Cement Screw Feeder Loss-in-Weight Calibration Guide

Cement screw feeder loss-in-weight calibration needs two different proofs: the installed weighing system must read known loads correctly, and the feeder must deliver the commanded mass rate in a timed material test. A successful static calibration alone does not establish flow-rate performance. Refill behavior also needs its own check because the normal weight-loss calculation is interrupted while material enters the weighed hopper.

The VOGO project-configured tubular equipment for cement conveying and controlled feeding may be specified as one part of such a system. The published VOGO data does not state a loss-in-weight controller, load-cell arrangement, or dosing accuracy. Those items, their integration, and the acceptance tolerance must be defined for the project.

This guide addresses continuous loss-in-weight rate control. It is not a receiving-hopper batch cutoff procedure; that separate problem is covered in the cement screw conveyor batch overshoot guide.

Cement screw feeder loss-in-weight calibration boundary

In loss-in-weight operation, the hopper, feeding device, and other components inside the weighing boundary sit on or hang from a weighing system. The controller derives feed rate from the reduction in measured system weight over time and changes feeder speed to reduce the difference from the requested rate. Coperion’s loss-in-weight feeder overview describes this principle and the temporary change in control during refill.

Define that physical boundary before touching calibration constants. Record whether the screw, motor, reducer, flexible inlet, discharge connection, vent, cables, level devices, and access platform are inside or outside the live load. Anything that transfers an unmeasured force into the weighed assembly can alter the reading without changing cement mass.

The screw’s mechanical duty also matters. A screw directly beneath a hopper, bin, or silo with a continuously flood-loaded inlet is a screw feeder. It is an ordinary conveyor only when an upstream valve or independent feeder controls material entering the screw. A shutoff valve that remains fully open during operation does not make the duty control-fed. The cement silo discharge design guide explains that system boundary in more detail.

For flood-loaded service, do not copy a normal conveyor capacity table into the feeder selection. The inlet may need variable or increasing pitch, tapered outside diameter, or a mass-flow design so extraction capacity increases along the outlet. KWS’s screw-feeder guide explains these arrangements; reduced pitch by itself is not a complete inlet design.

Prepare the installed weighing system

Static calibration is meaningful only after the equipment is installed in its operating mechanical condition. Rice Lake’s Load Cell and Weigh Module Handbook discusses vessel attachments and the need to prevent piping or connections from restricting movement. Flexible connections should isolate forces; they should not be pulled into alignment to correct a pipework error.

Before applying test loads, document these checks:

• The hopper and screw are empty to the agreed clean condition, with no buildup resting on surrounding steelwork.
• Load cells, mounts, restraints, junction boxes, and cables match the approved arrangement and show no visible binding or damage.
• Inlet, discharge, vent, purge, and electrical connections have the intended flexibility and do not touch adjacent structure.
• Nearby machines, dust-extraction fans, and air systems are in a stated condition that can be repeated.
• The indicator has warmed up and the zero reading is stable under the supplier’s procedure.

Coperion’s loss-in-weight troubleshooting guidance identifies vibration, air currents, flexible-connection forces, pressure effects, and refill-valve leakage as possible disturbances. Do not conceal an unstable zero with excessive signal filtering. Filtering that makes the display look calm can also delay the rate signal; any change requires a documented control-response test.

An enclosed tubular screw is not automatically airtight or pressure rated. Positive or negative pressure can affect both containment and the force seen by the scale. Pressure compensation, venting, seals, and casing rating must be engineered for the actual duty rather than inferred from the word “enclosed.”

Run static calibration and zero-return checks

Use the load-cell and controller manufacturers’ approved calibration method, verified test weights or another accepted force standard, and the site’s metrology procedure. Apply known loads through the same structure that carries the process load. Record the raw or displayed value at each agreed load point while loading and, where the procedure calls for it, while unloading.

At minimum, the record should identify the instrument, load-cell system, calibration standard, applied load, indicated load, error, date, environmental condition, and person performing the work. The project specification—not this article—must set the number of test points, allowable error, and recalibration interval.

Return to the empty condition after removing the test loads. A zero that does not return within the approved limit calls for investigation of buildup, mechanical contact, hysteresis, drifting electronics, or a changed connection. Re-zeroing without finding the cause can make one point look correct while leaving the operating range unreliable.

Static calibration proves the weighing chain under known loads. It does not prove that the screw delivers cement at the requested mass rate, that the totalizer is correct, or that the feeder behaves properly during refill.

