Chapter 5: Calibration
Shift Adjust
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5 Calibration
Shift Adjust
This adjustment should be made only after all mechanical parts are
checked, and the scale has proven repeatable. Repeatability is checked
by repeatedly placing a test weight on the same position of the platform
and checking for repeatable weight reading. Shift adjust is then done to
make the weight reading for each corner of the platform the same for the
same test weight.
The amount of test weight used for the shift test should equal 1/2 of the
rated scale capacity. Test weights should be concentrated at the center of
each quadrant of the scale platform.
Shift Adjustment for
Model 2888
The shift adjustment is made by adjusting load cell trim potentiometers
mounted on the junction box PCB.
1. Successively place the test weight at each of the four designated
locations (center of each scale quadrant). Note and record the
displayed indications.
2. Determine the location with the lowest indication. The corresponding
load cell is NOT trimmed.
3. Place the test weight at the location with the lowest indication. Note
and record the indication.
4. Proceeding clockwise, place the test weight at each designated
location; if necessary, adjust the trimming potentiometer
corresponding to that location to obtain the indication recorded in
step 3.
5. Repeat this procedure until all indications at the designated locations
are the same or within the specified National Institute of Standards
and Technology (NIST) Handbook 44 scale accuracy requirements.
6. Reinstall junction box cover plate.
Note: The scale has been roughly shift
adjusted at the factory. Before
proceeding, check the shift
characteristics to determine if any shift
trimming is required. In a new
installation, shift adjustment to a properly
shimmed scale should be minor.
Note: Because of the trim pots
interaction with each other, any
adjustment will affect all corner
indications.
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