SOP for Calculation of Weighing Range of Analytical Balance

OBJECTIVE 

To lay down the procedure for determining the Weighing Range of Analytical Balance. 

SCOPE 

This procedure is applicable for Balances installed in QC Department & IPQC Department. 

RESPONSIBILITY 

It is the responsibility of QC Executives to perform the procedure without deviation. 

ACCOUNTABILITY 

Manager – Quality Control 

PROCEDURE 

• Weighing range of analytical balance can be measured by using two parameters. 

1. Repeatability 
2. Accuracy 

• A test weight is suitable if it has a mass between 5% and 100% of the balance's capacity. 

Repeatability:

• Be sure the balance is warmed up, leveled and calibrated before starting. 
• Set the display of the balance to zero by pressing the "Tare" button. 
• Position the test weight on the center of the weigh pan. 
• When the display has stabilized, document the weight. 
• Repeat above two steps nine times. 
• Once the 10 test results have been taken, calculate the SD using excel sheet as a reference Attachment I. 
• Calculate repeatability using the following formula: 

       Where, 

          SD: Standard Deviation 

          N: Smallest net weight that the users plan to use on that balance 

• The weighing range of analytical balance can be measured by using two parameters. 
• The calculation to determine the actual starting point of the balance's operating range (ORmin). 

• If the SD < 0.41d, it must be replaced by 0.41d, where d is the readability of the balance. This special condition was put into place because a balance always has a measuring uncertainty error and the 0.41d accounts for the rounding error.

Accuracy:

Position the appropriate test weight on the center of the weigh pan. When the display has stabilized, document the weight to complete. 

Calculation of Minimum weight: 

• Calculate the min sample weight by using the following formula:

        Where, 

          SD: Standard Deviation of repeatability 

          d: Readability of balance 

          0.1% : Required weighing tolerance 

ATTACHMENTS 

Attachment I: Calculation of Weighing Range of Balance 

REVISION HISTORY

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