CALIBRATION
CALIBRATION FOR PARTICULAR APPLICATION
4 - 4
Zero Adjustment
The positioner zero adjustment can be used to set initial tension
on the range spring so that the actuator will not begin to move
from its minimum position until it receives an input signal between
zero and 50 percent (Fig. 4-3). This application of suppression is
useful when two or more actuators are to be operated in
sequence; where the actuator is equipped with a minimum stop; or
where the characteristics of the device that the actuator is moving
must be matched with the characteristics of another regulated
device.
Span Adjustment
The span adjustment affords a variation of actuator motion for a
given span of input signal. For example, the span may be adjusted
to allow full actuator travel to occur with a signal change as small
as 50 percent of its full span (e.g., split ranging) (Fig. 4-4). At the
other extreme, the span adjustment can be set to produce as little
as 50 percent of the travel capability of the actuator over the full
input signal pressure span (e.g., short stroking).
This flexibility in span adjustment is useful when the device being
regulated is oversized, since the adjustment allows operation of
the actuator or cylinder through its useful motion for desired full
change in control signal pressure. It is also useful in matching the
signal versus position characteristics of the actuator or cylinder
with the characteristics of related power devices in the same con-
trol system.
Figure 4-3. Zero Adjustment Graph
OUTPUT
POSITION
(0 TO 100%)
INPUT SIGNAL
(0 TO 100%)
T00775A
100
50
0
0 50 100
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