Cameron BARTON 289A, Руководство пользователя

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Section 3 Model 289A Differential Pressure Indicating Switch
7. If the switch is to be field-set at low differential pressure values (1% or
2% of pressure range), check the crank to prevent a top-dead-center posi-
tion. Otherwise, the minimum set point position will be restricted and the
set point may become reversed.
8. Adjust the switch to actuate at the desired pressure by applying test pres-
sures in a decreasing direction, in discrete steps. Allow the unit and the
pressure system to stabilize. Then change the pressure by a small amount.
The magnitude of the pressure change is determined by the desired
accuracy of the test. Tighten the lock screw before testing the switch
performance.
IMPORTANT: The high switch is usually set to actuate at increasing pressure — when
calibrating the high switch, apply test pressure in an increasing direction.
This amount of loading will prevent cam-runout of a similar condition.
IMPORTANT: Excessive plunger loading (more than 3 flats) may cause the roller to
drag on the cam. Cam friction will be apparent by excessive hysteresis,
erratic pointer readings and inconsistent switch operation.
9. Check the switch deadband, (actuate to reset) by applying differential
pressure, first in a decreasing direction, then in an increasing direction
(opposite for high switch direction). Observe pressures. To reduce dead-
band, advance the plunger screw (two flats maximum).
10. Adjust the high switch to actuate at the desired pressure. The procedure is
the same as for the low switch.
Changing Switch Set Point
(Tools: Screwdriver, 1/8-in. hex Allen wrench)
Definitions of Terms
Set Point. The measured pressure at which the snap-switch actuates and
thereby changes the states of the N.O and N.C. contacts. For example, the set
point of the low switch is 24 psid with decreasing pressure.
Deadband . The difference in measured pressures between switch-actuation
and switch-reset. Deadband is usually expressed as percent of full scale (%
of F.S.). Deadband is not adjustable. For example, the switch in the set point
example above was found to reset at 26.4 psid with increasing pressure. The
deadband was 2.4 psi, or 4% of the full scale for a unit calibrated 0 to 60 psid.
Best Practices for Set Points
1. Always check the set point after tightening switch lock screws.
2. Switch setpoints may be set at any point of the scale range, except in a
location that will prevent the deadband from enabling the switch to reset