Campbell Scientific CS431 Submersible Pressure Transducer - Manual (Page 18)

CS431 Submersible Pressure Transducer
7. Troubleshooting
7.1 Erratic Readings
Assuming that the datalogger is working properly, the first thing to check is the
connection. Look for moisture between contacts or a loose or broken wire. If
the connection appears alright, pull the transducer up to a known distance
while monitoring its output. If the transducer responds as it should, but the
reading is still erratic, most likely the cable is damaged. If the transducer does
not respond as it should, the CS431 is most likely damaged. In either case,
consult the factory.
Improper grounding can also cause erratic and erroneous readings (see Section
7.3—Grounding Issues).
7.2 Oscillating Readings Over Time
If your transducer is functioning properly but a cyclic effect is recorded in your
data when water level changes have not occurred, you are probably seeing
barometric changes. The amount is usually 0.5 to 1.5 feet of water. This can
be caused by a plugged vent tube in the cable or actual water level changes in
the aquifer itself in response to barometric pressure changes. This effect can
occur in tight formations where the transducer will immediately pick up
barometric changes but the aquifer will not. If you suspect you are having this
type of problem, you should record the barometric pressure as well as the water
level pressure and compensate the data.
If it appears that the vent tube is plugged, consult the factory. If a desiccant
tube is not installed in line with the cable, water may have condensed in your
vent tube causing it to plug. After you are finished installing the desiccant tube
you can test the vent tube by applying a small amount of pressure to the end of
the desiccant tube and seeing if this affects the transducer reading.
7.3 Zero Readings When Pressurized
An open circuit will cause continuous zero readings, which usually indicates a
broken cable, a bad connection, or possibly a damaged transducer. Check the
connector to see if a wire is loose, or if the cable has been cut. If these are not
causing the problem, the transducer needs factory repair.
7.4 Grounding Issues
Both personnel and equipment need to be protected from high power spikes
that may be caused by lightning, power line surges, or faulty equipment.
Without a proper grounding system, a power spike will find the path of least
resistance to earth ground – whether that path is through sensitive electronic
equipment or the person operating the equipment. In order to ensure safety and
prevent equipment damage, a grounding system must be used to provide a low
resistance path to ground.
When using several pieces of interconnected equipment, each of which may
have its own ground, problems with noise, signal interference, and erroneous
readings may be noted. This is caused by a condition known as a Ground
Loop. Because of natural resistance in the earth between the grounding points,
current can flow between the points, creating an unexpected voltage difference
and resulting erroneous readings.
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