| Calibration of Crane Scales |
Analysis of on-site calibration and testingof crane scales- and the need for an accurate calibration system.For a quality system to be effective, it must analyze accurate data.Crane scales, both legal for trade and non-legal for trade, have inherent use problems. Loads are often jerked or snatched, which exerts a shock load onto the sensitive weighing element. Likewise, off center loads exert a side load factor into the scale. Crane scales often exhibit non linear calibration curves. This means that the scale might be accurate at some weights and inaccurate at other weights. The ONLY way to know, is to do a calibration check at several load points, (for example, 25% - 50% - 75% and 100% of rated load capacity). Often times, it is not readily feasible to load more than 20,000 lbs. of certified class F test weights onto a scale. This guarantees accuracy at 20,000 pounds, but leaves all weights above 20K in doubt, and is expensive and time consuming. A common practice is to weigh something heavy (i.e., a coil of steel) on a truck scale and them use it as a transfer standard on the crane scale. Again, this is a relatively accurate check at the reference weight only. Truck scales have an acceptable maintenance tolerance of plus or minus .2% of applied load plus or minus one graduation, typically 20 pounds. This equals plus or minus two pounds per thousand pounds. Therefore, a 60,000 pound coil of steel ( or other substitute test weight) could be plus or minus 140 pounds, giving a band of uncertainty of 280 pounds. National Scales' National Crane Scale Calibration Kits are guaranteed accurate, with direct NIST traceability, to 0.1% of applied load from 10% of capacity to 100% of the rated kit capacity. Normal crane scales have a maximum scale count resolution of one part in 10,000 counts. The National Crane Scale Calibration Kit displays one part in 50,000 counts - over FOUR times GREATER ACCURACY resolution than a crane scale or eight times the accuracy resolution of a truck scale! For example, a 25 ton crane scale would count by 5 pound graduations. A typical truck scale would count by 20 pound graduations. The National Crane Scale Calibration Kit would count by 1 pound graduations. The finer the count resolution, the more accurate the test. The National Crane Scale Calibration Kit is both quick and easy to use. A typical test time is under 10 minutes. To use, merely hang the calibration kit load cell (using the optional Crosby safety rated 5 to1 shackles) onto a hook. Any object lifted becomes a known weight within one pound per thousand lbs. weight. Several loads of differing weights can be used to check the linearity of the crane scale. QA can quickly and accurately verify the calibration accuracy of any in plant crane scale as often as desired. The National Crane Scale Calibration Kit is absolutely ideal for all ISO9000 quality assurance systems. Weights can be read in pounds or kilograms at the touch of a button. An optional printer can record the time, the date, and weight(s) of your calibration checks. National Crane Scale Calibration Kits carry a two year warranty on the load cell and digital indicator. The optional printer carries a six month warranty. Periodic NIST traceable recalibrations can be done as often as your QA procedure dictates. Emergency recalibrations can be done on a priority basis with a one day turnaround. Sounds like a win/win situation? It is! The National Scale Crane Scale Calibration Kit will not only give you accurate test data, it will save you both time and money. For full Pricing and specifications, please call: Larry Eagan or Thomas Robusto at: 800-899-9988 This e-mail address is being protected from spam bots, you need JavaScript enabled to view it |
Specializing in the engineering of custom systems for standard and specialized environments, Measurement Specialists has worked with aerospace and defense contractors, steel mills and countless other industries to develop successful force measurement programs
Our efficient, high quality, manufacturing process allows us to design and build standard and custom load cells at a competive price while providing additional options and services such as high temperature load cells, specialized calibrations, custom electronics and PC programming, and systems integration.
