Relay Measuring Equipment

Visitors to the switching development areas in the Bell Telephone Laboratories are often surprised at the extensive amount of measuring equipment used to study so simple a device as the telephone relay. This is because, though the relay itself may be simple, the problems requiring study are extremely complex. Because relays are used in such large quantities, their characteristics affect the economy of the telephone switching system. Not only is their manufacturing cost important; their quality also affects the central office cost. For example, an efficient design lowers the central office power plant cost, and faster-acting relays enable fewer common control units to handle more traffic, which further reduces the cost. These and related objectives pose many complex technical problems involving mechanics, magnetics, kinetics, heating, and the like. The scope of relay analysis may be judged from the other articles in this issue. In every case there is need for measurement. Sometimes this quantitative work is needed to confirm an analytical relation, sometimes to learn more concerning (he basic phenomena, and often to characterize the performance of a test model. This article will describe some of the most-used measuring tools for the study of relays. Several kinds of measurements are required. In the first place, there are force measurements. Each relay must press the desired number of contacts together with a suitable force. To do this, a magnet must be provided which can move the springs, through whatever distance is required.