US2108012A - Oscillograph apparatus - Google Patents

Description

Feb. 8, 1938.

J. D. EISLER OSCILLOGRAPH APPARATUS Filed June 16, 1937 2 Sheets-Sheet l INVENTOR Joseph Dan/e/ Ens/er ATTORNEY Feb. 8, 1938. J. D. EISTLER 2,108,012

osc ILLOGRAPH APPARATUS Filed June 16, 1937 2 Sheets-Sheet 2 /Pr.i0r- Ant j nior Ant 7 Max/mun d/bp/dcemenf Max/mm ofispremenf 1 0 afefi'nife F 94 Fig.5 5

' D/recf/on mafia/7 g ail-1779s fwd/ion of friny 1 Fi 7 F1 19 INVENTOR- Jos ph Danie/Es/er ATTORNEY Patented Feb. 8, 1938 UNITED STATES OSCILLOGRAPH APPARATUS Joseph Daniel Eisle'r, Los Angeles, Calif., assignor to Western Geophysical Company, Los Angeles, Calif., a corporation of Delaware Application June 16, 1937, Serial No. 148,618

3 Claims.

This invention relates to improvements in oscillographs and particularly to improvements in multi-element oscillographs of the Einthoven, or

' string, type.

In multi-element oscillographs of the string type it is necessary that the strings be very close together. In prior art oscillographs of this type, thishas resulted in greatly limiting the movement of the strings since any large movement resulted in interference between the strings.

It is an object of my invention to produce an oscillograph of the harp type in which the strings can be caused to vibrate with a large amplitude without interfering with each other. Another object of my invention is to accomplish this result and still permit sharp focusing in photographing the strings. Further and more detailed objects of my invention will become ap parent asthe description thereof proceeds.

I will describe my invention more particularly with reference to the accompanying drawings, in which:

Figure 1 is a side elevation of a. multi-string oscillograph without magnets and otherassoelated equipment:

Figure 2 is a rear elevation corresponding to Figure 1 and showing, in addition to the struc- .ture of Figure 1, the relationship of the magnet poles to the oscillograph strings;

Figure 3 is a sectional plan taken along the lines 3-3 of Figure 2;

Figure 4 is a diagram showing 'one prior art arrangement of oscillog'raph strings;

Figure 5 is a diagram showing another prior art arrangement of oscillograph strings;

Figure 6 is a diagram showing my new arrangement of oscillograph strings;

Figure 7 is a plan, partly in section, showing one arrangement of magnets and oscillograph strings in accordance with my invention; and

Figure 8- is a plan, partly in section, showing an alternative arrangement of magnets and osciliograph strings in accordance with my invenion.

Multi-string oscillographs are used for various purposes. One important use of such oscillographs is in seismic surveying. In this art, artificial earthquakes are produced by the use of explosives and the reflected and refracted seismic 5O waves are picked up by seismometers which convert the mechanical vibrations into varying electrical currents. The varying electrical current from one seismometer or from a group of seismometers is amplified and the amplified electric current is fed to an oscillograph string. By similar circuits other seisrnometers are connected to other strings of the oscillograph and a composite record of the movements of the oscillograph strings is made by a conventional photographic system.

Referring particularly to Figures 1, 2 and 3, a plurality of very fine metallic wires or strings S, preferably at least six in number, are stretched parallel to each other by means of mounting posts A and B. The strings are held at their ends in fixed relationship to each other by grooves turned on the surfaces of mounting posts A. The tensions of the strings are adjusted by means of set screws C-one for each end of each string. The ends of each string or wire are brought outside to binding posts D at the front of the instrument. There are, of course,

two of these binding posts for each string of the instrument. The unit shown in Figure 1 is placed between the poles of the magnet M as shown in Figures 2 and 3 and the whole device is placed in a camera. Magnet M is preferably, but not necessarily, an electromagnet. The current flowing through any string moves it at right angles to the magnetic field and also at right angles to the direction of current flow in the string. Thus in Figure 3 the strings move vertically up and down. The optical system and the rest of the camera are not shown. Light from any suitable source passes through a small central opening 0 in. both magnet pole pieces and casts the shadows of the strings on an optical system which magnifies the shadows and projects them on a cylindrical lens. This lens in turn projects a shadow due to each string on a moving photographically sensitized film located just behind the cylindrical lens.- record of the movements of the strings is thus obtained. All of this is conventional and is no part of my invention. It is, of course, apparent that other optical and photographic systems can be used.

The various strings must be very close together in this type of instrument in order to simplify the optical and photographic system. In order to photograph the strings a hole through the A composite magnets is essential and the hole must, of course,

direction parallel to the strings (i. e. as shown in Figure 2) may be 1.25 inches while the dimension of the pole faces in the direction vertical to the direction of the strings (i. e. as shown in Figure 3) may be 0.10 inch. The spread of strings occupies about .08 inch and the spacing between strings is of the order of magnitude of 0.009 inch. The body of the magnet is, of course, larger than the pole faces and is tapered down at the poles at an angle of about 45.

