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The main advantage of ammeters of this class is that heavy cable connections do not require to be carried to the instrument. The current to be measured is passed through a shunt, and a pair of flexible wires connect the potential terminals of the shunt to the instrument terminals.

The moving parts of the voltmeters are constructed on the same principle as the ammeters. The resistance wire has a negligible temperature coefficient and the instruments possess a high degree of accuracy.

(2) " Kelvin ” Cell Tester, for testing the voltage of each cell in a battery. It is provided with a flexible and spike for connecting to the accumulator.

(3) " Kelvin" Portable Paralleling Voltmeter.—To enable paralleling of two or more machines to be accomplished with the least possible chance of producing alteration in the voltage. It is so constructed that when the bus bar voltage is equal to the dynamo voltage, the pointer of the instrument comes to zero. In practice it is usual to close one switch of the dynamo circuit, and to place the instrument across the terminals of the remaining switch, which is closed when the instrument indicates zero.

(4) “ Kelvin” Ampere Gauges are suitable for either direct or alternating circuits. The solenoid carries the whole current and produces a very intense and uniform field; and a dash pot is provided to render the instrument dead-beat.

(5) " Kelvin ” S.R. Recorders are constructed on the moving coil principle. A broad chart is employed which enables accurate readings to be taken. A 25 hour recording clock is fitted, and is so designed that the removal of the drum to put on a new chart, winds it up. It is thus impossible to forget, to wind the clock. A release gear prevents over winding.

(6) " Kelvin ” Continuous Chart Recorder.—A S.R. recorder is also shown fitted with a clock to give a continuous record on a chart for one week.

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