Koso REXA Electraulic Xpac, Installation And Operation Manual

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Xpac
Installation Manual -- Version 5.1 (5/09)
C-10
REXA
Electraulic Actuators & Drives
C.6.1 0.05% Deadband
The 0.05% deadband option will double the standard precision and
provide resolution within one half the thickness of a piece of paper
on a 2 inch rated stroke. The control of an Xpac actuator with this
setting is remarkable. The positioning is smooth and continuous
without resolution hop. Deadband (db) is set in the normal manner
per Section 6.3.1. The minimum allowable setting is now 0.05%.
There are two potential problems, noise and oscillation, involved in
such installations. Noise on the control and feedback signals may
be interpreted as real values. Isolated signal lines, shielded cables
and proper grounding are typical requirements for fine control.
Actuator oscillation around the control point will more easily occur
at low deadband settings. The acceleration of the actuator can be
adjusted to prevent continuous overshoot of position. A low accel-
eration rate can be set for a small change in control signal, while a
much higher rate may be set for larger changes (see section 6.3.2).
C.6.2 Minimum Control Point
Most specialized anti-cavitation or low noise valves reduce the fluid
energy by staged pressure reduction within a labyrinth cage. These
designs are only effective if there is sufficient fluid flow through
the resistive element. At plug lifts below a minimum control point,
pressure reduction will occur between the plug and seat ring which
may damage the valve.
The Minimum Control Point feature allows the setting of a point
below which the actuator will not modulate. Any control signal that
specifies a position below the minimum control point will result in
the actuator moving to the fully closed position. Normal operation
of the actuator will occur for control signals specifying a position
above this point.
CPt - CONTROL POINT SUB-MENU
Before establishing a minimum control point, the stroke of the ac-
tuator must be set by entering Position Low (PL) and Position High
(PH) in the Cal Sub-Menu.
Step over to the CPt Sub-Menu, and then step down to the Con-
trol Point parameter, CP. Using the Scroll Up/ Scroll Down keys,
position the actuator to the desired point and press (E)NTER. The
displayed value is the Minimum Control Point in percent of stroke.
For linear operation ([FCH:FC] = OFF), the control signal corre-
sponding to this point is the sum of the value of Signal Low and
If the value of PL or PH is changed,
the minimum control point must be
reset.
CONTROL POINT