Патент USA US2123045код для вставки
July 5, 1938. 2,123,045 's'. c.. HOARE ‘MAGNETIC’ DETECTOR _ Filed July 8. 1936 3 Sheets-Sheet l 8 0 4 ve DISTANCE ?‘fff/ m 20 > > 24 2a Inventxm~ : Stephen C. Hoer'e, by Attorney. July 5, 1938. 2,123,045 s. c. HOARE MAGNETIC" DETECTOR Filed July 8. 1936 3 Sheets—Sheet 2 40 M "a 32l 05 28 |l/ Sm PTm H. en?“cA60¢ro/Wr vm .@ a!I 0H. 0 n26 .% W. July 5, 1938. 2,123,045 s. c._ HOARE MAGNETI C DETECTOR Filed July s. 1936 ‘5 Sheets-Sheet s [III/[III]!Mill/IIIIIIIIIII/IIIIIlI/IIIIIIIIIIIIII/IIIIIIII/IIIIIII/I/I/I/II/I/I/II/I/ , Inventor: b LW. Hh 95 @l mi Law“ tC. a, . 0 n w H j 2,123,045 Patented July 5,' ‘1938 UNITED STATES [PATENT ‘OFFICE’ MAGNETIC DETECTOR Stephen 0. Hoare, Manchester, Mass, assignor ‘to General Electric Company, a corporation or New York Application July 8,.1936, Serial No. 89,620 3 Claims. (01.1-75-183) ‘ My invention relates to a detector of magnetic material and weak magnetic ?elds, such as may be caused by hidden magnetic material or hidden neutralize the in?uence of‘the earth's ?eld on nonmagnetic material in or about which a mag The detector apparatus is useful in‘ locating pipes the compass needle ll. Then, by adjusting the bar magnet towards the. magnetic north, it can 5 neutralize the in?uence of the earth’s ?eld on or other metal objects hidden from view in the the compass needle ll. ground‘ or in walls‘and the like. , In carrying my invention into eifect, I make Then, by adjusting the bar magnet towards the compass needle, overcompensation of the earth's 5 netic ?eld is created by a ?ow of» electric current. , such size and strength that, with its north seeking pole towards the magnetic north, it can . 10 use of a special sensitive compass device, which ismade nearly immune to the earth's magnetic ?eld and which, therefore,-isespecially sensitive as a magnetic detector. The features of my invention which are be “ lieved to be novel and patentable will be pointed out in the claims appended hereto. For a better ‘understanding of my invention, reference is made . ?eld can be obtained, causing the north' end of 10 the compass needle to point south, or, by ad justing the bar magnet away from the compass needle, undercompensation may be obtained.‘ \ H In the use of the apparatus as a‘ detector, it is ordinarily undesirable to exactly compensate for 15 in the‘ following description to the accompanying‘ the earth's ?eld because then the compass needle becomes so sensitive that it requires too long a time for the needle to come to rest in a detect drawings, Fig. -1 of which represents one form of ing position.‘ I have found that, if the earth's go my invention which employs in its construction an ordinary surveyor’s compass; Fig. 2 is a curve explanatory‘of the use of the detector of Fig. 1 in ‘locating a buried iron pipe when no current ?ows through the pipe; Fig. 3 is a curve ex 25 planatory of the use oi?the detector of Fig. 1 in locating a buried pipe whencurrent flows there in; Fig. 4 shows the use of this device as applied for measuring the depth of pipe after its‘lateral location has been determined; Fig. 5 represents 30 another form of the invention which is suitable for locating hidden magnetic parts; Fig. 6 is a perspective view of a magnetic detector which has a freely pivoted compensating magnet and which is self-compensating; Fig. 7 shows a sectional 95 view of a detector of the type shown in Fig. 6 with modi?ed structural details; and Fig. 8 is an explanatory diagram of the action of the self compensating detector. ‘ , Referring to Fig. 1, It! represents the box of an ordinary surveyor's compass having a magnetic needle l'l, leveling gauges l2, orienting sights l3, and tripod ll. The extra parts which may be used to convert this compass into a sensitive _\ magnetic detector comprise parts indicated‘ at IS, IS, l1, and l8. I5 is a nonmagnetic tube ?eld is over or undercompensated'by an amount 20 which causes the compass needle to have a period of about 6 times the period of the uncompen sated compass, satisfactory‘results will be ob tained for ordinary uses. By a period, I mean that, when de?ected from a balanced magnetic 25 position, the compass needle will oscillate back and forth on either side of a zero-de?ecting posi tion a few times before coming to rest. The time of ‘a complete oscillation is called the period. The ordinary surveyor's compass with which I 30 have experimented when uncompensated has a period of about ?ve seconds and when compen sated for practical use as a detector has a period of about thirty seconds. _ . It may be stated that, for a given de?ection; 35 'the sensitivity of a compass needle varies as the square of the period. Increasing the period from ' ?ve to