US2454845A - High-frequency oscillator circuit for induction heating apparatus - Google Patents

High-frequency oscillator circuit for induction heating apparatus Download PDF

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US2454845A
US2454845A US485582A US48558243A US2454845A US 2454845 A US2454845 A US 2454845A US 485582 A US485582 A US 485582A US 48558243 A US48558243 A US 48558243A US 2454845 A US2454845 A US 2454845A
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circuit
grid
source
oscillation
potential
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US485582A
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Vernon W Sherman
Wheeler Carson Mckeag
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Federal Telephone and Radio Corp
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Federal Telephone and Radio Corp
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    • 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
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/02—Induction heating
    • H05B6/04—Sources of current

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  • This invention relates to high frequency oscillator circuits particularly adapted for the energzing of induction heating apparatus such as is employed for example in the induction heating or hardening of steel or in like use wherein substantially the maximum load is employed as the normal operating condition.
  • induction heating of this type the work piece to be hardened or otherwise treated is placed within the heating coil prior to starting of the oscillator which, coupled with the f act that a peak load is presented by the work during the ini-tial period in the heating operation, establishes a load condition which makes it ydifficult to initiate high frequency oscillation in the oscillator circuit.
  • the object of the present invention is to provide an improved Icir-cuit arrangement which will produce a starting impulse or shock in a -grid circuit so as to star-t os-cillation in a heavily loaded tank circuit.
  • the improved circuit is accordingly designed to establish oscillation under the aforesaid lconditions of maximum load by the momentary appli-cation of a high value positive voltage pulse to the grid.
  • a supplemental energizing or shocking circuit including a positive voltage grid bias supply or source which is controlled by a relay to be effective with the initial energizing of the heating circuit and which operates to apply a positive potential to the grid of the oscillation tube as a supplemental positive impulse to effect an abrupt change of plate current to be instrumental in establishing or initiating the oscillation.
  • the yconventional induction heating -circuit arrangement as shown, of the Hartley oscillator circuit type includes the oscillator tube A having the plate p and grid g -connected to the oscillator circuit O including connections 2 and 3 connected to the plate and grid respectively, leads 4 and 5 provided with condensers 6 and 'I and connected to parallel leads l8 and 9 of tank circuit T having included therein a primary energizing coil 1 Iand condenser I0 respectively.
  • the coil r has the adjustable ground connection II to establish regeneration in the known manner.
  • the condensers 6 and 'I provi-de a low impedance path for the radio frequency current while forcing .the direct current to iiow through the tube.
  • the usual cathode c of the -oscillator tube is connected to ground as shown.
  • the input for the oscillator circuit is by the lead I2 from a high ltension source having the usual radio frequency choke I3 to prevent radio frequency current flowing into the high tension supply and a protective condenser I4 in a shunting connection is grounded as shown.
  • the load circuit is shown at L including the usual secondary or coupling coil s.
  • the normal negative grid b-ias voltage is developed across resistor I9, and is applied thru connection I5 and thence thru radio frequency choke coil I8 to the grid g. Connection 2l] :to the lead I6 functions normally to provide a xed negative grid bias voltage suicient to stop oscillation. This connects t-o the negative grid potential source 22 by means of a relay switch R normally engaging the -contact 25.
  • a supplemental circuit arrangement operative momentarily to impress apositive grid bias upon the oscillator tube resulting in an abrupt change of plate current in a manner and of a magnitude to be effective to start oscillation.
  • the relay R is of double throw type adapted on opening of contact 25 to close a second contact 26 of Va positive grid potential source 28 including batteries connected lto lead 29 through resistance 30 and provided with l a shunted and grounded condenser 3
  • the relay switch R is operated by the closing of circuit connections 32-33 having in series therewith the relay coil 35 anda suitable timer indi-cated at 36; this circuit being closed or initiated by a push button or manual switch at a convenient loca-tion.
  • the improved circuit is accordingly adapted to establish oscillation under the -condition of substantially maximum load by the momentary application of an increased positive grid bias occurring upon the discharge of condenser 3I.
  • produces an abrupt rate of change of the plate current and since this rate of change -controls the magnitude of voltage across the :tank -circuit it is the means for inducing a sufliciently high voltage at the grid of the tube to initiate yand sustain oscillation.
  • This shock voltage will rbe impressed ⁇ on the grid circuit immediately upon the closing of the relay on contact 25 and thereafter, the duration of the sustained oscillation will be determined by the timer 36 in accordance wi-th .the desired time of induction heat treatment of the Work piece or load as Will be readily understood.
  • an oscillator tube havingr anode, cathode and control grid electrodes; Va feedback oscillation circuit connected to said electrodes; a. source of voltage normallyconnectedto saidgrid, the ypotential of .said .source havinga value which prevents oscillation being.V developed vi in said. oscillation. circuit; a supplemental source of .voltagecomprising a capacitor, a resistance,. andascapacitorcharging means connectedin se. ries,v relation, thepotentialof said supplemental.. sourcewhavingfa value suicient to .initiate oscilf.;l lationscin said circuit.;.and means for .connectirg saidi supplemental voltagesource to said ⁇ gridfor a predeterminedperiodof time.
  • 3.1-A circuit foristarting;oscillations in a selffsi. excited oscillatoncircuit including gan electronic tube ⁇ having ananode, cathode and ⁇ control grid,... comprising,.in combinationz. a source of potential of -such-fvalueiiasto prevent oscillation in said.. oscillator whenvsaid source is connected between saidbcathodeand said control grid; a secondo? source. of-potential of such value 'as to initiate oscillations f in y said oscillator circuitiwhenl con;
  • a circuit for starting oscillations in a selfexcited oscillator circuit including an electronic tube having-gananode, cathode and control grid, comprising, in combination: a source of potential of -such value as toprevent oscillation in said oscillator when said source is connected between..said. cathode and said control grid;l a secondasource of potential of suchvalueas -to ini.
  • rstf. sourceyfromi said control. l grid and. iconv. nec-ting: saidssiecond. source ithereto; and. circuit, means connected to said. second source of ,po-

