Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Electrical signal parameter measurement system
Patent
1998-03-10
2000-11-21
Hoff, Marc S.
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Electrical signal parameter measurement system
702 64, 702 65, 361 7, 361 15, 315240, 324550, 324556, G01R 3100, H02H 700
Patent
active
061515604
ABSTRACT:
An open circuit failure monitoring apparatus for controlled electrical resistance heaters is disclosed. The heater failure monitoring apparatus allows controlled electrical resistance heaters to be continuously monitored for open circuit failures without applying an operational current flow through the heater, regardless of the operational status of the heater and without significant power consumption during periods when the heater is not operated. The failure monitoring apparatus includes a reactive current limiting element, such as a capacitor, and a current monitoring circuit. The capacitor is connected in parallel with the contact switch used to control line voltage applied to the resistive load. The reactance of the capacitor provides a small but continuous test current capable of being detected by the current sensing component, but not large enough to consume significant power. Current monitoring circuit includes a current to voltage (i/V) converter, an analog to digital (A/D) converter, a microprocessor, electrically erasable programmable read only memory (EEPROM), and an alarm circuit. The current monitoring circuit uses a microprocessor to continuously compare sampled test voltage values to reference voltage values stored in the EEPROM that have been prerecorded for both an active and inactive heater during normal operation (non-failure) conditions so as to determine the presence of a failure condition in the controlled heater.
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Bui Bryan
Crump R. Tracy
Hoff Marc S.
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