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4-2
CHAPTER 4 TESTING
4.2 PERFORMANCE TESTS (CONT.)
The following performance tests are used to evaluate the balance operation before and after repairs.
Each balance tested must meet the requirements specified in each test as well as the specifications
listed in Table 1-2. Tolerance values are expressed in counts. A balance which passes each of these
three tests meets the manufacturing specifications.
4.2.1 Repeatability Test
Repeatability is a word used in balance specifications meaning the Standard Deviation of a set of
similar weight readings. To determine whether a balance meets the calculated Standard Deviation
value in the Specification Table 1-2, perform the following test:
Test
1. Tare the balance. The reading on the display should be 0g.
2. Select a mass weighing near the maximum capacity of the balance and place the mass on
the center of the Pan (1). Observe and record the reading.
3. Remove the mass. Reading should return to 0g +1 count.
4. Repeat this test for ten readings. If the standard deviation of the readings is less than +1
count, the balance passes the Repeatability Test.
Adjustment
If the deviation for any set of readings (using the same mass placed on the center of the Pan) is greater
than +1 count, the balance does not meet the Repeatability Test specification. Inspect and correct the
following areas:
1. Check for mechanical obstructions. Any foreign object touching any part of the moving Pan
can cause a balance to fail the Repeatability Test. Inspect and correct as necessary.
2. An error in the Off-Center Load Test can affect the results of the Repeatability Test. Inspect
and correct if necessary. See Off-Center Load Test.
3. Foreign material or debris located in the balance between the Pan (1) and the Top Cover
(6) can cause the balance to fail the test.
4. Environmental influences such as vibrations, drafts or a non-level surface can also cause
failures.
5. If the balance fails the test, refer to table 2-1 Diagnostic Guide for assistance.
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