US2596994A - Fluxmeter alarm - Google Patents

Description

y 19.52 E. R. HABERLAND 2,596,994

" FLUXMETER ALARM I Filed Dec. 9, 1944 4 Sheets-Sheet 1 E Haberland May 20, 1952 E. R. HABERLAND ,5 4

FLUXMETER ALARM Filed Dec. 9, 1944 4 Sheets$heet z .ERJifizZerZarzd alike/W44 y 0, 1952 E. R. HABERLAND 2,596,994

I FLUXMETER ALARM Filed Dec. 9, 1944 4 SheetsSheet 3 EJBHaberZand May 20, 195 2 E. R. HABERLAND FLUXMETER I ALARM Filed Dec. 9, 1944 4 Sheets-Sheet 4 Patented May 20, 1952 UNITED STATES PATENT OFFICE (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G, 757) 8 Claims.

This invention pertains to indicating devices for use with detecting apparatus and more spe cifically to an indicating device in which a photoelectric control system is utilized to operate an audible alarm and a signal lamp in response to changes in physical variables detected by suitable detecting means.

The instant invention is particularly adapted for use in cooperation with magnetic detecting means employed on a surface craft for the purpose of indicating the presence of a submarine submerged within the Vicinity of the surface vessel.

In arrangements hitherto used for the magnetic detection of submarines, it has been the usual practice to employ indicating devices of the recording type in which a fiuxmeter galvanometer element is employed to activate photo-electric means, which in turn controls the operation of the recording element of the device. Such an arrangement is described and claimed in the copending application of Ellis A- Johnson for Submarine Detecting Device, Serial No. 409,774, filed September 6, 1941, which is now U. S. Patent No. 2,535,068, granted December 26, 1950, wherein a photoelectric recording fluxmeter operates to record, in graphic form, differences in flux linkages between two search coils caused by a change in the gradient of the field of a submarine as relative motion exists between the submarine and the detecting coils.

In devices heretofore proposed for use as deflecting elements for indicating devices, it has been the usual practice to employ instruments such, for example, as a fluxmeter galvanometer, such instruments comprising a rotatable coil supported by a wire suspension. However, such a suspension inherently subjects the rotatable coil to a restraining torque too great to permit the use of such galvanometers where high sensitivity is required or where it is desired to utilize the instrument as an integrating device. Accordingly, a small high coercive magnet is mechanically connected to the galvanometer coil, thereby providing a counteracting torque which reverses in direction at substantially the null or zero position of the coil and which compensates for the torque exerted on the coil due to the suspension thereof.

An arrangement is thus provided whereby the angular deflection of the coil from any initial position is proportional to the average electromotive force applied thereto and the period of time over which the force is applied. Suitable means are included on the instrument for adjusting the zero position of the suspension, the

strength of the compensating field, and the angular position thereof. In conjunction with the foregoing devices, it has been the usual practice to arrange the fluxmeter galvanometer and its cooperating elements Wholly within a metallic casing. For a more complete description of the structure and operation of a fluxmeter galvanometer of the type heretofore described, reference may be had to Patent No. 2,326,252, to T. A. Rich, issued August 10, 1943.

Such arrangements, however, have been found to be unsatisfactory for the reason that recording mechanisms usually present such problems as supplying ink and maintaining an inkwell therefor, clogged pens and keeping a supply of record rolls on hand with the possibility of the mechanism running out of paper at a crucial moment. Moreover, the utilization of a recording instrument as means for making manifest the presence of a submarine requires constant vigilance on the part of an observer. A further disadvantage resides in the location of the galvanometer adjusting means. It will be appreciated that when the fluxmeter galvanometer coil is in the null or zero position it is in a state of unstable equilibrium and therefore susceptible to the forces which may cause the coil to drift. This condition arises from the fact that the compensating torque must be so adjusted as to not exceed the restraining torque at any point. As a result, the coil will drift from its zero position due to small magnetic disturbances andto vibration disturbances.

A situation thus arises, wherein it is necessary to remove the casing of the indicating device in order either to adjust the coil to its null position or to adjust the compensating torque. A still further disadvantage follows from the necessity of having to remove the casing to make adjustments, by reason of the fact that the operation of the recording instrument is interrupted each time the casing is removed, thus providing an interval of time in which the presence of a submarine detected by the search coils will not be made manifest by the instrument.

