US2052434A - Electrical instrument - Google Patents

Description

Aug. 25, 1-936. s. WILSON ET AL 5 ,4

ELECTRI CAL INSTRUMENT Filed Aug. 2, 1955- lnverwtorfs;

Porn SWils rT, Richard GJ'ewel l,

The ir Attorney.

Patented Aug. 25, 1936 UNITED. STATE anac'mrcar. msrmmmn'r Myron S. Wilson and Richard G. Jewell, Lynn, Mass, assignors to General Electric Company, a corporation of New York Application August 2 3 Claims.

Our invention relates to current-responsive devices and concerns particularly instruments of the type used for tuning purposes in vacuum tube radio receivers. The principal object of our inventionis to provide a simple, inexpensive, rugged,

easily manufactured, and easily used arrangement for varying the sensitivity of a currentresponsive instrument or its deflection for any predetermined current.

Other'and further objects and become apparent as the description proceeds.

For the purpose of indicating when a radio receiver is in tune, tuning instruments of the shadow type have been employed. in which a broader shadow is produced when the radio receiver is out of tune and a narrower shadow is produced when the instrument is in tune or vice versa according to the arrangement of the instrument and the type of radio receiver. The variations in breadth of the shadowband are produced by deflection of a current responsive instrument carrying a shutter co -operating with a light source and a screen. The instrument is, of course, connected in a suitable portion of the circuit of the radio receiver.

Since the tuning is usually accomplished by adjusting the frequency dial of the receiver until either aminimum or maximum breadth of shadow band is obtained as the case may be, great pre-q cision of calibration of the tuning instrument is not required. Nevertheless, it is obviously desirable that the instrument be designed to produce approximately the maximum deflection in response to the maximum change of current produced by manipulation of the receiver dials and the picking up of various strong and weak radio stations. It has been found, however, that the presence of strong local transmitting stations in the vicinity of a receiver or other local conditions may so alter the current conditions therein that adifferent deflection .is obtained with the same piece of receiving apparatus installed in one location than with it installed in another location .although other conditions may be similar. It is, therefore, desirable to utilize a tuning meter havingmeans for adjusting its sensitivity in order to cause it to produce its maximum deflection in response to the maximum variation in current which may be encountered with the radio receiver in a particular location.

In carrying out our invention in its preferred form, we utilize a moving vane stationary coil type of instrument having a pair of C-shaped permanent magnets adjacent and substantially coaxial with the coil. One of the magnets is roadvantag es will- 1935, Serial No. 34.395

tatable about its axis to permit adjustment of the combined effect of the two magnets in oppos- 'ing the effect on the movable vane of current flowing in the coil.

The features of our invention which are be- 5 lieved to be noveland patentable will be pointed out in the claims appended hereto. A better understanding of our invention may be obtained by referring to the following description; taken in connection with the accompanying drawing in 10 which Fig. 1 is a side elevation mostly in section of a shadowtuning meter representing one embodiment of our invention; Fig. 2 is a perspective view of the instrument mechanism shown within the apparatus of Fig. l but with-the ad- 15 justing unit shown separated from the remainder of the instrument mechanism for the sake of clarity; Fig. 3 is an exploded view in perspective of the adjusting unit of Fig. 2; Fig. 4 is'an exploded view in perspective of the remainder of the apparatus of Fig. 2; and Fig. 5 is a schematic diagram in perspective showing the manner of operational the apparatus of Fig. 1, but representing the elements drawn apart for the sake of clarity.

In the drawing, like reference characters are utilized to designate like parts throughout. In the embodiment of our invention illustrated, a light-shielding case II is provided having a translucent screen I! at one end thereof and an opening it at the other end thereof opposite which an incandescent lamp it is mounted. An instrument mechanism I5 is mounted within thecasing ii and has a movable magnetic vane l6 carrying a shutter ll cooperating with the lamp it to throw a shadow band It on the screen I! varying in breadth. according'to the deflection of the vane i6.

'A current-conducting coil is is provided to produce deflection of the vane l8 and a C-shaped control magnet 20 is provided to bias the vane it to the position shown in the drawing in a plane perpendicular to the axis of the coil l9. An adjusting magnet 2! is placed flat against the control magnet 20 and is rotatably mounted to permit variation in the relative positions of the poles of the two magnets and modification of the influence exerted upon the movable vanes it.

