US2081233A

US2081233A - Galvanometer

Info

Publication number: US2081233A
Application number: US20923A
Authority: US
Inventors: Jr Harold Jansen Hasbrouck
Original assignee: United Research Corp
Current assignee: United Research Corp
Priority date: 1935-05-11
Filing date: 1935-05-11
Publication date: 1937-05-25
Anticipated expiration: 1954-05-25

Description

May 25;, 1937. H. J. HASBROUCK. JR I 3 GALVANOMETE R Filed May 11, 1935 mun lull!!! I INVENTOR- H.J. HASBPOUCK J12,

ATTORNEYS.

" Patented May 25, 1937 UNITED 1 STATES PATENT OFFICE GALVANOMETER H Application May 11, 1935, Serial No. 20,923

10 Claims.

This invention relates to sound recording apparatus and particularly to am element thereof employed for moving a light beam in accordance with the variations in sound to be recorded.

5 In the recording; of variable area sound tracks, that is, a sound track which varies transversely of the film, the usual method of varying the width in accordance with sound to be recorded is by an element known as a galvanometer. In brief this device comprises a pair .of conductors positioned in a magnetic field and current, corresponding to sound waves, is passed through the conductors. A mirror attached to the ribbons will vibrate in accordance with the movement of'the wires caused by the current passing therethrough. The moving parts of the galvanometer are; usually encased in oil to dampen their oscillation, while the case is provided with a lens .to permit light to be pro- :Ieeted onto the mirror and reflected therefrom. This lens is at an angle to the light beam to pre- 20 vent light reflected from its surface from being directed to the film. c

The galvanometer of this invention operates on well known principles but is so constructed as to increase its sensitivity to approximately three 0 times that of those now known in the art. In a galvanometer, the reaction to be obtained is dependent upon the current in the conductors and the strength of the field. The field is limited by 0 practical considerations and the conductors must be fine to avoid inertia thus limiting their current carrying capacity. Other means, therefore, must be provided for increasing the reaction of the mirror. such means forming the subject matter of this invention.

The object of the invention is to obtain greater sensitivity of the galvanometer and to provide a simple rugged construction which will produce this sensitivity. I I

o l-Iithertofore it has been the practice in constructing a galvanometer to string the conductors from a fixed point, over a bridge, through a magnetic field, over a second bridge, around a horn at some distance from the bridge, and back a over the two bridges to a point adjacent the first point. This made a long conductor length which dissipated more energy going to and from the magnetic field than was actually used in the field itself. The present invention is directed,v there- 50 fore, to a construction which reduces this conductor to a length which lies substantially. wholly within the magnetic field thus permitting all the current the conductors, or ribbons as they are sometimes called, and the entire length of the l ribbonsto function for deflecting the mirror attached thereto. Also, means are provided for adjusting the tension of the ribbons from outside the case of the galvanometer;

The invention will be more fully understood by reference to the following description read in conjunction with the accompanying drawing, in which i Fig. 1 is a sectional elevation view of a preferred form of galvanometer and is taken along the line i-l of Fig. 2.

Fig. 2 is a. sectional elevation view taken along line 22 of Fig. 1.

Fig. 3is a sectional plan view taken along line 33 of Fig. 1; and

Fig. 4 is a sectional plan view taken along line 4-4 of' Fig. 1.

As shown in Fig. 1, the equipment ordinarily employed in sound recorders of the variable area type comprises a light source i which sends a beam of light 2 through a light mask or diaphragm 3 one edge of which provides the light beam with a cutting edge to define the clear and the exposed portions of the sound track. Suitable lenses 4 and 5 associated with the diaphragm 3 project the light beam upon the mirror 6 of a galvanometer I. The mirror 6 is made to vibrate about a vertical axis in accordance with a modulated current introduced within the galvanometer, as will be explained later.

The light beam 2 which is modulated by vibratingmirror 6 is reflected through a slit disc 8 30 having a slit 9 therein and thence through objective lenses ill where it is projected upon the, film H in the form of a narrow strip of light of varying width.

