US3441876A - High-frequency oven - Google Patents

High-frequency oven Download PDF

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Publication number
US3441876A
US3441876A US721514A US3441876DA US3441876A US 3441876 A US3441876 A US 3441876A US 721514 A US721514 A US 721514A US 3441876D A US3441876D A US 3441876DA US 3441876 A US3441876 A US 3441876A
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US
United States
Prior art keywords
tube
voltage
oscillator
control
grid
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US721514A
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English (en)
Inventor
Gooitzen Zwanenburg
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.)
US Philips Corp
Original Assignee
US Philips Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by US Philips Corp filed Critical US Philips Corp
Application granted granted Critical
Publication of US3441876A publication Critical patent/US3441876A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • 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

Definitions

  • An electron tube oscillator for use with a high frequency heating apparatus comprises a pair of serially connected electron tubes connected in the control grid circuit of the oscillator tube.
  • One of the tubes is controlled by a control voltage derived from the oscillator load circuit, and the other is controlled by a separate control voltage derived from the anode current of the oscillator tube.
  • An increase of the latter control voltage causes a decrease in the impedance of the corresponding electron tube.
  • This invention relates to high-frequency ovens having a back coupled grid-controlled electron tube oscillator, wherein the control gird D.C.-circuit of the electron tube oscillator includes a grid-controlled electron tube, con nected as a variable resistor between the control grid and the cathode of the back coupled oscillator tube, said gridcontrolled electron tube being controlled by a control voltage derived from the load circuit.
  • the grid-controlled electron tube connected as a variable resistor between the control grid and the cathode of the oscillator tube may advantageously be formed by a pentode in order to obtain a sensitive control, for example, tor accurate stabilization of the voltage or current or the temperature of the workpiece such as desired, for example, for the purification of germanium or silicon.
  • An object of the invention is to provide a high-freq-uency oven of the kind mentioned in the premeable in which, in addition to a very sensitive control, considerable widening of the limits within which the output may be varied, for example, between kw. and 10 kw., is obtained in a simple manner.
  • control grid D.C. circuit of the oscillator tube includes, in series with the grid-controlled electron tube connected as a variable resistor, an adjusting tube controlled by a separate cotnrol voltage.
  • the impedance from which the separate control voltage for the adjusting tube is derievd is connected in series with the back coupled oscillator tube. An increase in the control voltage produces a decrease in the resistance formed by the adjusting tube.
  • the high-frequency energy required for heating purposes is derived from a grid-controlled electron tube oscillator having a class C connected triode 1.
  • the anode circuit of the tube oscillator which is designed as a colpitts circuit, includes an oscillatory circuit 2 that determines the oscillation frequency.
  • the circuit comprises a coil 3' shunted by two series-connected capacitors 4 and 4'. The junction of the capacitors is connected to the grounded cathode of triode 1.
  • One end of the oscillatory circuit 2 is connected, via a blocking capacitor 5, to the anode of tube 1, and the other end is connected, via a grid capacitor 6, to the control grid thereof.
  • the anode of tube 1 is energized through a high-frequency choke 7, from a DC. supply source 8, shunted by a high-frequency decoupling capacitor 9.
  • the oscillatory current which occurs in the oscillatory circuit 2 during operation is used for heating a workpiece 10 included in a load circuit 12.
  • the load circuit inclcdes a heating coil 11.
  • the heating coil 11 which is connected to ground at one end, is connected to the output terminals of a coupling coil 13, which in turn coupled by inductive means to the coil 3.
  • the inductive coupling between the coil 3 and the coupling coil 13 is variable to permit load matching.
  • the control grid D.C. circuit includes a variable resistor in the form of a pentode 14.
  • the pentode tube is shunted by a resistor 15 to prevent the grid resistance of triode 1 from exceeding a predetermined permissible limit.
  • the screen grid voltage of the pentode 14 is derived from a separate supply voltage source 16.
  • the control grid D.C. circuit also includes a high-frequency decoupling network comprising a series coil 17 and a by-pass capacitor 18.
  • the control of the grid excitation of triode 1 is used for stabilizing the voltage in the load circuit.
  • a control voltage derived from the load circuit 12 is applied through a control voltage circuit 19, to the control grid of pentode 14.
  • the control-voltage circuit 19 includes an input network comprising blocking capacitors 20, 20' and a high-frequency choke 21 in between, followed by a rectifying device 22 and an associated output resistor 23.
  • the output resistor 23 is connected to the input terminals of a direct voltage amplifier 24, via a source of constant bias constituted by a gas-filled tube 25 which is connected via a series-resistor 26 to a supply voltage source 27.
  • An input voltage equal to the output voltage from the rectifying device 22 minus the operating voltage of the gas-filled tube 25 is thus set up at the input terminals of the direct voltage amplifier 24.
  • This input voltage is applied, after amplification in the direct voltage amplifier 24, as a control voltage of negative polarity to the control grid of pentode 14.
