Figs. 2,556 and 2,557. Connections of Sangamo single phase induction meter. Fig. 2,556, 2 wire meter exceeding 100 amperes; fig. 2,557, 3 wire meter exceeding 100 amperes.
8. Frequency Adjustment.—This is often desirable, particularly for systems operating at 133 cycles. Most makes of meter are provided with means for changing the adjustment from 133 to 60 cycles in case of change in the system.
9. The Case and Cover.—These parts should be dust and bug proof, to avoid damage to the bearings, insulation and moving parts, and should of course be provided with means for sealing.
Terminal chambers so arranged that the cover of the meter element need not be removed in connecting up, are an important feature, particularly in meters that require no adjustment at installation, as they prevent entrance of dust into the main meter chamber.
A window through which the rotation of the disc can be observed in checking, should be provided for the same reason.
Fig. 2,558.—Faraday disc, or mercury motor ampere hour meter; view showing electric and magnetic circuits.
The Faraday Disc, or Mercury Motor Ampere Hour Meter.—On this type of meter the mercury motor consists essentially of a copper disc floated in mercury between the poles of a magnet and provided with leads to and from the mercury at diametrically opposite points. The theoretical relations of the various parts are shown in fig. 2,558.