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.
- Repeatability
- 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 following formula:
Where,
SD: Standard Deviation
N: Smallest net weight that the users plan to use on that balance
- Weighing range of analytical balance can be measured by using two parameters.
- 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
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Download Attachment I: from the given link.
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