[1]iL al%ented May 18, lk3 29319,406 UNITED STATES PATENT OFFICE 2,319,406 TEM:PERATURE CONTROL INSTRUMENT Harry S. Jones, Washinston, D. C., asdgmor to The Brown Instruinent Company, Phfladelphia, Pa., a corporation of Pennsylvania Application October 16, 1941,, Serial No. 415,252 7 Claims. (Cl. 250-41.5) The present invention relates to automatic control apparatus and more particularl to autc@- y matic control apparatus of the type An which there is provided follow-up to effedt proportionate control of a supply of a condition varying mediUM 5 and in which this control Is effected to give a respori@p that is proportional to the date at which the condition under control Is changing. .An object of the,invention is to provide automatic control apparatus of the type referred to 1( above wherein the primary controlhng element is a highly sensitive device having a delicate actuating member and one in which tl,.e adjust2nents of tb-e control deace for regulating the . sr-pply,,of a condiiion varying agent are effect-ad 111 in respt)nse to Pefup-tion of said actuatirig inember ivithout placl-ig eny rest.raining force up@on tl,le same. By irtiposiy,,g no v,7or,',, on the primary controlling ele.Laieii-t prlcision of its actuating element is sssured. 7-,,ie specific object of the 1-n- 20 vention is toprovide an apparn-tu@- of the -c,ype in which there is a follow-up mechanism wlich viiii egeet proportio-tial control of 'che conrlition varjing medium a-xid which control tekes Into account the rat-, at which'the cond-itioi-i Is var3,,ing. Such 25 a contibl will ciulckly bring baclp, to the cont2ol point any conditio.,i v;.hich is varying from satd 1.)oint. This is aconiplished since if the@ condition is changing quickly a larger co-ntrol et7ect will be tr m tiie prior are most automatic controlling devices , which are adapted to effect proportional regulations to the supply of the condition changing ag@nt were limited to arrangements wherein 3; 1 -) the primary control elemen:t was forced either to do some work and thereby reduce its sensi- I tivity or was clamped ailid then had some relay mechanism perfoi-m the control functioii. Flurtherinore, when rate response was added to the 40 ordinary control of the prior art this meant that a highly complicated mechanical or electrical arrangement was necessary. - In accordance with the present invention a highly developed type of control in which bbth 4.5 follow-up and rate response are used to adjust. the supply of a condition changing agent with-,,@ out in any way affecting the movement tyf the primary measuring element. -Tn the preferred form of the invention provisions are included for 10 res@My effectirig a throttling range adjustment whereby.ihe'eictent of the control'device is ad'Justed in response to a given change in the condition. There is also provided a means for - effect- - ing a rheostat adjustment-of a -change 'in an 55 operating condition such, for example, as a change in the load of a fumace to bring th-a condition back to its normal value without affectina the rest of the control system. The various featllres of novelty which characterize this invention are pointed Qut with partidularity in the claims annexed to and for--@ning a part of this specification. r@or a-better understanding of the inv@ntion, however, its advantages =d specific objecto obtained 'With it@ use, reference should be hp-d tci the accompanying drawings and descriptive matter in which is illustrrsted and descriL-,-ed a pieferred embodimeii-t of the invention. In 'the dravyings: Fig. i Is a diag:-ammatic representation of a preferredembodiment of my invent,ion; Pg. 2 Is a diagramrnatic drawin-g-' showing a top view o,.? 'thcoptical sy.,@tam; -mig. 3 L, r. view shov@fing r:@ modified form of the iriveiLit@'on; Fig.,@ is a viecl Gf f-,nother rnodiftatioii ox' tne L71vention; rlg. 5 is F, viet-,i of still another inodi:acation of the invention @,nd 6 is P- vievr of anot:-ie@: eml-,odiment of the. inve,-Lit,ion us4-ig a difierent(type of apparatus to det the rs@t-- rcsponse. VThile the coiitrol system@ of the present inpretsure, flow, liquid level, etc., it is disclosed lr, the drawings, for purposes, of Illustration, as c6ntrolling a temi3erature condition, and more Part'iculrrly, the temperature within the interior of a furtiace: i to which a thermocouple 2 is responsive. The supply of heating agent or Luel to the fumace- is controlled by a valve 3 which Is adapted to be adjusted in a plurality of positions under control of the thermocouple 2 and thereby in response to changes in the temperature within the furnace 0. The thermocouple 2 is connected by conduetors- 4 and 5 to the terminals of the movabiproll of a suspension type galvanometer indicated generally qt 6. -The galvanometer 6 is a highly sensitive measuring instrument capable of responding to extremely weak electric current flows in the conductors 4 and 5, and is utilized in accordance with the invention to control the selectiv6 actuation of an electric circuit indicated generally at 7. The manner in which the galvanometer 8 is utirud fqr effecting such control is illustrated diagrammatically in ngs - 1 and 2. The electric circuit 7,- In tum, controls the se. given to the con' olling medium than if 30- vention may be utilized for controlling the value the co,-idition is changing more slowly. of any variable condition such as temperatui,e.
