Weighing balance calibration in Pharmaceutical

Preparations before calibration

Before you can start the calibration of the weighing instrument, you should clarify a few things and get prepared.

You should find out the technical characteristics of the weighing instrument (max weight, d value), the accuracy requirement (max error allowed and uncertainty) and what to do if the calibration fails (adjustment).

Typically, the whole measurement range is calibrated and the calibration is performed in the location where the instrument is being used. Make sure you have enough weights for the calibration procedure available.

The weighing instrument should be switched on at least 30 minutes before the calibration. The temperature of the weights should be stabilized to the same temperature where the calibration is to be done.

The weighing instrument should be at a horizontal level, especially for small and accurate weighing instruments. Perform a few pre-tests by placing weights close to the maximum of the range on the instrument and to ensure it works normally.

In case the weighing instrument fails in calibration and it is adjusted, you should make an “as found” calibration before an adjustment and an “as left” calibration after adjustment.

In the Pharmaceutical industry calibration of weighing balance is done on a monthly basis to check the accuracy of the balance. While performing weighing balance calibration check the following parameters:

·         Accuracy

·         Reproducibility

·         Eccentricity

Accuracy:

Verify the balances for accuracy with the minimum weight (least count×100 ),5%, 20%, 50% and 90% the capacity of respective balances. Record the displayed weight in respective monthly calibration formats.

Tolerance:

The variation if any should be ± least count of the balance for ± 0.2 % of the certified value of the standard weight used whenever is higher and for analytical balance, the variation should be ± least count of the balance or ± 0.1 % of the certificate value of standard weight used whenever it is higher.

Reproducibility:

Check the Reproducibility by using the minimum standard weight of balance capacity. place the weight in the middle of the weighing pen and observe the displayed value. repeat the procedure 9 times for the standard weight and record the reading. Calculate % RSD for both the standard weight by the following formula.

where x= individual value

x̄= mean of the individual value

n= number of values.

RSD= SD*100/ X

Acceptance criteria: %RSD not more than 2.0 %. Record the observations in monthly calibration record as per “monthly calibration record of weighing balance”.

Eccentricity:

Take the minimum weight and keep at on specified position as shown below calculate %RSD by following the formula is specified above.

Acceptance criteria:

% RSD not more than 2.0 %. Record the details of calibration in labels with Marker Pen. write the identification number of the standard weight used during verification and calibration in the designated place of verification and calibration records. Calibration record shall be verified by

a quality assurance by putting “reviewed by quality assurance” stamp along with initials and date. calibration of analytical balance in the quality control department shall be done as per their respective SOP.

Calibration of balances by external agency:

Internal calibration (software calibration) of weighing balances shall be done by external agencies. calibration certificate received from an external agency shall be reviewed comprising the detail of balance and calibration summary.

Action to be taken if out of calibration:

If the balance is out of calibration to refer sop “handling of out of calibration” and rise deviation as per SOP “handling of deviation” and a fix the label “out of calibration” as per SOP (status labeling) and inform to Department Head of Investigation.

Raise maintenance memo and inform the engineering department for rectification action. if required take a balance of configuration from another section and department for carrying out the weighing activity. In Such situations, carry out Daily verification of transferred balance and used for Weighing. if the parameter of Daily verification does not meet with the specification, monthly calibration should be done. Once rectification of the balance is done, calibrate the balance and record the same in respective calibration records. the balance shall be released for further use only on satisfactory closure of the deviation with detail result of Investigation.