It is, therefore, an object of the present inven- 'tion to provide new and improved means for in-- angle of deflection of the galvanometer coil necessary to activate the alarm means.

A further object is the provision of a new and improved photo-electric control system adapted to control the operation of suitable alarm means in response to a predetermined angular deflection of the galvanometer coil.

A still further object is the provision of a new and improved indicating device which is simple in construction, reliable in operation and economical to manufacture.

Additional objects and advantages will become apparent as the description proceeds.

In accordance with a preferred embodiment of the present invention, an element adapted to be deflected in accordance with the difference in flux linkages existing between two search coils is employed to control the reflection of a beam of light to a suitable reflecting surface, when the element has deflected through a predetermined angle, from whence the beam of light is directed to a photo-sensitive device which controls the operation of an audible signal and a visual signal. In the event slight excursions of the element occur due to vibrations and/or small magnetic disturbances, the beam of light is reflected from the element to a screen whereby an observer may, if desired, note the drift and make necessary adjustments therefor. It will be understood that such an element maybe of the type heretofore described.

The features of the invention which are believed to be novel and patentable will be pointed out in the claims appended hereto. For a more complete understanding of the invention, reference is made to the following description taken in connection with the accompanying drawings, in which:

Fig. 1 is a view in perspective of the device of the present invention according to a preferred embodiment thereof;

Fig. 2 is a sectional view taken along the line 2-2 of Fig. 1;

Fig. 3 is a view in section taken along the line 3-3 of Fig. 1;

Fig. 4 is a sectional view taken along the line t 4 of Fig. 3; I

Fig. 5 shows in diagrammatic form a system of operation suitable for the device of Fig. 1 and according to a preferred embodiment of the invention;

Fig. 6 is a view in section showing an alternate form of the device of Fig. 1;

Fig, 7 is a sectional View taken along the line 7-1 of Fig. 6; a

Fig. 8 is a sectional view taken along the'line 88 of Fig. 6;

Fig. 9 is a perspective view showing the guide bar and mirror included in the alternate form of the invention;

Fig. 10 is a view in perspective of a mask suitable for use in the alternate form of my invention; and,

Fig. 11 shows in diagrammatic form a system suitable for use with the present invention, according to an alternate form thereof.

Referring now to the drawings in which like reference characters designate like parts throughout the several views and more particularly to Figs. 1 to 4, there is shown thereon a device of the present invention according to a preferred embodiment thereof which is indicated generally by the numeral 26. The device comprises a casing l0 secured to a non-magnetic base I l as by the screws [2. The casing it] may be composed of any suitable material which will shield the device 29 from external sources of light and from dust particles and the like. In the event that it may be desirable to utilize a casing composed of a magnetic material for shielding the device from external fields, the location of the adjusting means of the present invention external to the casing provides an additional advantage over previous devices, for the reason that, the earths magnetic field is not disturbed by the adjusting operation; whereas, in previous devices in which the adjusting means were arranged within the casing it is necessary to remove the casing in order to make necessary adjustments, thereby disturbing the earths field and effecting a change in position of the galvanometer element.

In the top of the casing 56 is a recessed aperture I3 adapted to receive an element Id, well known in the art as a fluxmeter element, and which may be of the type heretofore described. The element M is secured to a supporting member 15 by means of a flange I6 arranged on the element, and the screws ll.

Arranged within the casing it] are two photoelectric cells, hereinafter referred to as PI and P2. The cells P! and P2 are paralleled electrically and are mounted longitudinally on a bracket I8 which is secured to the supporting member l5 as by the screws !9. Also arranged within the casing ill and mounted on the base I l is a relay R and a grid controlled tube T suitable for the purpose such, for example, as a gas tetrode. The relay R is a direct current relay comprising a pair of normally open contacts and is adapted to be energized by the tube T when conductivity thereof commences.

