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‘ NOV.l2_,1946." ' . sTmsgNi 2,411,010 . ELECTRICAL MEASURING INSTRUMENT Filed June 9, 1944 , ‘ 2s’ v = ' l9 s sheets-sheet 1 , fl i ' J5‘: ‘ i _l. | : | - - 1 M77 i | . P l' l | l' | | I : ' " L ___v_..__ Fig.4. ' "~' I " - T ' _ _ ‘ _ _ ___.;___ _ s6 l I ..|.__ ' ‘7: l ' v l _ | 1 J _._-__-_.' 1 "' _ ' " ' 1F 3.; 71 ' 45 ' 7a - . Inventor. _ Allen 6. stims'oh, 14 ‘ I I by " ‘His Attorneg. NW- 12,1946- ‘A. G. STIMSCN ' ' " ‘2,411,010 ELECTRICAL umsunms INSTRUMENT , Filed June 9, 1944 s Sheets-Sheet 2 ‘ Inventor: Allen 6. Stimson, by ~ mttorneg. Nov. 12, 1946. - ’ '1 J’ ' i I " A. G. s'nMsoN ' 1, 2,411,010 ELECTRICAL‘MEASURING INSTRUMENT ’ Filed June 9, 1944 3 Sheets-Sheet 3 I . ' _ ' . Iriv‘entor: . Allen 6. Stimson, ‘ Hus Attorneg. . . Patented Nov. 12, 1946 2,411,010 ' UNITED STATES PATENT OFFICE " MTZTZZIZI'Z?ZZGMZT 213:?.. General Electric Company, a corporation of New York Application June 9, 1944, Serial No. 539,546 ’ 1 Claim. 2 (01. 172-245) , 2 . My invention relates to, electrical measuring in'series‘and, except for the split arrangement‘ instruments and particularly to miniature instru to balance the coil assembly with respect to the ‘ments for measuring frequency, although certain armature shaft, might be considered as a single features of the invention areapplicable to measur coil, since they are connected in boosting relation. ing instruments generally. An important object 5 The armature circuit includes a condenser ‘l, a of my invention is to provide a compact, rugged, . variable resistance 8, and a variable reactance 9. lightweight measuring instrument of goodac The armature circuit thus comprised is connected in parallel with the ?eld coil I0 across the source curacy which is easy to assemble. The instru ments to be described were designed for use on aircraft where it is especially, desirable that in struments be small insize and light in weight. The features of my invention which are believed to be novel and patentable will be pointed out in . I I, the frequency of which is to be measured. For the purpose of representing a, practicable example, it will be assumed that the normal frequency of the source of supply is 400 cycles and'that the“ scale range of the frequency meter is from 350 the‘claim appended hereto. Certain structural to'45‘0 cycles. features of the instrument described herein are 15 The ?eld coil I 0 is of high reactance and its claimed in a divisional application Serial No. current represented by vector 12, Fig. 2, lags ap 588,196, ?led April 13, 1945. For a better understanding .of my invention, reference is made in theiollowing description to the accompanying drawings in which Fig. 1 represents an improved circuit arrangement for a frequency meter embodying my invention; Fig. 2 is a vector diagram explanatory of the theory of operation of the frequency meter of my inven tion; Fig. ,3 is a diagrammatic representation of a frequency meter embodying my invention; Fig. 4 represents connections for a wattmeter em bodying'certain features of my invention; Fig. 5 represents a plan view and Fig. 6 a side view of a measuring instrument embodying my invention, the latter view‘showing a portion of a casing for , the instrument; Fig. 7 is an exploded view of the coil, laminated ?eld core, and supporting plate used in my invention; Fig. 7a shows one half of the ?eld core assembled; Fig. 8 repre sents an exploded view of the armature assembly and supporting structure used in the frequency meter of my invention; Fig.9shows the preferred shape of‘ ?eld pole tips and armature core for use in a, wattmeter; Fig. 10 represents ‘the type of armature used in a wattmete'r; Fig. 11 shows the armature circuit of the frequency meter ener gized from a secondary coil on the ?lled core to proximately 90‘degrees behind the applied voltage represented by‘vector l3. The armature circuit is tuned and the phase angle of its current varies 20 with the frequency. At app'roximatelyrated fre quency of 400 cycles the armature circuit is I preferably tuned for resonance ‘so that its current represented by vector‘ I 4 is in phase with the voltage l3 at this time. Since I B is 90 degrees out 25 of phase with the ?eld current I2,_no torque due to current flow will be present at this ‘time. The armature, however, is provided with a tiny mag‘ netic vane l5 