Abstract: Provided are an electrode for electrolysis having excellent durability against reverse current, and a method that enables production of the electrode for electrolysis at low cost. The electrode for electrolysis 130 includes a conductive substrate 132 on which a catalyst layer is formed, and a reverse current absorption body 134 that is coupled to the conductive substrate 132 in a detachable manner, wherein the reverse current absorption body 134 is formed from a sintered compact containing nickel. The method for producing the electrode for electrolysis 130 includes a sintered compact formation step of obtaining the sintered compact by sintering a raw material powder composed of any one of Raney nickel alloy particles containing nickel and an alkali-soluble metal element, metallic nickel particles, and a mixture of Raney nickel alloy particles and metallic nickel particles, and a coupling step of coupling the sintered compact to the conductive substrate 132.

Abstract: A LED lamp that includes a LED lamp controller with delayed startup after a fault condition is detected. The type of the fault condition is used in determining a length of the startup delay, such as a number of power cycles during which the LED lamp controller is prevented from completing its configuration. Examples of different types of fault conditions include faults in a supply voltage or faults in a feedback voltage to the LED lamp controller. Fault type information can also be stored in circuitry that retains data and is not reset across the power cycles.

Abstract: A simplified device for voltage supply of the cathode of a mass spectrometer comprises a push-pull transformer, wherein, apart from the normal rectifier diodes (7, 9), a controlled rectifier (8, 10) is provided. The gate of the first transistor (8) is connected to the second output (30), and the gate of the second transistor (10) is connected to the first output (32) of the transformer. A voltage supply device, consisting of at least one voltage multiplier, is connected via capacitors (13, 14, 15) to the output of the transformer and feeds, amongst others, the emission current measurement device.

Abstract: Provided is a system for improving rapid cycling performance of instant start compact self-ballasted fluorescent lamps. The system provides a ballast driver circuit including a lamp driver, a lamp voltage detector, an additional cathode heating driver, and a wire lamp. The additional cathode heating driver applies an additional amount of current to the cathodes of the wire lamp during the glow phase after the ignition of the lamp.

Abstract: A constant-current power source unit has a variable power source which can adjust an output voltage. To detect a voltage applied to the gas discharge tube, a voltage detection unit is provided. A power source controlling unit configured to control the voltage by adding a predetermined voltage to the voltage taken in from the voltage detection unit after the electric discharge is started in the gas discharge tube.

Abstract: A device for heating a substrate with light from a flash lamp having a semiconductor switch connected in series to the flash lamp. After triggering of a trigger electrode of the flash lamp, a first drive signal and a second drive signal are output from a gate circuit. The time period when the semiconductor switch is on due to the second drive signal is longer than the time period that the semiconductor switch is on by the first drive signal. Then, the semiconductor switch is switched on and off by the first drive signal and the substrate temperature is increased to a temperature, which is lower than the desired temperature to be targeted, and is maintained a that temperature for a short time, after which the surface temperature of the substrate is increased to the desired target temperature.

Abstract: This disclosure provides a device for heating a cathode of a magnetron, which includes a heater for heating the cathode of the magnetron, a heater current detecting module for detecting a value of heater current that flows into the heater, and a control module for determining the completion of preheating of the magnetron based on a change in the heater current.

Abstract: A universal dimming topology is provided for an electronic ballast having an inverter providing an output current across first and second output branches for driving a light source in accordance with a dimming control input signal. A filament voltage control block modulates first and second filament heating switches to provide filament heating voltage across first and second connection terminals associated with the output branches. During a preheat operating mode a control block disables the inverter and provides pulse width modulated control signals to the filament voltage control block to modulate the filament heating switches at a predetermined frequency. During a normal operating mode the control block enables the inverter and provides pulse width modulated control signals to the filament voltage control block to modulate the filament heating switches in accordance with a duty ratio based on a detected output current.

Abstract: The invention provides an apparatus and method of switching more than one bias voltage within an electron beam tube in order to achieve electron beam cutoff. The invention is particularly useful for high-perveance electron tubes in which a large change in focus-electrode-to-cathode or anode-cathode voltage might otherwise be needed to achieve cutoff. In one embodiment of the invention, the cathode and anode bias voltages are both switched by magnitudes well within the capabilities of standard high-voltage switches to achieve beam cutoff.

