Maintenance and Troubleshooting
Load-Cell Problems
Thermo Fisher Scientific Micro-Tech 9101/9201 Reference Manual, Rev J 4-3
Question Answer
Can I put a 100 lb. weight on the
weighbridge and see a reading of
100 lbs. in the Run screen?
The short answer is “No,” because a weight is not a rate.
The signal delivered by the load cell or cells, which represents the weight
per unit length of the belt (lbs./ft), is multiplied by the signal delivered by the
speed sensor, which represents the belt speed (ft/min). The result of this
operation is the instantaneous flow rate (lbs./ft x ft/min = lbs./min), which is
then multiplied by a suitable constant to obtain the value in the required
engineering units (kg/h, Tph, and so on). An adjustable damping filter is
provided separately for the displayed rate and current outputs.
What kind of information is available
from the digital output?
The programmable outputs are as follows.
• Alarm cumulative
• Shutdown cumulative
• Ready
• High load
• Low load
• High rate
• Low rate
• High speed
• Low speed
• Totalization pulse (remote
counter)
• Print ready
• Load weights
• Out of range
• Deviation alarms
This topic helps you solve problems with the load-cell circuitry, and is
divided into three sections that deal with the following components.
Please check which kind your particular system has before proceeding.
Four-wire load cell—with no field sense leads.
Four-wire load cell—with field sense leads.
Six-wire load cell—with field sense leads.
A load-cell signal failure is usually caused by one of the following.
Failed load cell
Bad or incorrect wiring
Failed A/D converter
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