A checkweigher measures packs after filling; a compatible feedback interface can adjust future doses when a reliable weight trend drifts. Neither weighing nor a correction command proves that a faulty pack was removed. Specify measurement, feedback authority, pack tracking and confirmed rejection as separate functions, then test them together on the actual line.
A net-weight filler uses a weighing result to stop the dose while the container is being filled. A downstream checkweigher makes a separate measurement after transfer. A reject device diverts a selected pack, and a confirmation system verifies that the intended pack left the accepted-product route. One function does not automatically provide the others.
Start with the decision the measurement must support. A gross pack weight includes the container, closure and any other packaging already fitted. The checking location therefore changes the measured value. A correct total weight cannot by itself prove the correct liquid quantity when container tare, closure presence or product density varies.
| Function | Required input | Evidence to request |
|---|---|---|
| Quantity check | Defined product target, packaging tare strategy and validated weighing conditions | Stable reference checks and repeat passes of representative accepted and rejected packs |
| Filler feedback | A valid trend, compatible dose adjustment and known transport delay | Bounded changes with a record of the command, recipe and affected filling head |
| Reject confirmation | Tracked pack identity, reject command and downstream confirmation | The selected pack is segregated, including after a stop, a close pair or a full reject bin |
Use net-weight filling guidance for dose control at the filling station and accuracy and repeatability guidance when setting the measurement requirement.
Feedback should respond to a validated process trend, not blindly to every individual reading. Define which readings are eligible, how many contribute to the trend, the permitted correction step, the total adjustment limit and the delay before another correction. Startup packs, double packs, missing closures and unreliable measurements need an explicit treatment.
Transport delay matters because packs already between the filler and checkweigher were filled using the previous setting. Correcting again before newly adjusted packs arrive can amplify an error. The controls design should associate results with the appropriate production period and, when supported, the filling-head identity.
A shared adjustment is not a substitute for head-level diagnosis. When one channel leaks or loses prime, reducing or increasing all heads may make otherwise good channels worse. Require an alarm or investigation boundary for isolated faults, persistent corrections and loss of valid data.
METTLER TOLEDO describes mean-weight feedback with a pause between corrections, and distinguishes compensation for process drift from an improvement in the filler’s inherent performance. See its feedback-control explanation and checkweighing principles. The interface available on a particular Lancing project must be confirmed rather than assumed.
| Challenge | What the test must establish | Boundary to record |
|---|---|---|
| An intentionally out-of-range test pack | The correct pack is identified, diverted and confirmed outside the accepted stream | How the test pack is introduced, identified and reconciled |
| Closely spaced packs | A rejected pack is not confused with the following accepted pack | Validated spacing and transfer behaviour |
| A stop with a reject pending | Tracked pack state is retained or the uncertain group is contained | Who authorises restart and product release |
| Loss of reject availability | The line prevents unverified packs reaching saleable output | Response to unavailable air, missing confirmation or bin-full indication |
| Recipe or container change | Weight limits, tare assumptions and tracking settings agree with the new pack | First-off release and removal of previous-format product |
Use safe, identified test packs and an agreed protocol; do not defeat guarding or create uncontrolled faults. Reject hardware must suit the container mass, shape, stability and product spill risk. Supplier documentation demonstrates that reject confirmation, bin monitoring and different reject mechanisms are distinct features, not capabilities implied by the word checkweigher. See reject verification features and pack-specific rejection methods.
A machine tolerance is not a complete packaged-goods compliance programme. For packs within scope, the chosen quantity-control system, suitable measuring equipment and applicable records need to be agreed. A checkweigher’s pass band, the filler’s target and the label declaration have different roles; do not use a generic percentage to stand in for all three.
The GOV.UK packaged-goods guide explains minimum and average systems. OPSS guidance for Great Britain identifies the packer’s responsibility and the role of local Trading Standards. Confirm requirements for the destination market and actual use of the measurement; this guide does not certify a machine or pack as compliant.
Only when the filler has a suitable control interface and a validated adjustment method. Review the controller, permitted setpoint access, recipe handling, data timing and response to communication loss. A dry contact or network connection alone is not proof that useful or safe feedback is supported.
Yes. A downstream gross-weight result includes all packaging present at that point. Changing container tare or a missing cap can look like a filling change. Establish a suitable tare and presence-check strategy before allowing those results to adjust product dose.
Head-specific correction needs reliable attribution of each measured pack to its filling head. Indexing sequence, rejected packs, manual removal, accumulation and restart can disturb that relationship. Without validated attribution, do not assume a downstream result identifies the faulty head.
No. Feedback may help compensate for gradual, measurable drift, but cannot replace a sound dosing system. Leaking valves, entrained air, unstable feed and invalid weight readings need investigation. A control loop should flag persistent adjustment rather than silently masking the cause.
Provide filled and empty pack samples, declared quantity, packaging tare information, conveyor layout, spacing, sustained output and the existing filler control details. Add reject handling, recipe count, records and acceptance requirements. Agree how uncertain packs will be contained when measurement or tracking is unavailable.
This is general machinery-selection guidance, not a confirmed specification or completed test result for a particular machine. Product and packaging trials, site conditions and the agreed supply scope determine suitability.
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