Rice Lake RL1900 Series - Manual (Page 8)

6
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
4. Junction Box Connections, Adjustments & Calibration
• Refer to Junction Box manual for trimming details.
• Refer to the indicator manual and/or the “Technical Information” section in the
Load Cell Product Selection Guide for system calibration guidelines.
5. Troubleshooting
If the system powers up and gives some type of stable digital readout that varies with
the load on the system, the system problems are probably caused by factors other
than the load cells. All too often, the load cells are blamed for a malfunctioning
system; 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
demonstrates non-linearity or non-repeatability, see the following chart for possible
causes and refer to the following list of checks.
1. Check load cell mount for debris restricting load cell movement or debris
between scale and structure. Check any overload stops for proper clearance.
2. Check that tank/vessel and mounts are plumb, level, and square at the critical
areas.
3. Check all piping and conduit for connections which restrict vessel movement.
4. If check rods are used, loosen all connections to finger tight only 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
load cell. Replace the load cell with a load cell simulator. Alternate so that each load
cell is individually disconnected and replaced with a simulator. If there is a problem
with a particular load cell, the symptom should disappear when that load cell is
disconnected and replaced with the simulator.