US1611089A - Adjustment of magnetic tachometers - Google Patents

Description

Dec. 14,1926. 1,611,089

c. T. WALLIS ADJUSTMENT OF MAGNETIC TACHOMETEHS Filed Sept.` 24, 1923 Fung. Il.,

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UNITED STATES PATENT OFFICE.

CYRIL T. WALLIS, OF ROCHESTER, NEW YORK, ASSIGNOR TO NORTH EAST ELECTRIC COMPANY, OF ROCHESTER, NEW YORK. A CORPORATION OF NEW YORK.

ADJUSTMENT OF MAGNETIC TACHOMETERS.

Application filed September 24, 192B. Serial No. 664,517.

This invention relates to the adjustment of tachometers of the magnetic type, in which a magnetic field, produced by a permanent magnet, is effective on an indicator by reason of eddy currents therein resulting trom relat-ive movement of the field and the indicator.

In instruments of the type in .question the correctness of the indications depends,

among other factors, upon the strength ot' the magnetic field, and accordingly it has been customary to provide, in the construction of such instruments, some means for varying this strength, either by shunting a 5 variable portion of the magnetic lines of torce or by changing the relative positions of the parts, so that the instrument may be calibrated or adjusted whenever necessary.

The object ot the present invention is to 3" simplify the construction and the adjustment of magnetic tachometers by eliminating the necessity oi the provision and the use of the adjusting means just referred to. To this end I have devised a method, and means for practising it, by which necessary changes in the strength ot the magnetic iield of such an instrument may be made by changing the density of magnetization of the permanent magnet, and whereby this may be accomplished by means external to the instrument, while the instrument is in operation.

In the accompanying drawings Fig. 1 is a partly diagrammatic front-elevation of apparatus embodying the present invention, together with a magnetic tachometer in position to be adjusted; and Fig. 2 is a sec- -tional side-elevation showing the relative position of the tachometer and of the electromagnet of the apparatus. In the apparatus illustrated in the drawings the tachometer 5, which is to be calibrated, is of the type commonly used on motor-vehicles and described as a speedometer. It is mounted on a supporting plate 6, which also carries a master speedometer or tachometer 7 of any preferred type. The two instruments are driven by flexible shafts enclosed in the usual tubular casings 8 and 9, and the two shafts are i 5") connected, through gears 10, with a pinion 11 which is fixed on the shaft of an electric motor 12.

The motor is arranged to be driven at variable speed, and for this purpose it is connected, with a suitable source 13 of electricity, through a rheostatlt.

The adjustment of the speedometer is effected through the instrumentality of an electromagnet comprising two parallel cores 15 provided with windings 16 and connected and supported by a yoke-plate 17. This yoke-plate is Vpivoted between arms 18 at the upper end of a column 19, so that the poles 20 of the magnet may be swung towards and from the front of the speedometer, and the arms 18 are also pivoted to the column for the purpose of adjustment. The pivots 34 connecting thesev several arts are provided with springs to cause frictional retention of the parts in any adjusted position.

. The electromagnet is arranged to be energized with variable strength and reversible polarity, for longer or shorter periods as required. For this purpose it is con nected with the source of electricity, 13, through wires 21 and 22, a rheostat 23, a circuit-closing key 24 and a pole-changing switch or commutator 25.

The method of adjustment is applicable to magnetic tachometers of various construction, but is illustrated as used in connection with an instrument having a ringshaped magnet 26 which is mounted in a non-magnetic cup 27 at the upper end of a rotary shaft 28. This magnet cooperates with an oscillatory indicator comprising outer and inner skirts or flanges 29 and 30, carried by an arm 31 which is fixed to a vertical pivot 32. The pivot is connected with a spring 33 by which the movement of the indicator is controlled. The operation' of the instrument need not be described herein, as it is of a well known type.

The speedometer may be calibrated either complete .or with the front glass and taceplate removed, but the latter method is preferable as it permits the electromagnet to be brought closer to the permanent magnet 26 of the instrument. j

With the parts in the position shown in the drawings, the operator starts the electric motor and adjusts its speed to cause the master speedometer to indicate some convenient speed of operation. If the speedometer to be calibrated is inaccurate it will give an indication diierent from that of the master. The operator then sets 'the rheostat 23 to minimum-current position, moves the commutator 25 to one position or the other, according as the strength of the magnet 26 is to be increased or diminished, and then taps the key 24 one or more times so as momentarily to energize the electromagnet. As the speedometer 5 is constantly running during this operation it at once gives an indication of any change which has been produced in its magnet. If the required'adjustment is not at once effected the operator continues -to tap the key 24, and at the same time moves the rheostat 23 gradually in the direction to increase the strengthof they current owing through the electromag'net, until the reading of the speedometer 5 indicates, by its coincidence with that of the master, that the required correction has been accomplished. j

If the effect at first produced happens t0 be in the Wrono' sense. or has been carried magnet'izing and demagnetizing ring-magnets disclosed in my application for Letters Patent of the United States tiled Oct.' 13, 1922, Serial N o. 594,415, since the eect of the electromagnet is to produce a magnetic field, of an intensity sufficient to overcome the coercive force of the speedometer magnet, thisield traversing a limited part of the length of the latter, and the rotation of the latter causing all parts of it to be successively passed through the i'eld. The invention is not limited to use with an instrument of this particular construction, however, since the electromagnet, by suitable modifications in'its size and strength,

and in the position in which it is applied to tbe tachometer, may be caused, in any case, to produce a eld eflectivc upon the permanent magnet of the instrument and of suiicient intensity ,to overcome the coercive force of the permanent magnet.

The invention claimed is:

1; Apparatus, for adjusting a magnetic tachometer,` comprising, in combination, means for supporting a 'tachometer; means for actuating the tachometer at different known speeds; means for simultaneously4 producing a magnetic field operative upon the magnet of the tachometer with a strength sullicientto overcome the coercive force of the magnet; and means-for varying the eiectiveness of the field according to the indications of the tachometer.

2. Apparatus, for adjusting a magnetic tachometer, comprising, in combination, means for supporting a tachometer; means for actuating the tachometer at a known' speed; an electromagnet; means for support# ing the electromagnet with its cles in proximity to the magnet of the tac iometer; and a rheostat and a commutator connected with the electromagnet. v j

Apparatus, for adjusting a magnetic tachometer, comprising, in combination, a speed-indicator; an electric motor; drivingconnections through which thev motor may drive the speed-indicator and the tachometer simultaneously; means for varying the speed of the motor; an electromagnet; means; for supporting the magnet in a position such that its lield is effective upon the magnet ot the tachometer while the tachometer ie actuated by the motor; and means for controlling the energization of the electromagnet to control its eiect on the magnet of the tachometer.

CYRIL T. WALLIS.

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