Method of and apparatus for monitoring for incipient electrode failure in the Joule effect heating of heat softenable material

摘要

A method of anticipating electrode failure by monitoring the current, voltage and resistance between electrode pairs in a Joule effect heating system. A relatively rapid change in monitored resistance is an indication of an incipient failure. Alarm indicators, instruction print out, and/or process controls can be actuated in response to a given current voltage or resistance change. Plural electrode pairs are monitored by multiplexing to provide a repetitive cyclic scan of the parameters between pairs. Distortion of current and voltage values is minimized, where selective portions of regular power pulses are gated for control of heating, and complex waveforms result by employing true r.m.s. values of current and voltage developed in true r.m. s. to d.c. converters.