Validation professionals spend extensive time validating temperature to ensure the integrity of controlled environments and to fulfill compliance requirements.

Pre- and post-calibrations—a necessary part of the process of thermal validation—typically take up 50-80% of the time it takes to map a given area. Carefully distributing and re-distributing thermocouple wires (after re-calibrating with each placement) is not only time consuming, it entails cessation of normal operations and—as this article will show—actually degrades measurement accuracy.

Despite a move toward ever leaner operations in regulated industries, thermal validation is one area that has eluded the cost and time savings associated with improving measurement technologies. In part, this is because of the imperative that cost-saving measures do not increase the risk of inaccuracy; especially when the application involves temperature-sensitive product and requires complete documentation.¹ This may explain why validation is still performed using thermocouples that require time-consuming preand post-calibrations.

The following article will discuss the major differences between thermistors and thermocouples, their appropriate measurement ranges, and give some real-world calibration statistics for thermistorequipped data recorders. These statistics provide evidence that the stability of thermistors supports their use in multiple validations with the benefit of time saved by fast deployment and the reduction of nonessential pre- and post-calibrations.

THERMOCOUPLES: A BRIEF HISTORY
Thermocouple systems have long been used for thermal validation. Their function is based on the thermoelectric effect discovered in 1821 by Thomas Seebeck, who found that when two dissimilar metals were joined and a temperature difference was present, a voltage was produced. Known as the Seebeck effect, this forms the basis of all thermocouples.