Abstract: A device for heating a substrate with light from a flash lamp having a semiconductor switch connected in series to the flash lamp. After triggering of a trigger electrode of the flash lamp, a first drive signal and a second drive signal are output from a gate circuit. The time period when the semiconductor switch is on due to the second drive signal is longer than the time period that the semiconductor switch is on by the first drive signal. Then, the semiconductor switch is switched on and off by the first drive signal and the substrate temperature is increased to a temperature, which is lower than the desired temperature to be achieved, and is maintained a that temperature for a short time, after which the surface temperature of the substrate is increased to the desired target temperature.

Abstract: A capacitively coupled plasma reactor comprising a processing chamber, a first electrode, a second electrode and a thermoelectric unit. The processing chamber has an upper portion with a gas inlet and a lower portion, and the upper portion is in fluid communication with the lower portion. The first electrode has a front side and a backside and is positioned at the upper portion of the processing chamber. The second electrode is positioned in the lower portion of the processing chamber and is spaced apart from the front side of the first electrode. The thermoelectric unit is positioned proximate to the backside of the first electrode and is capable of heating and cooling the first electrode.

Abstract: The present invention is to provide an electronic ballast connected in parallel to two filaments of a fluorescent light tube, which comprises a controller for generating two output signals, two power switches being switched according to the output signals, a resonant circuit oscillating according to switching of the power switches and thereby causing a resonant capacitor thereof to generate a voltage, a voltage sensor connected in series to the resonant capacitor and connected in parallel between the two filaments so as to sense an AC voltage proportional to a voltage across the fluorescent light tube, and a regulator connected separately to the voltage sensor and controller so as to convert the AC voltage into a DC voltage and deliver the DC voltage to the controller. Upon determining that the DC voltage exceeds a preset voltage level, the controller generates an interruption control signal for immediately stopping operation of the controller.

Abstract: A ballast circuit includes a control loop to reduce a filament heating voltage below after the lamp filaments have been pre-heated. A filament cutback circuit includes a filament cut-back inductive component magnetically coupled to the resonant inductive component in the inverter to receive a filament cutback control voltage associated with an AC voltage for powering the lamps. During the pre-heating period, the filament cutback control voltage is not high enough to charge a chargeable component to a switch threshold level. However, during lamp ignition, the filament cutback control voltage is increased and charges the chargeable component to the switch threshold level. This causes a switch device to operate in a conductive switch state and the filament cutback circuit suppresses the pre-heat voltage.

Abstract: A circuit arrangement is provided for operating a fluorescent lamp with a first and a second filament, the circuit arrangement including a heater for the first and the second filament, wherein the circuit arrangement furthermore includes: an apparatus for storing at least one threshold value for at least one operational parameter of the fluorescent lamp; an apparatus for determining the value of the at least one operational parameter; and a control apparatus, which is configured to activate the heater for the first and the second filament for a predeterminable period of time in the event of the at least one threshold value for the at least one operational parameter being exceeded by the determined value of the at least one operational parameter.

Abstract: The present invention relates to an ultraviolet radiation lamp. The lamp comprises: (i) a substantially sealed cavity comprising a mercury-containing material; and (ii) a heating unit disposed exteriorly with respect to the cavity. The heating unit is disposed in contact with a first portion of the cavity comprising the mercury-containing material. The heating unit has adjustable heat output.

Abstract: An electronic ballast includes a filament voltage control block having first and second switches and configured to receive a filament voltage control signal. An inverter includes an inverter driver having first and second gate drive output terminals for driving first and second inverter switches, and a gate drive transformer having a primary side coupled to the inverter driver. A first secondary side is coupled to the first inverter switch and a second secondary side is arranged to drive the first switch in the control block. The control block is effective in response to a first control signal state to drive the switches in the control block and generate a lamp filament heating voltage, and is further effective in response to a second control signal state to disable the second secondary side of the gate drive transformer and thereby disable the lamp filament heating voltage.

Abstract: The invention concerns an OLED device with a cathode 1, an anode 2 and an active stack 3, wherein the anode 1 is segmented into a plurality of anode segments 8 each defining an OLED segment 4. Further, a capacitance measuring unit 12 is provided which is arranged for measuring a plurality of capacitance coefficients between two anode segments 8 and/or between an anode segment 8 and surrounding earth, respectively. This way, an OLED device for illumination purposes with a reliable proximity sensing function is achieved.