positioned with its magnetic axis at right angles to the axis of the armature coils, 30 which vane is attracted by the ?ux across the armature air gap and positions the ‘armature so that its coil axis is at right angles to the ?eld 7. ?ux axis across the gap under these conditions, and at this time the pointer is positioned to'read 35 near the center of the scale at the 400-cycle graduation. Now when the frequency goes below 400 cycles, the armature current will leadthe . voltage 83 as represented by vector M’, and a down-scale instrument torque represented by" vector‘ 56' will exist, producing a down-scale de?ection. At frequencies above 400 cycles thev > armature current will lag the voltage l 3 as repre- ' .sented by vector l4", and an up-scale torque represented by vector I6". will move the pointer is a vector explanation thereof. . ‘ 45 up-scale from center. The magnitude of this First, I will explain ‘the theory of operation up-scale and down-scale torque may be increased of my frequency meter in connection with Figs. for a given armature current by increasing the 1, 2, and 3. The instrument has a stationary values of capacitance and reactance in the arma provide temperature compensation; and Fig, 12 U-shaped?eld core i energized by a voltage coil ‘ ture circuit in comparison to the resistance, and ‘ and has a moving armature winding split into 50 the scale distribution changed accordingly. When two coaxial coils 2 and 3 mounted on either side the details of the armature assembly are de- ' of the armature shaft it and a pointer ,5 cooper ‘ scribed, it will be pointed out thatthe torque ating with a scale 5. The connections for measur of the magnetic vane 15, which opposes the ing frequency are as represented in Fig. 1 where ‘up-scale and down-scale instrument torques de- I it is seen that the armature coils are connected 55 scribed, is alsoadjustable. The center restoring 2,411,010 torque furnished by vane I 5 varies with the voltage and makes the frequency meter substantially independent of voltage variations. 'It is desirable that the armature current be kept at a low value and that the physical dimen sions oir the circuit elements ‘I, 8, and 9 be small After the initial calibration adjustments these circuit elements have ?xed val a and light in weight. 4 , to the supporting plate II by screws 33 and-ll ‘which also clamp the support I! for the arma ture assembly to the upper pole piece surface of the ?eld core as shown in Figs. 5 and 6. The openings for the screws 33 and 24 are numbered 33' and 34' respectively. The supporting plate ll has peripheral recesses at ‘26, 21, 28, and II positioned to receive the large heads of the rivets 40 (see Fig‘. '1) which are used-‘in the holes 2|, ues. Without intending to limit my invention but 25, etc., to rivet the laminations together. This to give a practicable set of values for the dif m facilitates quick assembly and aids in a rigid eon ferent circuit elements and assuring a 110-volt structlon. supply, I may use a coil at l0 having 1800 turns replacement and repair of the coil and low-cost The splitcore arrangement facllitates- . of 0.008 inch copper wire, .425 henry, and‘ 56 assembly of laminations, since each stack can be ohms resistance. The two armature coils may assembled and each half of the split core assem 15 have 600 turns each of copper wire, the induct bled before the coil is added. ance 9 may have 5 'henrys, ‘and the capacitance It will be ‘evident that the generally U-shaped at "I may be a .03 microfarad condenser. The re > ?eld core described above has its laminations par-v sistance of the armature circuit is of the order allel with the plane of the U and is appreciably of 11,500 ohms. ‘Under these conditions the ?eld 20 thicker and of larger cross section in the pole current will be of the'order of 120 milliamperes piece portions than in the yoke portions by rea and the armature current of the order of 10 mil son of the pole piece parts I8 and is, Fig. '1, liamperes at rated voltage and frequency and which lie entirely above the plane of the remain with the aid of features to be‘ described herein der or the core in a direction at right angles to after, the entire instrument and ‘circuit devices the plane of the laminations. The thickness of ' 25 may be housed in a cylindrical casing having out the pole piece portions or the core is increased