Description
3
3.1 Function
● The electropneumatic positioner and an actuator form a control system. The current position
of the actuator is recorded by a servo potentiometer and the actual value x is fed back. The
setpoint and the actual value are also shown simultaneously on the display.
● The control system provides the setpoint w digitally to the positioner over the bus.
● The positioner works as a predictive five-point positioner, through whose output value ±Δy
the integrated valves can be controlled by pulse length modulation.
● These input signals change pressure in the actuator chamber(s) and displace the actuator
until the control deviation becomes zero.
● Using the three buttons and the display with the enclosure cover removed, operation
(manual mode) and configuration (structuring, initialization, and parameter assignment) can
be performed.
● By default, the basic unit has a binary input (BIN). This binary input can be individually
configured and used, for example, to block the control levels.
● It has a friction clutch and a switchable gear so that the positioner can be used with different
mechanical part-turn and linear actuators.
● In the case of positioners with the "Fail in Place" function, the current position of the actuator
is held if the electric and/or pneumatic auxiliary power fails. Does not function in conjunction
with SIL.
● Parameter "51.FSTY" must be set to "FSSP" in the case of the "Fail in Place" function if the
current position is to be held when switching on again following failure of the electric
auxiliary power.
3.2 Structure
3.2.1 Design overview
The following sections describe the mechanical and electrical structure, components, and
principle functionality of the positioner.
The positioner and the PROFIBUS PA communication interface function as components in a
digital process automation system. It functions as a slave and communicates with the master
through the PROFIBUS PA fieldbus. Apart from communication, the fieldbus also supplies
electrical auxiliary power to the positioner.
SIPART PS2 with PROFIBUS PA
Operating Instructions, 05/2019, A5E00127926-AC 23
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