[2]2 2,310,406L lective actuation of a relay 8 and thereby controls the operation of a reversible electrical motor 9. The motor 9 positions fhe valve 3 and also operates a follow-up mechanism. The follow-up mechanism, in turn, controls the operation of the circuit 7 and relay 8, providing a true follow-up control system. The valve 3 is opened and closed by inotor 9 v,hich is selectively controlled for rotation in one direction or the other by field windings 15 and 16, the arrangement being, such that when only the field winding 15 is energized, valve 3 is adjusted towards its open position, and when only the field winding 16 is energized, the valve 3 is moved toward its closed position. . The shaft of motor 9 is also operatively connected with a contact 17 which is disposed in engagement with a slidewire resistance 18, and is adapted to adjust that contact along the length of the resistance 68 whenever it operates- ?o to adjust the position of valve S. The contact 17 and slidewire resistance IS are connected in the follow-up arrangement I 0 refeired to hereinbefore, and for convenience will hereinafter be referred to as the follqw-up potentiometer. When the valve 3 is adjusted toward its open position, the contact 17 is moved toward the right. The relay generaby designated at 8 includes a pair of coils IC and 2 0 which are disposed in operative relation with 9, balanced armature 20. o Armature 21 is pivoted for rotation at 22, a point intermediate its ends, and carries an iron core 2 3 at one end, which core is adapted to move into and out of coil 90, and carries an Iron core 24 at the other end, which core Is adapted to move into and out of the coil 20. Armature 29 also carries a switch blade 25 which is disposed between a pair of stationary contacts 26 and 27. When the coils 09 and 20 are equauy energized, the switch blade 25 is, held interme- 40 diate and out of engpgement w-ith both of the . contacts 26 and 27, but when one, of the coils 19. or 2 0. Is energized to a greater extent than the other, the switch blade is moved into engagement with the contact 26 or 27 respectively. 4.@, Electrical power Is adapted to be suppred the reversible motor 9 through the switch blade 25 and'contacts 26 and 27 of relay 8 from alternating current supply conductors LI and L2. As illustrated, the right end of the :deld 'windings r)o 15 and I 6 of motor 9 are connected together and to the supply conductor LI. The other end of the field winding 05 is connected to the contact 27 and the other end of the field winding 16 is connected to the contact 26. The switch i-,:-) blade 25 of relay 8 Is connected to the supply conductor L2 so that on deflection of the switch blade into engagement with the contact 26, energizing current is supplied the field winding IS to produce rotation of the motor 14 in one. direction, and oii deflection of the switch blade into engagement with the contact 27, energization current is su]@plied the fleld winding 05 to produce rotation of the rotor 14 In the opposite direction. (i5 Electric power is supplied the relliy 8 under control of the circuit 7, referred to hereinbefore, from the high voltage secondary, winding 28 of a transformer 29 having a line voltage primary winding 30 connected to the alteinating voltage i) supply conductors LI and L2, and seaondaiy windings 31, 32, 33 and 34. To this end the lower terminals of relay coils 19 and 20 are connected together and are connected by a common conductor 35 to the right end terminal of the see1( i.-) ondary winding 28. The upper terminal of relay coil 19 is connected to a tap 36 Intermediate the terminals of winding 28 through a circuit which may be traced from said uplyer terminal to a c6nductor 37 through the anode to-cathode resistance of the triode section A of a twin type. electronic valve 36 which also includes a triode section B, a conductor 39 to a tap 40, which is acljustable along a slidewire rest@tance 42 resistance 42, and a conductor 43 to the tap 3i on transformer secondary winding 28. As ghown, the transformer secondary winding 32 Is con-: nected across the terminals of the resistance 42. :It Is noted the portion of the secondary winding 28 to the left of the tap 36 is so wound with iespect to the rest of the winding and with respect to the secondary winding 32 that the polarities of the voltages during one half cyclegre as shown. The upper terminal of relay coil 20 is connected to the tap 36 o,n winding 28 through a circuit including a conductor 46, the anode to cathode resistance of the triode B of valve 38, the conductor 39, tap 40, resistance 42, and conductor 63. When the otriode sections A and B of valve So are equally conductive, the relay coils 99 and 20 are