Abstract: At an initial stage of a discharge start, a shield electrode is connected to a ground potential via a bidirectional voltage trigger switch. Thereafter, when an electrical charge within the shield electrode flows to the ground potential, by being triggered with this potential, both terminals of the bidirectional voltage trigger switch are disconnected therebetween. Thus, at an initial stage of discharge, charging of the shield electrode is suppressed to suppress a decline in discharge, and in a sustained discharge, destabilization due to an unwanted discharge from the shield electrode to the anode can be suppressed, and using such an electrode automatically allows improving the lighting performance of a discharge lamp.

Abstract: An electronic ballast circuit includes a filament drive circuit that can adjust the pulse width of a pulsed heating signal in accordance with the lamp current to a gas-discharge lamp. A logic device, such as an SR flip-flop, is used to control a switch that is coupled to the primary winding of a filament drive transformer coupled to the lamp filaments. The logic device opens and closes the switch device to generate the pulses of the pulsed heating signal and thus controls the pulse width of the pulses. A clock signal triggers logic device to start a pulse while the end of the pulse is determined by a signal level across a resistor in series with the primary winding of filament drive transformer. Once this signal level is at or above a threshold level, logic device switches the switch device to end the pulse.

Abstract: A circuit arrangement is provided, which may include an input; an output; an inverter, configured to provide an AC supply voltage from a DC supply voltage; a control device configured to drive the inverter, the control device being configured to initiate a preheating phase once a preheating criterion has been met; a resonant circuit having a resonant inductor and having a resonant capacitor; and a transformer configured to preheat electrodes of a gas discharge lamp; wherein the primary winding of the transformer is connected in series with the resonant capacitor and is connected directly to the reference potential of the control device, and an electrical switch is coupled in parallel with the primary winding of the transformer, which switch has a control connection, which is coupled to the control device being configured to transfer the electrical switch into its electrically conducting switching state once the starting criterion has been met.

Abstract: A circuit arrangement for starting and operating one or more discharge lamps comprising a self-oscillating inverter (1), a resonant circuit (2), a low-pressure discharge lamp (5), a starting voltage controller (3) with a variable resistor (R1), and a lamp filament heating controller (4), wherein the lamp filament heating controller includes an additional variable resistor (R2) in the resonant circuit, which variable resistor measures the current flowing in the resonant circuit, and, in the event of a threshold value being exceeded, disconnects the half-bridge transistor (Q2) and thus limits the current flowing in the resonant circuit, this additional variable resistor (R2) being bypassed by a switch (Q3), depending on the lamp state.

Abstract: A ballast circuit includes a filament cutback circuit to reduce a pre-heat voltage after the lamp filaments have been pre-heated. The filament cutback circuit includes a filament cut-back inductive component magnetically coupled to the resonant inductive component in the inverter to receive a filament cutback control voltage associated with an AC voltage for powering the lamps. During the pre-heating period, the filament cutback control voltage is not high enough to charge a chargeable component to a switch threshold level. However, during lamp ignition, the filament cutback control voltage is increased and charges the chargeable component to the switch threshold level. This causes a switch device to operate in a conductive switch state and the filament cutback circuit suppresses the pre-heat voltage.

Abstract: Contamination may be removed from an emitter tip of a field emitter during operation of the emitter tip in a system having an electron beam column having an electrode with a beam defining aperture, an electron collector located proximate to the beam defining aperture between the electrode and the field emitter, and an electron deflector located between the emitter tip and the electron collector. At regular predetermined intervals an electron beam from the emitter tip may be deflected away from a path through the beam defining aperture and onto the electron collector. An electron beam current to the electron collector may be determined and the emitter tip may be flash heated if the current to the electron collector is below a threshold.

Abstract: A system for operating a fluorescent light is provided. The system comprises: a fluorescent lamp with at least one electrode having at least one corresponding heating filament; a filament signal power supply for providing a filament current signal having a filament current frequency, the filament signal power supply connected to create a filament current through the at least one filament; and a plasma signal power supply for providing a plasma power signal having a plasma power frequency, the plasma signal power supply connected to create a plasma current between the at least one electrode and a gas contained in the fluorescent lamp. The plasma power frequency is greater than the filament current frequency.