thirty seconds represents an increase in sensitivity of thirty-six times normal for such a compass. The degree of sensitivity which will be 40 most satisfactory in any particular case will depend. somewhat on the nature of the investiga tion undertaken, the strength and remoteness of the magnetic ?eld being located, the time available for the investigation, the degree of 45 such as brass secured across the central portion accuracy desired, and the presence or absence of the compass box. Fastened thereto and ex of other disturbing in?uences. Thus, while I 1 tending vertically above the pivot of the com pass needle is a support ii for a small bar mag 50 net H. The support I6 is made of telescoping . parts so that the bar magnet may be adjusted towards and away from the‘ compass needle II, also the upper telescoping part of support It may be rotated so as to orient the bar magnet l1 in 5‘ any desired direction. The bar magnet I ‘I is of. _have .indicated above a range of sensitivity which is generally satisfactory for the location of underground pipes, it may be desirable to 50 choose a different range of sensitivity for other purposes. ' ' . The operation of a detector of the typeshown in Fig. 1 can also be improved for certain pur poses by the addition of long magnetic ?ns ex- 55 2,128,045 tending horizontally in opposite directions from ?ection c. After a sufficient number ‘of readings were taken, the curve of Fig. 2 was plotted and the pipe :0 located below the point where the maximum de?ection was noted, namely, at four of the equipment, are tubular housings for such teen feet from the left curb. A ?fteen foot length magnetic ?ns. The tubes I! may be of brass of two and one-half inch pipe was located at at, and each contains one or more rods orstrips of four feet below the detector as set above this magnetic material. ' The disposition .of these point. After locating the pipe, its in?uence on the detector. The parts II, which have a tele scoping ?t into the ends of tube I! so that they may be readily pulled out to facilitate portability magnetic strips or ?ns are indicated by dotted 10 lines. They extend in opposite directions from approximately the outer edges of the compass box. These ?ns are preferably made of a mag netic material having high permeability and low hysteresis loss. They serve as a sort of magnetic 15 antenna. These ?ns tend to collect any stray ?ux lines in the vicinity of the instrument which have a direction generally parallel to the fins and direct these ?ux lines symmetrically across the instrument. Their presence makes a ?ne ad Justment of the bar magnet i1 unnecessary and would considerably improve the operation of the compass as a detector if the bar magnet H were omitted. In the use of the instrument, these fins are oriented, for example, in a direction gen 25 erally parallel with the direction of the magnetic an ordinary compass was tried out and it was estimated that, when brought to the fourteen foot station, the ordinary compass changed its de?ection (indicated by the dotted line curve between the 12 and 16 foot stations) by not more than two-tenths of a degree. / _ When a small direct current can be sent 15 through a buried pipe line or the like, its location is facilitated, but a somewhat different pro cedure is recommended as will be described in connection with Fig. 3. In Fig. 3, :1: represents a buried water main known to run parallel with 20 the street, the left curb of which is indicated at the zero foot station. A small direct current can be sent through this main by connecting a storage battery 2! to exposed connections such as the faucet l9 and the ?re hydrant 20 spaced apart lines of force emanating from the object to be ' along the street at points between which the de located as will be explained in examples of the tector is to be used. With a current ?owing use of the detector. through the main 3:, ?ux lines will be set up Fig. 2 is ‘an explanatory graph taken from ac about the main as indicated by the dotted line tual ‘data of the use of the detector of Fig. l encircling :r. In order to best in?uence the de in locating an iron pipe buried in a street. The tector by -such ?ux lines, the antennae or ?ns horizontal scale represents distance in feet from l8 thereof are oriented in a line‘ generally cross one curb used as a reference point. The vertical wise of the pipe line and the detector is moved scale represents de?ection in degrees of the de in a straight line across the street from station 35 tecting instrument. It was known that the pipe to station with the ?ns so positioned. Also, the ran generally parallel with the ‘street but its needle of the instrument is initially magnetically distance from the