energized to @he same extent and consequently the relay switch arm 25 will be held in an intermediate position out of engagement with both of the contacts 26 and 27,.but when one triode section A or B is more conductive than the other, the relay coU d9 or 20 will be energized to a greater extent de@ending upon which triode section Is more conductive. As illustrated, the triode section A includes an anode 65, a control grid asi a cathode @7, and a heating-Illament 68. The triode section B sim-; ilarly Includes an anode 49, a control grid 50, a cathode3faiida'heatingfilament52. TlkeheatIng Maments 68 and 52 may be connected In parauel as shown and receive energizing current through conducting leads, not shown in oider not to confuse the drawing, from the transforiner secondary winding 3C. Anode voltage is supplied the triode sections A and B through the energizing circuits traced above for the relay coils 1 9 and 2 0. . The P.,rid circuit for the trigde A may be traced from the grid 46 to a conductor 33, iri which a current limiting resistance 56 Is inserted to the left end terminal of winding 28, tap 36, conductor 43, resistance 42, tap 40, and conductor 39 to the cathode 47. It is noted the winding 32 and the portion of winding 28 to the left of tap 36 are so phasedas to oppose each other, the winding 32 tend'm 'i t6. render the grid 46 negative with respect to cathode 47 during the half cycle when the anode 45 is positive and the portion of winding 28 refeir6d to tending' tp render the grid 46 positive with respect to cathode 47 during the same half cycle. Whether the grid 46 is at the same potential as cathbde 47 or positive or negative with respect thereto -is determined by the adjustment of contact 40 along resistance 42. It Is noted the potential of grid 46 is substantially constant during the normal operation of the system. The grid circuit of the triode B ma@y be traced from the grid 50 tc> a conductor 55, in which a current limiting jresistance 56 and a resistance 57 shunted by a condenser 58 are inserted, to the resistance 42, tap 40 and conductor' 39 to the dathode 5 1. The potential of grid 50 relatively to cathode. 5 I is adapted to be varied In accordance with the ibutnination of a photoelectric cell
[3]2,819,408 It. The photoelectric ceH St may desirably be of the electron epimve type and Is c'onnected between the right end terminals of transformer amndary winding 28 and resistance 57. 7be current conducted by cell 51 passes through real3t&nee 57 so that a potential drop is established across the latter, ibe ' magniture of which potential drop depends upon the luumination of the photoeleteric ceU it., The ceU. 59 Is so connected in the circuit that the polarity -of the it) potential drop estabushed Is that shown. The energizing circult'for cell 59 may be traced from the right end terminal of wlnding 28 to con-'@ ductor 35, cell $9, conductor 55, resistance 57, and conductor 41 to the tap 36 on winding 28. 1.-) The iuumination of cell 59 Is controlled by the galvanometer 6 in response @D variations of the temperature within the furnace I by means wbich are described hereinafter. The.adJustable resistance 42 is included In a 20 connection which is common to the grid circuits of both '@riode sections A and B so thgt adjustment thereof opeiates tD simultaneously change the potentials of the grids 46 and 50 relativeiy to -their associpted cathodes. It is noted that ad- 25 justinent of the contact 40 in the direction to Include more of the resistance 42 in circuit is effective to render the grids more negative *ith respect to their 9:ssociated cathodes while adjustment of the contact 40 in the oPPosite direc- @@0 tion is effective to render the grids less negative, v.iith' respect to their associated cathodes. The ,-ontact 40 desirably is adjusted so as to suit the ebaracteristies 'of the triode sections A and , @ ,@o thereby establish the most efficient operat- :;5 Ing conditi-ons. A,s noted bereinbefore, the illumination of pho,@leelectric c@,U 59 bnd thereby the , selective aeti-lation o-f relays 19 and 20 is controlled by the ,@alvanometer 9, the latter of which in turn iS 40 ,isive to changes in the electromotive force ..,roduced by ther7nocouple 2 and thereby is rezponsive to the temperature variations ,vithin fu,-nar,e 0. To thig end the galvanoineter 5 is @py-ovlded with a pointer or needle 60 which is d.; 5 c,@rried by the movable coil thereof as Illustrated dlagranuna' ,ically In Mgures 1 and 2. A light aluminum vane 66 which is impervious to light Is disposed on the end of the pointer 0.@. Vne -alvanometer 6 is so a@-ranged witb 50 .Tespect to the phot6electric cell 59 and ivith respect to a svarce of hght, such as a lamp 61, that the vane 06 Is adapted to be motivated into and - o,ut of the path of the light impinging on PhGtoelectric ceB 59 in accordance with the deflee- r,5 t.lons of the movable coil theredf and thereby L?z accordancewith the furnace tem-perature va@lations. 