![Impact Flow Meter Weigh Feeder Air-lift System L-i-W System control concept volumetric gravimetric volumetric volumetric feed rates [t/h] up to 1000 up to 350 up to 500 up to1000 accuracy long term 2.0% 1.0% 2.0% 2.0% accuracy short term at best 2.0% 2.0% at best 2.0% worse than 2.0% sensitivity to adjustments low 1.0% at best 1.0% low sensitivity to external effects high high low high system design closed open closed closed maintenance low high low high](https://www.cementequipment.org/wp-content/uploads/2016/09/Feeder-Survey-2.png)
Quick engineering answer
A weigh feeder should be calibrated in sequence: stabilize the mechanics, verify belt speed, obtain a repeatable zero, perform the approved span/test-load procedure, then prove the complete measuring chain with a material test. Do not use calibration factors to compensate for belt tracking, buildup, bridge friction, wrong speed or unstable loading.
1. Stabilize the Mechanics Before Calibration
Accurate weigh-feeder calibration starts with stable mechanics. Zero and span adjustment cannot compensate for belt tracking, buildup, incorrect belt speed, excessive belt tension, misaligned weigh idlers or a mechanically constrained load cell. Before calibration, confirm the belt is clean and tracks consistently, the weigh bridge moves freely, load cells are not restrained, and skirts or scrapers are not applying force to the weighing section.
2. Verify Belt Speed Independently
Mass flow is calculated from belt loading and belt speed, so a speed error creates a feed-rate error even when the load-cell calibration is correct. Inspect the speed sensor, target wheel or coupling, confirm the configured constants, and compare indicated belt speed with an independent measurement where practical. If the measured and indicated speeds disagree, correct the speed-measurement problem before performing span adjustment.
3. Perform Repeatable Zero and Span Calibration
Zero calibration: run the feeder empty at its normal calibration condition and follow the integrator’s zero routine. The purpose is to establish the no-load baseline for the complete belt and weighing system. Repeat the zero result. If consecutive zero runs drift materially, investigate belt condition, buildup, tension, tracking, bridge friction and load-cell mounting instead of forcing the zero.
Span/test-load calibration: apply the known test load exactly as specified by the feeder manufacturer, enter the correct test-load value and complete the span routine. Remove and store the test equipment after calibration. An incorrect entered test-load value, wrong chain weight or incorrect placement creates a systematic error that can look like a process problem.
| Calibration stage | Pass condition | If it fails |
|---|---|---|
| Mechanical inspection | No rubbing, buildup, binding or external force on weighing zone | Repair mechanics before calibration |
| Belt speed | Indicated speed agrees with validated measurement | Check sensor, coupling and constants |
| Zero | Repeatable empty-belt result | Investigate mechanical drift or contamination |
| Span | Known test load applied and repeated correctly | Verify entered load and application method |
4. Verify the Complete System with a Material Test
A material test checks the complete measurement chain under real conveying conditions. Compare the feeder’s totalized mass with a reliable reference mass over the same interval. The reference itself must be suitable for the required accuracy; otherwise the test only compares two uncertain measurements.
Run enough material to make the comparison meaningful for the plant’s validated procedure and repeat the test. If several tests show a stable deviation, use the feeder manufacturer’s material-test correction method. If results scatter or change direction, do not average away the problem—investigate installation, belt tension, idler alignment, speed measurement, vibration, feed distribution and buildup.
5. Read the Error Pattern Before Changing Calibration
6. Calibration Acceptance Record
- Record feeder ID, product, belt condition and calibration date.
- Record mechanical inspection findings and repairs made before calibration.
- Record independent belt-speed verification.
- Record consecutive zero results.
- Record test-load identification, entered value and span results.
- Record each material test, reference mass and feeder total.
- Record any correction factor applied and the repeated verification result.
- Keep the record with the feeder’s maintenance history so drift can be trended over time.
Final verification after calibration
After zero and span are accepted, operate at representative feed and repeat the material test using the same independent reference. Confirm the correction repeats, belt speed remains credible and zero does not drift after several belt cycles. If the result cannot be reproduced, return to mechanics, speed measurement and sampling rather than applying another calibration factor.