Description

Nov. 30, 1948. V w SHERMAN A 2,454,845
El' L HIGH-FREQUENCY OSCILLATOR CIRCUIT FOR1 INDUCTION HEATING APPARATUS Filed May 4, 1945 Hes 5R26 'Tll-*I es "o ,Belg- Impl- 47mm l' Patented Nov. 30, 1948 HIGH-FREQUENCY OSCILLATOR CIRCUIT FOR INDUCTION HEATING APPARATUS Vernon W. Sherman, Summit, and Carson Mc- Keag Wheeler, Montclair, N. J., assignors to Federal Telephone & Radio Corporation, New- York, N. Y., a corporation of Delaware Application May 4, 1943, Serial No. 485,582
(Cl. Z50-36) 6 Claims.
This invention relates to high frequency oscillator circuits particularly adapted for the energzing of induction heating apparatus such as is employed for example in the induction heating or hardening of steel or in like use wherein substantially the maximum load is employed as the normal operating condition. In induction heating of this type the work piece to be hardened or otherwise treated is placed within the heating coil prior to starting of the oscillator which, coupled with the f act that a peak load is presented by the work during the ini-tial period in the heating operation, establishes a load condition which makes it ydifficult to initiate high frequency oscillation in the oscillator circuit. In the `desired economical operation under maximum load the condition may exist that an oscillator capable of sustaining oscillation With the applied load is normally unable to initiate oscillation under the same load level. The object of the present invention is to provide an improved Icir-cuit arrangement which will produce a starting impulse or shock in a -grid circuit so as to star-t os-cillation in a heavily loaded tank circuit. The improved circuit is accordingly designed to establish oscillation under the aforesaid lconditions of maximum load by the momentary appli-cation of a high value positive voltage pulse to the grid.
For the described purpose there is provided 'a supplemental energizing or shocking circuit including a positive voltage grid bias supply or source which is controlled by a relay to be effective with the initial energizing of the heating circuit and which operates to apply a positive potential to the grid of the oscillation tube as a supplemental positive impulse to effect an abrupt change of plate current to be instrumental in establishing or initiating the oscillation.
The improved circuit arrangement of the presen-t invention Will be more readily, understood by reference to the accompanying drawings wherein there is diagrammatically shown a conventional oscillator circuit arrangement with which is incorporated the relay controlled supplemental and positive voltage grid bias supply circuit for applying the momen-tary shocking voltage to initiate the oscillation.`
The yconventional induction heating -circuit arrangement as shown, of the Hartley oscillator circuit type, includes the oscillator tube A having the plate p and grid g -connected to the oscillator circuit O including connections 2 and 3 connected to the plate and grid respectively, leads 4 and 5 provided with condensers 6 and 'I and connected to parallel leads l8 and 9 of tank circuit T having included therein a primary energizing coil 1 Iand condenser I0 respectively. The coil r has the adjustable ground connection II to establish regeneration in the known manner. The condensers 6 and 'I provi-de a low impedance path for the radio frequency current while forcing .the direct current to iiow through the tube. The usual cathode c of the -oscillator tube is connected to ground as shown. The input for the oscillator circuit is by the lead I2 from a high ltension source having the usual radio frequency choke I3 to prevent radio frequency current flowing into the high tension supply and a protective condenser I4 in a shunting connection is grounded as shown. The load circuit is shown at L including the usual secondary or coupling coil s. The normal negative grid b-ias voltage is developed across resistor I9, and is applied thru connection I5 and thence thru radio frequency choke coil I8 to the grid g. Connection 2l] :to the lead I6 functions normally to provide a xed negative grid bias voltage suicient to stop oscillation. This connects t-o the negative grid potential source 22 by means of a relay switch R normally engaging the -contact 25.
