SOP No. 33
Standard Operating Procedure for
Calibration of Weight Carts

1. Introduction
   1. This Standard Operation Procedure (SOP) describes the procedure to be followedfor the calibration of weight carts used to test livestock and vehiclescales.
   2. Prerequisites
      1. Facility. Verify that the laboratory facilities meet the following minimumconditions to meet the expected uncertainty possible with this procedure.

         Table 1. Environmental Conditions

         Echelon	Temperature	Relative Humidity (percent)
         III	18 ° C to 25 ° C, maximum change 1.0 ° C/h	40 to 60 ± 10

         
         
      2. Balance/scale. Verify that the balance, scale, or load cell is in good operating condition with sufficiently small process standard deviation as verified by a valid control chart or preliminary experiments to ascertain its performance quality.
         1. If a scale or load cell is used for the calibration that is not a permanent piece of equipment in the calibration laboratory, appropriate verification and repeatability statistics must be obtained prior to a calibration to determine suitability and acceptability for calibration. Records must bemaintained of this verification. Minimum verification includes an increasingand decreasing load test to at least the capacity of the weight cart, ashift test, a sensitivity test at the test load, and evaluation of therepeatability based on a minimum of 7 repeated weighings (following thesame SOP to be used to test the weight cart).
         2. The expanded uncertainty (k=2) must be less than one-third of the applicable tolerance and should be evaluated prior to calibration.
      3. Standards. Ensure the availability of suitable working standards or recently calibrated (and unused) field standards in quantities up to the capacity of the weight cart(s) that will be calibrated. All standards must have known conventional mass values.
      4. Staff. Verify that the operator is experienced in precision weighing techniques and has had specific training in SOP 8, SOP 4, SOP 29, and GMP 10. Safety precaution: weight carts should always be calibrated with at least two people present.

Weight Carts Home | SOP 33 Home | Section 1 | Section 2 | Section 3 & 4 | Section 5 | Section 6 & 7 | Section 8 | Section 9 & 10 |
Appendix A | Inspection Checklist | Appendix B

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For technical questions concerning the Metrology Resources for State and Commercial Laboratories, contact us:

Weights and Measures Division, NIST, 100 Bureau Drive, Stop 2600, Gaithersburg, MD 20899-2600
Phone: (301) 975-4004, Fax: (301) 926-0647, Email: owm@nist.gov

Date created: May 21, 2002
Last updated: October 1, 2002

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