  • the arrangement so far described provides accurate stabilization of the voltage in the load circuit 12. More particularly, if the voltage in the load circuit 12 increases, the negative control voltage will increase.
  • the grid resistance of triode 1, which is formed by the pentode 14, also increases, resulting in a shift of the grid bias of triode 1 and a corresponding decrease in grid excitation which counteracts the increase of voltage in the load circuit 12.
  • an increase in grid excitation will occur due to reduction of the grid resistance of triode 1.
  • the increased grid excitation counteracts the decrease of voltage in the load circuit 12.
  • a sensitive control of the voltage in the load circuit 12 to a predetermined value is thus obtained which may be made adjustable, if desired, by utilizing a voltage divider as the output resistor 23 of the rectifying device 22.
  • the circuit in addition to a sensitive control, I obtain in a simple manner a considerable widening of the limits within which the magnitude of the output may be varied.
  • This is achieved by including in the control grid D.C.-circuit of the oscillator tube 1, in series with the pentode 14 connected as a variable resistor, an adjusting tube 28 controlled by a separate control voltage.
  • the circuit further includes, in series with the back coupled oscillator tube 1, an impedance from which the separate control voltage for the adjusting tube 28 is derived. An increase in said control voltage produces a decrease in the resistance formed by the adjusting tube 28
  • the series impedance is included in the form of a series resistor 29 in the D.C. supply circuit of the oscillator tube 1.
  • Resistor 29 is connected between the grounded cathode of the oscillator tube 1 and the negative terminal of the D.C. supply source 8.
  • the direct voltage set up across the series resistor 29 is applied, after conversion in a D.C.-A.C. voltage converter (chopper) 30, through a transformer 31, to a full wave bridge rectifying device 32 having an output impedance 33 for producing the control voltage for the adjusting tube 28.
  • the control voltage is applied with positive polarity to the control gr-id thereof. Because of different direct voltage levels of the cathode circuits of the oscillator tube 1 and the adjusting tube 28, the isolation obtained between said circuits by means of the transformer 31 is of great practical advantage.
  • the oscillator current will increase and the output voltage will decrease, resulting in a decrease in the grid excitation and the negative grid bias of the oscillator tube 1.
  • the voltage increase across the series resistor 29 caused by the increase in direct current of the oscillator will bring about, after conversion and possible amplification in the D.C.-A.C. voltage converter 30, and subsequent rectifica tion in the rectifying device 32, an increase in the positive control voltage at the control grid of the adjusting tube 28.
  • D.C. anode current of the tube oscillator by including the series-resistor 29 in the D.C. supply circuit of the oscillator tube 1
  • A.C. anode current of the tube oscillator by including a series-impedance in the anode A.C.-circuit of the oscillator tube 1, since the magnitude of the A.C.
  • anode current of the tube oscillator will vary with the load in exactly the same manner as the D.C. anode current.
  • an isolation transformer between the series impedance and the adjusting tube 28.
  • the alternating voltage derived from the separating transformer is applied in the manner shown, after rectification in a rectifier, as a control voltage of positive polarity to the control grid of adjusting tube 28.
  • the embodiment shown, in which the control voltage is derived from a series-resistor included in the D.C. circuit of oscillator tube 1 affords the practical advantage that a low-frequency transformer can be used as the isolation transformer 31.
  • the tube 14 may also be used for stabilizing the current in the load circuit 12 or the temperature of the workpiece 10.
  • a thermocouple for example, is connected to the Workpiece and produces an output voltage which, possibly after amplification, is applied to the pentode 14 through the gas-filled tube 25 and the direct voltage amplifier 24.
  • said impedance element comprises a resistor connected in bseries with the anode-cathode path of said first electron tu e.
  • High frequency heating apparatus comprising, a back coupled grid controlled electron tube oscillator, a grid controlled electron tube directly connected as a variable resistor between the control grid and the cathode of the back coupled oscillator tube, means for controlling said grid controlled electron tube by means of a control voltage derived from the load circuit, an adjusting tube connected in series with the grid controlled electron tube in the control grid D.C. circuit of said oscillator tube, means for controlling said adjusting tube by means of a separate control voltage, an impedance for deriving the separate control voltage for the adjusting tube, and means connecting said impedance in series with the back coupled oscillator tube, whereby an increase in said separate control voltage causes a decrease in the resistance formed by the adjusting tube.
  • a heating apparatus as claimed in claim 3 further comprising a transformer intercoupled between said impedance and the adjusting tube, means for supplying to said transformer an alternating voltage derived from said series impedance, a rectifier, means for applying the alternating voltage derived from the transformer to said rectifier to produce a rectified control voltage of positive polarity, and means for applying said control voltage to the control grid of the adjusting tube.
  • a heating apparatus as claimed in claim 5 further comprising a DC supply source,.means connecting the cathode of the oscillator tube to ground, and means connecting the series resistor in the DC. supply circuit of the oscillator tube between the grounded cathode of the oscillator tube and the negative terminal of the DC. supply source,

