Dynalyzer – High Voltage Unit
OPERATION MANUAL
28
Maintenance
System Pressure
The High Voltage Unit is insulated with pressurized Sulfur Hexafluoride Gas (SF
6
). Every effort has
been made to ensure a leak-tight system. The unit is pressurized to 30 psig when shipped and
contains a relief valve set at 30 psi. The unit is filled at sea level. Transportation in unpressurized
aircraft, or in cargo holds with reduced pressure, will result in an increase in the differential
pressure as compared to sea level (14.7 psi).
Effects of altitude variation such that the sum of internal pressure plus atmospheric pressure is
greater than 22 psi will result in satisfactory operation at voltages up to 150 kVp. If there is a loss in
pressure due to this effect, the unit should be recharged to 30 psi. Any leak due to other causes
should be identified. Recharging may be accomplished with the contents of a lecture bottle of
Sulfur Hexafluoride, C.P. gas, available from Matheson Gas Products Company. The contents of
one lecture bottle of SF
6
(
1
/
2
pound) is adequate to completely fill the system. As long as there is
positive pressure in the High Voltage Unit, purging of the unit will not be necessary.
Failure Modes
Protective circuitry in the High Voltage Unit has been incorporated to suppress high voltage
transients that may be generated under fault conditions. The anode current transmitter, under
extreme operating conditions, can sustain damage. This would be evidenced by either saturation
of the mA output signal, or a negative offset of 100 mV.
Loss of internal pressure will result in a decrease in the insulation properties of the internal gas
(SF
6
) which could reflect itself as internal arcing between components, or to ground. This could
result in the destruction of some semi-conductor elements.