Abstract: A magnetron has an anode 3 surrounding a tubular hollow cathode 4 which contains a heater 9. The cathode is supported by radial arms at each end. At one end of the cathode, the heater is supplied with one terminal of its D.C. supply by means of a radial arm 5, which also serves to support that end of the cathode. The arm has a portion 5a offset towards the cathode, and a cover of conducting material is interposed between the heater connection and the adjacent end wall 1 of the vacuum envelope. The cover may have a folded portion so that it can be carried by the arm.

Abstract: This disclosure provides a device for heating a cathode of a magnetron, which includes a heater for heating the cathode of the magnetron, a heater current detecting module for detecting a value of heater current that flows into the heater, and a control module for determining the completion of preheating of the magnetron based on a change in the heater current.

Abstract: The method according to the present invention relates to controlling a gas discharge lamp during a pre-heating period of said lamp, wherein a first terminal of a control circuit is connected with a first electrode of the lamp and a second terminal of a control circuit is connected with a second electrode of the lamp, and wherein means are provided, suitable for connecting the first terminal and the second terminal with each other, thus providing a conducting path, and suitable for disconnecting the first terminal and the second terminal. Furthermore the method comprises the use of a chargeable and dischargeable power buffer, for powering control circuitry for operating the switching means.

Abstract: An electronic ballast has control circuitry to operate a gas discharge lamp in both full and dimmed illumination modes. The electronic ballast also includes a full power circuit having a power control coupled to the dimming controller output to receive the dimming controller signal, a filament heating circuit having a heating input coupled to a reduced power circuit to receive a reduced power signal and a heating output that can couple to the filaments of one or more lamps. When the full power circuit receives the dimming controller signal, via the power control, and the dimming controller signal is not in the dimming request range (i.e. the full illumination mode has been selected), the full power circuit generates a full power signal capable of driving/operating the lamp(s) in the full illumination mode. When the reduced power signal is present, the filament heating circuit generates and provides a filament heating signal to the filaments, via the heating output.

Abstract: A method and apparatus for providing electrical current to a lamp, detecting a power supply voltage outage, detecting a return of the power supply voltage, determining how long the power supply voltage outage lasted, and preheating the lamp responsive to determining that the power supply voltage outage lasted greater than a threshold amount of time.

Abstract: An arrangement for the regulation of the electron beam power of an electron gun, which comprises a filament cathode, a block cathode and an anode. Between the filament cathode and the block cathode is applied a first voltage, while between the block cathode and the anode a second voltage is applied. With the aid of a first closed-loop regulated system the filament cathode is regulated to a constant current value, which has a filament temperature sufficient for the maximum beam power of the block cathode. A second closed-loop regulated system, such including a block power regulator, which is acted upon by the difference between instantaneous block power value and nominal block power value, regulates the voltage between the filament cathode and the block cathode.

Abstract: The present invention relates to glow-switch starters 1, lighting devices therewith and use thereof. The glow-switch starter 1 is suitable for use with three phase supply voltages substantially higher than the common 230V supply voltage 26. This allows more efficient gas discharges in e.g. fluorescent lamps 20, and/or more lamp power, and/or less energy losses in ballasts 22 and lamp electrodes. To make the glow-switch starter suited for such use, according to the invention, the gas filling 5 of the starter 1 is adapted. An important criterion is that the glow current in the steady state operation of the fluorescent lamp that is started by the starter is small enough to prevent closing of the (bimetallic) switch.

Abstract: A circuit arrangement is provided for operating a fluorescent lamp with a first and a second filament, the circuit arrangement including a heater for the first and the second filament, wherein the circuit arrangement furthermore includes: an apparatus for storing at least one threshold value for at least one operational parameter of the fluorescent lamp; an apparatus for determining the value of the at least one operational parameter; and a control apparatus, which is configured to activate the heater for the first and the second filament for a predeterminable period of time in the event of the at least one threshold value for the at least one operational parameter being exceeded by the determined value of the at least one operational parameter.

Abstract: A power supply for an insulation detector having a heating element and a temperature sensitive switch thermally coupled to the heating element, the power supply including a power circuit 120 operable to provide heating element power 102 to the heating element 32; a short protector 108 operably connected to the power circuit 120 to monitor current flow through the heating element 32; and an insulation detector sensor 110 operably connected to the power circuit 120 to monitor presence of the heating element 32.