The fluxmeter element l4 comprises a movable coil (not shown) which carries a mirror 2i. The movable coil is connected electrically to a source of electro-motive force such, for example, as the pair of search coils described in the aforesaid application of Ellis A. Johnson, by means of the cable 22. The element l4 further comprises several necessary adjusting knobs for the movable coil which is disposed exteriorly of the casing H]; the suspension adjusting knob 44, the zero adjusting knob 45 and the drift adjusting knob d5. Mounted on the supporting member I5 is a lamp housing 24 comprising a lens mount 25 which receives light from an incandescent lamp' 25 arranged within the housing 24, and a bearnof light from the lens mount is directed throug'fi'a transparent shield 28 on the fluxmeter element M to the mirror 2E. The member l5 also maintains a guide bar 27 having a grooved portion 28 therein adapted to receive the flanged edges of two supporting members 29 and 3!. The supporting members 29 and 3| have internally threaded cylindrical cavitiesadapted to receive an adjusting screw 32 having two oppositely threaded portions 33 and 3d. Eachjof the members 29 and 3! has a longitudinally grooved portion in its top surface adapted to receive the mirrors 35 and 36 respectively and the position of the mirrors 5, 35 and 33 is such that a beam of light directed from the mirror 2| to the mirror 35 will be reflected from the mirror 35 to the photo-electric cell Pl thereby causing it to conduct and, in the event that a beam of light is directed from mirror 2| to the mirror 35, the beam is reflected to the photo-electric cell P2 thereby causing it to conduct.

The supporting member I5 is provided with two threaded openings adapted to receive the externally threaded bearings 3! and 38, wherein the adjusting screw 32 is allowed to rotate. The adjusting screw 32 comprises an adjusting knob 39 brought out exteriorly of the casing I such that rotation of th knob 39 causes the supporting members 29 and 3| and the mirrors 35 and 36 held thereby, to move toward or away from each other in accordance with the direction of rotation of the knob 39.

A plurality of ventilating holes 4| are arranged in the casing I0, thereby providing means of escape for the air heated by the source of light 25 and the tubes PI, P2 and T. It will be noted, however, that the photo-electric cells PI and P2 are shielded from any direct light passing through the ventilating holes 4| by reason of the supporting member l5. The casing I0 is also provided with an opening adapted to maintain a signal light, hereinafter referred to as SL preferably equipped with a jewel glass lens 42. A frosted-glass screen 43 with appropriate indicia thereon is also mounted in the casing It] for the purpose of making manifest slight deflections of the mirror 2| due to the forces of vibration and/or small magnetic disturbances.

For a more complete understanding of the operation of the device of the present invention reference is made to Figs. 1 through 5. Fig. shows in diagrammatic form a system suitable for use with the device of Fig. 1 according to a preferred embodiment thereof. With switch S, Fig. 5, closed, an alternating potential is applied to the anode or plate 41 of the gas tetrode T and in accordance with the setting of the gridbias potentiometer 48, a bias is applied to the control grid 49 of the tube T which is sufficiently negative with respect to the cathode 53 to prevent a break down of the tube T. For the purpose of description, let it be assumed that the device 20 of the instant invention is carried by an attacking surface craft and is connected electrically to suitable detecting means such, for example, as the detecting coils described in the aforesaid application of Ellis A. Johnson. Let it further be assumed for the purpose of description that the movable coil (not shown) and the mirror 2| have been adjusted to the null or zero position thereof and the mirrors 35 and 35 have been adjusted to a'predetermined position or setting such that slight deflections of the coil may occur without effecting the operation of the alarm devices.

It will be noted that the audible alarm device A may be of any type suitable for the purpose and the location of this device on the vessel is.

purely optional.

As the attacking vessel enters the threshold of sensitivity of the magnetic field set up by a submarine, a cycle of operations of the fluxmeter element I4, including the movable element and the mirror 2|, is initiated, the term cycle of operations as employed herein being defined as the movement of the element, in response to a flow of current therein, from an'initial position toeachof two predetermined positions spaced on opposite sides of the initial position and thereafter returning to the initial position as the attacking vessel moves beyond the field of sensitivity of the submarine.