side dimensions 2% inches in diameter and 3 with respect to the yoke portion of the core by inches in length. I desire to point out at this the depth of these laminated ‘pole piece stacks point that the instrument above‘ described may l8 and it. One advantage or this is that I can be used as a position indicator by maintaining operate the yoke portion of the core at a higher: the voltage and frequency constant and varying 80 ?ux density than would be advisable for the pole the tuning of the armature circuit as by varying piece portions and thus save material in the yoke the reactance I, for example. section, and correspondingly reduce the inner and outer diameters of the coil II and the volume Field structure and weight of copper used therein for a. given The laminated magnetic ?eld core i is de number or ampere turns and coreloss. At 400 signed for minimum weight for a given iron loss, cycles, for which the frequency meter is intended, to facilitate assembly in a prewound coil and the core loss is likely to be considerable unless ' of the assem . to reduce the space requirements certain precautions are taken. The construction bled instrument. The core with its coil i0 and go permits of an accep 'ble core loss without sacri ‘ coil supporting plate I1 is shown disassembled ?cing coil space. The laminations 2| and 22 in Fig. 7. The core comprises six stacks of la'm- I which thread the coil III are preferably made of The stacks 2| and 22 the order of only 0.005 inch in thickness, which inations I. to 22 inclusive. are similar and may be stamped with the same reduces the core loss in the higher flux density piece sections integral , at‘ die, and include pole 45 yoke part of the core, while the laminatlons 01' one end with the yoke or coil enclosed parts which parts I8, It, 20, 22 which operate at appreciably are the‘ longerleg portions thereof and which lower flux density and where there is greater need are assembled side by side. The stack sections of- structural rigidity, are preferably made of the ll, 2|,, and 22 are assembled as one group or unit as shown in Fig. ‘la, and comprises one pole order of 0.014 inch in thickness. It is to be noted 50 that the laminations of the different core parts are not interleaved, as this would not permit of piece and one half the yoke, part‘ 22 being be tween parts II and 22, and these parts riveted to different thickness laminations in parts Y20 and gether by rivets that pass through the aligned 2|, forexample, which lie in the same plane, nor rivet holes 24 and 25. the. same rivet passing would it permit of the ease of assembly and dis through the holes which are numbered alike 55 assembly obtained. Instead of interleaving the inrlg?l. laminations, certain core parts as a whole over Core parts ll, 2i, and 22 are assembled as a lap and abut against other core parts at the junc group with part 2| between I! and 23 and riv- . ' tion of pole pieces and yoke sections and are the other pole piece and eted together to form then clamped rigidly together. one half of the yoke. The non-polar ends of the To reduce further the core loss of the lamina two half yoke portions are then slid through the w tions, the rivets and screws used therethrough coll I! from opposite ends, part 2| above and flat are kept as near the periphery of the core and against part 22, until the facing surfaces at 20, out of the main ?ux pathv as is possible. As Fig. ‘I, abut and the facing surfaces at 21 abut. shown at 28 and 29 in laminated parts 2i and and the bolt openings numbered 2! are aligned and as 22,.1-espectively. the bolt openings are not closed andthose numbered 2| are aligned. Bolts 22' ‘ by magnetic material. _-where ?ux can pass out 22', Fig. 5, are then passed through the openings side of a bolt or rivet, it will be noted that the respectively, and the corresponding cross section of the magnetic material op the numbered openings in the plate II. The assem outside of all rivets and bolts is substantially the bled eore structure with its supporting plate i1 same. _ Hence, it any flux does go outside the is then clamped together and against the upper 70 bolts and rivets, that part of the flux will evident ‘ ?at surfaces (see rigs. 5 and 6) of pedestals 3| ly stay outside all rivets and bolts around the insulating support and wall rising from a circular ll adapted to. ?t into a cylindrical