A thyratron is a type of Gas-tube used like switch for the strong powers. This tube can take the form of a Triode, a Tétrode or a Pentode, although the majority are triodes. The gases used can go from the vapor of mercury to the Xénon or the Néon, while passing by the Hydrogène (especially in the high voltages applications or the applications requiring of the very short switching times). Contrary to the electron tubes traditional, a thyratron cannot amplify a signal linearly.

Development

See also: Historical of the electron tubes

The thyratrons developed with the beginning of the year 1920 starting from the first electron tubes with gas such as the UV-200, which contained a small quantity of Argon to increase its sensitivity as a detector for waves radios; and relayage German LRS tubes it, which contained also argon. The Rectifying S with gases which preceded the electron tubes, such Tungar of General Electric, and the rectifier with mercury bath of Cooper-Hewitt, had them also their influence. A thyratron is basically “a controlled rectifier with gas”.

Irving Langmuir and G.S. Meikle of General Electric are often quoted like the first to have studied the rectification ordered towards 1914. The first marketed thyratrons were it only towards 1928.

Technology

A traditional thyratron with hot Cathode uses a heating filament like cathode, contained with its Grill of control in a shielding, which is open side of the Anode in the shape of plate.

Operation

During the application of a positive tension on the anode with respect to cathode, if the electrode is maintained with the potential of cathode, no running circulates. If the potential of the electrode of control increases compared to that of cathode, the Gaz between the anode and cathode ionizes and leads the current. Once made conducting, the thyratron will remain it as much as current sufficient will circulate between its anode and its cathode. When the anode current or the tension between anode and cathode goes down again to a value very close to zero, composing it blocks itself, like a “open switch”.

A spectacular aspect of the operation of the thyratrons lies in the coloring of the gas mixture during the conduction of these tubes.

The shielding prevents conduction by ionization between other parts of the tube. The gas in a thyratron is generally with a pressure much lower than that of the Air to the sea level, that is to say in the majority of the cases between 15 and 30 millibars (1.5 to 3 kPa).

Alternatives

The cold cathodes or heats can beings used. Hot cathodes have as an advantage a greater facility of ionization of gas, which makes control more sensitive.

Applications

In the past, of small thyratrons were manufactured for the control of electromechanical relays, of engines and for the equipment of welding to the arc. The large thyratrons are always manufactured, and are able to function to currents about ten kiloamperes (kA), and this with tensions of approximately ten kilovolts (kV).

Among the modern applications one finds: generators of impulses for the Radar S, Laser S with gas high energy, apparatuses of Radiotherapy, the equipment of research (winds of Tesla), and of many other applications.

The thyratrons are as used in the transmitters of Télévision, to protect the tubes from exits in the event of internal short-circuit by connecting the high voltage of the plate to the Ground time as protections start and that the loads stored in the cables and the condensing S is evacuated towards the ground. This earthing, called “ crowbar circuit ” in English, is very current in high voltage.

The thyratrons were replaced in the majority of the applications of weak and average power by the Semi-conducteur S equivalents like the Thyristor S and the Triac S. Cependant for the applications in the field of the tensions higher than 20kV and requiring very short switching times, the thyratrons are still best the Interrupteur S ordered. There exist several variations of the idea of the thyratron, like the Krytron or the Ignitron, which is still used nowadays in certain fields.

See too

External bonds

  • tpub.com
  • Article on the electron tubes being used as switches by John Pasley

References (in English)

  • Stokes, John, 70 Years off Radio operator Tubes and Valves, Vestal Near, NY, 1982, pp. 111-115.
  • Thrower, Keith, History off the British Radio operator Valve to 1940, MY International, 1982, p. 30,31,81.
  • Hull, A.W., “Gas-Filled Thermionic Valves”, Trans. AIEE, 47,1928, pp. 753-763.

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