The sensitivity requirement (SR) of a balance represents the absolute error in using that balance. It can also be defined as the cutoff weight below which a balance cannot measure accurately.
In other words, SR is defined as the minimum weight that causes the pointer of a balance to move by one division.
As per USP, sensitivity requirement (SR) is the maximum change in load that will cause a specified change, such as a particular quantity of pointer scale division marks, of the pointer or indicating component of the balance.
Sensitivity Requirement (SR) Formula
SR = Weight / no. of division moved
Example:
Calculate the SR of a prescription balance if a 30 mg weight on this balance was able to move the pointer by 2 divisions.
30 mg/2 divisions =x/1
x = 15
So, SR = 15 (This is not satisfy Class A prescription requirement).
Note: The sensitivity requirement for an electronic balance is supplied by the manufacturer and the class A prescription balance must have a sensitivity requirement (SR) of 6 mg or less.
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