casing 32 as entire periphery of the core. which would tend to induce currents therein oi the same phase and best shown in Fig. 6. The pole piece parts of ‘(5 magnitude but without a return circuit and as the assembled core iaminations are also clamped 2,411,010‘ 5- - . a consequence of the arrangement, negligible eddy current loss is occasioned by the presence of the bolts and rivets. For 400-cycle service I pre fer to use laminations made of the high per I by the flux is inserted an aluminum damping vane 58 secured on the armature shaft 59. The armature meability nickel iron alloy known to the trade UK as Nicaloi. . A ‘ It will be noted that the damping vane 58 is of an open or half cup shape between the point wherev it is fastened to shaft 59 and the ?at - outer peripheral portion, with the shaftinserted through the bottom of the cup and the cup open In Fig. 6 the upper half of the nearly square yoke section is outlined by dotted lines, while the lower half is shown in full‘ lines. It is to be noted that the pole piece portions of the core are offset from the center of the coil in one direction ing upward. This cup shape provides added strength and rigidity to the damping vane and at right angles to the plane of the laminations - provides space and‘protection within the cup ' towards the scale plate 6. This has the advan tage that the scale plate may be placed lower for the upper spiral lead-invwire 60 and the collar ‘to which the pointer 5 and the balancing down than would be the case if the coil were 15' arms 6i are secured. centered in the vertical direction with the pole The balancing arms Bl are at right angles to each other and 45 degrees pieces, ‘as viewed in Fig. 6, and requires less off from the pointer forward of and in the same plane set of the pointer 5 and saves a corresponding with the damping cup member 58 where they amount of space in the over-all height of the in are accessible for adjustment of their weights. strument as picturedin Fig. 6. 20 This arrangement allows of balancing with two The armature assembly and support counterweights instead of three as is usual. It also allows of quick balancing with few opera All parts of the armature, its pivots, lead-in ' tions as follows: With the instrument shaft held spirals, magnetic damper, armature stop, zero adjustment, and scale plate are supported by the 25 horizontal and with one balancing arm vertical, the armature is balanced with the other vor hori support 35 (see Figs. 5, 6, and 8), and all of these zontal balancing arm weight. Then the‘ arma parts are removable from the instrument as a ture is rotated 90 degrees so that the other bal unit by taking out the two screws 33 and 34. ancing arm is horizontal and its counterweight The support 35 is an integral die casting of non magnetic, corrosion-resisting material such as 30 is shifted until a balance is obtained. Theinstrument shaft 59 is a hollow bronze aluminum. The scale plate 6 is fastened there tube with the upper and lower pivots 62 and 53 to by two screws 4! (see Fig. 5). The support pressed into its upper and lowerrends. The mag 35 has a lower forward horizontally extending netic vane‘ I5 is secured to the shaft within the part 52 which supports the lower bearing 43 and 35 coils and is adjustable about its .center support stud which goes through the shaft 59 so that The upper bearing 85 and ' . the effective length of the vane and its torque in upper lead-in spiral adjusting means 46 are sup- the ?eld ‘of the instrument may be 'varied. The lower armature lead-in- spiral supporting and ad justing element 55. ported by a strap 6‘! which is fastened to the lateral and forward extending top part of the support 35 by screws 58 entering into threaded‘ 40 openings 59. The two spiral adjusting means 85 and 45 are clamped in place coaxially with the axis of rotation of the armature under the come pression of resilient slightly dish-shaped fric tion washers 50 which permits‘ of their being rotatively adjusted readily but without danger of accidental movement from adjusted position by vibration. \ ' ‘ Beneath the top bearing bridge strap 57 there is a central recess in the support 35 into which there loosely fit a kidney-shaped permanent mag-v net 5i and spaced return flux keeper 52 com prising the stationary part of a magnetic damper for the armature. The damping magnet parts 5| and 52' are secured near‘ the upper end of a strap 53 which ?ts into an elongated vertical slot 55 in vthe rear side of support 35 as viewed in Fig. 8, and secured in place by a screw which enters through a hole '55. The damping mag net parts may thus be polarized as a unit and added last during assembly of the instrument parts and kept clean'of magnetic particles. ‘The strap 53 in the ‘frequency meter also supports a removable armature stop 56. The stop‘ 55 has 45-degree position of the. vane shown inFig. 