The galvanometer 1 comprises a base l2 of a non-magnetic material such as brass and has a cover l3 attached thereto as by screws l4 and iii.

The mirror 6 is attached to a pair oi. thin metallic ribbons l6 and i| which are mounted at their lower ends on supports it and It. These supports i8 and I9 are spaced apart from each other slightlyand are insulated from the base l2 by a piece of insulation such as bakelite 20. Clamping pieces 2| and 22 clamp the ribbons l6 and I1 securely onto the surfaces of *thesupports l8 and It by screws 23. A thin sheet of insulation 60 may be inserted between the supports l8 and 19. to prevent accidental shorting across the ends of the conductors i6 and II. The upper ends of the ribbons i6 and I! are secured to the end of a bell-crank lever 24 by a clamping piece 25 and screws 26. The bell-crank 24 is pivoted at 21 (Fig. 1) in trunnion bearings comprising screws 28 and 29 (Fig. 2) mounted in blocks 55 38 and 3|, which are.secured to the base I2 by screws 30' and 3|. The screws 28 and 29 are conical at their ends and engage countersunk portions on either side of the bell-crank 24, as shown in Fig. 2. The end 32 f the bell-crank 24 is engaged by spring 33' mounted within a threaded aperturz 34. A screw 35 is provided at the rear of the spring 34 and may be operated by a suitable tool such as a screwdriver from the exterior of the base I2 to adjust the tension of the conductors I6 and I! to the proper amount. The interior of the galvanometer is filled with oil and to prevent it from leaking past the screw 35 a cap screw 36 is provided having a gasket 31 provided thereon.

The magnetic field of the galvanometer is provided by a pair of soft

iron pole pieces

38 and 39 mounted adjacent the conductors I6 and I! and are engaged at their outer ends by a U-shaped permanent magnet 40 which may be cemented or otherwise suitably secured to the base I2. The

pole pieces

38 and 39 are undercut at 4I and 42 (Fig. 3) to allow the bell-crank 24 to project therethrough. In order to adjust the

pole pieces

38 and 39 in respect to the conductors I6 and I1, elongated counterbored holes are provided therein in which are mounted screws 44 to clamp the

pieces

38 and 39 to the base I2. If, after adjustment of the pole pieces 38 and 39 a space intervenes between their outer edges. and the inner surfaces of the magnet 40, magnetic shims as 45 and 46 are interposed therein.

Referring to Fig. 4, a pair of

studs

41 and 48 are threadably mounted within the conductor supports I8 and I9 and project through holes in the insulating strip 20 and thence through

sleeves

48 and 50 of insulating material mounted in the base I2. An insulating strip I is provided at the rear of the base against which nuts 52 and 53 on the

studs

41 and 48 bear. The outer ends of the

studs

41 and 48 serve as terminals which receive current from suitable amplifiers in the sound recording circuit. Current passing, for example, through the stud 41, goes through the support I8, through conductor I6 to the bellcrank 24 where it returns through conductor I'l, thence through support I9 and on out through the stud 48. v

A lens 54 is placed in a threaded hole 55 provided in the cover I3 adjacent the mirror 6. A pair of

retainer rings

56 and 51 on either side of the lens 54 hold it in position and also prevent leakage of oil. Referring to Fig. 4, it will be noted that the lens 54 is mounted at an angle to the plane of the mirror 6. Thus any light which may be reflected from its front and rear surfaces will be directed to one side of the sound track of the film being recorded. As a further precaution against reflected light other than that from the mirror 6 striking the film, the conductors I6 and I1 and the sides of the mirrors are preferably coated with a black paint.