In accordance with the present invention there is further provided a supplemental circuit arrangement operative momentarily to impress apositive grid bias upon the oscillator tube resulting in an abrupt change of plate current in a manner and of a magnitude to be effective to start oscillation. For this purpose the relay R is of double throw type adapted on opening of contact 25 to close a second contact 26 of Va positive grid potential source 28 including batteries connected lto lead 29 through resistance 30 and provided with l a shunted and grounded condenser 3|. The relay switch R is operated by the closing of circuit connections 32-33 having in series therewith the relay coil 35 anda suitable timer indi-cated at 36; this circuit being closed or initiated by a push button or manual switch at a convenient loca-tion.
The improved circuit is accordingly adapted to establish oscillation under the -condition of substantially maximum load by the momentary application of an increased positive grid bias occurring upon the discharge of condenser 3I. The -positive grid bias established by the discharge of condenser 3| produces an abrupt rate of change of the plate current and since this rate of change -controls the magnitude of voltage across the :tank -circuit it is the means for inducing a sufliciently high voltage at the grid of the tube to initiate yand sustain oscillation. This shock voltage will rbe impressed `on the grid circuit immediately upon the closing of the relay on contact 25 and thereafter, the duration of the sustained oscillation will be determined by the timer 36 in accordance wi-th .the desired time of induction heat treatment of the Work piece or load as Will be readily understood.
The provisionnof condenser 3| 'insures that there is an-instantaneous potential of sufficient f magnitude to produce a shock and start oscillations in the circuit. However, the condenser isla immediately partially dischargedi and thus them potential of grid g is reduced to 'a normal?valuecg.A
suilicient to sustain oscillations. These oscillations continue until relay switch n1:?. yis operated-sv :to -connect the negative potentiallofcontact25jf`2 to .the grid, at which time the oscillationsfare-sup-Vrpressed.
What is claimed is:
1. In combination: an oscillator tube havingr anode, cathode and control grid electrodes; Va feedback oscillation circuit connected to said electrodes; a. source of voltage normallyconnectedto saidgrid, the ypotential of .said .source havinga value which prevents oscillation being.V developed vi in said. oscillation. circuit; a supplemental source of .voltagecomprising a capacitor, a resistance,. andascapacitorcharging means connectedin se. ries,v relation, thepotentialof said supplemental.. sourcewhavingfa value suicient to .initiate oscilf.;l lationscin said circuit.;.and means for .connectirg saidi supplemental voltagesource to said` gridfor a predeterminedperiodof time.
to saidgrid to start oscillations in said circuit. and
means lfor disconnecting-,said .supplemental volte 1 age source'to stop4 oscillations in said circuit;
3.1-A circuit foristarting;oscillations in a selffsi. excited oscillatoncircuit including gan electronic tube` having ananode, cathode and` control grid,... comprising,.in combinationz. a source of potential of -such-fvalueiiasto prevent oscillation in said.. oscillator whenvsaid source is connected between saidbcathodeand said control grid; a secondo? source. of-potential of such value 'as to initiate oscillations f in y said oscillator circuitiwhenl con;
nectedbetween said cathode and.v said control grid; switching means for disconnecting said first sourceof potential from `said' control.r grid. andi-...1 connectingsaid second source thereto; a resistor. connectedlbetweenvsaid second `source .of `potene tialand .said switching means; anda capacitor connected fromthe end of -said resistor adjacent. .I saidswitching means to said cathodejwherebys r, the operation *of-said switching means *ffromsaidid c 2,026`,8.7.4"fw; Eitel. v n Jane', 19363 rst- Ato said second positionapplies high-poen tential` to said controlgrid to vinitiate oscillationvsz'` andthereafter `said-voltage reduces. to a lower@4 value suiiici'ent to Vsustainoscillation.v