As the movable coil and the mirror 2| begin to rotate away from the null position, a beam of light from the lamp 25, deflected from the mirror 2| to th zero point on the screen 43, begins to move toward the mirror 35. When the coil has rotated through the predetermined angle, the beam of light is reflected from the mirror 2| to the mirror 35, from whence the beam is caused to impinge on the surface of the photo-electric cell Pl, thereby causing the cell PI to conduct. When this occurs, a positive potential is superimposed on the control grid 49 of the tube T over conductor 5|, photo-electric cell PI and conductor 52, whereby the net potential applied to the grid 49 is increased in a positive direction, thus causing the tube T to break down. As current flows from the cathode 53 of tube T to the anod 41 thereof, a circuit is closed from the source of power over conductor 5|, relay R, conductor 54, tube T, conductor 55, grid bias potentiometer, conductor 56, from whence the circuit is completed to the source of power, whereby the direct current relay R is energized and the armature 51 moves into engagement with contact 58 thereof.

Relay R is sufllciently slow releasing to prevent the release of the relay during succeeding pulses of current rectified by the tube T while the photoelectric cell PI is actuated by the light beam.

When the armature 51 of relay R is moved into engagement with the make contact 58 thereof, a circuit is closed from the source of power over conductor 5|, armature 5! and make contact 58 of relay R, conductor 59, signal lamp SL and alarm A in parallel, conductor 56 and thence to the power source, thereby causing the signal lamp SL to light and the audible alarm A' to be actuated. It will be understood, at this point, that the operation of the lamp SL and alarm A will not cease until relay R releases in response to the deactivation of the photo-electric cell Pl as the light beam moves out of engagement therewith.

As the attacking vessel continues to move with respect to the submarine, the coil returns to the null position, thereby causing the beam of light from the lamp 25 to be reflected from the mirror 2| directly to the frosted glass screen 43. Since the beam of light is no longer reflected from the mirror 35 to the photo-electric cell Pl, the

cell Pl become non-conductive, whereby the potential applied to the control grid 49 of tube T with respect to the cathode thereof is increased in a negative direction sufficiently to prevent the tube T from firing. When this occurs, relay R is deenergized and the armature 51 and make contact 58 thereof are disengaged and the circuit to the signal lam SL and alarm A is interrupted, thereby extinguishing the lamp SL and silencing the alarm A.

As the attacking vessel moves beyond the submarine, the movable coil and the mirror 2| rotate away from the null position such that a beam of light from the lamp 25 is reflected from the mirror 2| toward the adjustable mirror 36. When the coil and the mirror 2| have rotated through a predetermined angle, controlled by the settings of the mirrors 35 and 36, the beam of light will be reflected from the mirror 2| to the mirror 36,

from whence it is deflected to the surface'of the photo-electric cell P2, thereby causing the cell P2. to-conduct. The tube T breaks, down in re-' sponse to an. increase in grid bias and. the relay R. is: energized by the resulting current. The armature 51 moves. into engagement with the make. contact 58 of relay R. when the'relay becomes energized, thusclosing a circuit to the signal lamp SL and the audiblev alarmA and initiating operation thereof.

Operation of'the lamp SLand alarm A continues until the movable coil and mirror 2| return to substantially thenull position, whereupon the beam of light reflected from the mirror 21 is directed away from the mirror 36-and' to thescreen 43-; Consequently, the cell P2 becomes non-conductive'and the grid bias of tube T is made more negative, thereby cutting off thecurrentflow in the tube T and in the relay R. The armature 51 and make contact 58 of relay R are then disengaged and the circuit to the lamp- SL and alarm A'is: opened.

In the event that vibration or unrelated magnetic disturbances cause the movable coil to defleet through an angle of suificient magnitude to effect the operation of the lamp SL and alarm A, the cause of this spurious operation will be readily apparent for the reason that the fluxmeter element [4 is an integrating device. Once it has been deflected, the deflected position is maintained until another signal is received. Therefore, the operation of the alarm A and signal lamp-L in response to coil drift will be continuous; while operation thereof in response tov the presence of a submarine will be intermittent for the reason that, the coil passes through zero during its cycle of operation. Moreover, an observer can determine the cause. of operation by noting the position of the beam on the screen 43. If a spot of light becomes visible on the screen 43, the operation of the device is not spurious for the, reason that the. coil and, mirror 2| must be substantially in the null position in order to, reflect a'beam of light to the screen 43.

In the event that an observer notices. small excursions of the coil from the null position, he may make the necessary adjustments by rotating the knobs 45 and 46 in the proper direction, thereby rectifying an undesirable situation Without rendering the device inoperative during the interval of time required for the adjustments.