curb and depth were unknown. biased to approximately right angles to the line It was impracticable in this case to send an elec of the antennae. This is indicated at the three tric current through the pipe and the detector foot station. Readings of the magnetic needle was used for more de?nitely locating the pipe. de?ection of the detector are taken at each sta The detector was set up on one side of the street, tion both with current ?owing through the pipe such as at the point corresponding to the reading line and with no current ?owing therethrough, a, known or believed to be on one side of the pipe. and the angular difference in the readings of the The directions of the ?ns it were generally par needle at all stations under these two conditions allel with the suspected direction of the pipe, is recorded together with the distance measured a the bar magnet H was oriented so as to cause from the curb or other reference point. As the the compass needle ii to point approximately at detector is moved near the pipe line, the an right angles to the direction of the ?ns l8 and tennae catches more and more of the ?ux lines the indication of the compass needle on the angu-_ existing about the pipe line when the current is lar scale of the device was noted. The detector ?owing therethrough and the angular difference was then moved to other stations, crossing the in the detector reading with the current on and street, and readings were noted at each station, off increases. Thus, at the three foot station, this the sights i3 being used to sight on some distant angular difference is thirteen degrees and, at the objects so as to move from station to station twelve foot station, it is about ?fty—two degrees. along a straight line and to keep the orientation A su?icient number of readings are taken to plot of the compass box constant. The distances of the curve, such as is shown in Fig. 3, whereupon each station from the curb or starting point were the pipe line is located beneath the point of also noted so that the curve abcd of Fig. 2 could maximum de?ection. A pipe line four feet below be plotted. the road surface and ?ve feet below the detector In Fig. 2, the detector is indicated as being was so located. set up at the nineteen foot station for obtaining It will be understood that the exposed electric the reading d and, at the nine foot station, a top circuit between connections If! and 20 should be view of the detector is shown to illustrate the run well back, away from the street, otherwise orientation of the ?ns and the nature of the magnetic in?uences therefrom when current is . detector de?ection at this point. As the detec— ?owing will distort the readings and result in 65 tor was moved across the street and readings erroneous results. were taken at the different stations, the needle After having located the lateral position of the of the de?ector tended to turn more nearly par water main as above described, its approximate allel with the ?ns it! as these ?ns collected more, depth can be determined as follows: 70 and more magnetic lines emanating from the The detector is set up under the return elec ‘ buried pipe indicated at 3:. Thus, at the nine tric circuit and the wire thereof lifted above the 70 foot station, the de?ection was increased 1! de detector as indicated, in Fig. 4. The wire is given grees. This in?uence was, of course, strongest the same bearing as the pipe line, the latter hav at the station which was nearest the pipe line, ing been determined by two or more separated is namely, at the station corresponding to the de courses of detector travel. De?ection readings , - . . a ' ;' are'taken with the same current ?owing r " 1.1mm throughI - " needles? In the illustration, aldetectm‘ with only "the-return wire as was used in obtaining the ‘two such ' needles'_~3_l and 32 is‘ shown. These . curvepf Fig. 3. By raising-‘the wire above the‘ _ needles being magnetized are connected together detector such a distance as‘ to obtain. the same‘ magnetically but not mechanically except in so' maximum de?ection as wasobtained when-direct ‘ far as, their pivots 33and‘34 are in axial alignment ly'over the water main, ‘it can be assumed that and ‘have a common supporting structure. The V -_."-the. circuits were the same distance away from‘, _'shorter needle 3|‘ is the detector and'the longer , ' Thus, if _.it is needle 32 is the compensator'for the'effect of the 'the :detector ins both instances. earth’s magnetic ?eld. This compensator 32 is necessary to lift the wire, ?ve feet above the de tector tojobtain this maximum de?ection, it is‘ ‘freely-pivoted instead of 'b'eing‘?xed as in the‘ reasonable to' assume that the detector was ?ve device of Fig. 1. _'The compensator needle 32 is I _ feet above the water main when the same de?ec made long so that it can substantially compensate tion "was previously obtained. This assumption the‘ short needlewith respect‘to the in?uence of , _ 'works'out. to be approximately correct, and the the earth's ?eld ‘and yet be able to take up a ' water mainv :cwas found' within a few inches of 'thedep'th so deduced. 