Application of statistics to surety of contact make

Abstract

We shall distinguish between two distinct types of contacts or, say, relays; and shall call them macro- and micro-relays, or macro- and micro-contacts respectively. Macro-relays use contact loads of several up to more than 100 grams; micro-relays use loads of a fraction of one gram. Surety of contact make means surety to produce a relatively low contact resistance at make, in other words, to obtain metallic (or quasi-metallic) contact at contact make in relays. It is a commonplace that such a surety is higher the higher the load, thus higher with macro-than with micro-contacts. There are good reasons for this. First, the higher the load, the greater the ability of the contact to push away dust particles at make or to produce contact in adjacent points. Second, the resistance of contaminating films is inversely proportional to the film-covered contact area, see Eq. (3.04), while the constriction resistance varies inversely as the square root of the conducting area, see § 4. This makes the film resistance the more prevailing the smaller the contact area, i. e., the smaller the load, cf. Example at the end of § 7 A. Third, the higher the load, the larger the probability that plastic deformation will take place in portions of or in the entire contact area; such deformations lead to metallic contacts, cf. § 31 A.