Abstract: Instead of monitoring a thermal deburring operation by reference to whether a certain high temperature is reached and thereby indicting whether a successful ignition in the deburring chamber has taken place at every step of operation of the chamber, a circuit responsive to the rate of change of temperature is used to recognize a successful operation, thus permitting faster operation of the apparatus. Such a circuit is also useful for rapid detection of a short circuit circuit in electrochemical apparatus utilizing heavy electrical currents and variable amounts. In the latter case a digital circuit for measuring the amount of change at equal intervals of time is particularly useful.