Pioneer Scale has a validation process for every device and scale that we calibrate and certify. The validation process for belt scales has identified three critical areas that must be addressed in each belt scale application before we certify its accuracy. The critical areas for belt scales are belt speed, idler spacing and idler alignment. Our technicians never assume that any of these critical areas are correct when arriving on the job site and each must be verified before starting the calibration procedure. The most accurate way of calibrating a conveyor belt scale is through a comparison with a truck or rail scale in which a known amount is weighed using the belt scale and weighed on a certified vehicle scale. This is called a material test. However, this method is seldom an option in most operations. Where material tests are not available, calibration weights must be used to simulate the material load to calibrate a conveyor belt scale.
Belt scale integrators use the belt speed as a component in formulas used to calibrate a scale. Speed is determined by counts or pulses produced by an electronic sensor often mounted on a shaft or wheel and is subject to wear or failure. A reliable calibration is dependent on speed and the speed is verified using calibrated tachometers or direct measurement.
Often, idler spacing is assumed but seldom verified by personnel installing the equipment. Since a 2″ idler spacing can produce an error of +/- 4%, our technicians verify the idler spacing on each calibration to insure the scale’s accuracy.
Belt scales use electronic load cells to measure the force being applied to a conveyor’s idler(s). For a belt scale calibration to be accurate the idler must be aligned to eliminate forces from side loading and the weigh idler must be installed to within 1/32″ in line with the 2 idlers immediately proceeding and trailing the belt scale’s weigh idler.
Whatever the reason for utilizing a conveyor belt scale. It is only worth the reliability of the information that it provides to an operation. To address the accuracy of any scale, it is important to address a couple of key issues. First, if the same load were to be applied to the scale more than one time would the results or the weights recorded be the same each time? This is called repeatability. Often, the environment has a great deal to do with this measure of uncertainty. Is there an excessive amount of debris built-up on the idler assemblies, particularly the weigh idler? Are the idler assemblies in good working condition?
