1. Process Requirements: These are the process requirements coming from you. What do you actually require to be successful in your process?
2. Specified Scale: This is the recommended balance or scale that achieves your process requirements and matches them the closest. This is based on:
- The aprocess requirements include the maximum gross weight, the smallest net weight you want to weigh on this instrument, the weighing tolerance in relative unit and the safety factor.
- The standards and regulations
- The so-called typical measurement uncertainty, which is based on the typical performance most instruments can reach under good conditions.
3. Process Requirements Evaluation: For the specified scale the measurement uncertainty and its associated costs are calculated based on typical loads you plan to weigh (which are provided by you). The measurement uncertainty is expressed in absolute and relative numbers and is based on the typical specifications, which means that most instruments reach this measurement uncertainty under good conditions.
These requirements can be expressed in absolute terms (in weight unit) or relative terms (in %). For example: 10 kg ± 0.1% (relative) or ± 10 g (absolute).
The calculated safety factor is determined based on the required weighing tolerance and the measurement uncertainty calculated.
4. Cost of Measurement Uncertainty: This is how much the measurement uncertainty will cost you with the selected instrument. For a target load, the respective measurement uncertainty in absolute terms is multiplied by the cost of the material on 100 weighings. Real-life example: For a filling application this reflects the cost of systematic overfilling during the filling process, to reach at least the target weight. If the measurement uncertainty is smaller, then the overfilling can be reduced according to the reduction of the measurement uncertainty.
5. Evaluation: The fit for purpose check in terms of accuracy. The traffic light color scheme provides the status of the selected weighing instrument compared to your process requirements.
Green: the instrument meets your requirements and therefore is fit for purpose in terms of accuracy.
Yellow: The instrument is accurate enough, but the safety factor you need is not met.
Red: The instrument is not accurate enough for your needs.