Balance

Balance Calibration

The University Instrumentation Center now performs balance calibrations that are fully NIST traceable. The full text explaining NIST Traceability can be found at <http://ts.nist.gov/traceability/suppl_matls_for_nist_policy_rev.htm>. In summary, the University of New Hampshire will now be using weights that have been calibrated through an unbroken chain of comparisons, with stated uncertainties, all the way back to the National Institute of Standards and Technology (NIST), which is an agency of the U.S. Department of Commerce whose role as the National Measurement Institute was established in 1901.

The American Society of Testing and Materials has established different tolerance classes as defined below. UNH weights meet ASTM Class 1 tolerances. Please note that calibration weights must be recertified annually and that the cost of certification is directly related to the tolerance class.

· ASTM Class 0: used as primary reference standards for calibrating other reference standards and weights.

· ASTM Class 1: can be used as a reference standard in calibrating other weights and is appropriate for calibrating high-precision analytical balances with a readability as low as 0.1mg to 0.01mg.

· ASTM Class 2: appropriate for calibrating high-precision top loading balances with a readability as low as 0.01g to 0.001g.

· ASTM Class 3: appropriate for calibrating balances with moderate precision, with a readability as low as 0.1g to 0.01g.

· ASTM Class 4: for calibration of semi-analytical balances and for student use.

· NIST Class F: primarily used to test commercial weighing devices by state and local weights-and-measures officials, device installers and service technicians. Class F weights may be used to test most accuracy class III scales, all scales of class III L or IIII, and scales not marked with a class designation. Calibrated according to NIST Handbook 105-1.

Balances which perform internal calibrations will be verified with the NIST traceable weights.

The Instrumentation Center will also begin providing a printed report of calibrations including all relevant information and graph(s) showing both specified and measured values. The decision on whether to continue using a balance that is out of specification will continue to be made by the lab manager, professor or department.

In order to cover the annual tooling cost of NIST certification of weights, the UIC will charge $10.00 per balance. Labor is free for teaching balances; research balances will be charged a nominal amount for labor.

Please contact Rob Cinq-Mars (University Instrumentation Center, 223 Parsons Hall, University of New Hampshire, Durham, New Hampshire 03824) via telephone at 603-862-0174, fax at 603-862-4104, or email at Rob.Cinq-Mars@unh.edu, or see the URL at www.unh.edu/uic.