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5. Troubleshooting
If system powers up and gives some type of stable digital readout that varies with
the load on the system, system problems are probably caused by factors other than
theloadcells.Alltoooften,loadcellsareblamedforamalfunctioningsystem;90%
of the time, the problem lies elsewhere. Look for mechanical causes for your
problem first.
If the system can be calibrated but doesn’t return to zero, loses calibration, or
demonstratesnon-linearityornon-repeatability,seethefollowingchartforpossible
causes and refer to the following list of checks.
1. Checkloadcellmodulefordebrisrestrictingloadcellmovementordebris
between scale and structure. Check overload stops for proper clearance.
2. Checkthattank/vesselandmodulesareplumb,level,andsquareatcritical
areas.
3. Check all piping and conduit for connections that restrict vessel move-
ment.
4. If check rods are used, loosen all connections to finger tight for testing.
5. Check load cell cables for physical or water damage.
6. Check all electrical connections, especially in the junction box.
If the problem still is not found:
7. Check possible indicator malfunction by using a load cell simulator to
input a known good signal into the indicator.
8. Disconnect each load cell’s signal leads at the junction box and check
individual load cell outputs with a multimeter. Then check input/output
impedances for comparison with load cell manufacturer’s specifications.
If after all these checks the problem still cannot be isolated, reconnect all but one
loadcell.Replacetheloadcellwithaloadcellsimulator.Alternatesothateachload
cellisindividuallydisconnectedandreplacedwithasimulator.Ifthereisaproblem
with a particular load cell, the symptom should disappear when that load cell is
disconnected and replaced with the simulator.
Possible Cause
No return to zero Mechanical binding or debris in seals or under load cells; may have lost system
calibration
Non-linearity Thermal expansion or deflection under load causing binding or side load
Non-repeatability Loose load cell mount; drifting caused by moisture, load cell overload or shock
damage; mechanical binding
Lost calibration Out of level or plumb; moisture problem; mechanical binding
Drifting readout Moisture in junction box, cables, or load cell; mechanical binding
Symptom
