the invention relates to the conducting and to the monitoring , using an automatic machine , of the temperature rise of electrically heated components with which there is associated an identification chart comprising parameters which can be used for conducting and for monitoring this heating , the machine comprising apparatus for reading the chart and for initiating the determined heating program . according to the invention , the chart is divided into a number of zones into some of which are entered , in addition to the said parameters , additional data concerning some of them , the parameters and their associated data are read off using the said reading apparatus , and provision is made for at least some of these parameters to undergo conversions which are induced by some of the other associated zones as a function at least of the data which are contained therein . the invention applies particularly to the monitoring of welding together of plastic components .