Define the target, tolerance and measurement method before the machine is run.
The word accuracy is often used for several different questions: whether the average is on target, how widely individual fills vary, whether the machine returns to the same result after a stop, and whether finished packs meet the packer's legal or customer requirements. These are related but not interchangeable.
State whether the target is net mass, gross mass, volume or another agreed measure. Identify the tare method, scale resolution, calibration status, sample handling and whether the result is taken immediately after filling or after the product has settled. If a scoop, desiccant, liner or closure forms part of the finished pack, define whether it is included in the measurement process.
| Measure | What it answers | What must be stated |
|---|---|---|
| Mean or average | Whether the recorded sequence is centred on the agreed target. | Target, number of results, treatment of rejected or start-up fills and calculation method. |
| Minimum and maximum | The observed range in the recorded sequence. | Product and machine state, including any refill or restart. |
| Standard deviation | The spread of results around the mean for the stated sample. | All individual values and a consistent measurement method. |
| Reject rate | How many packs fail the agreed process or finished-pack criteria. | The acceptance limits and whether rework or adjustment was allowed during the sequence. |
| Recovery after interruption | Whether the process returns to control after refill, stop or changeover. | The interruption, adjustments made and first acceptable result. |
Separate product, dosing, pack and measurement variation.
Powder filling results can move because the bulk density changes, the hopper feed becomes unstable, the auger or feeder cut-off changes, product remains in the nozzle, the container is presented at a different height, the pack is vibrating, or the weighing method is inconsistent. A troubleshooting plan should change one factor at a time and preserve the original settings and result sequence.
- Product: density, aeration, moisture, segregation, particle damage and batch-to-batch variation.
- Machine: screw or feeder selection, speed profile, agitation, cut-off, refill level and control settings.
- Pack: opening, fill height, static, vibration, tare variation, stability and headspace.
- Measurement: scale suitability, resolution, calibration, draughts, vibration, tare method and transcription.
- Operator and line: pack presentation, manual topping-up, intervention, upstream starvation and downstream blocking.
Use a sequence that challenges the states expected in production.
Begin with an agreed set-up and record any tuning fills separately. Once the trial sequence starts, retain every result and note every intervention. A useful sequence includes start-up, stable running, at least one representative hopper refill, a routine stop and restart, the smallest and largest dose where relevant, and the least stable or smallest-opening pack.
| Stage | Record | Decision |
|---|---|---|
| Set-up | Product batch and state, tooling, hopper level, agitation or feed settings, target and measurement equipment. | Confirms the condition to which the result applies. |
| Consecutive fills | Every individual result and any visible dust, dribble, spillage or product build-up. | Shows repeatability without cherry-picking. |
| Refill challenge | Fill results immediately before and after the intended refill method. | Shows whether head or aeration changes move the process. |
| Stop and restart | Duration, reason, adjustments and first acceptable pack. | Tests normal production recovery. |
| Finished-pack check | Headspace, closure or seal cleanliness, presentation and any reject reason. | Confirms that weight performance produces a saleable pack. |
Keep machinery performance and legal quantity control connected but distinct.
In the UK, packaged goods may fall under minimum or average quantity systems depending on the product and process. The packer must use a suitable system, measuring equipment and records for the applicable rules. The current GOV.UK guidance on packaged goods and equipment and records should be reviewed with the business's competent adviser or Trading Standards contact.
A machine trial can demonstrate process capability under stated conditions; it does not by itself define the packer's legal sampling plan, tolerable negative error, record retention or inspection system. Those requirements should be reflected in the production control plan and in any checkweigher or data-capture scope.
Make the acceptance record reproducible.
Keep the raw results, calculations, product batch, pack identity, tooling, settings and video or photographs that explain visible behaviour. State the agreed acceptance limits and whether any result was excluded, repeated or adjusted. If the machine is later installed in a line, repeat the relevant checks with the intended product feed, conveyor, closing or sealing equipment and production operators.
Do not accept an unsupported percentage.
An accuracy percentage without the target, product, sample size, test state, measurement method and acceptance rule is not enough to compare two powder filling routes.