. The Encyclopædia britannica; a dictionary of arts, sciences, literature and general information. ith tools after anneahng; also it should be preferablynot too elongated in shape so that it may not acquire permanentmagnetization but that its magnetic condition may follow thechanges of the current in the coil. If these conditions are notfulfilled sufficiently, the ammeter will not give the sime indica-tions for the same current if that current has been reached (a) byincreasing from a smaller current, or (b) by decreasing from alarger current. In this case there is said to be hysteresis in ther
. The Encyclopædia britannica; a dictionary of arts, sciences, literature and general information. ith tools after anneahng; also it should be preferablynot too elongated in shape so that it may not acquire permanentmagnetization but that its magnetic condition may follow thechanges of the current in the coil. If these conditions are notfulfilled sufficiently, the ammeter will not give the sime indica-tions for the same current if that current has been reached (a) byincreasing from a smaller current, or (b) by decreasing from alarger current. In this case there is said to be hysteresis in thereadings. Although therefore most simple and cheap lo construct,such soft-iron instruments are not well adapted for acrurate much better form of electromagnetic ammeter can be con-structed on a principle now extensively employed, which consistsin pivoting in the strong field of a permanent magnet a smallcoil through which a part of the current to be measured is an instrument is called a shunted movable coil ammeter,and is represented by a type of instrument shown in fig. 3. The. Fig. 3.—Shunted Movable Coil Ammeter, Isenthal & Co. construction of this instrument is as follows:—Within theinstrument is a horseshoe magnet having soft-iron pole piecesso arranged as to produce a uniform magnetic field. In thismagnetic field is pivoted a small circular or rectangular coilcarried in jewelled bearings, the current being passed into andout of the movable coil by fine flexible conductors. The coilcarries an index needle moving over a scale, and there is generallyan iron core in the interior of the coil but fixed and independentof it. The coil is so situated that, in its zero position when nocurrent is passing through it, the plane of the coil is parallel to thedirection of the hues of force of the field. When a current ispassed through the coil it rotates in the field and displaces theindex over the scale against the control of a spiral spring like thehairspring of a
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectencyclo, bookyear1910