Abstract: A lamp driving device includes a switch circuit for supplying a signal; a transformer which boosts a voltage of the signal from the switch circuit and supplies the boosted voltage to at least one lamp; a safety circuit which compares a threshold value with at least one of the boosted voltage and a current through the lamp, and intercepts at least one of the boosted voltage and the current through the lamp in accordance with the comparison result; and a warming part for warming the lamp in an early stage with a voltage less than or equal to the threshold value.

Abstract: An exemplary electron emission device includes an electron emitter, an anode opposite to and spaced apart from the electron emitter, a first power supply circuit, and a second power supply circuit. The first power supply circuit is configured for electrically connecting the electron emitter and the anode with a power supply to generate an electric field between the electron emitter and the anode. The second power supply circuit is configured for electrically connecting the electron emitter with a power supply to supply a heating current for heating the electron emitter whereby electrons emit therefrom. Methods for generating an emission current with a relatively higher stability also are provided.

Abstract: A magnetron has an anode 3 surrounding a tubular hollow cathode 4 which contains a heater 9. The cathode is supported by radial arms at each end. At one end of the cathode, the heater is supplied with one terminal of its D.C. supply by means of a radial arm 5, which also serves to support that end of the cathode. The arm has a portion 5a offset towards the cathode, and a cover of conducting material is interposed between the heater connection and the adjacent end wall 1 of the vacuum envelope. The cover may have a folded portion so that it can be carried by the arm.

Abstract: The electronic ballast with lamp type determination for an electronic ballast providing power to a lamp filament 208 includes a filament current sensing circuit 220 operably connected to the lamp filament 208 and generating a sensed filament current signal, and a microprocessor U2 receiving the sensed filament current signal and operably connected to control the power to the lamp filament 208. The microprocessor U2 is programmed to heat the lamp filament by applying the power at a first frequency, measure the filament characteristics, and determine lamp type from the measured filament characteristics. The microprocessor U2 can also be programmed to update operating parameters for the electronic ballast to suit the determined lamp type.

Abstract: One embodiment relates to a thermal field emission electron gun. The electron gun includes a high-vacuum chamber, a thermal field emission cathode including a filament and a tip, a suppressor electrode, an extraction electrode, and a high-voltage power source. The high-voltage power source is coupled to the filament and to the suppressor and extraction electrodes such that the suppressor electrode is at a negative voltage potential in relation to the filament and the extraction electrode is at a positive voltage potential in relation to the filament. A current-limiting resistor is electrically coupled in series with the suppressor electrode. Applicant has determined that such a current-limiting resistor substantially reduces undesirable discharges and improve the reliability and lifetime of the electron gun. Other embodiments, aspects and features are also disclosed.

Abstract: A ballast (10) for powering at least one gas discharge lamp (70) having heatable filaments (72,74) includes an inverter (200), a resonant output circuit (400) coupled between inverter (200) and lamp (70), and a filament heating and ignition control circuit (600) coupled to inverter (200) and resonant output circuit (400) having a first resonant frequency and a second resonant frequency, wherein the first resonant frequency is substantially greater than the second resonant frequency. Filament heating and ignition control circuit (600) controls inverter (200) and resonant output circuit (400) during a preheat phase and during a normal operating phase. During the preheat phase, resonant output circuit (400) has an effective resonant capacitance corresponding to the first resonant frequency, and provides a first level of heating to the lamp filaments (72,74).

Abstract: A starter for a gas discharge light source is configured to measure an initial resistance of one or more filaments of the gas discharge light source, such as a fluorescent light, each time the gas discharge light source is initially powered via a ballast. The starter may initiate a preheat cycle to heat the one or more filaments. The duration of the preheat cycle may be automatically customized by the starter based on the initial resistance and a target hot resistance that is calculated by the starter based on the initial resistance. The duration of the preheat cycle may be automatically customized by the starter to optimize reliability and the life of the gas discharge light source.

Abstract: A ballast (10) for powering at least one gas discharge lamp (70) having heatable filaments (72,74) includes an inverter (200), a resonant output circuit (400) coupled between inverter (200) and lamp (70), and a filament heating and ignition control circuit (600) coupled to inverter (200) and resonant output circuit (400) having a first resonant frequency and a second resonant frequency, wherein the first resonant frequency is substantially greater than the second resonant frequency. Filament heating and ignition control circuit (600) controls inverter (200) and resonant output circuit (400) during a preheat phase and during a normal operating phase. During the preheat phase, resonant output circuit (400) has an effective resonant capacitance corresponding to the first resonant frequency, and provides a first level of heating to the lamp filaments (72,74).

