LiquidWatch Installation Manual
21
3.7 Probe Tests
All LiquidWatch probes change resistance when switched from the normal “Good” state to the “Active”
state. The probe leads can be removed from the terminal strip and a probe tested with an ohmmeter
according to the “resistance” columns in the following table:
PROBE READING WITH PROBE ADAPTER INSTALLED
*Note: The PWS-LW probe active resistance range is an initial reading when an ohmmeter is connected. The
value will increase after a second or two. Reverse the meter leads to obtain a new reading.
The probes and connecting wiring can also be tested without removing them from the circuit. This is
described in Setup, Section 5.3 of this manual. If the probe is not “Good” as determined from the “A/D
Reading” columns then check the probe and wiring and correct the problem.
3.7.1 PHL-LW - Tests
The PHL probe cannot be exposed to water for long periods of time. Continued exposure will damage
the probe and it will no longer respond to hydrocarbons. The probe should be installed in normally dry
locations. It will be available for a limited time for those applications which require the smaller, 5/8”
diameter.
The PHLR series probe replaces the PHL and is strongly recommended for all applications, including
those where the probe is exposed to water frequently.
WARNING: If a hydrocarbon probe is submerged in water, a hydrocarbon spill may float on the surface
of the water and not contact the sensor.
The hydrocarbon probe, PHL-LW, can be tested by gently placing it into a volatile solvent such as
trichloroethylene or Coleman fuel. The resistance reading should match the chart above. (DO NOT
agitate or swirl the probe in any hydrocarbon liquid. It may damage the sensor element). When
the probe is removed and the solvent evaporates, the resistance reading should return to the normal
range.
3.7.2 PHL-LW - Reset
The probe will need to be flushed with a volatile solvent if it has been exposed to non-volatile liquids,
such as diesel fuel or oil. To flush the probe, gently place it in the solvent for several seconds and then
remove it. As the solvent evaporates, the resistance reading of the probe should return to the normal
range. These steps may need to be repeated several times. Exposure to non-volatile hydrocarbon
liquids may require the probe to be replaced.
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