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.