Scale Trouble Shooting (1)

This section is dedicated to describing trouble shooting procedures for the weighing portion of the scale. It does not attempt to address failures of the scale indicator, nor communications with other devices.

There are two basic situations where trouble shooting of scales may be required:
1) The scale is weighing (weights displayed on the indicator display), and the weights are questionable.
2) The scale is not weighing at all (no weight on the display), or the weights displayed are clearly bad (like a large negative weight or positive weight outside of the normal operating range).

Questionable Weights
This section covers the testing to be done if the weights are in a reasonable range, but are questionable in accuracy.
The first step is to determine if the weights are accurate or not. This is a two part process, the first of which is a cornering test, and the second is a gross calibration test.
1. Cornering Test
The purpose of this test is to determine if the scale weighs the same no matter where the weight is placed. This will help identify mechanical binds or bad load cells.
A. Arrange for the availability of test weights near the scale. These should be as large as possible, but small enough that they can be applied to different sections of the scale.
B. Empty the scale, and let it stabilize.
C. Record the displayed weight on the indicator.
D. Place the test weights as near as possible on one corner of the hopper/platform structure.
E. Record the new weight displayed on the indicator. It should be greater than the weight recorded in step C by the amount of the test weights, +/- .3% of the test weight amount. Note that sometimes as you apply the weights to the scale you can cause a zero shift due to the mechanical impact of the weights. Repeat this step at least twice to make sure you get an accurate reading.
F. Remove the test weights and make sure that the scale weight returns to that recorded in step
C, +/- 2 divisions (a division is the smallest amount of weight change the indicator can measure, which is set up during calibration).
G. Repeat steps C thru F on all corners of the scale.
H. All corners should respond the same when the test weights are applied. It is possible that all weigh the same, but not exactly the amount of the test weights, in which case the scale needs calibration. If the corners are inconsistent in their weights then see next articles………….

to be continued………….

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