'rne lami3 67 is connected to and receives.cziergizing current from the transformer @econd-.,x,y wixiding .33 60 As ihustrated, an opaque plate 68, in which a focusing le= 69 is mounted, is als ' 6 positioned between the photoelectric cell 59 a.nd lamp 67, the optical system is so arranged that the only light-from lamp 07 wwch is permitted to 65 impinge on cell 59 is that wwch is tranqmitted by the lens so. The iens 69 and the length of the galvanometer Pointer 60 are so proportioned . that the vane If is adapted to move into the pgth (f the light impinging on cell 59 at ap- .0 proximately the point of focus on the lens 11. Thus, ivslight movement of the vane 66 in one direction or the other is sumelent to fully Illuminate the cell to or to cut off all of the light thereto. In gecordanee Witli the present invention, -.i the podtion oi the shield 68 and lens 49 is adJustable by an arrangement described herelnafter Tn the normal operation of the systein the triode sections A and B of valve 38 are equally conductive when the iuumination of the photoelectric ceH ' 59 Is a predetermined valtie. Ulider this condition, the relay coils 19 and 20 ate equally - energlzed and consequently the motor 9 is notactuated for rotation In either direction and remains stationary. Upon slight moveme'nt of t@he vane 60, for example, in a clockwise dtreetion in Mgure 1 in response to a decrease in furnace temperature from the de&ed value the iuumination of photoelectric cell 59 is substantia-Ily increased whereupon the grid 50 Is rendered less negative in potential with respect to its associated cathode 51 and consequently the conductivity of the triode section B is increased. -I'his causes An increase in the energization of relay coil 20 and as a result the relay switch blade 25 is actuated into engagement with the contact 27 to thereby cldse the energizing circuit for niotor field winding I 5. The mot.or 9 Is then operated for rotation in the direction to effl@et an opening adjt@stment of the fuel valve 3. Upon slight -movement of the vane 66 in the countereldckwise direction in response to an increase In furnace temperature from the desired value, the Illumination of the photoelectric cell US is substantially decreased, whereuuon the grid 00 is rendered more negative in pDtential with respect to the cathdde 51 t-o thbreby reduce the conductivity of the triode section B. This effnts a decrease in the energization of relay coil and consequently actuation of the switch blade 25 intid engagement with ihe contacu 20 aiid thereby closure of the energizing circuit to motor 'tield winding @0. The motor 9 is then aetup-ted in the direction 'to produce a closing adJustment of ihe L@Llel valve S. As notdd hereinbef -ore, rotation of the motor 0 to effect a fuel valve adjustment also eftects a-.i adjustment of th,- follow-up potentiometer 6 ?, 9 0. Tt is noted that deflection of the galvanometer Pointer 60 in the counterclockwise direction of an arliount to cause the vane 66 to move completely through the light beam and thereby permit 11 umination of photoelectric cell 59 even though the furnace temperature is higher than the desired value Is prevented by -the vane 66 striking azainst a stop 70. In accordance with the present invention, adjustment of the fgllow-up potentiometer 17, 18 effects an adjustinent of the plate 68 a nd lens 69 relatively to the lamu 67 and photoelectiic cell 59. Such adjustment effects a transverse shift In the focal point of the light beam impinging on cell 59 relatively to the vane 66, and i.@ in the proper direction to restore the illumination of cell 59 to that value which equalizes the conductivities of the triodes A alnd B and thereby restores the relay switch arm 25 to a Point intermediate the-contact 2 6 and -27. In tWs manner the valve 3 is modulat ed to an open or closed 'Position in accordaiice with the decrease or increase respectively of -the temperature within furnace 1. The lens 69 is mounted on a support 71 which is In tum mounted on a pair of bimetallic members 72 and 73 which, when heated, will warp-in opposite directions. These bimetallic members are rigidly'mounted on a supporting member 74, which Is attached in any suitable manner to the framework of an instrument, Surrounding the
[4]4 2,819,406 bimetalue elements 72 and 73 are iblectric heaters 75 and 76 respectively which are electrlcally c6finected at their upper ends by a wire 77 that Is conmcted to the left hand end of transformer secondary cofl 31. The electileal circuits for 5 the heaters are completed through a wire 78 and a resistance 79 that can be varied by means of a slider 80 wlitch serves a purpose to be later described. -From the resistance 79 a connection is made to the slider 07 for the potentiometer 10 resistance 28. Heaters 73 and 76 are connected respectively through resistances DI and 82 which can be adjuged by means of slidirfg contacts 88 arid 06. These resistances serve a purpose as the slider 17 is moved to the right or to the left more or less of the resistance 10 will be put Into the circuit contawng the lieat--rs 75 and 76. In this manner the bimetallic strips will be