Monochromated X-Ray Source with XR5 Electron Gun
Issue 5
Monochromator and XR5 (HA600054)
13
5. Note the position of the beam spot relative to the cross hairs centre.
6. If the spots are less than 1 mm from the cross hairs centre the spot can
probably be re-centred without causing a significant change in the detection
sensitivity.
7. Record a spectrum from any convenient sample (e.g. a silver standard) before
making any changes and then use the two lateral shift micrometers on the
crystal manipulator as shown in to adjust the beam position to the cross hairs
centre. Do not adjust the height or leg angle of the crystal manipulator. Re-
record the spectrum as before and if the count rate has not fallen by more than
5% there is no need to realign further. If the spot is more than 1 mm from the
centre or if this procedure needs to be repeated on more than three occasions,
then a more complete realignment should be performed. Only if a major service
or repair has been undertaken should a more extensive re-alignment be
necessary.
Figure 3-6: Adjustment of the Crystal Manipulators
Lateral Shift
Micrometers
Lateral Shift
Micrometers
Height Change =
Diagonal Movement of
Spot (
NOT
Wanted!)
Dispersive Change =
Vertical Movement of Spot
(Along HPT X-axis)
Non-Dispersive Change =
Horizontal Movement of Spot
(On the HPT Y-axis)
Monochromated X-Ray Source with XR5 Electron Gun
Monochromator and XR5 (HA600054)
Issue 5
14
3.7
T352/NT Computer-Controlled Power Supply
The power supply is a multiple output unit generating all the voltages needed to
operate both the Twin Anode and Monochromator guns. It also controls the cooling
water pumping for both guns.
The specification of the outputs for the monochromator gun are shown below in an
abbreviated form.
Output
Maximum Operating Ratings
Main HT
15kV/60mA (Normal operating)
or 20kV/20mA (Source conditioning)
Monochromator Filament
2.5A
Bombard
3000V
Cathode
1200V
Focus
3500V
Table 2: Specification Outputs for the Monochromator Gun
Control is entirely from the computer, no manual controls are fitted except for the rear
panel mains power switch.
The supply requires five interlock loops: Vacuum; Water-flow; Twin anode cover; Mono
cover; Mono source cable-guard, to be closed before the high voltage outputs can be
switched on. The state of the interlocks is reported to the software. To clear an
interlock the physical fault must first be rectified (e.g. replace a safety cover) and then
reset by software before the high voltage outputs can be switched on. The interlocks
require a voltage free closing contact to operate. Shorting interlocks to earth will not
operate them.
Communication between the control computer and the power supply is via an optical
modem and a fibre optic serial line from an RS232 port (generally COM1). The mains
power to the T352/NT is NOT vacuum-interlocked (although the outputs are) so that
the communications circuitry is always powered even when T352/NT output trips
occur. The output circuitry is protected by the separate vacuum interlock.
The T352/NT outputs will trip if any interlock fails or if certain levels are exceeded. The
most relevant of these are the Leakage Current and the HT Current. The leakage
current is due to the conductivity of the anodes cooling water and the HT current is the
total current comprising leakage c electron-beam current. Trips will occur if the
leakage current exceeds 20mA, (so water purity must be maintained periodically if the
drain current becomes too high), or if the HT current exceeds 60mA.
The state of all outputs, interlocks, trips and the values of achieved voltages and
currents are displayed by the control software.
There are no user serviceable parts in the T352/NT power supply. Contact your local
agent for service.