AMPEREMETER, or Ammeter, an instrument for the measurement of electric currents in terms of the unit called the ampere.
In order to measure the value of a continuous electric current, and therefore to calibrate any amperemeter we proceed as follows: The amperemeter is placed in series with a suitable low resistance strip, say of 0.01 ohm.
An observation is then taken of the reading of the amperemeter and of the fall of resistance down the low resistance when a certain steady current is passing through the strip and amperemeter.
If then the amperemeter scale reading was 100 it would show an error of that scale reading of minus 1.9 amperes or nearly 2%.
The principles of telegraphy (land, submarine and wireless) and of telephony are discussed in the articles Telegraph and Telephone, and various electrical instruments are treated in separate articles such as Amperemeter; Electrometer; Galvanometer; Voltmeter; Wheatstone'S Bridge; Potentiometer; Meter, Electric; Electrophorus; Leyden Jar; &C.
His ampere-balances, voltmeters and electrometers, and double bridge, are elsewhere described in detail (see Amperemeter; Electrometer, and Wheatstone'S Bridge).