heated to different degrees and will serve to move the lens 69 In one direction or the other so that the light rays from the lamp 67 will be swfted with respect to the photoelectric cell 50. The resistances 81 and 02 are manually adjusted by manipulation of the knob 85. Rotation of the knob 85 in one direction operates to Increase the amount of resistance 82 In circuit and to decrease the amount of resistance 61 in circuit and conversely rotation of the knob 85 in the 0 other direction operates to decrease the amount of resistance 82 and to increase the amount of resistance 80 in the heater circuits respectively. BY reason of the above construction a true follow-up control system is provided. Upon an :1.5 iricrease in the temperature of the furnace I the galvanometer pointer 60 and thereby the @ane 60 are moved in a counter-clockwise direction. Such movement of the vane produces a sharp decrease in the illumination of the ph otoelectrie 40 cell 52 and thereby throu@h the electronic eircuit that has been described, causes the motor 9 to be actuateci for rotation in a direction to close - the valve S. This operation of the motor also effects an adjustment of the contact 17 along 45 the resistance I 0 to the right. Such a movement of the contact 17 will cause an increase In the heat p@oduced by the heater 75 and a decrease In the heat produced by the heater 76 thereupon causing the bimetallic strip 72 tO WB;RP 50 in such a fashion that the lens 69 is moved to the right in Plg. 1. When the lens has been moved an amount to restore illuniination to the photoelectric cell 59 to a degree in which the s ections A and B are equally conductive, the motor 9 is deenergized and the system is stabfflzed. In this manner the fuel valve 3 is modulated toward a closed pbsition in accordance with the amount of Increase in fumace action of the lens 69 to restore the Mun ation _ @ n to the cell 59 to a value at which the motbr 9 Is deenergized. Accordingly, a small fuel vilve adjustment will be made for a given fumace temperature change. An adjustment of the contact 80 along the resistance 79 in a direction to increase the amount of the resistance. of the circuit wUl have the opposite effect upon the op. eration of raotor 9. The portion of adjustable resistances 8 I alid 8 2 in the follow-up srrangement permits a socalled "reset" adjustment of the system so that on a change In the operating condition of the ftimace 1, for example, on a change in the load temperature. The operation of the systeni fok CO, paratively large adjustment of the valve 8 before a furnace temperature decrease is similar to the photoelectric cell is again properly lighted. of said load change fuel heating valve change, or other operating condition change, to Increase or decrease the furnace temperature may be neutralized. As explained herei,- &ibefore, the resistances 81 and 82 are adapted to be simultaneousl y adjusted in opposite directions by manipulation of the knob 85. Such manipulation of,knob 83 operates t6 change the'lnitial position 'of support 7,1 and thereby the position of lens 99, for a given position of contact 97 along resistance 98, and thereby operates to 'change the relation between the position of the lens 62 and the adjustment of fuel %,alve 3 for a giv6n furnace temperature value at which the motor 9 is not energized for rota@ion in either direction. Accordingly, on such manipulation, the motor 9 is energized for rotation to effect an adjustment of fuel valve 3 and an adjustment of contact 17 along resistance 18 as required to restore' the lens 69 to the position in which the motor 9 is deenergized for rotation. Thus, the provision of resistances 01 and 82 permits load compensatin g or "reset" adjustments to,be readily made. As will be apparent to those skilled in the art the provisi'on of the adjustable resistances 79, 80 and 82 permits of a wide range of variation in the furnace operating characteristi cs thereby peripitting a desirable good regulation under very different conditions of operation. The speed with which the lens 69 is shifted as a result of a change In the temperature of the furnace I will have'an effect on the amount 6f change in the valve opening. If for example, the bimetalhe strips and the heaters are so designed that they act quickly as a result of a movement of a given moveinent of the contact 07 along resistance 18 a comparativel y small adjustment of the valve 3 will take place before the photdelectric cell 59 has the proper amount of light again upon it. If, on the other hancl, the heaters and the bimetallic strips are so designed that the lens 69 will move slowly then there will be a coinwhich wiU be described below. I.-,. thereof, or on a change in the B. t. u. content From the above description it will be seen that of the fuel being supplied thereto, the tendency that above described except that the motor 9 Is operated In a direction to op@6n the fuel valve and the contact 17 Is moved to the left alon6 tesistance@ 18. 