1 ‘ In Fig. 5, I have shown the essential elements 1-15- position nearly in the earth’s magnetic meridian. 15 In this. arrangement, advantage .is taken-of the sensitivity of the detector needle to the adjust f oftanother form of magnetic detector that may be ‘. ment of the compensator, small changes in ad used.for ?nding quite small masses of hidden justment of the latter producinga greater change in the detector. The pivoted compensator acts as 20 magnetic material-aswell as larger masses. does not require the somewhat unwieldly ?ns of further ampli?cation ‘on the detector., A' weak. ~ the device of Fig. 1' to make it highly responsive to ‘ .weak magnetic ?elds. It consists of a long piv oted spindle 25 of nonmagnetic material with I25 ‘magnetic ‘needles‘26 and Y21 on either end. The '- needles 26 and 21 are iixed- to spindle 25 so that they lie in the same‘plane but with their mag netic polarities reversed as indicated by the desig~ nations N and S. If these needles are of equal strength and length and ?xed at their centers at right angles to the spindle‘25, and the device is ‘ i used with the spindle 25 in a vertical position the‘ device will be substantially immune from in?u ence by_ the earth’s magnetic ?eld. If, however, magnetic ?eld to be detected'produces an appre ciable de?ection ‘of the detector needle as before and also a slight de?ection of the compensator‘ needle, but a slight de?ection of‘ the compensator 25 makes for still greater de?ection of the detector and ampli?cation is the result. M ' This type‘ of ‘detectorhas certain‘ advantages as follows: - . . The sensitivity of the‘ detector needlci'is ad 30 justed once for all when the device is‘manufac- . tured. .The compensator needle is pivoted ,and' needs no adjustment other than that which auto matically takes place. All that is necessary in 35 one of the needles 26 is‘ adjustable so thatit can ‘ conducting‘ a search is to turn the compass box 35 be more or less inclined to the spindle 25 in the or support so that the longer needle reads zero on same plane with needle 21, the radius to its pole the scale 35 and note the de?ection of the smaller . tip and its in?uence by the earth’s magnetic ?eld are reduced as'compared to needle 21. In this 40 vway the device may have its sensitivity adjusted to any ‘desired degree of astaticism. The needles are positioned a su?icient distance needle on-its scale 36. The de?ection _of the shorter needle increases with stronger ?elds. I have obtained goods'results with this type, of de 40 tector where the ‘shorter needle was one and three-eighths inches in- length and the longer needle four. and one-half inches in length with as indicated at28', located below the device will ' the needles located in planes two and three-quar ' , _ . , ' 45 45 have a relatively greater in?uence on the nearer ters inches apart. Suchan instrument may be built with a single or' lower needle 21. This greater in?uence on needle .2‘l'is augmented by the fact that its torque scale 35 as shown in Fig. 7 where the short needle arm is slightly longer than that of the inclined 3| is provided with aluminum extensions‘ 31 which needle 25. The spindle 25 will, .therefore, be extend‘ over and indicate on scale 35 with the turned until the lower needle points toward the long needle 32. ‘ " a ' Fig. 8 is typical of the positions of the pointers ' hidden mass of iron. The de?ection may be noted on a scale-indicated at 23.‘ - ~ of the form of ‘detector shown in Fig. 6 when ad This form of detector is usedby exploring the justed for good results and when unin?uenced by region where the hidden magnetic 'material is external ?elds except the earth’s ?eld. The po 55 suspected. The magnetic'mass is located at the sition of 32 is mostly determined by the earth’s 55 position of maximum de?ection. \ ?eld but is oil the magnetic meridian by about I have found that a spacing of about ?ftee ?ve degrees because of the in?uence of‘ the‘short inches between needles 26 and 21 and the relative needle 3|. The short needle is mostly in?uenced proportions indicated in Fig. 5 gives a satisfactory by the large needle 32, to a lesser extent by the detector for general use. ; earth’s ?eld, and takes up the position shown at The device can be used as above described; an angle of about forty degrees from the magnetic however, I