Guest Article
As with any scale examination, the first part is the inspection. During this phase the inspector will look at zero indication as found, suitability and appropriateness of design, correct installation, accessibility for testing (often this is a problem for older hoppers, particularly with respect to application of adequate test weights), marking requirements, and anything else required in the specifications section of Handbook 44. In an NTEP State, this also includes a determination that the scale and significant components are covered by an NTEP Certificate of Conformance. If only the load cells and indicator have Certificates ofConformance, this does not meet the requirements for an NTEP device. The load receiving element (hopper) must also have a Certificate of Conformance. Next are the pretest determinations for the device under test.The inspector considers items discussed earlier, including capacity and division size, test loads to be applied, and the tolerances for those test loads. The actual test is next. Ideally, the test will use known test weights to at least 25 percent of capacity and substitutions to the capacity of the device. If that is not possible, strain load testing may need to be incorporated.Regardless of the method used, the actual errors at the various test points will be determined and recorded. Finally, once the actual performance of the scale has been determined, it will be evaluated as to whether or not any errors are within tolerance.Appropriate action based on compliance with requirements can then be taken. Summary. The test procedures for hopper scales are not much more difficult than those for many other devices. The most difficult and time-consuming task can be the process of obtaining the necessary amount of known test weights and the process of applying weights to the load receiving element. Proper installation of new devices which include on-site test weights can aid immensely in that regard. For older devices, the addition of proper permanent test weights, where possible, can pay off in labor savings as well as increasing scale accuracy and reliability.The keys to a successful hopper scale test are having the right equipment for the test to be performed, knowing how to do them, and understanding how to interpret the results.
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