Types of thermometers and their application

Types of thermometers and their application

Medical Equipment

A medical thermometer is an indispensable element of every home medicine cabinet. Measuring body temperature correctly greatly facilitates differential diagnoses and is a guide to taking antipyretics (substances which reduce fever). What kinds of thermometers are there? Which thermometer should you choose to find the most reliable measurement?

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Types of thermometers

Liquid thermometers

Medical grade or clinical thermometer

Fig. 1. Medical thermometer Mesmed MM 109

They use the phenomenon of thermal expansion of liquid (mercury or alloys of liquid metals).

Phase-change or dot matrix thermometers (liquid crystal, chemical)

Phase-change or dot matrix thermometers (disposable)

Fig. 2. Phase-change thermometers (disposable): NexTEMP (Medical Indications) and TempaDOT (3M). Fig. Medical Indications, 3M

Phase-to-phase reactive thermometers and most disposable phase thermometers are designed to measure the temperature in the armpit and in the mouth. Some thermometers belonging to this category are used in the first wave to measure the temperature of the forehead. Thermometers of this type do not require power and are not susceptible to the influence of the electromagnetic field from medical diagnostic equipment.

Among the chemical thermometers one can distinguish constructions whose life is about 5 years (after this time they should not be used). They can be stored at extreme temperatures, and within a short time are able to achieve readiness for measurement in a wide range of clinical conditions. Some device models require a "thermal reset" when the storage temperature exceeds 35 ° C.

Digital thermometers

Digital thermometers

Fig. 3. Electronic touch thermometer. Fig. Beurer

In electronic touch thermometers, the element responsible for temperature measurement is the electronic circuitry termed the thermistor (a type of resistor). Most of these devices are designed to measure the temperature in the mouth, axillary (armpit) or rectum (anus). The measurement time varies from 10 to 15 seconds. Some thermometers operate in the prediction mode based on the estimated temperature measurement when the thermal balance of the tissues surrounding the measuring tip is reached. This mode significantly accelerates the reading (up to several seconds). Although, the accuracy of this type of measurement doesn’t work as well when compared to continuous measurements.

The basic disadvantage of this type of device is having a tip made of nickel, which can be dangerous for people who are allergic to the compounds of this metal. If a person is allergic, we can use thermometers with a gold-plated tip instead or simply use a different kind of thermometer. Another disadvantage of digital thermometers is the susceptibility to electromagnetic fields generated by medical devices and telecommunications devices (cordless phones and cellular telephones). They are also more costly as the battery needs to be replaced every so often and the metal tip needs to be disinfected after each use.

Non-contact thermometer (infrared)

Non-contact infrared thermometer

Fig. 4a. Non-contact infrared thermometer: Beurer FT55. Fig. Beurer

Non-contact infrared thermometer

Fig. 4b. Non-contact infrared thermometer: Beurer T90. Fig. Beurer

Optical sensors have been used to build contactless thermometers that are able to detect infrared radiation emitted by hot objects.

You can also read about fever, what it is and how to measure it.

Bibliography:
  1. Interna Szczeklika 2018 Internal Diseases Handbook, Authors: Piotr Gajewski, Andrzej Szczeklik Publisher: Medycyna Praktyczna
  2. http://www.mp.pl
  3. https://www.mp.pl/pacjent/
  4. https://infekcje.mp.pl/publikacje/122369,rodzaje-termometrow-lekarskich-i-ich-cechy
  5. https://medyczny-rzeszow.pl/_blog/10-Rodzaje_termometrow_medycznych_i_ich_zastosowanie.html
  6. Figure B: Thermometers. http://www.wydawnictwoapteka.pl/files/UserFiles/File/maj-pdf/36-38.pdf
  7. https://zdrowybajtel.pl/termometr-pomiar-temperatury/
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