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Section 3 Model 288A Differential Pressure Indicating Switch
Troubleshooting
For indicating switch troubleshooting tips, see Table 3.2 below. For informa-
tion related to the Model 224 DPU, see Table A.3, page A-15.
Table 3.2—Troubleshooting Tips
Problem Possible
Source
Probable Cause Corrective
Action
Low or No
Indication
Indicator,
Alarm Switch
Mechanism
Loose linkage or movement Tighten or replace
Out of calibration Calibrate
Pointer loose Tighten pointer
Dirty or corroded mechanism Clean or replace
Wiring interfering with movement Re-route wiring
Dirty mechanism Clean mechanism
High
Indication
Indicator,
Alarm Switch
Mechanism
Loose linkage or movement Tighten or replace
Out of calibration Calibrate
Linkage dragging or dirty Adjust or clean
Pointer dragging on scale plate Adjust pointer
position
Inaccurate
or No
Electrical
Alarm
Power Supply Blown fuse Replace fuse
Broken or loose wire Repair
Alarm Switch Switch not properly adjusted Adjust switch
Dirty or burned Replace switch
contacts
Switch
Drifts
(set point
not repeat-
able)
Process
Changes
Transients or surges cause switches to
actuate prematurely
Add time delay
gages or add time
circuit
Set point and/or deadband are too wide in
pressure valves
Specify DP range as
low as practical; set
point repeatability
and deadband are
percentage of full
range
Electrical overloads aff ect the spring prop-
erties 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 fl uids in piping generate
artifi cial signal
Vent gas or drain
liquids from signal
lines
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