Cathode ray tubes real life1/20/2024 and the interior of the tube would glow in lovely patterns. They took a glass tube with wires embedded in opposite ends. Thomson,Ĭience lecturers who traveled from town to town in the mid nineteenth century delighted audiences by showing them the ancestor of the neon sign. Us so promising an opportunity of penetrating the secret of electricity." - J.J. You do not need to use a stand by condition to ensure maximum filament life, but you may find it beneficial as your power supply will achieve a steady state sooner."There is no other branch of physics which affords Using the chart in Figure 2, this translates to approximately 40,000 hours of expected life.Ī stand by condition of ~50% maximum filament current rating places the filament in a very low region of evaporation where the filament life is not measurably affected. For example, if the user normally operates the X-ray tube at 40kV and 1.0 mA, this requires a filament current of approximately 1.60 A. ![]() Once estimated, the rate of evaporation can be used to estimate the normal filament life as shown in Figure 2. To determine the anticipated life of a helical tungsten filament, one must estimate the average filament current employed throughout its life. ![]() The filament current required to heat and achieve a given X-ray beam current differs depending upon the required applied high voltage, as shown in Figure 1. The rate of filament evaporation, and thus the total number of hours required to thin the filament to the point of failure is a function of the chosen operating conditions. ![]() After a certain number of hours of normal operation, the filament will thin to the point of failure. The process of heating the helical tungsten filament to produce electrons naturally causes the filament to evaporate. The Shasta power supply is perfectly matched to our X-ray tubes. Our Shasta X-ray tube power supply has a tightly designed circuit which prevents the filament from exceeding its maximum allowable current. Therefore careful control of the filament circuit is essential to a long lived X-ray tube. However above 1.7 amps the filament enters a very high region of evaporation, and by 1.75 amps the filament reaches its melting point. This is due to the important relationship between filament current and actual temperature of the filament wire itself.īy example, the Jupiter Series 5000 X-ray tube requires more than 1.5 Amps current at 2 Volts to achieve the required filament temperature necessary for electron emission. Since a smaller filament is preferred where possible, a typical filament “driver” circuit must be able to control the current to the filament quite carefully. In the case of microfocus X-ray tubes, a dispenser cathode is typically employed.) ![]() (This applies only to small focal spots when utilizing a tungsten wire filament. Of importance to those users seeking a small X-ray focal spot, the relationship between a smaller wire filament and a small focal spot is well established. The resulting design of a modern X-ray tube seeks to balance the relationship between performance and filament longevity. When heated to approximately 2000 degrees Celsius, tungsten is a copious emitter of electrons.įrom this point several trade-offs in design become factors, which must be considered. The process of producing electrons necessary for the production of X-rays in an X-ray tube begins by heating a tungsten wire.
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