. The London, Edinburgh and Dublin philosophical magazine and journal of science. ux Nwill be such that V = rA + mN, (1) where r is the resistance of the coil and A the currenttraversing it. If the coil and electromagnet be so designedthat for currents of the frequencies used the resistance isnegligible in comparison with the impedance, we can neglectthe term rA. It follows that the rate of change of N will beat each instant a measure of V, and this will be true what-ever the permeability or hysteresis of the core. We thushave a magnet whose strength is accurately determined bythe applied volt
. The London, Edinburgh and Dublin philosophical magazine and journal of science. ux Nwill be such that V = rA + mN, (1) where r is the resistance of the coil and A the currenttraversing it. If the coil and electromagnet be so designedthat for currents of the frequencies used the resistance isnegligible in comparison with the impedance, we can neglectthe term rA. It follows that the rate of change of N will beat each instant a measure of V, and this will be true what-ever the permeability or hysteresis of the core. We thushave a magnet whose strength is accurately determined bythe applied voltage whatever the physical properties of thecore. Such an electromagnet can easily be made verystrong. Moreover, the shorter the air-gap between the polesis made, the denser is the magnetic flux due to a givencurrent, and the greater is the ratio of impedance to resist-ance for a given winding. Thus the stronger the electro-magnet is made by improving its magnetic circuit, the moreaccurate it becomes, provided this electromagnet is excitedby the voltage of the circuit. Fiff. The instrument here described has a laminated electro-magnet formed, of stampings shaped like figure 1. These * Proc. Roy. Soc. vol. lxxx. (1908), Alternate Current Measurement, Galvanometer for Alternate Current Circuits. 311 stampings are of two kinds—a rectangular portion with twostraight limbs, a, b, forming the core of the electromagnet, an Ia specially shaped stamping, p, between the poles. Thestamping, p, is separated from the magnet limbs on eachside by an air-gap. Each gap consists of two portions, anarrow part about 1 mm. across bounded by the straighte:lo-es of p, and a wider portion in which one of the verticalsides of the moving coil can turn round the curved edgesof p. The moving coil, of oO turns, is similar in shape,suspension, and mode of control to that of an ordinarypermanent magnet instrument. It has a central spindleindicated at s and working in a recess suitably stamped in p
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Keywords: ., bookcentury1800, bookdecade1840, booksubjectscience, bookyear1840
