3900001 Rev. C
Page 14 of 24
User Manual
Issue
02
/
February 2015
/
Shasta User Manual
Shasta High Voltage Power Supply
Grid Voltage Output
Type:
Voltage source
Voltage:
-300V
Output Current:
0.25mA, (short circuit current 2-4mA)
Polarity:
Negative
Ripple voltage:
<300mV peak to peak
Load regulation:
<2%, 10kΩ Output Impedance
Line regulation:
<0.2% for a 10% change in input voltage at rated output load
Temperature coefficient:
300ppm/C over operating temperature range
Stability:
+/-0.5% over an 8 hour period after 30 minutes warm-up
Control:
The Grid bias is automatically adjusted by the kV output voltage
kV = 0, Grid bias = 0 and kV = +50kV Grid bias = maximum setting
Please note that the full scale Grid bias voltage is set by the front panel
m
ounted ‘Bias Adj’ potentiometer
Grounding
The system is designed to be used with a grounded cathode X-ray tube.
No isolation is provided between input and outputs, Ground (zero volts) is common to input and outputs.
Protection
The HV power supply is protected against short circuits of any duration and intermittent arcs.
The filament is protected against open circuit by a dedicated voltage control loop; it is also protected
from continuous short circuits and intermittent arcs.
Control of the High Voltage Power Supply
Analog Control Overview
Analog Control involves setting the kV and uA set points, adjusting the grid voltage (where applicable),
turning on/off x-rays and monitoring x-ray levels and fault conditions. The analog inputs can be set
either with the potentiometers located in the front panel, or by a remote voltage controller.
The filament current limit can also be adjusted, but in most cases the factory default setting should be
maintained.
Interlock
An interlock circuit is implemented that interrupts the supply to the high voltage power stage when open.
When the interlock circuit is open the high voltage and filament are turned off.
Connect pin 4 of J4 ‘INTLK’ to either a 12V 0.5W lamp or a 330R 1W resistor to the front panel earth
stud to close the interlock.
NOTE: Do not connect the
‘INTLK’ pin directly to 0V or the chassis, the unit will be
damaged if this is done as it uses a 12V internal relay.
Once the interlock is closed, the HV output and filament will be ramped up over a period of 4-6 seconds
to the demanded values.