Verify actual flow with a collected-material test

The technical paper “Loss in Weight Feeder Systems” separates static weight calibration from flow-rate verification. Its verification method runs the feeder for a set time, collects the discharged material, weighs it on a conventional scale, and compares the result with the theoretical quantity and the feeder totalizer.

Use a safe collection arrangement sized for the test mass. Establish a stable gravimetric feeding period, record the actual start and stop boundaries, and do not include unrecorded material already sitting in a chute. The independent collection scale needs a suitable range, resolution, and current verification status.

For a constant setpoint:

Expected mass = setpoint × test duration

Consider a hypothetical commissioning test at 3.0 t/h for 120 seconds:

Expected mass = 3,000 kg/h × (120/3,600 h) = 100 kg

Suppose the independent scale measures 97.5 kg and the feeder totalizer reports 99.0 kg. Then:

• Delivery error against the command = (97.5 − 100) / 100 × 100% = −2.5%.
• Totalizer difference from collected mass = 99.0 − 97.5 = +1.5 kg, or about +1.54% of the collected mass.

These numbers demonstrate the calculation; they are not VOGO results or recommended acceptance limits. Repeat tests at the rates and material conditions in the approved commissioning plan. Preserve individual results rather than reporting only an average, because scatter can reveal unstable supply or weighing interference.

Test refill as a separate operating state

During refill, material entering the weighed hopper masks the loss caused by discharge. Coperion states that weight control is interrupted and the controller uses historical weight and speed information during this period. Exact terminology and algorithms vary by controller, so verify the installed manual rather than copying another brand’s settings.

Run at least one representative refill transition after steady-rate verification. Trend gross weight, calculated rate, screw speed, refill command, refill-valve feedback, mode status, and alarms on a common time base. Check whether cement delivery before, during, and after refill remains within the project’s agreed criteria.

A refill valve that leaks after the close command adds mass while the controller expects only weight loss. That can produce an incorrect calculated rate even when screw speed is steady. Also check refill duration and hopper level limits: an extended refill period can leave the feeder in its temporary control mode longer than the validation assumed.

Do not use control tuning to hide irregular silo discharge. Arching, rat-holing, and bridging depend on cement condition, moisture, consolidation, hopper geometry, outlet size, wall friction, and flow-aid operation. Jenike & Johanson’s storage and feeding guidance treats the hopper, outlet, and feeder as one withdrawal system. The screw alone cannot solve every flow problem.

Diagnose a failed calibration or rate test

Use the pattern of failure to choose the next check instead of changing multiple parameters at once.

For a silo-mounted feeder, retain checks for head load, full-load starting torque, VFD low-speed torque, reducer mechanical and thermal ratings, application service factor, and stall protection. The cement screw conveyor VFD control guide covers drive permissives and protective logic. Calibration at low speed does not authorize operation below the motor, VFD, reducer, or feeder supplier’s approved range.

Write a commissioning acceptance record

Before testing, the owner, feeder supplier, weighing specialist, and controls integrator should agree on:

• The weighed boundary and an as-built list of every mechanical, electrical, air, and vent connection.
• Static calibration points, standards, permitted error, zero-return limit, and evidence format.
• Minimum, normal, and maximum feed-rate tests, test durations, material condition, and independent scale.
• Separate acceptance rules for steady gravimetric operation and refill transition.
• Start/stop definitions for collected mass and totalizer comparison.
• Silo level, aeration or flow-aid state, cement condition, and allowable test interruptions.
• Alarm, permissive, stall, and loaded-restart tests that may affect safe feeding.
• Change control and retest requirements after mechanical, load-cell, controller, or flexible-connection work.

Physical inspection, cleaning, test-weight placement, and material collection can expose rotating parts, stored material, gravity, pneumatic pressure, and electrical energy. Follow the site’s energy-control program. OSHA’s control-of-hazardous-energy guidance describes the purpose of lockout/tagout for servicing where unexpected energization or stored-energy release could cause injury. Do not reach through an opening or defeat a guard or interlock to improve a test observation.

Conclusion

Cement screw feeder loss-in-weight calibration is complete only when the installed scale passes static load and zero-return checks, actual discharge passes a timed collected-material test, and refill transition is separately verified. Keep weighing disturbances, feeder mechanics, silo flow, drive limits, and containment ratings visible in the acceptance record. For a project review, send VOGO the material data, required rate range, weighed boundary, layout, and agreed test criteria.