Accelerator Electron Gun Filament Ground Fault

       

When
the machine is working, voltage of acceleration tube electron gun
filament detected by console monitor panel is normal. In the normal
treatment of the machine, people can observe from the current scope that
the magnetron MAG CU is normal, voltage of acceleration tube electron
gun filament detected by console monitor panel is higher than the normal
value. It can be seen that problems would be in the accelerating tube
or filament assembly. Open the rack enclosure, for checking accelerating
tube filament assembly and the filament voltage. Find that a filament
wire sealing off filament assembly, this may because of rosin joint.
After welding, the machine still cannot beam, malfunction is still
exist. And then check the filament assembly again, but filament lead
still has the sealing-off phenomenon. Welding the lead again, observe it
in the open state of the switch. Four minutes later, the lead again
sealing off the assembly. After welding again, measuring the voltage of
the both ends of filament is only 2.7V, and the voltage of the resistors
R1, R2 are 5.5V respectively, but it should only 2.4V under normal
circumstances. This shows that the voltage of the failure filament
assembly R1, R2 is more than twice the normal voltage value. The current
is proportional to voltage, so the filament current is also more than
twice the normal situation. 

And
what causes the filament current is too large? First, check the ground
of filament (including lead). Measure the lead resistance to ground, it
is 2.5 kΩ, but it should be infinite under the normal state. This
indicates that the gun filament insulation is not good. It is ground
fault that cause the filament current is too large.

Electron
Gun filaments are made of selected high-quality material of tungsten,
with the properties of excellent thermal conductivity, finely processed,
and long duration. Unusual stranded tungsten wires are applied as
evaporator (heating element) in the vacuum metalizing (evaporation)
process to coat thin film on surface of mirrors, and various decoration,
etc.