Infrared tympanic thermometer validation system

Sensor Review

ISSN: 0260-2288

Article publication date: 1 June 2004




(2004), "Infrared tympanic thermometer validation system", Sensor Review, Vol. 24 No. 2.



Emerald Group Publishing Limited

Copyright © 2004, Emerald Group Publishing Limited

Infrared tympanic thermometer validation system

Infrared tympanic thermometer validation system

Keywords: Temperature, Calibration, Thermometers


Infrared tympanic thermometers (ITT's) measure the temperature of the Tympanic membrane in the ear. Connected to the hypothalamus the tympanic duct is very close to the body's core temperature, closer than either the tongue or rectum.

Infrared thermometry with averaging and peak measuring circuitry combined with accurate digital display with freeze mode and memory has been developed to offer a thermometer that sells for around £20.00. Some 40 per cent of all human body temperature measurements are made with ITT's.

The problem is their validation, especially after they have been used in the hospital environment.

A clever solution has been proposed and developed at the National Physical Laboratory (NPL) by using the basic properties of materials.

Any pure substance will melt or freeze without change of temperature.

By choosing a substance that is available commercially in ultra pure grade, and whose melt/freeze temperature is close to and below the body's core temperature (36.3°C) NPL have produced a simple, reliable way to revalidate ITT's.

The material used – ethylene carbonate (EC) is almost non-toxic and so is safe to use in medical applications.

NPL formed a Teflon housing to offer the ITT a blackbody cavity surrounded by EC, which during its melting or freezing creates a constant temperature of 36.38°C.

The fixed temperature cell has been patented by NPL who then looked for a partner to commercialize the design for the benefit of health authorities everywhere.

Isothermal Technology Ltd

Isothermal Technology Ltd has been producing fixed point cells for temperature calibration purposes for the past 15 years, and so it was an obvious choice as a partner to commercialize the design.

The idea was to produce a cell whose cavity did not deviate from the original, but that could be produced in bulk and economically, together with an apparatus to melt and freeze the cell cheaply and without the need for skilled operators.

Simple operation

The fixed temperature cell is first melted in a melter supplied with the cell (Plate 7), then the cell is cooled with air until it is part frozen at 36.3°C and can be used to validate ITT's.

Plate 7

As Ultra Pure EC has only one freeze temperature, it will not drift or change with time or use, making it the ideal solution for revalidating ITT's.

The unique features of these cells are accuracy, stability, ease of use, and their economical price.

In its insulated housing, the cell will not change temperature over a 2 h period.

For laboratory or large volume usage a maintenance bath will keep the cell on its freeze for over 8 h.

For more information, visit the Web site:

Related articles