The fact that the strings must be extremely close together results in interference of any given string with the neighboring strings if the amplitude becomes at all great.

The original arrangement of strings in this type of instrument was as shown in Figure 4. The strings were all in a single plane and the direction of motion of the strings was also in this plane so that the maximum permissible displacement of any string (assuming the adjacent strings to be at rest) was twice the spacing between strings. This motion proved insufficient and the arrangement shown in Figure 5 was produced in which alternate strings were staggered. In other words, the strings were placed in two parallel planes, separated just enough so that during motion no string could strike an ad- J'acent string but must strike the alternate string. This doubled the maximum deflection but placed the strings so that their shadows could not be focused accurately on the same plane. Moreover,

the maximum available deflection was still seriously limited.

My invention overcomes these diiiiculties and permits a much greater maximum displacement together with sharper focusing than in the case of the arrangement of Figure 5. As shown in Figures 6, 7 and 8, which illustrate my invention, the strings are arranged in one plane but the direction of motion of the strings is no longer in that plane. For this reason the strings can never hit each other. Being all in one plane at their rest positions, their shadows can be brought to a sharp focus. As the strings move, the focus becomes poorer but not until the time any string passes behind the next one will its image be as far out of focus as is the case at all times using the staggered arrangement of Figure 5.

In accordance with my invention the strings are caused-to move in a plane other than the plane defined by their rest positions. This is accomplished by so constructing and arranging the magnet with respect to the strings that the direction of the lines of force in the magnetic field is no longer vertical to the plane of the strings but is at a small angle to the vertical. This angle may suitably be about 12 to 15 or any angle from about 5 to about 45. As long as the strings do not strike, any acute angle can theoretically be used, although small angles are preferable because the focus will be sharper at maximum string deflection.

The change in the direction of motion can be secured in several ways. Probably the most simple consists in shaping the pole faces of the magnet so that the magnetic field is at right angles to the desired direction of motion. This is shown in Figure '7. The faces of the magnet poles are no longer parallel to the plane of the strings but are at an angle thereto. This angle is, of course, the same as the angle between the direction of the lines of force and the perpendicular to the plane of the strings and, as above indicated, the angle can suitably be about 12 to 15 or somewhat smaller or larger than that a gle. This angle is, of course, dependent on the string spacing. As the strings are moved farther apart, the angle can be reduced to maintain the same clearance. between adjacent strings. The angle 9 at which the strings will just touch is given by the equation:

D sin 9 where D=diameter of strings, and

S=spacing between adjacent strings.

Any acute angle greater than 9 can be used but it is desirable that the angle be only sufilciently in excess of 9 to provide adequate clearance.

The motion of the strings in the arrangement of Figure 7 is, of course, perpendicular to the direction of the magnetic fieldin other words, parallel to the plane of the pole faces. The angle should be the minimum which will give adequate clearance between the strings since in this way the focus is kept as sharp as possible for all string positions.

Another embodiment of my invention is shown in Figure 8. In this embodiment the plane of the strings is placed at an angle to the pole faces and the hole through the magnet M is bored in a direction perpendicular to the plane of the strings. This achieves exactly the same result as the arrangement of Figure '7 but is mechanically somewhat more difficult to construct.

My invention is particularly applicable to an arrangement in which the strings are all in a single plane, but it can be applied to an arrangement in which the strings are in two or more planes.

While I have described my invention in connection with certain specific embodiments thereof, it is to be understood that these are by way of illustration rather than by way of limitation and I do not mean to be limited thereby but only to the scope of the appended claims which should be construed as broadly as the prior art will permit.

I claim:

I. Oscillograph apparatus comprising a plurality of oscillograph strings closely spaced and parallel to each other, said strings lying substantially in a given plane, and a magnet having pole faces on opposite sides of said strings, said pole faces being at an angle of from about to about 45 to said plane, said magnet being provided with a small hole passing therethrough in a direction substantially perpendicular to said plane and so located that the movements of said strings can be photographed by means of light passing through said hole.

2. Oscillograph apparatus comprising at least six oscillograph strings closely spaced and parallel to each other, said strings lying substantially in a given plane, and a magnet having pole faces on opposite sides of said strings, said pole faces being at an acute angle to said plane slightly greater than the angle 6 given by the equation S=spacing between adjacent strings, said magnet being provided with a small hole passing therethrough in a direction substantially perpendicular to said plane and so located that the movements of said strings can be photographed by means of light passing through said hole.

3. Oscillograph apparatus comprising a plurality of osciiiographic strings closely. spaced and parallel to each other, sad strings lying substantially in a given plane, and a magnet havingpoie faces on opposite sides of said strings, said pole faces being at an angle of from about 5 to about 45 to said plane, said magnet being provided with means for the passage of. light therethrough, whereby the movement of said strings canbe photographed by means of said light and safl strings can be when at their rest positions.

JOSEPH DANIEL EISLER.

brought to a sharp focus 5

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