Landscapes

  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Inductance-Capacitance Distribution Constants And Capacitance-Resistance Oscillators (AREA)
  • Amplifiers (AREA)
US721514A 1965-07-02 1968-04-15 High-frequency oven Expired - Lifetime US3441876A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
NL6508506A NL6508506A (lv) 1965-07-02 1965-07-02

Publications (1)

Publication Number Publication Date
US3441876A true US3441876A (en) 1969-04-29

Family

ID=19793546

Family Applications (1)

Application Number Title Priority Date Filing Date
US721514A Expired - Lifetime US3441876A (en) 1965-07-02 1968-04-15 High-frequency oven

Country Status (7)

Country Link
US (1) US3441876A (lv)
AT (1) AT257765B (lv)
BE (1) BE683486A (lv)
CH (1) CH451311A (lv)
DE (1) DE1516908C3 (lv)
NL (1) NL6508506A (lv)
SE (1) SE326514B (lv)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3973105A (en) * 1973-10-24 1976-08-03 Mitsubishi Denki Kabushiki Kaisha Protective device for induction heating apparatus
US4292487A (en) * 1977-07-07 1981-09-29 Topsil A/S Method for initiating the float zone melting of semiconductors
US5214258A (en) * 1991-02-01 1993-05-25 Tocco, Inc. Apparatus and method of ultra rapid annealing by induction heating of thin steel strip
US5266765A (en) * 1990-08-06 1993-11-30 Contour Hardening, Inc. Apparatus and method of induction-hardening machine components with precise power output control

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
None *

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3973105A (en) * 1973-10-24 1976-08-03 Mitsubishi Denki Kabushiki Kaisha Protective device for induction heating apparatus
US4292487A (en) * 1977-07-07 1981-09-29 Topsil A/S Method for initiating the float zone melting of semiconductors
US5266765A (en) * 1990-08-06 1993-11-30 Contour Hardening, Inc. Apparatus and method of induction-hardening machine components with precise power output control
US5214258A (en) * 1991-02-01 1993-05-25 Tocco, Inc. Apparatus and method of ultra rapid annealing by induction heating of thin steel strip

Also Published As

Publication number Publication date
CH451311A (de) 1968-05-15
DE1516908A1 (de) 1970-02-19
AT257765B (de) 1967-10-25
BE683486A (lv) 1966-12-30
DE1516908B2 (de) 1974-04-25
SE326514B (lv) 1970-07-27
DE1516908C3 (de) 1974-11-21
NL6508506A (lv) 1967-01-03

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