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

Abstract

A method of detecting electrode displacement in an opaque melt of heat softenable material heated by Joule effect through said electrode by monitoring the current, voltage and electrical displacement characteristics of a body of heat softenable material and the electrodes. A relatively rapid change in monitored resistance is an indication of and often characteristic of given changes in the geometric relationships between an electrode the heat softenable material and other electrodes which can accelerate the failure of a system if corrective action is not taken. Alarm indicators, instruction print out, and/or process controls can be actuated in response to a given current voltage or resistance change. Slumping of electrodes and the direction of the slumping is indicated by the nature and magnitude of changes detected on a long term basis at least of the order of days in length. Plural electrodes and 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. An approximation circuit for producing a d.c. voltage which is approximately proportional to the r.m.s. values of current and voltage resulting from phase controlled firing of controlled rectifiers into the electrode melt load.

Dependencies are inferred from the claim text.