CHAPTER 4 – FINAL TESTING
MB90 MB120 Series Service Manual
55
Ohaus Corporation www.ohaus.com
4.4.1 Precision Test
In Analyzer specifications, the term Precision means the Standard Deviation of a set of similar
weight readings. To determine if an Analyzer meets the calculated Standard Deviation value in
the Specification Table 4-1, perform the following test:
5. Tare the Analyzer. The reading on the display should be 0.000g.
6. Place a 50g mass on the
center
of the sample pan. Observe and record the reading
when the stable indicator comes on.
7. Remove the mass. The reading should return to 0.000 within the published
tolerance when the stable indicator is on.
8. Repeat this test for ten readings. If the standard deviation of the readings is less than
the indicated tolerance, the Analyzer passes the Precision Test.
CAUTION
: Remove the mass from the pan after testing.
Adjustment
If the deviation for any set of readings (using the same mass placed on the center of the pan) is
greater than the indicated tolerance, the Moisture Analyzer does not meet the Precision Test
specification. Inspect and correct the following areas:
1. Check for mechanical obstructions: any foreign object touching any part of the
moving pan linkage assembly will cause the Analyzer to fail the Precision Test.
Inspect and correct as necessary.
2. An error in the Off-Center Load Test can affect the results of the Precision Test.
Inspect and correct if necessary. (See Off-Center Load Test.)
3. Foreign material or debris between the pan and the base will cause the Analyzer to
fail the test.
4. Vibrations, drafts or a non-level surface can cause failures.
