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Standard Interpretation

Standard: 2009 TNI
Section: V1M2, Section (b)


This section requires support equipment to be calibrated or verified annually with references "bracketing the range of use". The 2003 NELAC standard had comparable language requiring calibration or verification "over the entire range of use". Under the 2003 standard, an exception was permitted allowing the use of a single point calibration for narrow range use thermometers, such as those used for sample storage (>0-6C), BOD (20+/-1C) and micro incubators (35+/-0.5C and 44.5+/-0.2C), drying ovens (103C-105C), etc. However, the same exception has not been extended to the 2009 TNI standard requirement. As a result, labs are being cited for not performing bracketing checks for these thermometers. Although the AB for the state where this issue developed allows the use of a temperature at or below and at or above the boundary of the range of use, the requirement still requires the lab to take the equipment out of normal use and re-adjust the settings multiple times. The process provides data that is probably less reliable than a single point check and requires significantly more time to perform. For example, a single point check in the range of 44.3-44.5 C for a fecal incubator would seem to be better data than a check around 40C and a second around 50C.

The use of a single point calibration/verification check for narrow use range thermometers has worked well under the 2003 NELAC standard. I would like to propose that TNI extend the single-point exception used under the 2003 NELAC standard for narrow range use thermometers to the 2009 TNI standard.


(Quality Systems Expert Committee and NELAP AC, 10-4-14)

An exemption for narrow range use thermometers is not described in the 2003 NELAC Standard and historical data does not provide that an exemption was made on an organizational level. The use of a single point calibration/verification check for the narrow use range thermometers exemption is not described in the 2009 TNI Standard.