8 gives approximately the correct restoring torque for the frequency meter described. When cor rectly adjusted it is permanently secured in place. , g y The armature coils 2 and 3 are shell-less and are held to the shaft by two ?at-surfaced bush ings 64 of insulating material ?tting against the inner surfaces of the coils and to which the coils are secured at top and bottom by cement andlashings. The armature coils are wound with formex wire with the turns cemented to gether into a solid mass andv are su?iciently stiff to provide their own support without using a shell or other coil ‘form support. This gives an exceptionally high ratio of useful armature, torque to armature weight and space. On the shaft below the coils theremay be a washer 65 of mica to protect and, insulate the lower lead in spiral 56. The lead-in spirals of the fre- v, quency meter are adjusted to have minimum torque. , , In order to give a better idea of dimensions, it may be stated that the total length of the ar mature coils is' 1% inch, with other dimensions in the proportions pictured in the exploded view of Fig. 8. When the parts shown in Fig. 8 are a screw part threaded in the support 53 and a 65 assembled, the total height of the assembly is. forward'ceram'ic' bushing part of insulating ma terial which extends freely through the open ing 57 in the support 35 and into the path of ‘approximately 1% inches. This assemblyyto gether with the scale plate which is omitted in Fig. 8 may be removed as‘a unit from the pole piece assembly by removing the two dowel screws of the armature as viewed in Fig. 8, and serves 70 33 and 3.5, Fig. 5, and when this‘ assembly is in to stop their swing at suitable limits in both place in the ?eld and the dowel screws are directions. The permanent magnet 5| is po tightened, the armature coils are correctly po larized as indicated in Fig. 8 so as to produce sitioned in the ?eld air gap. swing of the armature coils 2 and 3 to the rear ‘ a flux across the air gap between it and the flux ‘ The circuit elements of the frequency meter return part 52, and into this gap so as to be cut 75 comprising the condenser l, the resistance 8, £2,411,010 and the reactance 9 are housed'in the same a secondary winding" inductively coupled with insulating partition base 31 which supports the the ?eld coil ill instead of being connected across the line II as in Fig. 1. In case the coil l0, Figs. 1, 3, and 11, increases considerably in tempera instrument as indicated. The supporting en closure for the condenser 1 may be held be tween the partition SI and a cross plate indi cated at'i'l by bolts 68. The casing 32 may com likely to shift as represented by the dotted vector 12', Fig. 12, at any given frequency. If the ar casing 32 (see Fig. 6) with the instrument and are preferably mounted on the rear wall of. the ture so that its resistance component increases in comparison to its reactance, the field flux is is mature circuit is connected across the line as in Fig. 1, there is no corresponding shift in its phase '10 10 both secured to the base partition SI of the prise two telescoping cylindrical parts 89 and instrument. Casing part ‘Iii which is the outer rear telescoping part is held in‘ place by nuts on bolts 68. Casing part 69 is held in place by position due to temperature rise. If, however, the armature circuit, including coils 2 and 3, is energized inductively by transformer action from ?eld coil in acting as a primary of a transformer. screws, one of which is shown at ‘H, and which are accessible when the casing part ‘I0 is re 15 any shift in the'phase position of the flux in the core i due to rise in temperature of the winding It will produce a corresponding shift in the ar of the instrument. Frequency meters and mature voltage because here the armature volt wattmeters such as described are now being age is referred to the field ?ux I: rather than built for use on airplanes, enclosed in cylin to the linevoltage ii. Thus, at a given fre drical casings less than'three-inches in total 20 quency, if the field ?ux shifts from It to II’, Fig. length and about 2% inches in diameter. moved. 