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Standard Interpretation

SIR #: 290
Standard: 2009 TNI
Section: V1M2, Section (b)


Our laboratory is required to calibrate all thermometers annually against a NIST traceable thermometer, bracketing the range of use. If the 2 temperatures that the thermometer is calibrated produce different correction factors, which correction factor is used?


TNI EL-V1M2 Section b states "All support equipment shall be calibrated or verified at least annually, using a recognized National Metrology Institute, such as NIST, traceable references when available, bracketing the range of use. The results of such calibration or verification shall be within the specifications required of the application for which this equipment is used or:
i) the equipment shall be removed from service until repaired; or
ii) the laboratory shall maintain records of established correction factors to correct all measurements."

The TNI Standard does not prescribe control limits which must be met in order for a piece of equipment, whether analytical or support, to be determined to be acceptable. TNI EL-V1M2 Section 5.5.7 states "Equipment that has been subjected to overloading or mishandling, gives suspect results, or has been shown to be defective or outside specified limits, shall be taken out of service. It shall be isolated to prevent its use or clearly labelled or marked as being out of service until it has been repaired and shown by calibration or test to perform correctly. The laboratory shall examine the effect of the defect or departure from specified limits on previous tests and/or calibrations and shall institute the "Control of nonconforming work" procedure (see 4.9)."

Correction Factors that are within the error of measurement of the thermometer in question are not expected to impact the results of that thermometer. Unless prescribed by method or regulation, it is up to the laboratory to determine which correction factor shall be used.