4 Operation
4.1 Setting the positioner at the
valve
Starting point and reference variable
When adjusting the positioner directly at the
control valve, the travel (opening angle)
must be adapted to the reference variable.
With a reference variable, for example, 4 to
20 mA, the valve must pass through its en
-
tire travel range from 0 to 100 % (Fig. 13,
left).
For rotary positioners, an opening angle, for
example, 0 to 70° must be assigned to the
reference variable.
The starting point refers to CLOSED position
of the valve.
Depending on the actuator version (Actuator
stem extends or Actuator stem retracts) and
the operating direction of the positioner (>>
or <>), this starting point can be represented
by either the lower or upper range value
(0.2 or 1 bar) of the reference variable.
The reference variable range and thus the
upper range value determine the travel of
the valve.
In split-range operation (Fig. 13, bottom),
the control valves operate on smaller refer
-
ence variables. The controller output signal
is used to control two control valves, divid
-
ing it such that the valves pass through their
entire travel range at half the input signal
range each (e.g. first valve set to 0.2 to
0.6 bar, second valve set to 0.6 to 1 bar).
To avoid overlapping, allow for a dead
band of
±
0.05 bar as shown in Fig. 13.
The starting point (zero) is adjusted at the
zero adjuster screw (6.2); the span, i.e. the
upper range value, is adjusted at the span
adjuster screw (6.1).
When adjusting, connect a suitable pressure
adjuster to the signal input and apply supply
pressure to the supply air input.
32 EB 8355-1 EN
Operation
100%
0%
0.2 1 bar0.6
0.2 1 bar
100%
0%
< > < <
< > < <
Fig. 13 · Normal and split-range operation
Open
Travel
Closed
Open
Travel
Closed
Valve 2 Valve 1
Dead band
Reference variable
Input signal
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