The temperature distribution of film resistors

The paper is in two parts. In the first part a rough calculation is made of the temperature distribution along the length of a rod, and it is shown that this is affected by the length of the terminal lead. A comparison is made between calculated and observed temperatures and there is good agreement. In the second part the temperature of a pyrolytic carbon film is calculated when subject to a rectangular pulse of energy, the range of pulse length being 0.1¿100¿s. From these calculations a rating is derived for a number of commercial types of resistor. It is shown that, if a limitation of 1000 V per inch of film is applied, this largely overrides any limitation based upon the instantaneous temperature rise of the film and this has to be taken into account only for pulse lengths greater than 10¿s and on resistances of the order of a few tens of an ohm.