US1904485A - Control system - Google Patents

Control system Download PDF

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Publication number
US1904485A
US1904485A US562359A US56235931A US1904485A US 1904485 A US1904485 A US 1904485A US 562359 A US562359 A US 562359A US 56235931 A US56235931 A US 56235931A US 1904485 A US1904485 A US 1904485A
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United States
Prior art keywords
voltage
grid
control
circuit
source
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Expired - Lifetime
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US562359A
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English (en)
Inventor
Orrin W Livingston
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
General Electric Co
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General Electric Co
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Filing date
Publication date
Priority to BE390886D priority Critical patent/BE390886A/xx
Priority to FR699545D priority patent/FR699545A/fr
Application filed by General Electric Co filed Critical General Electric Co
Priority to US562359A priority patent/US1904485A/en
Priority to DEA66332D priority patent/DE639192C/de
Priority to FR42283D priority patent/FR42283E/fr
Priority to FR42437D priority patent/FR42437E/fr
Priority to GB24969/32A priority patent/GB407073A/en
Application granted granted Critical
Publication of US1904485A publication Critical patent/US1904485A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P13/00—Arrangements for controlling transformers, reactors or choke coils, for the purpose of obtaining a desired output
    • H02P13/12—Arrangements for controlling transformers, reactors or choke coils, for the purpose of obtaining a desired output by varying magnetic bias
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
    • G05F1/00—Automatic systems in which deviations of an electric quantity from one or more predetermined values are detected at the output of the system and fed back to a device within the system to restore the detected quantity to its predetermined value or values, i.e. retroactive systems
    • G05F1/10—Regulating voltage or current 
    • G05F1/12—Regulating voltage or current  wherein the variable actually regulated by the final control device is AC
    • G05F1/32—Regulating voltage or current  wherein the variable actually regulated by the final control device is AC using magnetic devices having a controllable degree of saturation as final control devices
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
    • G05F1/00—Automatic systems in which deviations of an electric quantity from one or more predetermined values are detected at the output of the system and fed back to a device within the system to restore the detected quantity to its predetermined value or values, i.e. retroactive systems
    • G05F1/10—Regulating voltage or current 
    • G05F1/12—Regulating voltage or current  wherein the variable actually regulated by the final control device is AC
    • G05F1/32—Regulating voltage or current  wherein the variable actually regulated by the final control device is AC using magnetic devices having a controllable degree of saturation as final control devices
    • G05F1/34—Regulating voltage or current  wherein the variable actually regulated by the final control device is AC using magnetic devices having a controllable degree of saturation as final control devices combined with discharge tubes or semiconductor devices
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B47/00—Circuit arrangements for operating light sources in general, i.e. where the type of light source is not relevant
    • H05B47/10—Controlling the light source

