Humboldt State University ® Department of Chemistry

Robert A. Paselk Scientific Instrument Museum

From : Kimball, Arthur Lalane, A College Text-Book of Physics, 3rd ed., H. Holt and Co., New York (1923) pp.473-4.
© Copyright 1998 R. Paselk

694. Ammeters. - An ammeter is some form of galvanometer or electrodynamometer graduated so that the current strength in ampéres may be directly read from the scale. A form of ammeter much used for direct currents is shown in figure 401. It consists of a sensitive moving-coil galvanometer in which the coil instead of being suspended is mounted in jeweled bearings and is held in equilibrium by two non-magnetic spiral springs which also serve as conductors for the current. The main current passes through a strip of metal (called a shunt) having very small resistance, only a minute portion of.the current passing through the delicate movable coil. But the current in the movable coil is always the same proportional part of the whole current, and therefore the scale over which the pointer moves may be so graduated as to show directly the number of ampéres in the total current. An instrument of this type has the advantage of having a very small resistance.

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Last modified 22 July 2000