Automatic control system for an electrode-type air humidifier

Abstract

An electric resistance humidifier which increases atmospheric humidity by boiling water in a tank. Spaced conductive plates, or electrodes, are fixed in the tank. As the tank water level rises, the immersed area of the electrodes increases. An electric supply causes the electrodes to pass electric current through the tank water therebetween for heating and vaporizing such water. Electric current and heating cease automatically when the tank water level falls below the electrodes. A control includes comparator circuitry responsive to a reference signal and a signal related to electrode current for actuating and deactuating a water supply to the tank. In one embodiment, the control includes further comparator circuitry responsive to electrode current and a further reference signal for controlling a tank drain, to compensate for rising conductivity of the tank water as it warms toward boil and thus prevent substantial overshoot in heating current flow. In one embodiment, humidity sensing circuitry varies the reference signal level, to increase the upper water level limit in the tank, and hence heating current flow and speed of vaporization, in response to decreasing atmospheric humidity, thereby to increase atmospheric humidity to a desired level. The aforementioned apparatus, if desired with a fan for distributing vapor boiled from the tank water, is housed in a cabinet. A manual adjustor for selecting a fixed reference or humidity level is conveniently located on a panel of the cabinet.