Guest Article
It is also desirable to have a way to apply small weights to the load-receiving element.I have found that a small plastic bucket works well. It can be hung on one of the chains used for lifting test weights. One thing that is often omitted from an equipment list is NIST Handbook 44. It is a “tool” and is very important. You should not play the game without having the “rule book” handy. Terms to know. Before discussing the actual test, it is necessary to discuss some terms used in hopper scale testing and explore their meanings, specifically, error weight testing, substitution testing, and strain load testing. “Substitution tests” and “strain load tests” may be used independently as separate tests of a scale; they may also be used in combination in the testing of large capacity hoppers. “Error Weight Testing”. Error weights are used to determine the amount of error at a particular test load more accurately than can be determined from reading the indicator directly. On a mechanical beam scale, some small weights in increments equal to one tenth of the scale division can be applied to the load receiving element prior to establishing the zero load balance. Additional small weights can be used to re-establish a balance condition for the beam with the poise seated in the notch on the beam related to the applied test load. By using error weights the actual error of the device at a given test load can be determined to a more precise value than the smallest division of the beam. For example, the smallest division on the beam may be 20 lb. At a given test load if there is an error and the beam is not balanced, moving the fractional poise by 20 lb in either direction may be too much to establish a balance condition. With error weights added to or removed from the scale, the beam may be brought to an exact balance condition, and the actual error can be determined based on the amount of error weights used to balance the scale. On an electronic device the principle is similar, but a little more difficult to visualize.
29
Made with FlippingBook - Online magazine maker