The mechanical construction and the manner of assembling the parts will be apparent from Figs. 3 and 4. A plate 22, which may conveniently be of insulating material, serves both as one wall of the casing II and as a base for the instrument mechanism ii. A brass shell 23 carrying the mechanism l5 is-provided having projections 24 registering with openings 25 in the plate 22. The projections 24 are bent over as shown in Fig. 1 to fasten the shell 23 to the plate 22. A rim 26 of greater diameter than the rest of the shell 23 is provided and the C-shaped control magnet 20 fits over the shell 23 and against the shoulder formed by the rim 26. A washer 21, preferably of insulating material, having leadsupporting ears 28 is provided to form with the shell 23 and the base plate 22 a spool for confining the turns of the coil l9. It will be understood that the magnet 20, and the washer 21, are mounted upon the shell 23 before it is fastened to the plate 22. The coil l9 may be wound upon the spool thus formed. A brass shell 29 having a slit 30 therein its full length is slidably mounted within the shell 23. Indentations 3| are provided in the shell 29 to engage pivots 32 formed in the vane I6, thus providing a pivotal mounting for the vane IS.

The adjusting magnet 2| is bound between two nonmagnetic rings 33 and 34 to form a rotatable adjusting unit 35. The ring 33 may be composed, for example, of resin-impregnated fibre and is provided with a toothed or roughened edge 36 to form a thumb wheel for rotating the adjusting unit 35. The ring 34 may be of brass, for example, and is provided with fingers 31 which may be bent around the fibre ring 33 to bind the parts together. The ring 34 may be upset at 38 to lock with the air gap 39 of the adjusting magnet 2|. The internal diameter of the adjusting unit is such that the unit 35 fits loosely on the rim 26 of the shell 23 and projections 40 are provided which may be bent over, as shown in Fig. 1, to hold the adjusting unit 36 in place axially and to hold it in a given angular position by friction. An opening 4| is left in the casing ll, through which the toothed edge 36 of the thumb wheel 33' is permitted to project.

It will be apparent that the lamp M will illuminate the screen l2. The shutter 1, however, will cast a shadow l8 upon the screen |2, dependent in breadth upon its angular position. Current flowing through the coil l9 will tend to deflect the vane I6, whereas the control magnet 20 tends to bias the vane |6 to a posi tion parallel to a line joining the centers of the poles 44 and 45 of the magnet 20. When the adjusting magnet 2| is in the position with the open part of the Cor the air gap 39 down and adjacent the air gap 46 between the poles of the contact magnet 20, the adjusting magnet 2| will tend to re-enforce the deflection-restraining effect of the magnet 20. However, whenthe magnet 2| is rotated away from that position (see Fig. 5), its magnetomotive force will tend to oppose that of the magnet 20 and the vane l6 will be permitted to deflect a greater amount in response to a given current in the coil I9. Further rotation of the adjusting magnet 2| will increase the eifect on the instrument deflection. We have found a satisfactory range 01' adjustment to be obtained by rotating the magnet 2| between 0 and 90 degrees away from the position where the two air gaps 39 and 46 register.

In accordance with the provisions of the patent statutes, we have described the principle of operation of our invention together with the apparatus which we now consider to represent the best embodiment thereof, but we desire to have it understood that the apparatus shown is only illustrative and that the invention may be carried out by other means.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. An adjustable radio-tuning instrument comprising in combination, a stationary current-conducting coil, a vane of mag'netizable material mounted pivotally with a pivot axis substantially intersecting and perpendicular to the axis of said coil, a C-shaped control magnet mounted in proximity to said coil and substantially coaxial therewith, a Cshaped adjusting magnet mounted in proximity to and substantia ly coaxial with said control magnet and rotatable about its axis, and means for varying the angular position of the adjusting magnet with respect to the control magnet to bring the open portions of the 0's into or out of registry and varying the sensitivity of the instrument.

2. An adjustable radio-tuning instrument comprising in combination, a stationary current-conducting coil, a vane 01 magnetizable material mounted pivotally with a pivot axis transverse to the axis of said coil, a control magnet mounted with pole portions on either side of the pivot axis of said vane with itsfield or influence including said vane, a movably mounted adjusting magnet having pole portions, and means for varying the position of said adjusting magnet between a position with its pole portions on either side of the pivot axis of said vane with its field of influence including said vane and positions with both pole portions at one side of said pivot axis.

3. An adjustable current-responsive instrument comprising in combination, a current-conducting coil, 9. vane of magnetic material mounted on a pivot axis transverse the axis oi! said coil, 9. cshaped control magnet with an air gap cut by a plane through the axis of said coil and the pivot axis of said vane, a C-shaped adjusting magnet adjacent said control magnet and mounted rotatably around the axis of said magnets, and means for varying the rotary position of said adjusting magnet.

MYRON 8. WILSON. RICHARD G. JEWELL.

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