The alternate form of the invention shown in Figs. 6 to 8 contemplates an arrangement whereby a beam of, light isv reflected from a fixed reflectin surface to a light sensitive device when th rotatable element has moved throughv a predetermined angle, in either direction from the null or zero, position. thereof. A pair of adjustable masks, mounted in a manner similar to that of the mirrors 35 and 35 in the preferred form of the invention, regulate the angle through which the element must deflect in order to activate the light sensitive device.

For a more. complete understanding of the structure and operation of the alternate form of the invention reference is made to Figs. 6 through 11, inclusive. The general structure is similar to that of the preferred form with the excepti'on that only one photo-electric cell, P3 is employed. The cell P3 is arranged longitudinally within the casing 10 and is mounted on a bracket 6| secured to the member l by the screws 62. A guidebar 63, Fig. 9, secured to the member l5 by the screws 64, has a flanged portion 65 with a groove therein adapted to receive and maintain a fixed mirror 66. The device is also provided with a. pair of adjustable masks 68 and" 69,- preferably nonconductive.

composed of a metallic substance having a light absorbing or non-reflecting surface. Fig. 10 of the drawing shows a masking element having a non-reflecting surface 61 and a flanged portion Tl adapted to fit a groove 12 in theguide bar 63 of Fig. 9. Each of the masks 68 and 69 has a cylindrical cavity 13 threaded internally in such a manner as to cooperate with the oppositely threaded portions 33 and 34 respectively of the adjusting screw 32.

Fig. ll ofthe drawings shows in diagrammatic form a system suitable for use with the device of Fig. 6. The circuit of Fig. 11 functions in substantially the same manner as that shown in Fig. 5. It is assumed that the operation of the circuit will be apparent from a consideration of the circuit or'Fig. 5, a detailed description of the circuit, therefore, is not deemed necessary for a complete understanding of the invention.

For a better understanding of the operation of the device of the-present invention'inits alternate form, let it be assumed that the device is carried by air-attacking vessel and is electrically connected, by means of the cable 22', to a suitable pair of detecting coils such, for example, as those described in the aforesaid application of Ellis A. Johnson. Let it further be assumed that the switch S, Fig. 11, is closed and the movable coil and mirror 2| have been adjusted to the null position. Furthermore, the masks E8 and 69 are adjusted to a predetermined position in order that slight excursions of the galvanometer element will not effect spurious operation of the photo-electric cell, P3.

As the attacking vessel enters the threshold of sensitivity of the magnetic field set up by a submarine, the coil and the mirror 21, carried thereby, begin a cycle of operations, as-previously described herein. When the cycle of operations is initiated, the coil ismoved away from its null position and a beam of light from the lamp 25 is directed from the lens mount 2 8 through the transparent shield 23 to the mirror 21, from whence the beam is reflected to the light absorbing surface of the mask 68, whereby the beam is prevented from striking the mirror 66.

When the coil has rotated through an angle sufficient to cause the beam oflight reflected from the mirror 2| to strike the mirror 66, the beam is reflected therefrom and impinges on the surface of photo-electric cell P3. When this occurs, the cell P3 becomes conductive, thereby effecting a current flow through the tube T and relay R. The energization of the relay- R causes the armature 5'! to be moved into engagement with contact 58 thereof, and concurrently therewith, a circuit to the signal lamp SL and alarm A is closed and operation thereof is initiated. The lamp SL and the alarm A continue to operate until the coil returns substantially to the null position, whereupon the beam of light is prevented from impinging the surface of the photo-electric cell P3 due to the arrangement of the masks E8 and 69, thus causing the cell P3 to become When this occurs, no current is passed through the tube T or relay R and relay R releases, thereby interrupting the circuit to the lamp SL and alarm A.

As the attacking vessel'movesbeyond the submarine, the movable coil rotates away from the null position in a direction opposite to that of the initial deflection and the beam of light moves away from the mask 69 until it strikes thesurface of the mirror iifi'from whence it is reflected to'the cell P3. When the beam strikes the cell 'P3,conductivity thereof commences and operation of the lamp SL and alarm A follows in the same manner as heretofore described. When the surface vessel moves beyond the field of sensitivity of the submarine, the coil again returns to the zero or null position, thereby restoring the system of Fig. 11 to a nonconductive condition and rendering the signal lamp SL and the audible alarm A ineffective. In the event the alarm devices operate in response to coil drift, the coil is returned to substantially the null position thereof by an attendant by alternately opening the switch S, rotating the zero adjusting knob 45 and closing the switch S until the alarm devices do not respond as the switch S is closed.