4 anode, cathode and control grid electrodes; a feedback oscillation circuit connected to said electrodes; a voltage source including a direct current source and a condenser charged thereby, the potential of said voltage source having a value-sucientgtoinitiate oscillations in said circuit; means for connecting saiddirect current voltage and condenser in parallel to said grid to start oscillations in said circuit; said `connectingmeans .being such as thereby to discharge ,said condenser and to reduce the potential oi said source to a potential less than its initializvalue .butsuiiicient to permit sustained oscillations in said circuit.
l 5. A circuit for starting oscillations in a selfexcited oscillator circuit including an electronic tube having-gananode, cathode and control grid, comprising, in combination: a source of potential of -such value as toprevent oscillation in said oscillator when said source is connected between..said. cathode and said control grid;l a secondasource of potential of suchvalueas -to ini. A tiateoscillations in said oscillatorircuitwhen. connectedbetween saidc'athode and: said control Vgrids.;:switching means for disconnecting said..lv
rstf.: sourceyfromi said control. l grid and. iconv. nec-ting: saidssiecond. source ithereto; and. circuit, means connected to said. second source of ,po-
tential. operative upon commencement lof oscill' 4lations,...in :said..;oscillat'or circuit: to reducerthe4 potential; of `saidisecond 4source to 5a potential lesslithany its z initial'` Value. 1 but `sufficient .to sustain. oscillations 1in said .oscillator circuit, wh ereby-operationof Isaid: switching means/from said i. fiirseto ;said;secondi position applies a high.y pory tential` tol said, 'controlgrid to initiate oscillation fr. r
and-thenreducesgsaidvoltage to a lowerfvalue duri-ngi thendesircdjperiod of joscillationl.
6. A circuit .for .starting oscillations in .fa Seli-f excitedloscillator circuitxincluding an electronictube ghatzingan;-anodepcathode and control grid,V i, comprisingan Combination: `a source of potential 5,.; 0f .-Sllch-'iualue as ato initiate oscillationsin said voscillatprvcircuitg when. connected between .said ycatlnide..-1rr,1d; saidcontroL-g-rid; switchingmeans for.Y connecting said sourceof .potential vto4 lsaid: .f control grid; a resistor connected;betweemsaid;.1 source of potential-and fsaid; Silvitchingil.means; ;-A and a; capacitor conneetedffrom-thetend .of saidf resistor. adjacent :asaiol-y switchingfmeans to said@ cathodeqfwhereby Aoperationfof said switching meansifappliesma high; potential gto said control; grid-tto gin-(itiate oscillation 'andv thereafter said. voltagegis reduced-to a lower fvalue .suiicientto fsustain; oscillation.. Y
appearances v cI-'ren- Ovb Tlieciollowing references are of record-1in the Non'lber...E Name Datei:`
2,118,414 Moullin:; May;24,z1938f 2,311,631 Bach Feb123zzt943p 2,318,0611-wf Dailey i May-4, 1943 2,329,525: i Mittelmanfni JulyiZO, '1943 4. In fcombinationcfan oscillator:tubehaving 7o .fc2,330,"82i'1y Heppi; Sept. 28,'194311l
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Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2536331A (en) * 1944-02-15 1951-01-02 Hartford Nat Bank & Trust Co Superheterodyne receiver
US2697781A (en) * 1950-06-05 1954-12-21 Stromberg Carlson Co Automatic ring starting circuit
US2706247A (en) * 1949-10-14 1955-04-12 Jacobs Means and method for storing information in digital computers
US2773190A (en) * 1952-11-29 1956-12-04 Hartford Nat Bank & Trust Co High-frequency heating system
US2839674A (en) * 1953-10-22 1958-06-17 Hyman N Laden Frequency shift transmitter system
US3012208A (en) * 1958-03-14 1961-12-05 Gen Electric Keyed oscillator with spike injecting starting means
US3030502A (en) * 1947-03-14 1962-04-17 Otto H Schmitt Automatic radio spectrum monitor
US3185939A (en) * 1958-09-12 1965-05-25 Relax Acizor Inc Generator with blocking oscillator controls
US3208010A (en) * 1960-11-28 1965-09-21 Westinghouse Freins & Signaux Start-stop oscillator having rectifier to obtain bias from the output voltage

