner is mounted
on pneumatic control valves and is used to
assign the valve position (controlled variable
x) to the control signal (set point w). The po-
sitioner compares the electric control signal
of a control system to the travel or opening
angle of the control valve and issues a signal
pressure (output variable y) for the pneumat-
ic actuator.
The positioner is designed depending on
which accessories are selected either for di-
rectattachmenttoSAMSONType3277Ac-
tuators or for attachment to actuators ac-
cordingtoNAMUR(IEC60534-6).
Additionally, a coupling wheel included in
the accessories is required to transfer the ro-
tary motion for rotary actuators according to
VDI/VDE3845.
Springless rotary actuators require a revers-
ingamplierincludedintheaccessoriesto
permit the powered operation in either direc-
tion.
The positioner consists of a travel sensor sys-
tem proportional to resistance, an analog
i/p converter with a downstream air capaci-
ty booster and the electronics with microcon-
troller.Thepositioneristtedwithtwoad-
justable software limit contacts as standard
to indicate the valve's end positions.
The position of the valve stem is transmitted
as a either an angle of rotation or travel over
the pick-up lever to the travel sensor (2) and
supplied to an analog PD controller (3). An
%
S
mm
%
mm
w
x
Q
PD
A2
A1
4
5
3
11
12
6
7
8
10
1
w
9
x
y
2
G
13
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
10 Volume restriction
11 Limit contacts
12 Display
13 Inductive limit contact
(optional)
Fig.1: Functional diagram