Whereas in the foregoing descriptions it was assumed that the initial position of the coil and mirror coincided .with the null position thereof, it will be understood that such an assumption is not necessary to the successful operation of the device and. in the event the coil is not in the 'null position when a cycle of operations thereof tion contemplates the provision of a new and improved indicating device in which photo-electric means are employed to control the operation of an audible alarm and a visual signal lamp in response to a change in the gradient of a magnetic field of a submarine detected by suitable detecting means. The present invention also contemplates the provision of manually settable means which may be adjusted to prevent spurious operation of the indicating means. In the event false operation of the indicating means does occur, additional means are provided whereby the galvanometer element can be restored to zero without interrupting the normal operation of the device.

, While my invention has been described with reference to two examples thereof which give satisfactory results, it will be understood that this has been done for the purposes of disclosure and that various modifications and. changes may be readily apparent to those skilled" in the art, after understanding the invention herein disclosed, and that the terms employed in the appended claims are, therefore, to be considered as words of description rather than of.

for governmental purposes without payment of any royalties thereon or therefor.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. In a device carried by a surface vessel for indicating the presence of a submarine moving in the vicinity thereof, the combination of a magnetic casing carried by said vessel and comprising a magnetic shield, means including a fluxmeter element arranged substantially within said casing and operable in unit cycles in response to a change in a physical variable produced as the submarine moves into the vicinity thereof and with respect thereto, photo-sensitive means adapted to conduct a current only when a beam said element has progressed beyond a predetermined degree, and manually settable means manipulatable exteriorally of said casing and arranged for coaction with said reflecting means for preventing impingement of said light beam on said photo-sensitive means until said cycle of operations of said element has progressed beyond said predetermined degree.

2. In a system for indicating on a surface vessel the presence of a submarine moving into the vicinity thereof, the combination of means including a movable light reflecting element carried by said vessel and adapted to be actuated from a null position to a moved position in response to a change in a physical variable pro duced by the submarine as it moves into the vicinity of the vessel, immovable photo-electric means adapted to conduct an electric current only when a light beam is cast thereon, means for producing and directing said light beam against said reflecting element, light reflecting means cooperating with said light reflecting element for projecting the light beam on said photoelectric means when said element has been moved beyond a predetermined angle from said null position, said light reflecting means including a pair of relatively movable members, and manually settable means for moving said members equally in opposite directions from the light beam reflected from said element when the latter is in said null position thereby to prevent said beam from being projected on said photo-electric means while the element is'in the null position and until said element has been moved beyond said predetermined angle.

3. In a system of the character disclosed for indicating on a vessel having a pair of balanced search coils thereon the presence of a submarine moving in the vicinity of the vessel, the combination of a magnetic casing comprising a magnetic shield, a galvanometer including a moving element arranged substantially within said casing and operatively connected to said coils whereby said element is moved from a null position to a moved position in response'to signal currents generated in said coils as a submarine moves into the magnetic field thereof, means for producing a beam of light, immovable light sensitive means adapted to be energized when said light beam is impinged thereon, beam reflecting means arranged in cooperative relation with respect to said element for causing said light beam to impinge on said light sensitive means when the element has moved from said null position beyond a predetermined angle, said reflecting means including a pair of relatively movable members, and manually settable means arranged for coaction with said members and manipulatable exteriorly of said casing for moving said members equally in opposite directions from the light beam reflected from said element when the latter is in said null position thereby to prevent impingement of said beam on said light sensitive means until said element has moved from said null po ition through said predetermined angle.

