TM 5-3895-374-10
..................................................................................................................................WEIGHED LOAD TEST SUGGESTIONS
The following suggestions are for belt scale calibrations although many of the ideas apply equally well to asphalt meter or
other calibration procedures.
Accurate and repeatable calibration runs are possible. They do require an understanding of and appreciation for the
details of the test. Basically the procedure is as follows:
1) Run the equipment until it will respond stabily and uniformly.
2) Obtain a stable zero on the totalizer.
3) Run aggregate across the belt scale and directly into a truck.
4) Weigh the truck and calculate the net weight.
5) Compare the actual truck net weight and the indicated scale total weight. If the indicated weight is not in
tolerance, readjust the scale span calibration value and repeat this test starting at Step 2.
Sometimes it does not seem this simple. Pitfalls to watch for include:
In Step 1
-Often equipment does not stabilize until after it has been used for a while. This may especially be
true of new equipment, rusty equipment or moist materials. Sometimes it is necessary to "waste"
or disregard several truck loads of material in order to get the most stable results. Use material
that is uniform. For aggregates this means material, preferably dry, of uniform moisture content
and gradation. For dusts or fillers the material should be of uniform density, free flowing and free
of clumps. For liquids this means uniform temperature and density. Liquids often must be
"stirred" until uniformity is assured.
In Step 2
-Do not rush at this point. If calibrating at 100 TPH a 1 TPH zero error is 1I.This 1% is often a
greater error than the maximum allowed. When repeating a test, material buildup on the belt will
often change the zero. The answer may not be as simple as waiting for the belt to clear. After all,
material will again build up on the belt during the test and create an error. The system can appear
to calibrate and may even repeat, but only because the "calibration" value includes an equal and
offsetting error. The best solution is to select material that does not stick to the belt. In the worst
case, course material may need to predried and stockpiled for this calibration.
page F - 111
SYSTEMS Equipment Corp. 8/31/89 Page (62)
APPENDIX G
