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163

becomes appreciable at very low power factors. This consists of an additional coil with self-induction equal to that of the voltage circuit of the instrument—5'7 millihenry—which can be put in circuit by a switch without altering the resistance.

By subtracting the difference in the reading thereby caused from the original reading, the instrumental error from this cause is eliminated.

The instrument shown has 10 circuits, each carrying 10 amperes. It is made in other forms for 1 ampere and 0’1 ampere, and also with insulation for operation at 10,000 volts. The Duddell-Mather sub-divided gauze resistance box, with negligible inductance and capacity, is constructed of resistance wire, silk-covered and woven with silk threads into a continuous fabric about 20 cm, wide, and of any length, according to the resistance required. It is then mounted on insulators, and connections brought out to terminals, as required. (Fig. 24).

FIG. 24.

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—7'

This example shown is arranged for use with the wattmeter, and has resistances suitable for 125 and 250 volts, which will carry 0’01 and 0’1 ampere, and an additional coil of 5’7 millihenry for use, as mentioned above, in obtaining the correction for the inductance of the voltage coil of the wattmeter. . These instruments have been constructed with oil insulation foi pressures up to 25,000 volts.

L 2

Le texte affiché peut comporter un certain nombre d'erreurs. En effet, le mode texte de ce document a été généré de façon automatique par un programme de reconnaissance optique de caractères (OCR). Le taux de reconnaissance estimé pour cette page est de 99,19 %.

La langue de reconnaissance de l'OCR est l'Anglais.