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MEASUREMENT AND CONTROL 

 OF TEMPERATURE 



J. W. L. BEAMENT 



INTRODUCTION 



The measurement and control of temperature is a practical problem in 

 almost all biological work, although usually an adjunct to a particular 

 investigation. Electrical methods of control are virtually the only ones in 

 use — the most refined methods involve electronic control gear.' For many 

 purposes, electrical methods involving electronics offer very great advantages 

 in temperature measurement too, and for very accurate purposes are again 

 essential. This chapter starts with a basic summary of the essentials of heat, 

 temperature, etc., which is followed by a discussion of methods of measuring 

 temperature, together with practical details of the equipment; the third 

 section discusses the theory of methods of temperature control, and is 

 followed by examples of equipment layout for the principal biological 

 needs — the temperature controlled environment of air or of water. 



TEMPERATURE AND HEAT 



Energy transformation 



For all practical purposes, a current / passing through a resistance R 

 produces a quantity of heat, PR; current and resistance are readily con- 

 trolled quantities and since this heat is produced without gaseous by-products, 

 etc., electrical heating is the only one envisaged in biological work except 

 for such crude purposes as the heating of laboratories and greenhouses. 



Temperature 



Temperature is the thermal equivalent of electrical potential ; when two 

 bodies of different temperature are in contact, heat tends to flow from the 

 higher to the lower temperature; generally speaking the rate of transfer 

 is proportional to the temperature difference, regardless of size and the 

 'amount' of heat in the two. Without recourse to very complex methods, 

 such as are used in refrigeration processes, only a temperature difference 

 can promote such a passage of heat — a body can otherwise only be heated 

 by causing it to transduce another form of energy put into it into heat. 



Thermometry 



Many physical properties change in a reliable, repeatable and reversible 

 way with temperature changes; those which are amenable to accurate 

 mensuration are thus useful as indicators of temperature. A thermometer 

 displays the change produced by temperature change ; as we are not interested 



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