Patent ID: 6151560
Filing Date: 2000-11-21
Classification: G01R,H02H

Abstract:
In a controlled electrical resistance heater system including, a resistance heater and a thermostat controller for controlling the operation of said heater and has a switching means for selectively switching between an open and closed condition to control a current flow through said heater thereby controlling the operation of said heater, a heater failure monitoring apparatus for continuously monitoring said heater without applying an operational current flow through said heater to indicate open circuit failures, said heater failure monitoring circuit comprising:means connectable in parallel with said switching means between said voltage source and said heater for limiting the current flow from said voltage source through said heater when said switch means is in said open condition, means connectable in series with said heater for continuously monitoring current flow through said heater to determine and indicate open circuit failure in said heater, said current monitoring means includesmeans for generating a first and second initial reference values, said first reference value corresponding to the current flow through said heater when said switch means is in said closed condition and no open circuit failure condition is present, said second reference value corresponding to the current flow through said heater when said switch means is in said open condition and no open circuit failure condition is present,means for electrically storing said first and second reference values,means for continuously generating a test value corresponding to the present current flow through said heater,means responsive to said switch means and said test value generating means for comparing said test value to said first reference value when said switch means is in said closed condition and to said second reference value when said switch means is in said open condition, and for generating an output signal when said test value is less than said first or second reference values, andalarm means responsive to said output signal for indicating an open circuit failure condition in said heater.