Abstract: An electrostatic air cleaner has at least one hole in one of the plates over which air with charged dirt particles is passed. A light source is mounted adjacent to the hole so as to direct its light through the hole. A light sensor detects the level of light passing through the hole. As dirt particles deposit on the plate, they fill in the hole over a period of time, reducing the amount of light passing through the hole. It is possible by measuring the amount of light passing through the hole, to determine the amount of dirt deposited on the plate. In a preferred embodiment, each of the plates contain a hole in alignment with each of the other plates' holes so that light from a single light source can pass through each of the holes. Such a configuration allows both the light source and the light sensor to be located outside of the entire group of plates.

Abstract: An electrical connector for an oxidized surface includes a plurality of spaced apart parallel connector legs integrally formed as extensions of a central connector spine. Each connector leg has a free standing integral barb projecting therefrom toward an adjacent one of the connector legs. A group of legs is arranged to straddle a metal plate having an oxidized surface with the pointed ends of the barbs having a separation less than the thickness of the plate to enable the barbs to scrape the oxide from the surface to establish electrical contact to the underlying metal layer. The connector, in turn, is made of phosphor bronze to enable a spring-loaded electrical contact to be made to the connector surface by providing a low resistance non-oxidizing contacting surface.

Abstract: The method for spacing the folds of a folded filter media assembly includes the steps of separating the folds of the filter media by the use of the tapered assembly comb having uniformly spaced teeth and subsequently inserting a rigid divider into the separated and spaced media folds to produce a uniformly spaced filter media. The comb can be discarded after the divider is inserted, and, accordingly, the comb is made of an inexpensive material having a desired degree of rigidity for handling, e.g., cardboard. The uniformly spaced filter media assembly is inserted into an operative position for filtering, e.g., as an air filter.

Abstract: A battery holder for a control device is integral with the base of the control device and has a first support member with battery connections and a second support member which is made up of a L-shaped lever comprising a portion of the base. The second support member is flexible whereby the battery can be placed between the first and second support members and a force moving the battery toward the connection means by the second support member will connect the battery to the connection. The battery can be removed from the battery holder by lifting the second support member. Adjacent support members which are hooked to hold the battery in place are flexible to move away from the battery when the battery is lifted to be in a position so that the battery can then be manually pulled out of the battery holder and disconnected from the battery connection means.