14
EB 8387-5 EN
Design and principle of operation
3
Design and principle of oper
-
ation
Î
The electropneumatic Ex d 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 positioner compares the electric control
signal of a control system to the travel or ro-
tational angle of the control valve and issues
a signal pressure (output variable y) for the
pneumatic actuator.
The positioner consists of an electric travel
sensor system (2), an analog i/p converter
(6) with a downstream air capacity booster
(7) and the electronics with microcontroller
(5).
When a set point deviation occurs, the
actuator is either vented or filled with air. The
signal pressure supplied to the actuator can
be limited by software or on site to 1.4, 2.4
or 3.7 bar. The fixed flow regulator (9)
ensures a constant air flow to the
atmosphere, which is used to flush the inside
of the positioner housing and to optimize the
air capacity booster (7). The i/p converter
(6) is supplied with a constant upstream
pressure by the pressure regulator (8) to
compensate for any fluctuations in the supply
pressure.
All parts are enclosed in an Ex d enclosure.
The electrical connection is established over
a separate terminal compartment also with
Ex d protection.
The extended EXPERTplus diagnostics are
integrated into the positioner. They provide
information on the positioner and generate
diagnostic and status messages, which allow
faults to be pinpointed quickly.
The positioner is suitable for the following
types of attachment using the corresponding
accessories:
−
Direct attachment to SAMSON
Type 3277-5 Actuator:
Î
See section 5.3
−
Direct attachment to SAMSON
Type 3277 Actuator:
Î
See section 5.4
−
Attachment to actuators according to
IEC 60534-6 (NAMUR):
Î
See section 5.5
−
Attachment to Type 3510 Micro-flow
Valve:
Î
See section 5.6
−
Attachment to rotary actuators according
to VDI/VDE 3845:
Î
See section 5.7
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