Guest Article
In that case, phone conversations with all of the parties to be involved in the test may be the next best option; this may include the testing official, the scale service agency, and representatives of the scale owner. Initial questions to address are: What is the capacity and division size?Is it full electronic, mechanical, or electromechanical? Once the capacity has been determined the following questions are very important: Can at least 25 percent of that capacity be applied in known test weights? What size of test weights can be used? Are the test weights already in place (i.e., permanently at the scale)?If they are not in place, what is required to get the appropriate weights to the load-receiving element?If the weights are in place, do they have a current laboratory certification? Once these questions have been addressed, the inspector must determine how the weights will be applied to the scale. The method of applying known test weights often presents the greatest challenge for the test. I am sure that many of you have been involved in the testing of a large capacity hopper scale using only fifty-pound test weights. Doing substitution testing of a hopper with as much as 10 000 lb in fifty-pound weights becomes very labor intensive, time consuming, and sometimes downright dangerous. I was involved in one test that required stacking 10 000 lb of fifty-pound weights on a bridge plank suspended from two chains on one side of the scale, and only one side was accessible. During the third time of stacking the weights on the plank, at more than 9 000 lb, the plank broke, sending the entire load scattering across the concrete floor. Fortunately, no one was injured. The preferred method of applying test weights to the scale is to use large block weights with chains of sufficient length and strength and “come-a-longs” in the appropriate capacity and quantity to apply the known test load to the load-receiving element. The better systems today have weights “permanently at the scale.” Some also incorporate hydraulic cylinders for lifting the weights. In addition to the larger test weight and equipment outlined above, it is necessary to have small weights in increments down to one tenth of the scale division for error weight testing. It is also helpful to have enough small weights to be able to trim substitution loads to an exact value, as will be discussed in detail in the next section. For an official test, you also need the proper report forms, seals, tags, sealing, pliers, etc.
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