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Section 3
Model 580A Differential Pressure Switch
Table 3.2—Troubleshooting
Problem
Possible
Source
Probable Cause
Corrective
Action
Switch
Drifts
(set point
not repeat-
able)
Process
Changes
Transients or surges cause switches to actu-
ate prematurely
Add time delay
gages or add time
circuit
Set point and/or deadband are too wide in
pressure values
Specify DP range as
low as practical; set
point repeatability
and deadband are
percentage of full
range
Electrical overloads affect the spring proper-
ties of the leaf actuator in the switch
Examine circuits for
voltage, amperes
DC inductive loads cause arcing and burning
of contacts
Consider arc-
suppression devices
or relays
Accumulation of fluids in piping generate
artificial signal
Vent gas or drain
liquids from signal
lines
Calibration
Techniques
Failure to check set point after locking
Verify set point
repeatability after
locking switch plate
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