Definitions

  • This invention relates to control systems, more particularly to regulating systems, and it has for an object the' provision of a simple, reliable and improved system of the 5 kind. Morespecically the invention relates to regulating systems in which the regulated characteristic of a circuit is controlled by ⁇ means of electric valve apparatus, and ac cordingly a further object of this invention is the improvement and simplification, of the circuit arrangement and apparatus em-. ployed to control the valves.
  • the invention relates to voltage regulating systems in which the voltage of 'a circuitis subject ,to wide variations roma desiredvvalue responsively to changes in some operatingcondition of the circuit, such as the load, and a -urther objedtI electricyalves 'are employed to maintain the f voltage of a translating circuit'substantially Iconstant at a desired value'. f n
  • the invention is particularly advantageous in connection with systems in which the voltage of a translating circuit is ycontrolled by means of a variable series connected current limiting devicesuch for example as a theatre dimming system in which the' intensity oilum'p illumination lof ,the various lamp 'circuits is controlled by series connected impedances,suclpas'variable resistances or reactances.v
  • a variable series connected current limiting devices uch for example as a theatre dimming system in which the' intensity oilum'p illumination lof ,the various lamp 'circuits is controlled by series connected impedances,suclpas'variable resistances or reactances.
  • the voltage drop across the series impedance device will decrease proportionate ⁇ ly and /consequently the lamp voltage andl brilliancy Will increase to ⁇ a value that is considerably greater than the'lifty per centindicated by the indicating device. Similar-V ly if the lamp load is doubled, the voltage drop across 'the series impedance will be correspondingly increased with thev result 4that the lamp voltage and brilliancy will decrease toa value less Athan that indicated.
  • an object of lthis invention is the provision of a control system in which means are provided for adjustingand maintaining the lamp voltage substantially constant at any desired value withina Wide -range of lamp load.
  • An advantage of the invention is that a very ⁇ inexpensive type of reactor may'be utilized instead of the ex-y pensive specially designed reactors heretofore employed and since the reactor is the most expensive item in the lcircuit and a separate reactor is required for each circuit,
  • a' control device is employed to control an operating condition of an electric circuit, and this device is conrtrolled responsively to the difference of a control voltage and a voltage derived from the controlled circuit. More specifically, an
  • control electrode provided with a control electrode is employed to vary the reactance ot' Aa saturable reactor connected in circuit relationship with the controlled circuit vand this valve is in turn controlled by supplying to the control electrode a control voltage, andija regulating voltage derived from the controlled circuit and of opposite polarity Ito that of the control voltage.
  • This control voltage is variable to provide foradjusting the regulated characteristics to a desired value and the regulating voltaffe is preferably pulsating direct current rfor the pur.- pose of facilitating'its utilization to vary the bias of the control electrode.
  • Fig. 1- is a simple diagrammati-cal representation of an embodiment -of lthe Ainventign
  • Eig. 2 is a chart of curves employed o explain and clarify theI operation of the sys- ⁇
  • a suitable I translating circuit including a translating device such as represented by the conductors 10, 11 and a plurality of lamps 12 is supplied from any suitable source such for eX- ample as the alternating current source represented by the conductors 13, 14.
  • the voltage supplied tothe lamp and the degree of illumination thereof are controlled by means of. an impedance device, illustrated in the drawingas.
  • a saturable core reactorl the reac ance 'of which is controlled. by suitable electric valve apparatus 16, the operau tion of which in turn is controlled by a suitable. source of control voltage 17 and a volt- ⁇ age-derived Afromithe load circuit 10, 11.
  • the saturable reactor 15 is lshown conventionally in the drawing with the core member omitted.
  • This reactor comprises a plurality of reactance windings 18,19 each ⁇ wound upon a separate leg of the iron core and connected lin series relationship between the supply source and the load.
  • the reactance windings 18, 19 are connected in parallel relationship with each other and in Leo-1,485
  • the saturable the source and the lam reactor 15 is also provided with a control winding 20.
  • Direct current of a variable 'magnitude is supplied to the control windthe source 13, 14 remains substantially constant, a variation in the reactive drop across the .windings 18 and 19 effects a 'correspond- ⁇ ing change in the voltage applied to the lamps 12 and consequently in the intensity of their illumination. It will thus be seen Y that a variation in the current flowing in the control winding 20 effects a corresponding change in the voltage'applied to the lamp 12; an lincrease in the current resulting .in a decrease in the reactive voltage .drop across the reactance windings 18, 19
