Home >> Encyclopedia-britannica-volume-15-maryborough-mushet-steel >> Charles Mohun Mohun to Estimate Of Moliere >> Electric Meters

Electric Meters

meter, mercury, current, disc, read and arranged

METERS, ELECTRIC. These include induction-motor, mercury-motor and commutator meters, which register the revo lutions of a disc or other armature caused to revolve, by the action of the current, at a speed proportional to the amperes or watts passing through the meter, and electrolytic meters in which the current or a shunted fraction of it passes through an electro lyte and decomposes it. The rate of decomposition in the electro lyte is proportional to the amount of current passing through the meter.

Induction-motor Type.

In the Ferranti alternating current watt-hour meter, a series coil of a few turns of thick wire carry ing the main current is arranged below, and a shunt coil of many turns of fine wire is arranged above a horizontal rotary disc of aluminium. This disc is situated in the gap between the poles of a permanent magnet and the lower bearing of its vertical spindle is a sapphire carefully selected to reduce friction to a minimum. The magnetic fields due to the shunt and series windings produce a resultant rotating or shifting field which interacts with eddy currents, induced io the disc so as to exert a driving torque propor tional to the watts. A retarding torque is produced by the action of the permanent magnet also causing the speed of the disc to be proportional to the watts. A worm on the spindle drives the registering train ; the registering dials are of the clock pattern, or of the cyclometer pattern.

To read the meter is a simple operation. In the clock pattern, starting from left to right, the figure last passed by the thousands pointer in its revolution is written down and the same procedure is followed for the hundreds, tens and units pointers in succession, the tenths registered on the small lower dial being read only when testing the meter. In the cyclometer pattern, the figures are written down just as they appear on the register. The cyclometer figure wheels are actuated by a falling weight ; thus, the changing of the figure wheels does not throw any extra load on the meter.

Mercury-motor Meters.

In the Chamberlain and Hookham direct current ampere-hour meter, a copper disc is caused, by the action of the current, to rotate in a mercury chamber subject to the influence of a magnetic field due to a large permanent mag net. The vertical spindle of the disc, arranged to rotate with the minimum friction, is connected to the registering train with its series of clock dials. The peripheral wall of the mercury chamber is formed by a leather-lined metal band which is readily removable to permit inspection and refilling with mercury.

Commutator Meters.

.Commutator meters have a wound armature connected in parallel with a shunt and arranged to ro tate in the field of a permanent magnet.

Electrolytic Meters.

In the Reason syphon-tube meter, a solution of a mercury salt is hermetically sealed in a container, at the top of which are arranged a mercury anode and a cathode. During the operation of the meter, mercury is liberated at the cathode and collects in a syphon tube in the container; this tube, when full of mercury, discharges into the lower part of the con tainer. Close to the right limb of the syphon tube is a vertical scale which registers the mercury level ; in one form of the meter, this scale reads from o to Zoo units. Below the scale is another which registers the level of the lower mercury column; this scale may read from o to 4,00o units. When reading the meter, both scales are read and the sum of the readings is taken. The Reason single-tube meter has one vertical mercury tube, which is read like a thermometer. In both forms, the mercury can be used repeatedly, the meters being re-set by tilting; the container is flexibly mounted to facilitate this operation.

In the Bastian electrolytic meter, acidulated water is decom posed by the action of the current, and the amount of water de composed is read off on a vertical scale. (T. E. L.)