have found it convenient to provide a meridian. The forces determining the position of small stationary but adjustable bar magnet 30 needle 3i are a counter-clockwise force due to the pivoted on the same axis near and preferably earth’s ?eld and a clockwise force due to the atabove the upper needle 26. This is convenient as traction between-the unlike poles of the pointers 65 a zero adjuster for needle 21 and as an adjust and a repulsion between the like poles of the ment for the desired degree of sensitivity‘ When pointers. These needles will have other zero bal the bar magnet 30 is included as a part of the de anced positions where needle 32 is rotated ten vice, the inclination adjustment of needle 25 may degrees counterclockwise and ne'edle.3l eighty de 70 be permanently made at the time of manufacture. grees clockwise. The needles will come to rest in 70 In Fig. 6, I have shown still another form of either one of such balanced positions. By mov detector which is particularly suited for con . ing needle 3l._ away from 32, it will be less in _. apart on spindle 25 sothat a mass of iron, such venience and rapid work in locating water pipes and the like. This detector comprises a cascade 75 arrangement of a plurality of pivoted magnetic ?uenced by 32 and the ?ve degreeangle will be decreased and theyfor'ty degree angle increased. The relative lengths of the pointers will also have 75 4 2,123,045 an in?uence on‘ the zero balanced positions of the pointers. . Now assume that I bring a mass of magnetic material Ill within" the in?uence or the detector. 5 Pointer 32 tends to turn toward it. The pointer Ii also tends to turn toward it. This upsets the magnetic forces between the two pointers and changes their ratios with the result that the new de?ection of pointer 3| due‘to the presence of 10 the magnetic mass 40 is further ampli?ed by rea son of the shift in pointer 32. ‘ , The cascade arrangement last described may, if desired, be provided with the antenna of Fig. 1. 'l‘heantenna is ‘indicated by the parts l8a, Fig. 8. 15‘ ,In accordance with the provisions of the patent ' statutes, I have described the principle of opera tion of my invention together with the apparatus which I now consider to represent the best embod~ ' iment thereof but I desire to have it understood 20 that the apparatus shown is only illustrative and that the invention may be carried out by other 'means. _ What I claim as new and desire to secure by 25 letters Patent of the United States is: 1. A magnetic detector comprising, a magnetic compass having a polarized pivoted needle, an lecting weak stray ?ux lines and directing them across the axis of rotation of the ?rst mentioned needle so as to amplify their in?uence on such needle. 2. A magnetic detector comprising, a magnetic compass having a pivoted magnetic needle, and another ‘magnetic needle of shorter length than the ?rst, mounted adjacent the ?rst needle, and adjustable about the same axis of rotation and towards and away from the ?rst mentioned nee die, the shorter needle serving to substantially ' compensate ‘the ?rst for the in?uence of the earth’s magnetic ?eld thereon, whereby the ?rst mentioned needle becomes sensitive to weak mag netic ?elds in the vicinity which would have a negligible in?uence thereon ‘without such com pensation. , ' 3. A magnetic detector comprising in combina tion, a surveyor’s compass having a pivoted mag netic needle, a permanent magnet or. shorter 20 length than the magnetic needle mounted so as to be adjustable about the axis of rotation of the pivoted needle and toward and away therefrom for the purpose of neutralizing the‘in?uence of the earth’s magnetic ?eld on said pivoted needle 25 to the extent that the period of oscillation of said other polarized needle mounted adjacent the ?rst . compass needle in the earth’s magnetic ?eld is needle and adjustable about the axis ‘of rotation approximately thirty seconds, and'magnetic an of the ?rst needle, said second needle having such tenna means comprising strips of high-permea 30 location, polarized strength, and dimensions as bility magnetic material having a low-hysteresis 30 to substantially compensate the ?rst needle for loss extending in opposite directions from said the in?uence of the earth’s magnetic ?eld there compass at right angles to the axis of rotation of on, the degree of suchcompensation being adjust; able, whereby the ?rst mentioned needle becomes 35 su?iciently sensitive to weak‘ magnetic ?elds in the vicinity thereof to be used in detecting the location thereof, and a magnetic antenna for col its needle for increasing the sensitivity of said needle with respect to weak magnetic in?uences in its vicinity. 35 STEPHEN C. HOARE.