  • the electric valvel apparatus 16 may be of any suitable type it is illustrated in the drawing as an electric discharge device', preferably o f the three electrode type into the envelope of which a small quantity of an Pinert gas such for example as mercuryvapor is introduced after exhaust; the presence of the gas within the tube serving lto change the usual pure electron discharge into an are stream constituting the tube a grid controlled arc rectifier.
  • the electric discharge device 16 may be. either a full wave or a half wave rectifyin device; the half wave rectifyin device ing ⁇ shown in the drawing for .t e purpose of illustration due to the simplicity of the necessary controlling circuits.
  • the electric rdischarge device 16 is provided with an output electrode or anode 22, a control lelectrode -or grid 23 and a ilamentary cathode 24;
  • the latter being heated to the necessary degree of incandescence by energy supplied to it from' the secondary Awindlng 25 of a supply transformer the primary winding 26 of which is supplied with energy 4from any suitable source such as the alternating' current source 13, 14 to whieh'iit is connected as illustrated.
  • the anode 22 is connected to one side of the supply source over a circuit that may be traced through the conductor 21, the control winding 20 and conductor 26 to :the side 14 of the suppl source.
  • the grid has no control of the instantaneous value of the current in the outi Vput circuit but only has control over the time in the cycle at which current starts t0 iow and it will thus be seen that if the volt-' age applied to the grid is either an alternating or an undulating voltage that the average value of the current flowing inthe output circuit may be controlledby shifting the phase of the'grid voltage relative to ⁇ that of the anode.
  • the grid'bias voltage may be derived from any suitable source 17 rwhich is illus-A trated in the drawing as al variable potentiometer resistance one'terminal of'which is Yconnected to the side 13 of the suppl source by means of the conductor 29 and t e other terminal of which isconnected to the opposite side ofthe supply source by means .of the conductor-30..
  • the potentiometer 17 f is variableso that the control voltage su -pliedto the gridmay varied as ⁇ desired and. a.
  • rectifyin'g device 31 of vany suitable typeis included' in theconnections between ⁇ themovahle contact 32o ⁇ fthe potentiometer 1ra-glatte South in the grid ecircuit for, the-purpose of rectifying fand applying av directfrurrent controlling voltage ⁇ the v.Wave the voltage applied to the Once current has started to flow grid., lt will be seen, l1cwever, that the rectifyin device 35i onlyvrectiies onelial 'cycle of 'te voltage across the potenticineter 17. In order that this halffwave rectilied voltage may be converted into a voltage of N 'line 37 parallel to the axis 0 0.
  • a regulating voltage is derived 'treni the u voltage ef the lamp 'circuit 10, 11 by ineens of lthe ltranstorifner 38-and is supplied the grid 23 to which one terminal ⁇ of the sec ondary winding ci the transformer 33 is connected as illustrated.
  • the opposite terminal of the secondary winding of the transformer 38 is connected to a second electrcde l of the rectiying device 3l and the polarity' of the transformer winding is so chosen that the rectifying device 31 rectifiesthe inverse half-cycley oi the lamp voltage wave, i. e.,
  • a suitable filter device compr1sing a reslstance 39 ⁇ and a condenser/40 con-l nected in parallel therewith is' lconnected in the gridlcircuit one terminal of the resistance 39 being connected to the terminal .33 of the resistance 34 and the ,opposite terminal oi" the resistance 39 being connected to one terminal of the secondary-winding Y' of the transformer 38.
  • the electrical constants of the resistance 39 and the condenser 40 are so chosen that the rectified voltage is.
  • the actual or resultant grid voltage is the difference between these two voltages and is represented in Wig. 2 by the dotted curve 41.
  • the potentiometerjl? is ⁇ variable so thatv the magnitude of the control voltage can be varied at the will ofthe o erator and it 'will ⁇ 'be clear by reference to magnitude of either the control volta e 37 ig. 2 thatif the or the 're ulating voltage 40 is change this" i "will resu t' in 'either raising or lowering the v thus effect a chan 'e in the i-current owing in the output ciicult o f the electric discharge ydevice 16.
  • control voltage 37 ⁇ is preferably a smooth direct current voltage it will be clear that this might be derived from a sep arate source of direct current voltage instead of from the alternating current source 13, 14.
  • the arrangementy shown in the drawing, however, is preferable in that it eliminates the expense of a separate source.
  • a suitable half- Lwavev rectifying devi'c'e 42 is connected in4 parallel with the control winding; the anode v 43. being connected to the anode 22 ofv the electric discharge device 16 andthe filamen- Vtary cathode 44 being connected to the distant terminal of the control winding 20 and heated to the necessary degree of incandescence by currenty supplied to it from the secondary winding 45 of the supply transformer.
