A Handbook of Electrical TestingE. & F. N. Spon, 1876 - 204 páginas |
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ance angle battery whose resistance C₁ cable cells charged condenser compensating resistance conductivity resistance connected copper core deflection obtained deflection of 300 determine discharge deflection discharge key E₁ earth ebonite electricity electro electromotive force emery paper enable equal equation equilibrium error example farad farther end fibre formula galva galvano galvanometer needle galvanometer whose resistance increase instrument insulation resistance joined joint known resistance left-hand key loop test magnetic needle megohms meter microfarads mirror multiplying necessary noted ohms a deflection placed plano-convex lens plugs pole potential proportional R+r+G R₁ R₂ removed resistance box resistance coils resistance G reversing key S₁ sensitiveness ship shown by Fig shunt is inserted spot of light strength of current suppose t₁ taken tangent galvanometer tangent scale temperature terminals tion total resistance v₁ vanometer WHEATSTONE BRIDGE wire zinc current دو وو
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Página 82 - The mirror is placed in the axle of a coil of wire, some four or five inches across, which completely surrounds it, so that the needle is always under the influence of the coil at whatever angle it is deflected to. A beam of light from a lamp placed behind a screen about three feet distant from the coil falls on the little mirror, the bottom of which is slightly in advance of the top, and is reflected back on to a graduated scale placed just above the point where the beam of light emerges from the...
Página 12 - ... the coils becomes less and less, until at length a point is attained at which the needle remains parallel with the coil. When this point is reached the influence of the earth's magnetism exactly balances the deflective force of the current. The strength of the current that produces the deflection will then be directly proportional to the sine of the angle through which the coil is turned. The...
Página 147 - Fahrenheit, and the resistance be increased a certain amount by a rise of one degree in temperature, it will be increased by the next degree of rise at the same rate per cent., calculated on the original resistance, plus the amount increased by the first degree of rise.
Página 88 - ... made is at all damp. Sometimes little ebonite cups are provided for the levelling screws of the instrument to stand in, which answers the purpose of insulating very thoroughly. The instrument should be set up on a very firm table in a basement story.
Página 14 - When wound, the bob bins are saturated in hot paruffine wax, which thoroughly preserves their insulation, ahJ prevents the silk covering from becoming damp, which would have the effect of partially short-circuiting the coils and thereby reducing their resistance. The small resistances are made of thick wire, the higher ones of thin wire to economise space When bulk and weight are of no consequence, it is better to have all the coils made of thick wire, more especially if high battery power is used...
Página 2 - This test, although exceedingly simple, is a very good and accurate one if a little ordinary care be taken in making it. Its correctness is only limited by the sensibility of the galvanometer to small changes of strength in the current affecting it...
Página 7 - ... resistance of telegraph lines, the standard resistance p being usually 1000 ohms. When the insulation resistances of several lines are to be measured, the constant would first be taken and worked out, and the several lines to be measured being inserted one after the other in the place of the resistance p, the deflections are noted ; and the constant being divided by the several deflections, the resistances are thus obtained.
Página 38 - In making this test practically, having made the connections as shown by the figure, we should depress the left-hand key, and then, according to the example, we should take out the two 100 plugs between A and C, and proceed to adjust between D and E. This being done, we should replace one of the 100...
Página 1 - Testing, that it is unnecessary to dwell upon them here ; without, therefore, staying to discuss their meaning, we will at once proceed to examine the theory of the simplest method of measuring a resistance. Suppose a battery of a resistance r, and electromotive force E, a galvanometer of a resistance G, and a wire of a resistance E, be " joined up
Página 10 - FIG. 2. rule, sufficiently accurate for all practical purposes. Greater accuracy may, however, be obtained with but little extra trouble by allowing for the resistance of our battery and galvanometer in the following manner : Instead of multiplying the constant deflection by the...