Testing Your Laboratory Balance (Page 5 of 6) in pdf

Testing Your Laboratory Balance Page 5

Linearity Testing

Linearity testing verifies the accuracy of the instrument at intermediate values of

weight. Manufacturers often use the term "accuracy" in advertised

specifications.

1. Use two weights, each of approximately one-half the weighing capacity of

the instrument. It is imperative that these two weights not be interchanged

within this procedure. Refer to the individual weights as "weight A" and

"weight B."

2. Rezero the display. Place "A" on the pan (at the center), and record the

reading on the "Linearity Chart" in the column marked " 0% – 50% ."

3. Remove "A" and place "B" on the pan next to the center. Rezero the display.

4. Again place "A" on the pan. Record the reading under the column marked

"50% - 100%."

5. Calculate the difference between the two (0-50 and 50-100) readings.

6. The difference should be less than the advertised tolerance for linearity or

accuracy.

Linearity Chart

0%– 50%

50% - 100%

Special Note:

error

A common

in linearity (accuracy) testing is to simply place test weights

on the weighing pan and observe the difference between the indicated weight

and the nominal value of the test weight. This process fails to account for the

fact that test weights are imperfect and that the difference between the nominal

value and the actual weight might be significant. This is especially true with

analytical balances, where the balance may be more accurate than any standard

test weight. The above procedure nullifies this problem by comparing the

weight readings of the same object, both with and without a preload. The

accuracy of the test weight is thus immaterial.

IES Corporation

Repair of Laboratory Balances

(800) 541-0852

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Testing Your Laboratory Balance Page 5