The Weighing Balance Tolerance Limit of a pharmaceutical weighing machine refers to the maximum acceptable range of balance while material weighing that is considered acceptable for installed balance at the manufacturing area.
Weighing Balance Tolerance limits are usually calculated by using a %age of the minimum and maximum capacity of the balance. For example, a balance with a capacity of 500 grams and a tolerance limit of ±0.1% would allow for a maximum limit of 495 to 505 grams in the measurement.
A weighing balance’s tolerance limit is normally determined by the manufacturer and is based on the balance’s accuracy and level of quality. Balances that are more precise and accurate will have smaller tolerance limits, whereas balances that are less precise or of poorer quality may have wider tolerance limits.
When utilizing a weighing scale for any application that calls for exact measurements, it is crucial to take the tolerance limit into account because going beyond it can produce unreliable or inaccurate results.
Related: Calibration of Weighing Balance
Weighing Balance Tolerance Limit example
For example, we have a weighing balance of 50 kg full capacity, and the least count is 0.005 kg. so based on that, first, we determine their operating ranges. so for operating ranges simply calculated as:
Balance Operating Ranges:
Minimum Operating range: 0.005 (Least count) x 50=0.250 kg
Maximum operating Range: It is 80% of the full capacity weight. so 80% of 50 kg weight is 50 x 80/100= 40.000 kg.
So let’s understand with the help of the table by considering the above example (accounting for minimum, 20%,40%,60%, and Maximum) or it may differ from company to company procedure.
| %age of Capacity | Calibrated Standard weight (kg) | Tolerance Limit (kg) (Acceptance Criteria ±0.1%) |
| Minimum | 0.250 | 249.75 to 250.25 |
| 20 | 10.0 | 9.99 to 10.01 |
| 40 | 20.0 | 19.98 to 20.02 |
| 60 | 30.0 | 29.97 to 30.03 |
| Maximum | 40.0 | 39.96 to 40.04 |
Guidelines on Weighing balance
USP Chapters 41 and 1251 Described the Guidelines for requirements of the analytical balance to use for materials. Although, USP also states that Requirements are not for the production scale. However, Production scales also may have an impact on the quality of drug attributes, thus it is required to meet GMP.
Related:
References
USP General Chapter <41>, “Balances,”.
USP General Chapter <1251>, “Weighing on an Analytical Balance,”.
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