Flashtube

The flash tube is a gas discharge lamp, in which the gas discharge is not continuous but proceeds in the form of short pulses. During such a pulse, a previously charged energy storage ( capacitor ) is discharged in a very short time by the flash tube.

Design and function

A flash tube made ​​of a glass bulb which is filled with xenon or a rare gas (especially for laser pumping lamps) with krypton and sealed into the two electrodes. In him is when a sufficiently high voltage rather than a gas discharge or formation of a spark, which is visible as a bright flash of light. The necessary electrical energy is provided by a capacitor in battery-powered flash units ( photoflash ) is charged for example by a flyback converter to about 400 volts.

By impact ionization of the discharge current increases after the ignition period of about 0.1 ms to values ​​of several 100 A, and the storage capacitor discharges. It occurred briefly to enormous benefits in the range of a few to over 100 kW. This increases the temperature and pressure in the lamp and the spectrum is improved due to the line broadening toward daylight-like quality.

The flash energy can be controlled with photo flash units via shorting the discharge, but in particular about the switching off of the discharge current. Both methods allow turning off the flash after delivering a fixed amount of light.

Application

Flash tubes are used in flash of light equipment, such as strobes and flashing lights in the field of photography, the xenon flash tubes have the formerly used magnesium flash bulbs replaced entirely practical.

Flash tubes used in signal and warning lights are used, such as position lights in aviation, for firing of aviation obstacles or light signal transmitters to life-saving appliances, as well as for the hearing impaired as an alternative to acoustic signals ( alarm clock, doorbell ). For applications where high reliability and long life are required flash tubes can be used with gas reservoir.

Furthermore find flash tubes used as pump sources of pulsed solid-state lasers (see also pulse lasers, Nd: YAG laser) and for short-term heating of surfaces (annealing, recrystallization and annealing / annealing of crystal defects ).

In metrology, spectroscopy and flash tubes when LIDAR (measurement of cloud height ), in fluorescence spectrometers for the determination of the fluorescence lifetime and in pulsed solar simulators to accommodate the power curve of solar modules can be used.

In general, flash tubes also serve to expose (Examples: contact print, some copiers ).

Ignition

To control the timing of discharge and to provide a low ignition voltage, an auxiliary electrode is often used. The auxiliary electrode may be configured as a wire wrap or as a conductive coating, and often extends over a longer part of the discharge tube. The auxiliary electrode is connected to an ignition coil, which produces a low-energy high-voltage pulse (about 1 to 8 kV). This pulse acts capacitively through the glass bulb through and causes a partial ionization of the gas filling, whereby the gas is conductive. The ignition coil is supplied with a discharge of a small auxiliary condenser by means of a contact or a thyristor.

More Zündvarianten are:

  • At a tube: series-connected coil that can withstand the high discharge
  • In two series tubes: Creating the ignition pulse to the junction of the two tubes

Spontaneous ignition between the main electrodes is dependent on the tube length is from 0.5 to 25 kV. Limiting the charging voltage of the storage capacitor.

The firing voltage and the voltage of the storage capacitor must always be lower than the spontaneous ignition and can in mains-powered photo flash units, for example, with a voltage doubler circuit ( Greinacher circuit ) are generated from the mains voltage:

At Unetwork = 230 V.

Specifications

Characteristic parameters of a flash tube are:

  • Maximum energy per flash in joules ( watt-seconds ), this usually corresponds to the energy content of the storage capacitor:

With

  • Amount of the required ignition voltage
  • Charging voltage of the storage capacitor area
  • Maximum flash frequency and maximum average power dissipation
Electric discharge in gases Spectral line#Spectral line broadening and shift Air traffic obstacle Fluorescence spectroscopy Hamamatsu Photonics
132685
de