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APPENDIX G
WEIGHED LOAD TEST SUGGESTIONS - TM-5-3895-374-10_315

TM-5-3895-374-10 Paving Machine Bituminous Material: Crawler Mounted Diesel Engine Driven Manual
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TM 5-3895-374-10 APPENDIX G ........................................................................................................................... WEIGHED LOAD TEST SUGGESTIONS Wind is often a problem.  If calibration tests are to be stable and repeatable the scale readings can not be erratic from any cause.  Although each plant is different, a 1 TPH rate may be caused by only 1 lb.  of wind pressure on the belt at the position of the weigh idler.  Wind screens may help but may not protect against wind blowing directly down the belt.  Top covers or tarps tied over the belt may be helpful.  Calibration may have to be delayed until the wind subsides although most people recognize that this will not eliminate the errors that will be present on windy days of actual production. Remember too, that the factors that cause errors when calibrating a belt scale also cause errors when calibrating feeders to the belt scale. In Step 3 -All  of the material that crosses the belt scale must be delivered to  the  truck.    Ideally  there  is  a  useable divert  mechanism  at  the  end  of  the  scale  conveyor  so  that  the  truck  can  be  loaded  directly.    All  chutes between the scale and the truck should be clean before the sample is loaded and cleaned into the truck at the end of the sample. It is generally not accepted practice to move the scale after calibration.  If it’s absolutely necessary to move the scale in order to calibrate, it should at least be at the same slope as it will be in its operating position. Again, this is not an accepted practice and should be avoided whenever possible. Special precautions must be observed if the material must  be  run  through  the  drum  in  order  to  load  the truck.    The  most  successful  procedure  is  a  midstream  sample.    In  doing  this  each  test  must  be  done  in exactly the same manner.  The stockpile material must be uniform and as dry as possible.  A stopwatch should be used to time out an exact 15 minute interval after the feeders stop at the end of a sample run. At exactly 15 minutes after the feeders stop, the drum and material hot elevator should be stopped.  The silo, batcher etc.  should be completely emptied and the truck then weighed.  The first test at any  given rate should be done precisely but the results ignored.  If everything is constant, the material remaining in the system after this run will be the same amount remaining at the end of the next actual calibration run. To the extent that this is true, the calibration is therefore accurate and repeatable. Obtain as large a sample as possible.  Accurate belt scale calibration usually requires loads of at least 15 TONS.  Asphalt meter calibrations to a 1% limit require loads of 1000 gallons if weighed on a truck scale with 20 lb.  grads.  For meter calibrations to 0.25x, loads of 4000 gallons are required.  The effect of minor imperfections in the procedure or equipment can be minimized by the use of larger loads. page F - 112 SYSTEMS Equipment Corp.  8/31/89  Page (63)







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