STANDARDISATION RULES (Jf- Ulh. A I /UL 



RISB OF TEMPERATURE. 



(I) MEASUREMENT OP TEUPERATl 



(A) METHODS. 



361 There are two methods in common use for determining the hse tn tern- 

 per.* by thermometer, and (2) by increase in resistance of 



an r! 

 262 .Mowing precautions should be obecnred 



in the u*c of thermometer*: 

 - < rmometers indicating the room temper- 



hou tn thermal r . heated bodies, or 



>porary fluctuations of temper- 

 be used. In using the thermometer 



by applying it i<> a heated part, care should be taken so to prote 

 as t radiation (rum it. and. at the tame lime, not to interfere 



mal radia the part to which it is applied. 



264 icrmometer : . applied to the free surface of a ma- 



.at the bulb of the thermometer should be covered 

 A convenient pad may be formed of cotton 



waste in a shullo box about one and a half inches in diameter. 



ugh a .slot in the !- tn which the thermometer bulb is inserted 

 the thermometer tend;> .in the n .1 



heat from the surface to which the thermometer is applied. 

 266 The resistance may be measured 



louble bridge, 

 method. If a 



ist be as pper may be 



takei "i. 00394 per deg. cei at 20 deg. cent., or 0.00438 



:i and at holds for average com- 



:t the 1-05. 



coefficient should 

 be taken, ai explanation and discussion of the temperature 



The rise may be i 1) by dividing the 



per cent increase e coefficient for the 



-. it ure expressed in per cer. 



resistance :iperature 



legrees cent., and then dividing ihe pmdt: 



d absolute zero temperature of resistance " and is given in the last 

 :rnn of the table in Appen -r average commercial a**t*lt4 



copper S). 



266 .;.' COMPARISON or METHODS. In electrical conductors, the rise of tem- 

 perature should be determined by t: ise of resistance where prac- 

 ticable. Temperature elevations measured in this way are usually in ex- 

 cess of temp* :evations measured by thermometers. In very low 

 resistance circuits, thermometer measurements are frequently more relt- 

 abl< isurements by the resistance method. Where a thermometer 

 applied to a coil or winding, indicates a hjher temperature ele-. 



t> that shown by resistance measurement, the thermon .ilion 



should be accepted. 



(B) NORMAL CONDITIONS FOR TESTS. 



267 1. DURATION OP TESTS. The temperature should be measured after a 

 run of sufficient duration for the apparatus to reach a practically constant 

 temperature. This is usually from 6 to 18 hours, according to the wie and 

 construction of the apparatus It is permissible, however, to shorten the 

 time of the lest by running a lesser time on an overload in current and 

 voltage, then reducing the load to normal, and maintaining it thus until 

 the temperature has become constant. 



268 2. ROOM TEMPERATURE. The rise of temperature should be referred to 

 the standard condition of a room temperature of 25 deg. cent. 



269 TEMPERATURE CORRECTION. If the room temperature during the teat 



