• Name & address of the person that ordered weight(s)
• Date of calibration
• Serial number (Storage case has serial #. If you want weights themselves to have serial numbers laser marking is available at an additional cost of $50 per weight. If you want laser marking please call us before placing order.)
• Tolerance Class of weight (i.e. Class 1, Class 2)
• Nominal value
• Conventional mass correction: "As found data" (not provided with new weights)
• Conventional mass correction: "As left data"
• Uncertainty of measurement process
• Construction and density of weights
• Statement of traceability to NIST
• Use only one series of comparisons using a single standard
• NIST test number
  

• Identification of the balance used in the calibration – calibration due dates for equipment
• Date the primary standards were last tested at NIST and the NIST test number
• Conventional mass value "As found data" (not provided with new weights)
• Conventional mass value "As left data"
• True mass value: (mass in a vacuum) "As found data" (not provided with new weights)
• True mass value: (mass in a vacuum) "As left data"
• Environmental conditions (temperature, barometric pressure, humidity) during test
• Calibration procedures used
• Pass/Fail result of magnetic testing
• Helpful list of terms and definitions
• Use only one series of comparisons using a single standard ASTM Classes 2, 3, 4, 5, 6
• Multiple comparisons using a check standard for ASTM Classes 0 & 1 weights
• Meets ISO, FDA, GMP, DOD, ANSI/NCSL Z540-1, NCR 10CFR50 Appendix B
• NVLAP Accreditation Logo and laboratory code

Who do you feel needs a NVLAP Accredited Certificate verses Report of Traceability?

If you are under ISO, FDA or other regulation we recommend you get a NVLAP Accredited Certificate.  Also, anyone that plans to calculate uncertainty for their own process would need the NVLAP Certificate.

If you have a balance or scale with the ability to read to a milligram or better it is always recommended you know the corrected value of the weight and this is only available with the NVLAP Certificate. Additional information to help you decide can be reviewed HERE.

We recently had a customer that ordered the Class 1 500g weight with Traceability Certificate and then determined he ordered the wrong certification and required the NVLAP Certificate and the cost for changing to NVLAP Accredited Certificate was $94 plus shipping both ways. The only way to get the NVLAP Accredited Certificate is sent the weight in for recertification and this is a costly an time consuming process. You need to fill out a calibration service order form along with a statement of decontamination form. We feel with regulations always increasing just buy weights with NVLAP Certificates.

Recertification Service
Weight values can change over time due to scratches, fingerprints, wear and even corrosion resulting from atmospheric contaminants.  Regular checks on the accuracy of mass standards ensures the accuracy of measurements.  We have access to mass metrology lab providing this service at a very competitive prices. 

The rates vary depending upon the size of the weight (1 gram cost less than a 5kg weight) are listed below and subject to change.  Typical turn around time (excludes transit time) is 7 to 10 business days upon receipt at the metrology lab.  You are responsible for both in and out bound freight and insurance costs.

• Single weights - 1g - $59, 5kg - $144
• Weight sets depend upon the amount of weights in a set - 21 piece set 1mg - 100g - $894

Please call us for up to date pricing and the procedure involved in sending your weights in for recertification. A statement of decontamination form must be completed certifying the weight(s) are free of any radioactive, biohazards or otherwise dangerous substances / gasses and are safe for human handling.

What does calibration of a laboratory weight entail?

All calibrations are accredited calibrations performed using weights by NIST weighing designs, where all weights are compared against a weight standard.  The mass comparators used for performing the calibration ascertain and measure differences to 10, 1, and even 0.1 micrograms (one ten-millionth of a gram).  The value of the unknown weight is computed using a least sum squares technique by the NIST mass code software.  The software performs statistical checks on the balance performance and the computed values of the second standard.  If the balance performance or computed value of the second standard are found to be unacceptable the software requires that the measurement be repeated.  It is only when the process standard deviation and computed value of the check standard are acceptable that metrologist is confident in the value for the customer's weight.  All measurements in metrology laboratory, including tolerance testing, use this Echelon I weighing technique.  The weighing designs are the same ones developed and used by NIST.  All measurement results are traceable to the International Prototype Kilogram (IPK) through a NIST calibration of our primary standards.

Calibration technicians must wear appropriate static free clothing, as well as gloves, hair nets and face masks, to reduce the possibility of contamination (and changing the weight of the weights) from skin oils, hairs, or airborne droplets.  Calibration weights are never touched directly by human hands.

What is True Mass Correction?

Basically, the only people who use "True Mass" are calibration laboratories and other people who apply air buoyancy corrections to the measurements.  Conventional mass is what a weight would weigh at sea level at standard temperature and pressure.  Since most people use their weights in air and don't have the equipment or desire to measure and calculate the air density they have no need for the true mass values.  NVLAP published NIST Handbook 150-2G requiring calibration certificates to reporting "true mass".  If someone needs true mass they typically will know how to calculate it from the Conventional mass.

What is Uncertainty?

Uncertainty is more than just the repeatability of the balance it is a summation of all things which contribute to the error in the measurement process.  Uncertainty is the root sum square of balance deviation, repeatability on the check standard, variability in the density of the standard, variability in the density of the weight under test, variability of the temperature, variability of the barometric pressure, variability of the humidity, operator skill and the uncertainty of the standard used multiplied by two.

Construction and General Shape:

Surface Finish:

Polycarbonate Cases for Individual Weights:

Selecting The Right Weight:

• Check you scale's manual or specification sheet to find the weight value required to calibrate your scale.
• It is recommended that the weight selected to calibrate a balance and/or scale have a tolerance small enough as not to be detected by the balance and/or scale. Troemner recommends the tolerance of a weight selected for calibrating a balance and/or scale is no more than 1/3 of the readability or precision of the balance and/or scale being calibrated. If this cannot be achieved, it is suggested that a Class 1 Electronic Balance Calibration Weight with a NVLAP certificate be ordered which provides the actual mass value for the weight which reduces measurement uncertainty.
• Electronic Balance Calibration Weights can also be used to check or verify the accuracy of your balance and/or scale between calibrations. It is recommended that the user check a balance and/or scale prior to each use. Keeping the weight at or near the balance and/or scale keeps the weight at the same temperature as the equipment.
  

See entire range of Calibration Weights and Sets

Copyright © 2017 Precision Weighing Balances, All Rights Reserved.