46-622 Series 3 Liquid Level Switches ASME B31.3 Construction
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4. Vibration may sometimes cause terminal screws to loosen.
Check all terminal connections to be certain that screws
are tight.
5. On units with pneumatic switches, air (or gas) lines
subjected to vibration, may eventually crack or loosen at
connections causing leakage. Check lines and connections
carefully and repair or replace, if necessary.
NOTE: Spare switches should be kept on hand at all times.
4.1.3 Proof Test Procedure
(To be performed annually at a minimum)
1. Bypass the logic controller or take other action to avoid a
false trip.
2. Perform a detailed inspection of the unit inside and out
for physical damage that may impact the structural
integrity, and for evidence of environmental or process
leaks. Repair or replace the unit if needed.
3. Using a calibrated multimeter set to measure electrical
resistance (ohms), at the field connections measure and
record the resistances across the Common (C) and the
Normally Closed (NC) contacts, and the Common (C)
and the Normally Open (NO) contacts.
4. Change the process level to cause the switch mechanism to
change states.
5. Again, measure and record the resistances across the
Common (C) and the Normally Closed (NC) contacts,
and the Common (C) and the Normally Open (NO) contacts.
6. Ensure with the multimeter readings that the switch mech-
anism did in-fact change states. A closed switch contact
should measure less than 1 ohm, and an open contact
should measure greater than 5 megaohms.
7. Repeat steps 3 through 6 for all other sets of switch
contacts (if any).
8. Restore the installation to normal operation.