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Model 288A Differential Pressure Indicating Switch Section 3
Table 3.2—Troubleshooting Tips
Problem Possible
Source
Probable Cause Corrective
Action
Switch
Drifts
(set point
not repeat-
able)
Calibration
Techniques
Failure to check set point after locking Verify set point
repeatability after
locking switch plate
Switch
Drifts
(set point
not repeat-
able)
Calibration
Techniques
Rapid pressure change or venting system During calibration,
make pressure
changes in slow,
discrete steps
Pressure application in reverse Test low-alarm with
decreasing pressure
and high-alarm with
increasing pressure
Reference gage inaccuracy Suitable pressure
standard such as
manometer, dead-
weight tester, or
Heise-type gage
may be required
Damage to switch contacts Adjust plunger
screws carefully
to avoid damage
to internal parts of
switch
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