Referring now to Fig. 2, a pair of screws 58 and 59 are provided in the top of the cover I3. When the galvanometer is to be filled with oil the screws 58 and 59 are removed and oil is inserted through one of the holes, the other allowing air to escape therethrough. In stringing the gal-- vanometer the ribbons I6 and I! are placed upon the supports I8 and I9. A piece of thin metal such as shim stock is placed between the ribbons so as to space them apart a required distance which in actual practice may be about .005 inches. The clamps 2| and 22 are then secured and the piece of shim stock removed. The same procedure is followed in securing the upper ends of the ribbons I6 and I! to obtain the correct spacing. The mirror 6 is then secured by a suitable cement so that it bridges the two ribbons. After the cover has been attached and the galvanometer is filled with oil, the tension screw 35 is adjusted until the ribbons will vibrate. at a required resonant frequency which in this case may be about 8,000 cycles per second.

What is claimed is:

1. In a galvanometer, a casing, a magnet within said casing, pole pieces for said magnet, a pair of movable conductors having a comparatively high resistance and positioned between said pole pieces and attached immediately adjacent both ends of said pole pieces, and means for electrically connecting one set of the terminals of said conductors externally of said casing.

2. In a galvanometer, the combination of an oil-tight casing, a magnet within said casing, a pair of pole pieces adjustably mounted between the poles of said magnet, a pair of movable conductors having a comparatively high resistance and positioned intermediate and attached immediately adjacent both ends of said pole pieces, a metallic clamp for adjustably positioning and electrically connecting one set of adjacent terminals of said conductors, insulated clamps for positioning and individually connecting the other terminals of said conductors, and a mirror attached to said conductors substantially midway between said clamps.

3. A galvanometer in accordance with claim 2 in which said clamp for said first mentioned terminals is adjustable from without said casing for tensioning said conductors.

4. In an instrument for producing mechanical motion corresponding to the variations in electrical current, the combination of a base, a cover of insulating material having therein a lens for admitting light to and from the interior of said instrument, said lens being positioned at an angle with respect to light passing to and from the interior of said instrument, a permanent magnet having adjustably mounted pole pieces arranged to form a narrow air gap, an L-shaped member pivoted within said instrument. means for mounting one set of terminals of a pair of movable conductors having a comparatively high resistance and to one end of said L- shaped member positioned immediately adjacent one end of said air gap, means for adjusting the position of the other end of said L-shaped member from without said instrument, means positioned immediately adjacent the other end of said air gap for attaching the other terminals of said conductors, a reflector on said conductors for reflecting light through said lens in a predetermined direction, and means for supplying current to said last mentioned terminals.

5. In a galvanometer the combination of an oil-tight casing, a permanent magnet within said casing, a pair of pole pieces forming a narrow air gap, and a pair of movable conductors having a comparatively high resistance for carrying current in opposite directions and having a suspension located substantially wholly within said air gap.

6. In a galvanometer the combination of an oil-tight casing, a permanent magnet, within and attached to the base of said casing, a pair of adjustable pole pieces between the poles of said magnet and forming an air gap between said pole' pieces, a pair of movable conductors having a comparatively high resistance for carrying ourrent in opposite directions, means for suspending I said conductors substantially wholly within the air gap of said pole pieces, a mirror attached to said conductors, and means for passing light to and from said mirrors.

7. A galvanometer comprising a casing having a. light transmitting opening therein, means with- 'in said casing for producing a steady magnetic field, a pair of movableconductors having a comparatively high resistance located in said field, each of said conductors carrying current in a direction opposite to the other, a mirror attached to said conductors, means for impressing current on said conductors, and means for mounting said conductors-so that the current in said conductors and the entire length'of said conductors is effective to move said mirror.

8. A galvanometer in. accordance with claim 7 in which said casing is oil filled and contains means for adjusting said conductors from without said casing.

9. A galvanometer-comprising an oil filled casing having a light transmitting opening therein, means within said casing for producing a steady magnetic field, means for positioning a pair of movable conductors having a comparatively high resistance in said field for carrying current in opposite directions, a lightrefiector adapted to be moved by said conductors and means for conducting current to and from said conductors, only that portion of said conductors lying within said field carrying said current.

10. A galvanometer in accordance with claim 9 in which said conductor positioning means is adjustable to vary the tension of said conductors externally of said casing.

HAROLD JANSEN HASBROUCK, JR.