3900001 Rev. C
Page 16 of 24
User Manual
Issue
02
/
February 2015
/
Shasta User Manual
Shasta High Voltage Power Supply
Setting Grid Bias Scaling (Optional Feature)
The grid bias scaling, available only on the 9700002 and 9700004 models, can be adjusted locally using
the ‘Bias Adj’ potentiometer on the front of the unit.
Setting the Grid Bias Voltage
1. Ensure the output voltage is set to 0kV, the unit is powered off, the HV cable is disconnected
from the power supply, and the HV well is covered with the red shipping cap.
2. Turn on the unit, and adjust the output voltage to 50kV.
3.
Adjust the Grid Bias via the ‘Bias Adj’ potentiometer on the front of the unit to the optimal value
provided by Oxford Instruments (see note below). The Grid Bias may be measured directly
between J2 pin 3 (Grid Bias) and J3 pin 2 (Filament Return).
4. Adjust the output voltage back to 0kV. The Grid Bias will decrease linearly as the kV drops.
5. Power off the unit, then reconnect the cables and operate the tube normally.
NOTE: The optimal grid bias setting will vary from X-ray tube to X-ray tube. Please refer to
the documentation provided with the X-ray tube from Oxford Instruments for the optimal
grid bias setting.
CAUTION: The grid bias output can reach up to -300V. Ensure that appropriately rated
meters and cables (High impedance meter, 500VDC minimum voltage rating on meter and
test probes) are used to measure the grid voltage during programming.
Filament Current Limit
The filament current limit is a feature designed to protect the X-ray tube filament from overheating. By
default, this is set at the factory to 1.7A. It is recommended that this value not be changed by the
customer; however, instructions on how to change the filament current can be found below if it is
required by the application.
Adjusting Filament Current
– Off Tube
1. Completely disconnect the X-Ray tube from the power supply
2. Place a Multimeter set to a current range greater than 4A directly across the filament output
connections J3 pins 1 and 2
3. Demand an output voltage of 500V and a beam current of maximum
4. Apply the 24Vdc to the power supply and close the interlock
5.
Adjust the front panel ‘Fil Limit’ potentiometer to set the desired maximum filament current
Adjusting Filament Current
– On Tube
1. Ensure that the 24Vdc is turned off
2.
Adjust the front panel ‘Fil Limit’ to 0 by turning fully counter-clockwise (this may need up to 20
turns)
3. Demand the required output voltage and beam current
4. Apply the 24Vdc to the power supply and close the interlock
5. Adjust the front p
anel ‘Fil Limit’ clockwise to increase the maximum filament current while
monitoring the beam current monitor, stop adjusting when the required beam current has been
achieved
