Meter, Chemical Electric.
A current meter in which the current is determined by the amount of
chemical decomposition which it can effect. In the Edison meter the
solution is one of zinc sulphate. Two electrodes of zinc are immersed in
it, and a fractional part of the current is passed through it. The gain
in weight of one electrode and the loss in the other are proportional to
the current. Both electrodes are weighed periodically, one acting as
check upon the other.
Meter, Current.
An instrument for measuring the quantity of electricity in current form
supplied to consumers. It may be of various types. The general principle
involved is that in commercial installations for incandescent light and
power supply a fixed potential is usually maintained, the multiple arc
system being employed. Hence all that is requisite is to measure the
coulombs or the ampere-hours to know what quantity of energy has been
supplied.
Meter, Electro-magnetic.
A current meter in which the current is measured by its electro-magnetic
effects.
Meter-millimeter.
A unit of resistance. (See Resistance, Meter-millimeter.)
Meter, Thermal Electric.
A current meter in which the current is measured by the heat it imparts
to a conductor. In one meter a very light helix of mica is poised
horizontally over a conductor, and the whole is enclosed in a case. As
the wire is heated it causes an ascending current of air which rotates
the vane, and the latter moves delicate clockwork which moves indicating
hands. The hotter the wire the more rapidly the air ascends, and
consequently the speed of the vane is proportional to the current,
because the heat of the conductor is proportional thereto.
Meter, Time Electric.
An electric meter which measures the length of time during which current
is used. It assumes a constant current and potential. It is virtually a
clock, which is turned on when the current passes, and is turned off
with the current.
Meter, Watt.
A combined current and potential meter. It is constructed on the general
lines of a Siemens' Electro Dynamometer. If in it one coil is made of
coarse wire and is placed in series with the current conductor, and if
the other is wound with fine wire and is connected as a shunt from point
to point whose potential difference is to be determined, the instrument
becomes a watt meter.
Synonym--Energy Meter.
Methven Standard or Screen.
A standard of illuminating power. It is the light emitted by a
three-inch Argand gas flame through a rectangular aperture in a silver
plate carried by a screen. The aperture is of such size and so far
distant from the flame as to permit the passage of exactly two candles
illuminating power.