4. In a system of the character disclosed for indicating on a surface vessel carrying a pair of balanced search coils thereon the presence of a submarine moving into the vicinity thereof, the combination of a casing formed of magnetic material and comprising a magnetic shield, a galvanometer including a movable element arranged substantially within said casing and electrically connected to said search coils whereby said element is moved from a null position to a moved position in response to signal currents generated in said coils as a submarine moves into the vicinity thereof, a light reflecting device carried by said galvanometer element and movable therewith, immovable light sensitive means arranged within said casing and adapted to conduct an electric current only when a light beam is cast thereon, means for producing and directing a light beam against said reflecting device, a light reflecting surface cooperatively arranged with respect to said light reflecting device for projecting the light beam on said'light sensitive means only when said device has been moved beyond a predetermined angle from said null position, manually settable means arranged for coaction with said reflecting-surface and including 'a shaft manipulatable exteriorly of said casing for preventing said beam of light from being projected on said light sensitive means until said light reflecting device has been moved from said null position beyond said predetermined angle.

5. In a system for detecting electrical signals of a predetermined magnitude and of different polarity, the combination of a movable mirror, means for casting a beam of light on said mirror, means responsive to sa'idsignals for moving said mirror from a null position to a moved position in either direction from said null position selectively in accordance with the instantaneous polarity and magnitude of said signal, photoelectric detecting means adapted to conduct current only when light is projected thereon, reflecting means for directing the light beam reflected from said mirror to said photo-electric means to actuate thelatter, said reflecting means including a pair of relatively-movable members, means mounting said members formovement in a path perpendicular to the null position of the light beam reflected from saidmirror when the latter is in its null position, and unitary means for moving said members equally in relatively opposite directions from said null position of said light beam to prevent reflection of said light beam on said photo-electric means until said mirror has moved a'predetermined angle in either direction from said null position thereof.

6. In a system for detecting electrical signals of a predetermined magnitude and of different polarity, the combination of a movable mirror, means forcasting a beam of light on said mirror, means responsive to said signals for moving said mirror from a null position to a moved position in either direction from said null position selectively in accordance with the instantaneous polarity and magnitude of said signal, photo-electric detecting means adapted to conduct current only when light is projected thereon, an elongated reflecting member disposed transverse the light beam reflected from said mirror for directing said reflected light beam to said photo-electric means to actuate the latter, a pair of overlapping relatively movable masks, means mounting said masks between said mirror and said reflecting means for movement parallel to said reflecting means, means for moving said masks equally'in relatively-opposite directions ifrom said lightbeam reflected from said mirror when the latter is in said null position to :prevent reflection of said light beam from said reflecting'means to said photo-electric means until said mirror has moved a predetermined angle in either direction from said null position.

7. In a system for detecting electrical-signals of a predetermined magnitude and of different polarity, the combination of a movable mirror, means for castingabeam of light on 'said mirror, means responsive to said signals for moving said mirror to deflect said'light beam from a null-position to a moved position in either direction from said null position variably in accordance with the instantaneous magnitude and polarity of said signal, photo-electric detecting means adapted to conduct current only when light is projected thereon, a pair of relatively movable reflecting members for directing the light beam reflected from saidmirror to said photo-electric means to actuate the latter, means ior-adjustably moving said members equally in relativelyoppositedirections from the null position of saidlight beam and in a path perpendicular thereto to prevent reflection'of-said lightbeam to said photoelectric means until said light beam has moved a predetermined angle in either direction from said null'position.

8. In a system ,for detecting electrical signals of a predetermined :magnitude and of different polarity, the combination ofxa movable mirror. means for casting a beam of light onsaid mirror, means responsive to said signals formoving said mirror from a null position to a moved position in either direction from saidnullposition variably in accordance with the instantaneous polarity and magnitude of said signal, photo-electric detecting means, reflecting means forprojecting .the light beam reflected from saidmirror on said photo-electric means when said mirror has moved a predetermined angle in either direction from said null position, and means for adjusting said reflecting means tosimultaneously vary the magnitude of the angles through which said ,mirror must move in both directions from said null position to cause the light beam to impinge upon said photo-electric means and actuate the latter.

ERNEST R. HABERLAND.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 948,424 Long Feb. 8, 1910 2,077,451 Wilson et al Apr. 20-, 1937 2,113,899 Gram Apr. 12, 1938 2,118,082 Hammond May 24, 1938 2,180,413 Harvey NOV. 21, 1939 2,326,252 Rich Aug, 10, 1943 2,356,579 Gardner Aug. 22, 1944 2,365,601 Sipman Dec. 19, 1944 2,483,417 Johnson Oct. 4, 1949

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