  • sustain-v charge device 16 ⁇ causes very .little current to flow in the control winding 20 with the result that the reactice drop across the vwindings 18, 19 is large and the lamp voltage is very small; so small in fact that the lamps are dark.
  • the regulating voltage represented by the curve 4U is likewiselincreased which resultsin shifting the phase of the actual grid voltage relative to the anode voltage toward the ri ht to a position in which a balance is establlshed between the positive control voltage and the nefrativ'e regulating voltage.
  • the magnitude of the control voltage 3.7 is 'further' increased in a positive ⁇ direction which results inshifting the phase of the actual gridvoltage further to the left to a position in phase with the anode voltage as a resultof which the current in the control winding becomes maximum, the reactive drop across the saturable reactor 15 becomes minimum, and the voltage applied to the lamps 12 becomes maximum and the lamps 4burn at maximum brilliancy.
  • the reactive drop across the saturahle reac- .tor is increased and the lamp voltage de;l creased to a value that is lower. than the' value indicated hy the position of the mov .able contact 32.011 its indicatin device.
  • a control system comprising in comicin nation an alternating current load circuit? control means for said circuit comprising electric valve apparatus provided with a conn trol grid, means for supplying a varialol'e di rect current control voltage to said grid, and means comprisin a rectifying device ener-z gized from said a ternatin'g current load cir' ling electric valve apparatus provided with a control grida means for supplying a variable direct current control voltage-tog said grid, and means comprising a rectiiying device energized.
  • a control system comprising an altern natingcurrent load' circuit, ⁇ control means lfor said circuit comprising electric; valve apparatus provided 'mth a control grid-9 and ⁇ means for supplying a pulsating direct current voltage to said grid comprising a device connectedin circuit with said grid9 means Jfor supplying a direct current centrol voltage to said grid, and a 'jrectiiying device energized from said alternating current load circuit and connected to said grid# sofas to supply thereto a regulating voltage having a dlrect current component oi oppoliti site polarity vwith respect to said control voltage.
  • control system comprismg analternating current load circuit, anvariable reactance device Ifor controlling the voltage of said eircuit, means for varying the reactance of said device comprising electric valve ap- P31' me s for supplying a variable phase pul- ,sating direct current voltage to said grid comprising a filter device connected in circuit with said grid, a rectifying device energized from said alternating current -circuit and connected to said grid for 'supplyelectric valve controlled by said control vo'ltlage and said derived voltageA for controlling said reactance device.
  • a lamp circuit In a control system for theatredimming apparatus and thelike, a lamp circuit, an impedance device for controlling the voltage of said circuit, asource of control voltage and means controlled by said lamp.
  • a control system for theatre dimming apparatus and the like comprising a lamp circuit, a variable impedance device included in said circuit for controllingthe voltage ⁇ thereof, a source ⁇ of control voltage, means for deriving a voltage from said lamp circuit, and an electric valve responsive to the difference of said control voltage and said derived voltage for varying the impedance of said impedance device.
  • a control system comprising in combi nation, an alternating current translating circuit, ⁇ means .for'controlliijig an operating' condition of said circuit comprising an electric valve provided with a control grid,
  • n a control system, a load, means for supplying alternating voltage to saidload; and means for maintaining the voltage of.
  • said load substantially constant at a desired value
  • means for supplying a l variable direct current bias to saidgridya'nd supplying a slightly pulsating bias of opposite polarity to said grid comprising a filter device connected in circuit with. ⁇ said grid and a rectifying device energized from said'p. alternating load .voltage and vconnected to said grid.
  • control system comprising .in 'conitus comprising a control grid, andcuit for supplying to said gri a -bias of opi gosite polarity, and means for varying said rst mentioned. bias. ⁇
  • a source of alternating current a load circuit supplied from said source, means for controlling an operating condition of said circuit comprising an electric valve energized from said source and provided with a contrbl grid, and phase shifting means for energizing said grid comprising a source of bias voltage for said grid and/ means res onsive to variations in said operating con ition for supplying to aid grid a pulsating bias of 'opposite poarit 12.
  • a circuit including a variable load supplied from said source, means for controlling the voltage of said load com prising an electric valve'energized from said source and provided with a control grid, and phase shifting means for energizing said grid comprising a variable source of bias and means responsive to variations in said load for supplying to said grid a pulsating bias of opposite polarity.