'The iesistance 79 permits an adjustment of the throttung range of the system. so that the amount fuel valve 3 is adjusted in response to a given change of temperature may be varied. rbr example, upon an adjustment of the contact 70 80 in a directign to decrease the amount of resistance 79 In the circuit, the voltage applied to the@ heaters wtU be ineressw whdreby a, sm0er &Qustment of the contacts, 17 along the reabtauce 11 WM be required to effect the follow-up 75 Thus it will be seen that if the strips 72 and 73 and the heaters 75 and 76 are properly designed for the lag in the conditioli being' measured or the furnace characteristics that there will be a correction given.in proportion to the rate with which the temperature is changing. In the normal operation of the device, the lag in time between when the motor 0 Is energized and when the heater 75 or 76 has become hot enough to move the lens 69 sufficiently to produce deenergi@ati on of the mo6r will be enough to cause on overcorrection of the valve S. Duftg this time the lem So win have been moved to such an extent relative to the vaft It that the
[5]2,319,406 motor will be energized for rotation in the opposite direction to back off the valve adjustment to the proper place. At the same time the current in the heaters 75 and 76 will be correspondingly changed so that the lens 69 will be slowly moved @i back to its egrrect position for the furnace temperature. If the rate of heating of the bimetallic strips is properly related to the rate of heat change of the fumace in response to fuel changes, the over-correction and backing off of the valve I o will be sufficient to quickly return the value of the temperature in the furnace to normal. If the temperature is changing at a faster rate the valve and the shder IT will be adjusted more before the lens has moved su!Eciently to produce I.-, deenergization of the motor than it wowd if the temperature hade..only deviated a small amount. It will, therefore, be seen that the arrangement disclosed above not only gives P- proporfidnal movement of the valve for each chazige in temperature but the correction is so made that it takes into account the rate at which the condition is changing as well as the direction and the amount of the change. . . in order tG change the cor-tro't Po-ant o' this instrument, or the normal temperature whi@h the 'instrumerit tends to maintain in the -iurnace i, it is necessary to shift the photoelectric cell 59 with respect to the galvanometer 6 so that the baffle 3C, will intercept the light to the p7notoelectric cell at some other Doint. Gen-ei-ally speaking, in ar, instrument of this type the D7no,@,celectric cell 56-, the,light 07, the stop 79 and the lens supporting bracket 76 will be mourit@-d to.@et,.ber on a support which-swhlgs arolind a pivo@u- coaxial with the galvanometer suspensions. In this fpshion, as will be seen from Fig, 2, the photoelectric cell and the lens vvill b.- changed relative to the baffle 66 so that in order for the cell EO to get the proper a-w-ount of light the baffle viill have 40 to be at some c@theroosition@. in Fig. 3 there is shown a modific,@itior. of the '@nvention ir- which there is provided a concave mirror 36 ori the galvanometer 0 in place of the pointer 60 and the bafile 60. -,,',vht from the 45 lamp 37 is directed toward the mirror Q@', through a lens 87 which is rigidly mounted in a s-apport 80 that is carried by the light supporting bracket 7 @ - From the mirror the light Is reflected on to the photoelectric cell 69. Therefore, any deflec- 50 tion of the galvanometer will shift the light beam away from the photoelectric cell thus causin.- a 'dif-Ferential heating of tne heaters 75 and 76. Such action of the heaters will shift the light 67 in a direction so that its beam (>f light can again 55 be deflected upon the p7notoelectric cell 59. 1- This operation of the light 67 also gives the follow-up movement of the control instrument that was obtained in Flg. I by movement of the lens 69 indepqndently of the light. The speed 00 with which the light 67 is shifted to one side or the other gives a rate response to the control instrument similar to that described in Fig. 1. This arrangement of shifting the light with the lens accomplishes the same res:ults that have been 65 previously described except in a " slightly different manner. In some cases it is possible that this arrangement may be preferable to @hat shown in Fig. 1. . in Figure 4 there is sho . wn another embodi- 70 ment of the invention In which only one eleetronie'tube is used and in which the photoeleetri,c cell - is shifted rather than the lens. The single electronic tube 89 in this embodiment has and from the other end of the transformer through the wire 97 to the cathode 98. The energizing circuit for the photoelectric 'cell -59 extends from the right end teriiiinal of the transformor secondary winding 95 through thd ceR 59 to the resistance 100 and bael, to the transformer. The cell 59 is, in this case, also connected so that current flowing through it will cause a potential drop actoss the resistance 100 The