NATA News Archive
- Published: 14 May 2014
NATA’s Technical Note covering user checks and maintenance of laboratory balances has received a major update in response to correspondence from our members expressing concerns with the method for conducting the monthly single point check.
Today’s precision laboratory balances are generally the electronic type, have an internal check mass and advanced software that assists in providing good stability of measurements over time. However even with these advances, most manufacturers will still recommend recalibration intervals of 12 months.
Technical Note 13 suggests the recalibration interval may be extended (guidance intervals are provided in NATA’s publication General Equipment - Calibration and Checks) by providing information on performing a robust and valid method for a monthly single point user check.
However feedback from our members has highlighted a number of issues in the single point check method previously described in the Technical Note, including:
- the uncertainty of the balance calibrator’s mass not being taken into account;
- a user assigned mass has no uncertainty determination; and
- the uncertainty of the monthly check mass (calibrated externally or user defined) is not being taken into account.
Addressing these issues, the method for conducting a single point monthly check has now been amended to take into account these uncertainties.
At the same time, an equivalent amount of feedback has been received by other members requesting assistance with their understanding and application of the user check methods. The differences in the feedback highlights the diversity of testing activities amongst NATA’s members and the difficulty in producing a Technical Note that is fit for purpose for all applications.
Thus a second method for user checks of balances has been included with this revision where in place of the precision method for monthly user checks, laboratories may instead perform a single point user check daily or before use, comparing any variation from their calibrated check mass to their own action limit or error allowance. By performing the single point check to this method, it is recommended the recalibration interval be 12 months.
To ensure the value associated with the single point user check mass is suitable for use, these masses must be calibrated and the uncertainty of measurement reported on the calibration certificate compared to the repeatability of the balance being checked.
How to calculate a minimum mass has also been added to the Technical Note as guidance on what the minimum mass value is appropriate for each balance to measure.
Plus acknowledging the advances in technology of design of weighing devices mentioned above, guidance has been included for verification checks to be conducted after a balance has been moved. These verification measurements maybe performed in place of a full re-calibration after a balance is relocated.
For any further questions on the application of Technical Note 13 please contact your NATA client manager.