  • a control system comprising a source of alternating current, a. translating circuit supplied from said source, means for varying the'voltage supplied to said circuit comprising an electric valve energized 'from said source and provided with a control grid, and phase shifting means for energizing said rid comprising a source of direct current bias for said grid, and a rectifyng device energized from said circuit and g filter device connected therewith for applying to'said grid a pulsating bias of opppste polari t 14.
  • Illa regulating system aL source of alternating current, a load supplied from said source, voltage control means forsaid load comprising a saturable reactor provided with 'a control' winding, means for controlling the reactance ⁇ o -isaid comprising anelectric valve connected' to said.. control winding and' /energized from laid source, said valve being provided with a-control grid, a variable lpotentiometer conmeans responsive to said vload voltage 'for' nectedito said source, and means for applying a pulsating bias to said grid comprising a rectifying -device connected to said potentiometer and to said load, and a filter device connected to said grid.l
  • saidrectifying device and to control'system a source of alternating current, a load supplied from said source, voltage control means for said load comprising a variable saturable reactor connected in series relationship with said load and provided with a control Winding, means :tor varying the reactance of said reactor comprising a half-wave rectifying electric valve energizedfrom said source and connected to said control Winding, said -valve being provided with a control grid, a second valve connected to said control winding for sustaining the current flow during the inverse half-cycle, and phase shifting means for said grid comprising a rectifying device connected to said load and to said source for supplying to said grid a bias derived from the inverse half-cycle of said load voltage and a bias of opposite polarity, filter means for rendering said deing bias of opposite polarity and having a variable magnitude proportional to said lamp circuit voltage, and a variable potentiometer for varying said first mentioned bias.
  • a Icontrol system for theatre dimming apparatus comprising a source of alternating current, a lamp circuit supplied from said source, means for vai'yiiig the voltage of said circuit comprising a saturable reactor provided with a control Winding, means for varying the reactance of said reactor comprising an electric valve energized from said source and connected to said control Wiiiding, said valve being provided With a con-trol grid, and phase shifting means for energizing said grid comprising a source of grid bias voltage, a variable potentiometer rivcd bias slightly pulsating and said oppofor varying said bias voltage, and means site bias substantially non-pulsating, and a comprising a half-wave rectifyiiig device en.- variable potentiometer for varying said opergized from said lamp circuit and a filter posite bias.
  • a source ot supply,va lamp circuit supplied from said source; and means for varying Vand maintaining the voltage supplied to' said circuit substantially constant at adesired value, comprising an impedance device for controlling thel voltage of said circuit, an electric valve provided With a control electrode for varying the impedance of said device, means for supplying a bias voltage to said electrode, means'responsiveto the voltage of said lamp circuit foi-.supplying a bias voltage of opposite polarity to said electrode, and means for varying said first men' tioned bias.
  • a control system for theatre dimming apparatus comprising an alternating current source, a lamp circuit supplied from said'source, avariable reactance device for varying the voltage of said lamp circuit, means for varying the reactance of said device comprising an electric valve energized from said source and provided with a control grid, phase shifting lmeans for energizing said grid comprising a source for sup? plying a bias to said grid, and -imeans responsive to variations in theload of said circuit for supplying a variable bias of opposite polarity to' said grid.
  • a source of alternating current a lamp circuit supplied' from said source, a variable saturable reactor included in said vcircuitl for varying the voltage thereof, means for varying the reactance of said reactor comprising an electric valve energized from said source and provided With a control grid, phase shifting 'means for energizing said grid comprising a source for supplying a bias to said grid, means responsive to the voltage of said circuit for supplying to said grid a pulsatdevice connected to said rectifying device :tor applying .to said grid a pulsating bias lvoltage of opposite polarity to said first my hand.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Automation & Control Theory (AREA)
  • Circuit Arrangements For Discharge Lamps (AREA)
  • Circuit Arrangement For Electric Light Sources In General (AREA)
US562359A 1929-06-28 1931-09-11 Control system Expired - Lifetime US1904485A (en)