magnitude of this drop will depend upon the light falunc., on the cell. As the piotoelectric ceE- 59 is moved by the bimetallic strip 04 it shi-fts a contact 103 along a resistance I CC, which resistance forms two legs of a bridge circuit that is energized from a transformer secondary winding 105. The other legs of -the bridge circuit are formed by the resistance 106 that is engaged by a movable contact 107 which is connected to the other side of transformer winding 1,00. Connect--d between each end of the resistors 90@ and qoo are coils 998 and 909 that are variably energized depending upon the positions of the contacts 98S and 107. Cooperating with the coils O CC') and 900 are cores 23 and 2@ -that are attached to a'rocldng s-@vitch carrying arm 2 0 such as ,7as used in the embodiment o-f Figure 2. As one of the coils is energized more'than t-lie other, the con@cact 23 will be brougb-t Into er4gagement witn concact LPG or 27 to energize motor "j' for rotatiod- i-Li one clireetion or the otiier. The motor, in this casl-, simulTpneously adjusts the valve 8 P-nd the co-Litact @,@7 along t-'qe resistance 1,00. In- the operation of @his modification of the invention the fiow of current f@or one half cycle will be as indicated by the symbols on the drawing. At this time, if the temperatuze is at its normal value, the _Palvanometer iooi@-iter 60 will be in the position shown and a, 7jort'io-7i of the Jig-ht4 'rom lamp 67 vi)ll fall on the cell 39. A small amount of current will then flow through the cell and the plate clrcui'c, of the tube 89 wiE pass enough current to the heuer 93 so 'chat thebimetallic elemeii-t will hold the photoelectrir, cell in the position shown. 'EJ@non an increase in the temperature of the furna e, v - e a.1 GE wiu move in a counterclockwise dikecti . on or downwardly to cut off more light to thereby reduce the current flow tbrough the cell SC. Accordingly the grid 99 will become more negative and less current can flow through the plate circuit to the heater 93. As a result of this the bimetauic strip 99 will cool off and move the cell 59 downwardly until the proper amount og Ught again falls on it to hold the cell in its position. Movement of the cell 59 causes a movement of contact 103 along resistance 104 In the same direction. If the bridge cirewt was balanced, the downward movement of the contact 103 will unbalance it In such i; direction that coil 1.09 will become more energized than coil 108@ As a result of this the core 23 wfll be pulled to the left bringing contacts 25 and 26 into engagement to energize the motor field 16 for rotation to close its filament hiated from a secondary, winding 90 75 the vaive 3. While the valve is being closed the of a, transformer 0 1. The plate circuit of this tube extends from the plate 92 -through a heater 93, that acts on a bimetabic element 94, to the rig4t end of a transformer secondary winding 95. A tap is taken from this winding at 90 and is connected through wire 97 to cathode 98. The grid circuit extends from grid 99 through a resi@stor 100, that is shunted by a condenser 101, tb one end of a transformer secondary winding 102,
[6]contact 107 is @being moved upwardly ;tlong resistance 106 to rebalance the bridge. From the above it will be seen that If the rate of movement of the photoelectric cell 59 Is correlated with the rate of change of the temperature in the fumace 1, the valve 3 wlU be so adjusted that the temperature will be quickly brought back to normal. The embodiment of the invention shown -In Fig. 5 corres@onds very closely to that of Mg. 1 in that the same heater control circuits are used for the two heaters 75 and 76 in Fig. 5 as those .shown in Mg. 1. In this. case, however, there is shown a concave mirror 86 of the type disclosed in Mg. 3 so that upon a movement of the gaivanometer coil light wiU be reflected from the lam , p 67, by this mirror, to the photoelectric cell .59. In this embodiment of the invention the galvanometer coil is suspended by two bimetaric suspension elements I I 0 and I I I ea.ch of which, when it is heated, tends to tum the giilvanometer coil In opposite directions. The heaters 75 and 76 are associated with suspeiisions II 0 and III respectively. With thisembodiment,. as. the cont@et 17 Is moved b inotor 9 relati e to the -Y v resistance 18 the amount of current flowing through the heaters 75 and TO is varied. This causes one of the suspension elements I I 0 or I I I to be heated more than the other so that the galvanometer coil 6 carrying fts mirror 00 will be rotated by this force in addition to the one supplied by the thermocouple 2. Therefore, it will be sec@n that when the temperature of the furnace 2 changes the galvanometer 6 wiR be deflected to reflect, for example, more light on the photoelectric cell. 50. In response to the light on the cell, triode section B of the tube 38 will be made more conductive than the section A so that motor 9 will l@6 energized for rotation In the proper direction to readjust the valve 3 to bring the temperature' of the furnace back to*ard