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Factors for Determining Scale Calibration Frequency

Factors for Determining Scale Calibration Frequency
Over time, weighing scales start to show inaccurate readings for a number of reasons. Sometimes the internal components wear out due to frequent use or aging, while in other cases environmental factors can play a role. Calibration is the process by which the accuracy of a weight scale is put to the test, and to ensure that scales are working properly, they have to be calibrated from time to time. 
 
How Can You Determine the Ideal Calibration Intervals?
 
In general, manufacturer recommendations can help to determine scale calibration intervals. Commercial calibration laboratories may also make suggestions during inspections, but they are often not conversant with the specifics of a scale’s application. OEM (Original Equipment Manufacturer) calibration intervals are usually based on drift rates.
 
This often leaves the operator with the responsibility of determining calibration intervals while also taking into account the manner in which the scale in question is used. Scale recalibration frequencies are determined by a number of factors, like:
 
  • Industry, Processing or Customer Accuracy Requirements

    Scale operators that have to comply with high industry, processing or customer accuracy requirements need to ensure that their weighing equipment receives regular recalibration. Failure to do so can be very costly!

    If, for instance, you sell 1000 lbs. on average of a product per day at a rate of $10 per lbs., this comes to a total trade value of $10,000. Let’s assume the scale is out of tolerance by 0.5%. If you do the math, this could amount to a discrepancy of $50 a day, $250 per week and $1000 in a month. However, shorter intervals between calibrations can save a lot of money and unnecessary hassles too.
     
  • Contract or Regulation Requirements

    If you are a major supplier of raw materials or bulk products, chances are that you sell by the weight. Your scales will therefore be subject to inspection by the State or Local Weights and Measures Department.

    Customers may also want to have your weights inspected by their own independent and certified weighmaster. In certain industries, ISO standards or other quality control regulations can mandate periodic calibration. As such, contract requirements or legal regulations also determine how often you should calibrate your scales and weighing equipment.
     
  • Environmental Factors that May Affect the Scale

    Extremely cold and hot conditions or frequent temperature variations tend to degrade scale performance. Weighing equipment that is exposed to other external conditions like lightning, snowstorms, humidity or dust will also show decreased performance over time. If your weighing scales are subject to extreme environmental factors of any sort, they will require calibration more often than scales used in controlled conditions.
     
  • Where the Instrument is Stored and Used

    Where a scale is used and/or stored has a direct correlation in determining calibration frequencies. If a scale has to be moved frequently from the storage room to where it is required for operation, odds are that it might be handled incorrectly. If your scales are constantly being moved or used, regular calibration will keep them accurate, by revealing any damage they may have occurred during movement or due to the rigors of daily use.
     
  • Required Uncertainty in Measurement or Accuracy

    Almost all scales start to lose accuracy with time and regular usage. Scales that weigh hundreds or even thousands of loads every day require calibration more often than those that experience less frequent use. Even a tiny error in a heavily used scale can reach unacceptable levels over just a few weeks. Therefore, the acceptable out-of-tolerance errors your scale application can bear will also help determine the intervals between calibrations.

    It is only through calibration that inaccuracies in weight scales can be detected and adjusted. Therefore, scale owners must know the ideal frequency between calibration intervals. This ensures that weighing equipment returns correct measurements at all times, which in turn prevents merchants from overcharging customers or giving away free merchandise.
 
Images Courtesy: U.S. Department of Agriculture (Flickr Creative Commons)
 
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