TXR 325D, Руководство по обслуживанию

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Standard Frequency Series Generators
Maintenance
16
M-2008-7-15
7.8 TROUBLESHOOTING GASSY X-RAY TUBE
SYMPTOM MOST COMMON PROBLEM HOW AND WHERE TO TEST
HIGH MA (continued) Gassy X-Ray Tube Gassy X-Ray Tubes are the result of three actions. The normal
evaporation of filament and anode material over the normal
life of an X-ray Tube, accelerated evaporation of filament
and breakdown of anode material caused by exceeding tube
limits, and immediate breakdown in new tubes caused by
defective material or workmanship. The latter is pre-dominate
in causing extensive damage to High Voltage Rectifiers and
High Voltage Winding when the defect is not detected and
corrected quickly. All these actions result in gasses becoming
active inside the vacuum tube. This gas is impure and allows
accelerated movement of electrons. The pre-dominate cause
is usually the anode run speed is too slow. See “ Anode Run
Speed Too Slow .”
• This gas is impure and allows accelerated movement of
electrons. As KVP is increased MA begins to increase.
Space Charge cannot be changed to correct and stabilize
mA. How radically a tube reacts to the set level of MA and
kVp is determined by how gassy the tube may be. For
instance, some tubes react quite well up to 200 MA and
100 kVp, while others react quite violently when the tube
is exposed above 50 kVp at 50 MA. Tubes may conduct
properly when cold, but become unstable when they warm
up. There is no one set way to measure how gassy a tube
has become. If a tube is only slightly gassy, it must be
replaced because it will cause extensive damage to
Rectifiers and to the High Voltage Winding. To test for
slightly gassy X-ray Tubes, decrease KVP until the current
stabilizes. The only sure way to test an extremely gassy
X-ray Tube is by replacing the X-ray Tube and both High
Voltage Cables.
Defective High Voltage Cable. • Shorting High Voltage Cables may cause higher MA’s or
kicking the circuit breaker. Defective High Voltage Cables
are the result of breakdown of insulating material that
eventually leads to a short between wires or ground. This
short allows a path for current to flow to GROUND. During
a partial short the cable will cause symptoms much like a
gassy X-Ray Tube. The result is higher MA.
In most cases the cable will short completely pegging the MA
Meter. In this case there will not be output from the X-Ray
Tube. Shorting X-Ray Cables if left uncorrected can cause
opening of High Voltage Rectifier and High Voltage Winding
in the Transformer.
Most breakdowns occur at the receptacle ends, where the
cable enters the plastic and is bound by a pressed ring and
at 90 bends. Also pinching, twisting, puncturing or allowing
cables to become saturated with oil or other chemicals will
break down insulation. To test, replace the High Voltage
Cables.