normal. TWs same rotation of the motor 9 wiR shift contact 17@ along resistance 98 and vary the current -flowing.through the heaters 7 5 and 76 in such a manner that the galvanometer coil 6 will deflect in a direction to reflect a smaller amount of light upon the ceU 59. If the rate at which the suspensiort elements I I 0 and I i 1. warp is correlated with respect to the constants of the furnac6 2 and the galvanometer, the latter will be deflected in such a fashion that it will compensate for the rate at which the temperature in the furnace Is changing. If the temperature is changing fast, a la@rge movement of the contact 17 wfll take place befor.e the heating has an effect on the galvanometer suspenslons, so that the motor wlll cause the valve to over@travel. Therefore, the galvanometer will deflect to such an extent that it will reflect less light on the photoelectric cell thus 'causing. b@ bacldng off movement of the valve, and of the galvanometer, to bring the temperature to its normal value quickly. As the temporature is returning toward its normal value the galvaiiometer will be slowly moving toward its normal position and a state of balance will be reached with the galvanometer deflecting properly and the temperature at the. control point. The embodiment of the invention disclosed in Mgure 6 differs from those previously described in that the rate response or, in effect, the del9jyed follow-up is pyocured by means of a dash-pot rather than from heeting coM. In Mgure 6 the 2,819,406 a float 113 which Is made of some magnetic material. Thefloatislocatedinacontainerif4made of non-Magnetic material and fllled with a suitable Aquid such as mercury dr in some cases oil. A cylirider If 5 is formed in the container and receives a piston 116 that Is attacbed to the lower face of the float 113. Liquid In the chamber 115 and below the piston I IS may communicate with the liquid above the piston through an opening 1,) 117 at a restricted rate that is governed by the setting of a tapered screw II 8 which cooperates with a valve seat 119 formed at the right end of the opening 117.' The 'transformer 29 in this case is provided i,-) with,a secondary winding I - 20 that is connected In a series circuit with a solenoid 121 which surrounds the upper part of the chainber II 4. This circuit also Includes a current limiting resistimee 122 and a variable resistance 023. A con21) tact 124 is slidable along the latter resistance to regulate the amount of It in the circuit and Is moved by the m6tor 9 while the valve 3 Is being adjusted, as was contact 17 in Mgure 1. In this embodiment of the invention the lens I 1 2 and the float I 1 3 must move in a vertical direction, so in order for the vane 66 to properly cut the light it must also move In a vertical direction instead of horizontal as shown In the otber embodiments of the invention disclosed :,i) hereiii@ In order to counterbalance the weight of the pointer 60 and vane 66 extending forwardly a weight 125 is shown on the back end of the pointer 60. It is 6f course obvious that similar weights should be used if necessary on the galvanometers in the bther embodiments of the invention. In the operation of tlle Figure 6 embodiment, an electronic eirewt And a relay circuit such as are shown at 7 and 8 respectively, in Mgure 1 are 11) used. Thus, when the temperature of the furnace I decreases the galvanometer will deflect upwardly to permit more hght to fall on the photdelectric cell 59. This operates to make the grid 50 of the triode section B less negative so that more current will flow in the plate circuit and through the coil 20. The energization of the coil 20 operates to move contact 25 Into engagement. with contact 2 7 en6rgizing motor fleld IS so that the motor will open valve 3. As the motor rotates it will also shift contact 124 to the right along resistance 123 to place riiore of that resistance In the circuit of solenoid 12 1. Such a movement of contact 124 decreases the energization of the solenoid 12 1- and permits the float I IS, which normally sits higher in thb liquid in chamber 114 than is shown, to rise and move lens 112 upward. This movement shifts the path of the beam of light so that it is again partially blocked by the vane 66 to give the follow-up movement. In this case the speed of the fohow-ul? movement is determined by the rate at which the liquid in chamber 114 can ]@ass through the passage 107 into the cylinder 115 below piston ,116. Whether the follow-up movement Is upward or downward the speed at which it takes place depends upon the adjustmerit of the resistor II S. Due to the delayed follow-up, the motor 0 will b6 energized an amount of time sufficient to give an 711 over-C(>rrection to the valve 3 and will move contact 124 to,the right enough so that the lens 112 will rise high enoiigh so that vane 66 will cut off more light than is necessary for equihbrium of the electrical system. 'As a result the motor will lens II 2 is mounted on a stem that is attached to 7:) be run In a rever8e direction far. enough to re-