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2026874A (en) * 1934-02-27 1936-01-07 Heintz & Kaufman Ltd Keying circuit
US2118414A (en) * 1933-07-24 1938-05-24 Rca Corp Thermionic oscillation generator
US2311631A (en) * 1940-08-22 1943-02-23 Patents Res Corp Discharge tube oscillator
US2318061A (en) * 1941-05-29 1943-05-04 Westinghouse Electric & Mfg Co Automatic bias circuits
US2324525A (en) * 1943-07-20 Method of and apparatus fob heat
US2330582A (en) * 1940-07-20 1943-09-28 Hepp Gerard Circuit arrangement

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2324525A (en) * 1943-07-20 Method of and apparatus fob heat
US2118414A (en) * 1933-07-24 1938-05-24 Rca Corp Thermionic oscillation generator
US2026874A (en) * 1934-02-27 1936-01-07 Heintz & Kaufman Ltd Keying circuit
US2330582A (en) * 1940-07-20 1943-09-28 Hepp Gerard Circuit arrangement
US2311631A (en) * 1940-08-22 1943-02-23 Patents Res Corp Discharge tube oscillator
US2318061A (en) * 1941-05-29 1943-05-04 Westinghouse Electric & Mfg Co Automatic bias circuits

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2536331A (en) * 1944-02-15 1951-01-02 Hartford Nat Bank & Trust Co Superheterodyne receiver
US3030502A (en) * 1947-03-14 1962-04-17 Otto H Schmitt Automatic radio spectrum monitor
US2706247A (en) * 1949-10-14 1955-04-12 Jacobs Means and method for storing information in digital computers
US2697781A (en) * 1950-06-05 1954-12-21 Stromberg Carlson Co Automatic ring starting circuit
US2773190A (en) * 1952-11-29 1956-12-04 Hartford Nat Bank & Trust Co High-frequency heating system
US2839674A (en) * 1953-10-22 1958-06-17 Hyman N Laden Frequency shift transmitter system
US3012208A (en) * 1958-03-14 1961-12-05 Gen Electric Keyed oscillator with spike injecting starting means
US3185939A (en) * 1958-09-12 1965-05-25 Relax Acizor Inc Generator with blocking oscillator controls
US3208010A (en) * 1960-11-28 1965-09-21 Westinghouse Freins & Signaux Start-stop oscillator having rectifier to obtain bias from the output voltage

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