12 represents the electrical terminals 12, the armature voltage phase position will shift When used as a wattmeter the connections are as represented in Fig. 4.‘ The wattmeter ar from H to ll’, which tends to compensate for the temperature error that would otherwise exist mature coil is represented at 13, and the arma ture circuit is the potential circuit and contains 25 due to this shift in the ‘?eld ?ux phase position, . since in Fig. 11 the phase relation between the an adjustable resistance H for calibration and ?eld flux and armature current-is substantially a‘ ?xed inductance 15 to obtain correct phase unaffected by the changes in field resistance with angle adjustment between the ?eld and arma temperature changes. The armature circuit is ture. ?uxes. The field 16 is preferably ener gized from a current transformer 11 connected 30 nevertheless tuned and shifts as in Fig. 2 with frequency‘ variations. The change in power vin the current circuit of the line 18 metered. factor of ‘the secondary armature circuit in Fig. In the wattmeter I prefer to use an iron core 11 due to changes in frequency has an insis 19 in the ‘armature and change the shape of ni?cant effect upon the power factor of the pri the pole pieces to that represented in Fig. 9. The same split core and offset pole piece assem 35 mary field coil circuit ll, because the secondary transformer burden represents a very small‘ bly of the laminations are employed as in the percentage of the input to coil vl0. frequency meter, the only difference being in In accordance with the provisions of the pat the pole face shape of the pole piece laminations. ent statutes I have described the principle of op In the frequency meter the pole tips were square to obtain better magnetic vane, center restor 40 eration of my invention together with the ap paratus which I now consider to represent the ing torque. A conventional style of wattmeter best embodiment thereof, but I desire to have armature is used as represented in Fig. 10, but it understood that the apparatus shown isv only the cup-shaped damping vane 58 and armature illustrative and that the invention may be car balancing arrangement 6| previously described is used thereon. The lead-in spirals 60 and 88 45 ried out by other means. What I claim as new and desire to secure by Letters Patent of the United States is: An alternating current electrical measuring in strument comprising ‘a magnetic field core struc in Fig. 8 are used. The opening 51 in support 35 which ‘in the frequency meter contained a 50 ture and energizing coil therefor, a moving coil armature within the field produced by the field removable armature stop is used in the watt core structure, said armature having a tuned meter to hold a screw which supports a ceramic circuit and the instrument operation being due armature stop 80 (Fig. 9) and a holding screw to changes in the phase angle of the fluxes pro ill entering from the rear of such opening is threaded into support 35 to securely hold the 55 duced by the field and armature by reason of a shift in the phase angle of the armature flux in part 53 in correct position. The core is held in response to a variable to be measured. and a sec place between parts one of which is shown in ondary coil on the field core, from which said part at 82 (Fig. 9) which extend laterally from armature circuit is energized by transformer ac the support 35 just inside the armature coil and tion from the field coil acting as a primaryin. grasp the core ‘I! from the top and bottom. order to maintain a substantially ?xed phase In case the frequency meter is likely to be sub relation between the field flux of the instrument jected to considerable temperature variations, a are here used in place of an iron vane for zero restoring torque. The same armature assem ' bly support 35 and damping magnet SI, 52 shown further improvement may be had by employing - and the excitation voltage of said tuned arma- _ the circuit shown in Fig. 11 where the armature circuit, including coils 2 and 3, is energized by 65 ture circuit. ' ALLEN G. S'I'IMSON.