Priority Applications (7)

Application Number Priority Date Filing Date Title
BE390886D BE390886A (is") 1931-09-11
FR699545D FR699545A (fr) 1931-09-11 1930-06-27 Perfectionnements aux systèmes d'asservissement électriques
US562359A US1904485A (en) 1931-09-11 1931-09-11 Control system
DEA66332D DE639192C (de) 1931-09-11 1932-06-21 Einrichtung zur Speisung elektrischer Verbraucher
FR42283D FR42283E (fr) 1931-09-11 1932-07-23 Perfectionnements aux systèmes d'asservissement électriques
FR42437D FR42437E (fr) 1929-06-28 1932-09-07 Perfectionnements aux systèmes d'asservissement électriques
GB24969/32A GB407073A (en) 1931-09-11 1932-09-07 Improvements in and relating to electric control systems employing saturable reactances

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US562359A US1904485A (en) 1931-09-11 1931-09-11 Control system

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US1904485A true US1904485A (en) 1933-04-18

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US562359A Expired - Lifetime US1904485A (en) 1929-06-28 1931-09-11 Control system

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US (1) US1904485A (is")
BE (1) BE390886A (is")
DE (1) DE639192C (is")
FR (2) FR699545A (is")
GB (1) GB407073A (is")

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2432529A (en) * 1943-08-28 1947-12-16 Albert R Locke Arc welder control circuit
US2435965A (en) * 1942-10-09 1948-02-17 Honeywell Regulator Co Electrical motor control apparatus
US2443006A (en) * 1944-05-24 1948-06-08 Farnsworth Res Corp Voltage regulator
US2511981A (en) * 1947-09-26 1950-06-20 Rca Corp Electronic thermostat
US2516298A (en) * 1945-06-20 1950-07-25 Allis Chalmers Mfg Co Regulating system utilizing voltage responsive thyratrons
US2554218A (en) * 1948-03-27 1951-05-22 Gen Electric Temperature control system
US2573094A (en) * 1946-03-09 1951-10-30 Cutler Hammer Inc Electric welding system
US2586498A (en) * 1951-02-28 1952-02-19 Gen Electric Electronic frequency changer and stabilizing control means therefor
US2675515A (en) * 1947-02-06 1954-04-13 North Electric Mfg Company Battery charging apparatus
US2732477A (en) * 1956-01-24 Control system

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2732477A (en) * 1956-01-24 Control system
US2435965A (en) * 1942-10-09 1948-02-17 Honeywell Regulator Co Electrical motor control apparatus
US2432529A (en) * 1943-08-28 1947-12-16 Albert R Locke Arc welder control circuit
US2443006A (en) * 1944-05-24 1948-06-08 Farnsworth Res Corp Voltage regulator
US2516298A (en) * 1945-06-20 1950-07-25 Allis Chalmers Mfg Co Regulating system utilizing voltage responsive thyratrons
US2573094A (en) * 1946-03-09 1951-10-30 Cutler Hammer Inc Electric welding system
US2675515A (en) * 1947-02-06 1954-04-13 North Electric Mfg Company Battery charging apparatus
US2511981A (en) * 1947-09-26 1950-06-20 Rca Corp Electronic thermostat
US2554218A (en) * 1948-03-27 1951-05-22 Gen Electric Temperature control system
US2586498A (en) * 1951-02-28 1952-02-19 Gen Electric Electronic frequency changer and stabilizing control means therefor

Also Published As

Publication number Publication date
FR699545A (fr) 1931-02-16
DE639192C (de) 1936-11-30
FR42283E (fr) 1933-06-21
BE390886A (is")
GB407073A (en) 1934-03-07

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