Question 19

College Answer

A good answer included a definition of temperature and a classification of the methods of 
measuring temperature such as electrical, non-electrical and infrared. There followed a brief 
description of the physical principles of thermistors, thermocouples and resistance 
thermometers; mercury and alcohol thermometers, bimetallic strips; and of infrared methods. 
Candidates who did well reproduced the content of the chapter on temperature measurement 
in the recommended text book. Candidates who were not familiar with this material attempted 
to answer the question by falling back on clinical experience of measuring temperature in 
different sites or occasionally referring to concepts of thermoregulation. Neither approach 
gained credit. 
Some candidates interpreted “methods” incorrectly as "site of measurement" so scored poorly.

Discussion

Definition of temperature:

• Temperature is the average kinetic energy of the molecules or atoms of a system (i.e. the average microscopic kinetic energy).

Classification of devices:

• Electrical vs. non-electrical vs infra-red
• Contact vs. noncontact

Liquid in glass thermometers:

• Principles: Heat is transduced as a change in the volume of a heated liquid, which is represented as a change in the position of a fluid level. A substance with a large thermal coefficient of volume expansion (β) such as mercury or alcohol is used.
• Mechanism:  a thin walled glass-filled tube contains the liquid; liquid meniscus is read through the walls of the tube. Glass in the wall magnifies the size of the fluid column.

Bourdon gauge thermometers

• Principles: Heat is transduced as a change in the pressure of liquid contained inside the probe, transmitted to the gauge via non-compressible liquid 

Bimetallic strip thermometers

• Principles: a coiled (spiral or helical) length of two different metals sandwiched together, which expand unequally on one side, causing the strip to deform and deflect the position of a gauge.

Thermal resistance thermometers (platinum wire)

• Principles: Heat-related change in the resistance of a conductor (usually platinum) is measured by the drop in current being passed through it.

Thermistors

• Principles: Heat is transduced as a change in the resistance of a metal oxide semiconductor 

Thermocouples

• Principles: A potential difference is generated at the junction of two different conductors when it is exposed to heat (Seebeck effect)

Infra-red temperature readers

• Principles: Heat radiation in the human temperature range is emitted as IR radiation with a wavelength of 10 - 12 μm, and this can be filtered and used to generate a current in a thermocouple

Sullivan, Gavin, and Matthew Spencer. "Heat and temperature." BJA education 22.9 (2022): 350.

Childs, Charmaine. "Body temperature and clinical thermometry." Handbook of clinical neurology 157 (2018): 467-482.

Kenny, Glen P., and Ollie Jay. "Thermometry, calorimetry, and mean body temperature during heat stress." Comprehensive Physiology 3.4 (2011): 1689-1719.

Commission for Thermal Physiology of the International Union of Physiological Sciences: Glossary of terms for thermal physiology, 3rd ed. Japn J Physiol 2001; 51:245-280

Kenny, Glen P., Sean R. Notley, and Daniel Gagnon. "Direct calorimetry: a brief historical review of its use in the study of human metabolism and thermoregulation." European journal of applied physiology 117 (2017): 1765-1785.