Meter and instrument jewels and pivots

With a view to obtaining a more fundamental knowledge of the phenomena relating to meter and instrument bearings and to improving such bearings, research has been carried out for a number of years on behalf of the Electrical Research Association at the Meter Testing Laboratories of The Northmet Power Company. This paper gives a brief survey of the various aspects covered by this research, dealing mainly with the sapphire/steel combination, both dry and lubricated, but also includes other combinations of materials. The apparatus and methods of test are outlined, followed by a survey of the results from life tests, including an analysis of the various factors which contribute to wear. The results of a microscopical examination of the units at the end of their life run are discussed. A brief theory of the boundary lubrication existing in such bearings is given, with a short extract of the detailed discussion of the various factors disclosed in E.R.A. Reports T/T31 and T/T39. Mathematical formulae developed during the research have been simplified into nomograms. The results of experiments on the resistance of sapphire jewels to impact forces are given. The phenomena associated with bottom bearings at various loads, caused by parasitic forces existing in meters, are also dealt with. The actions of the ball-type bearing and that of the pivot bearing are compared, and an approximate estimation of the life of bearings in practice, based on life tests, is made.