Automatically adjustable weir and environmentally protected sensor

Abstract

A liquid level sensor for occluded water is provided to detect the surface water level as in a spray booth tank. The water level sensor may control the water level in the tank or it may be used to maintain a relatively constant outflow of water from the tank through a vertically movable weir. The weir is moved in response to changes in the liquid level detected by the sensor which includes an electronic signal sensor capable of detecting a level of a liquid relative thereto. The sensor is mounted in an elongated housing that has its lower end disposed in the liquid in the reservoir. The upper end of the housing is vented to the atmosphere to equalize the pressure between the interior thereof and the atmosphere ambient the housing. A flexible diaphragm is secured to the housing so as to seal the open lower end, and a substantially pure test liquid is held within the housing isolated from the liquid in the reservoir. The flexible diaphragm constricts or expands in response to changing liquid levels in the reservoir so that the level of the test liquid stays substantially the same as that of the level of the liquid in the reservoir. The electronic sensor measures the position of the test liquid and sends an appropriate signal to a control system that actuates the weir to raise or lower it in response to changing liquid levels in the reservoir.