Abstract: An indirectly heated cathode C1 comprises a heater 1, a double coil 2, a mesh member 3, and a metal oxide 10. An electrical insulating layer 4 is formed on the surface of heater 1. Heater 1 is inserted into and positioned at the inner side of double coil 2. Mesh member 3 is disposed along the length direction of double coil 2 at the outer side of double coil 2. Double coil 2 is grounded by being connected to the ground terminal of heater 1 via a lead rod 7. Metal oxide 10 is held by double coil 2 and disposed to be in contact with mesh member 3. Metal oxide 10 and mesh member 3 are exposed to the outer side of indirectly heated electrode C1 so that the surface of metal oxide 10 and the surface of mesh member 3 make up a discharge surface and mesh member 3 is in contact with the surface part of metal oxide 10.

Abstract: A germicidal UV reactor for use in fluid purifiers is provided, in which the UV reactor comprises an UV lamp with an UV transparent primary envelope and also an UV transparent secondary envelope around the primary envelope. The outer surface of the secondary envelope is in contact with a flowing fluid to be purified. There is an isolating space between the outer surface of the primary envelope and the inner surface of the secondary envelope. At least one of the outer surface of the primary envelope and the inner surface of the secondary envelope is provided with electrical means for heating and thus enhancing UV emitting efficiency of the UV lamp.

Abstract: Apparatus and methods are disclosed for measuring cathode fall within a fluorescent lamp that contains an electrode and a gas. A level of cathode fall associated with the electrode may be identified based on an intensity and wavelength of radiation emitted by the gas.

Abstract: The invention relates to a ballast for low-pressure discharge lamps, comprising a controllable inverter circuit for the generation of a high-frequency supply voltage for a discharge lamp (1), a lamp inductance (L1) connected to the inverter circuit, a lamp parallel capacitor (C1) which is serially connected to the lamp inductance (L1) and connected in parallel to the discharge lamp (1), and a preheating circuit supplying heating current to the electrodes (2, 3) of the discharge lamp (1). In order to minimize electrical losses and to enable universal use of said ballast for various types of discharge lamps the invention proposes that current is supplied to the preheating circuit via an auxiliary winding (7) arranged on the lamp inductance (L1) with said auxiliary winding (7) being connected with the preheating circuit via a controllable switch or a parallel resonant circuit (9).

Abstract: Apparatus and methods for measuring cathode fall in fluorescent lamps are disclosed. Together with measurements of cathode temperature, such measurements of cathode fall may inform a determination of cathode heater voltage as a function of discharge current (i.e., a cathode-heating-profile) that avoids both sputtering and excess-evaporation.

Abstract: A method of operating an arc discharge lamp that has first and second electrodes is described. First, the first electrode is heated with a third electrode with a first arc until the first electrode temperature is sufficiently elevated to allow for thermionic emission. Then, a first voltage is applied between the first and second electrode at a voltage less than 1000 volts to create a second arc.

Abstract: Apparatus and methods for measuring cathode fall in fluorescent lamps are disclosed. Together with measurements of cathode temperature, such measurements of cathode fall may inform a determination of cathode heater voltage as a function of discharge current (i.e., a cathode-heating-profile) that avoids both sputtering and excess-evaporation.

Abstract: Apparatus and methods for measuring cathode fall in fluorescent lamps are disclosed. Together with measurements of cathode temperature, such measurements of cathode fall may inform a determination of cathode heater voltage as a function of discharge current (i.e., a cathode-heating-profile) that avoids both sputtering and excess-evaporation.

Abstract: An indirectly heated cathode C1 comprises a heater 1, a double coil 2, a mesh member 3, and a metal oxide 10. An electrical insulating layer 4 is formed on the surface of heater 1. Heater 1 is inserted into and positioned at the inner side of double coil 2. Mesh member 3 is disposed along the length direction of double coil 2 at the outer side of double coil 2. Double coil 2 is grounded by being connected to the ground terminal of heater 1 via a lead rod 7. Metal oxide 10 is held by double coil 2 and disposed to be in contact with mesh member 3. Metal oxide 10 and mesh member 3 are exposed to the outer side of indirectly heated electrode C1 so that the surface of metal oxide 10 and the surface of mesh member 3 make up a discharge surface and mesh member 3 is in contact with the surface part of metal oxide 10.