Foam, drain and fill control system for humidifier

Abstract

The control system for a humidifier, which is part of a heat, ventilation or air conditioning HVAC system, detects the level of water and generates control signals by detecting the capacitance of the water in the humidifier. These control signals are used to fill the humidifier with water and control heater elements and, to some degree, drain cycles. A capacitor is utilized to detect the change in capacitance as the water level changes. The control circuit, coupled to the capacitor, generates fill control signals based upon first and second predetermined capacitive levels. In one embodiment, the capacitor sensor includes an electrically conductive element extending into the water as a first electrode which is shielded by an insulating cover, where the water acts as a medium through which capacitance is measured and the humidifier casing or another electrically conductive element in the water functions as the second electrode for the capacitor. Further refinements of the control system include a converter which converts the capacitive value of the capacitor into a frequency signal and a microprocessor which monitors that frequency signal to determine the capacitive level and hence the water level. Increasingly higher frequencies represent increasingly lower water levels. In an enhanced version, the control system further includes an electrically conductive sensor mounted in an interior top region of the humidifier for detecting the presence of foam thereat. When the capacitive sensor detects normal water levels and the conductive sensor mounted above normal water level detects foam, the microprocessor triggers corrective action. Corrective action consists of turning OFF power to the heater elements and initialing a drain cycle to clean out the critical level of impurities which created the foam. In another enhancement, the control system is configured as an adaptive feedback drain control system.