ICL Calibration Laboratories Inc.

Mass (Laboratory Weight Sets) Calibration Services

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CALIBRATION: The set of operations which establish, under specified conditions, the relationship between values indicated by a measuring instrument ....,  and the corresponding known values of a measurand.

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What does calibration of a laboratory weight entail?  

The best equipment:  ICL uses Mettler & Sartorius mass comparators.  Mass comparators compare a weight to a known mass (a NIST calibrated reference weight) and report the difference, to a very small value.  The best mass comparators can ascertain and measure differences to 10, 1, and even 0.1 micrograms (one ten-millionth of a gram); multiple weighings, averaged, can resolve the differences to even smaller amounts.  

ICL's mass comparators:

  • Mettler UMX-6 (7 decimal places of resolution to 6 grams)
  • Mettler AT106 (6 decimal places to 100 grams) shown at left
  • Mettler AX1005 (5 decimal places to 1011 grams)
  • Sartorius CC-10000 (10 kilograms to 4 decimal places)

The best reference weights: The weight under test must be compared to a known weight, so a set of calibrated reference weights, calibrated by an unimpeachable source, is essential..  ICL's reference weights are OIML E-1 masses calibrated by NIST, with the smallest measurement uncertainties obtainable.

Environmental control: The laboratory in which the calibration takes place must be CLEAN and temperature and humidity controlled.  Temperature control (stability of the room temperature) is critical; Echelon 1 calibration requirements specify that temperature may not drift more than 0.5C per hour.  Air is filtered through HEPA filters.  Sources of vibration are eliminated.  Temperature, relative humidity, and atmospheric pressure must be accurately measured in order to precisely calculate the air density, as the buoyant effect of air on the reference weight and the client's weight must be calculated and accounted for in the weighing process.

The right measuring equipment: We measure temperature inside the weighing chamber of each comparator with standards-grade thermistor sensors (accuracy +/-0.02oC) connected to a Hart Scientific Black Stack readout.  The temperature is measured before and after the weighing of each weight and the average is used, along with atmospheric pressure and humidity, to calculate the air density.  We use a calibrated GE Druck digital pressure calibrator to read atmospheric pressure to .01 mm of mercury, and a Vaisala digital humidity meter to measure humidity to better than 1%.

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