Fluid heating control system

An improved system, method and apparatus for control of an instantaneous flow-through fluid heater system is disclosed. The control incorporates a logic control method providing modulation of power in small steps to a plurality of heating elements retaining responsiveness to closed-loop control need...

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Bibliographic Details
Main Authors EVERETT LOUIS J, SHARP DAVID PAUL, SEITZ DAVID E, HARMAN THOMAS LAMSON, NEUMANN RODNEY H
Format Patent
LanguageEnglish
Published 12.06.2001
Edition7
Subjects
BLASTING
CONTROLLING
ELECTRIC HEATING
ELECTRIC LIGHTING NOT OTHERWISE PROVIDED FOR
ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
ELECTRICITY
FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEATGENERATING MEANS, IN GENERAL
HEATING
LIGHTING
MECHANICAL ENGINEERING
PHYSICS
RANGES
REGULATING
SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
VENTILATING
WEAPONS
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Summary:An improved system, method and apparatus for control of an instantaneous flow-through fluid heater system is disclosed. The control incorporates a logic control method providing modulation of power in small steps to a plurality of heating elements retaining responsiveness to closed-loop control needs without inducing light flicker. Further, the life of the coils of heating circuit electromechanical relays are extended by energizing the coils with a pulse-width-modulated drive decreasing in duty cycle and thus the latent coil heat when an increase in mains voltage is sensed. The life of the contacts of same relays are extended by inhibiting heating element triac drive immediately upon sensing loss of relay coil power, such as by an over temperature limit switch opening, thus ensuring that relay contacts open with zero heating element current. In addition to the software "watchdog timer" internal to the microcontroller, a redundant fail-safe circuit external to the microcontroller prevents a program lockup condition from leaving any heating element triac or relay drive in an energized state. A combination of control hardware and program provide self-diagnostic detection of an inoperative thermistor, stuck relay, or a failed triac or heating element. An improved means of sensing water level is disclosed incorporating a low-level, high frequency signal, allowing detection of non-conducting distilled water and the reliable detection of water in the presence of main-frequency currents as would exist in ungrounded sheathed heating elements with electrical leakage or as would exist with bare-elements.
Bibliography:Application Number: US19990334337