Belt Weigher Accuracy: Troubleshooting and Calibration

Operating principle and purpose

The integrator multiplies measured belt load by belt speed. Errors therefore enter through force measurement, speed measurement or mechanical influences that change apparent force. Buildup, misaligned idlers, belt stiffness and changing tension are frequent causes of drift.

Zero testing checks the unloaded running system; span testing applies a known simulated load; a material test compares accumulated indication with an independent mass reference. Each test isolates different parts of the measuring chain and should be performed in a consistent sequence.

Engineering workflow

Convert the application into written requirements before comparing products. A controlled workflow makes technical differences visible and prevents a familiar part number from being applied outside its limits. Include normal and abnormal operating states, who may be exposed, how quickly the condition develops and what the conveyor must do after detection. Mark field locations on a drawing so quotations, installation and later proof tests all refer to the same scope.

• Inspect and clean the weigh area without altering reference alignment.
• Warm up the conveyor and run repeated zero tests.
• Check load-cell balance, mechanical freedom and speed signal.
• Perform the approved span calibration with test weights or chain.
• Complete a controlled material test and calculate error.

Selection and design criteria

Choose a stable straight conveyor section with uniform idlers, steady tension and minimal curvature. Calibration cannot compensate reliably for changing mechanical conditions. Record test duration, belt revolutions, load rate and product because short tests can hide repeatability problems.

• Weighbridge alignment and idler runout.
• Belt tension, tracking, splice and stiffness.
• Load-cell mounting, cabling and balance.
• Speed-sensor target and pulse scaling.
• Integrator filtering, zero tracking and totalization settings.

Common failure modes

Most field problems arise from a mismatch between the device, mechanical interface, environment or control logic. Investigate the whole sensing chain before changing settings. Review recent maintenance, process-rate changes, weather and event history, then compare the physical actuator state with the terminal signal and controller indication. A higher delay or wider trip point may silence the symptom while allowing damage or risk to grow.

• Calibrating before removing buildup.
• Changing span to correct an unstable zero.
• Using a speed value from the drive instead of the measured belt.
• Performing too few belt revolutions in a zero test.
• Accepting a good test-weight result without material verification.

Commissioning and lifecycle verification

Commission the physical device through to the final control action and record the baseline. Inspection frequency should reflect consequence, environment, duty and failure history. Any bypass or failed proof test requires controlled corrective action before normal service. The equipment record should contain the full model code, approved datasheet, mounting photograph, initial settings, normal contact state and cause-and-effect reference. After replacement or adjustment, repeat the relevant acceptance test and confirm that reset restores readiness without issuing an unintended start command.

• Record model, settings, mounting dimensions and terminal state.
• Test the field actuator, input indication, alarm or trip and reset sequence.
• Inspect sealing, cable entry, hardware, actuator freedom and contamination.
• Revalidate after mechanical, electrical, software or process changes.

Frequently asked questions

What causes belt scale zero drift?

Buildup, changing tension, idler alignment, mechanical binding, temperature and belt condition are common causes.

What is a material test?

A known mass of actual conveyed product is compared with the belt scale total over the same run.

Why repeat zero tests?

Repeatability shows whether the system is stable enough for a meaningful span adjustment.

Can calibration fix bad idlers?

No. Mechanical faults must be corrected before calibration.