1.Purpose:

To lay down the procedure for the calibration of weighing balances.

2. Scope:

Applicable to all weighing balances except analytical balances.

3. Responsibility:

Department Head

4. Definitions:
 

Calibration: The set of the operations which establish under specified conditions , the relationship between values indicated by a measuring instrument & the corresponding known values of a certified & traceable reference standard.

5. Procedure:

  • Check the cleanliness of the area.
  • Check that platform and exposed parts of the balance are clean and dry.
  • Check the level of the balance with the help of spirit level. Adjust the level, if not leveled.
  • Switch on the main power supply of the balance.
  • No repairs should be made to any balance by anyone other than a qualified validation person.
  • Do not use balance if it is not calibrated.
  • Following parameters to be checked while performing calibration.
  1. Accuracy
  2. Linearity
  3. Precision
  4. Corner Load Test
  • Frequency: Every Month (± 7 days)

    5.1 Accuracy 

    Check the accuracy of the balance by using 5 standard stamped weights.
    Place standard weight one by one in the increasing order in the center of the platform and record the observations in the balance calibration record.
     

Acceptance Criteria: Standard Weight  ± 2 x Least Count

5.2 Linearity


Draw the linearity curve for the above readings and find out the correlation factor. Record the observations in the balance calibration record.

Acceptance Criteria: Limit: Not Less Than 0.9999

5.3 Precision

 
Check the Precision of the balance by using standard weight equivalent to 5 % of
Maximum capacity.
Repeat the procedure for five times and record the readings.
Repeat this using standard weight equivalent to 50 % of maximum capacity.
Calculate   Relative Standard Deviation (RSD) for both the standard weights. Record the observations in the calibration log.

Acceptance Criteria: % RSD Not More Than 0.5 %

5.4 Corner Load Test
 

Place standard weight equivalent to 30 % of maximum capacity in four corners and center of the balance and note down the readings in record. Calculate % Relative Standard Deviation (RSD).
Record the observations in the balance calibration record.

Acceptance Criteria:
Deviation: Standard Weight  ±  2 x Least Count
% RSD: Not More Than 0.5 %

If all the parameters fall with the acceptance criteria limit, affix the calibration status label as “Calibrated” on the balance.

If any of the observation is out of limit, correct and reset the balance.

After resetting, calibrate again all the parameters as mentioned above.

Switch off the balance at the end of day.


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