Note: part of the text is missing and needs to be restored. (MTV 8/9/2002)
off their power switches.
4. Align Base Z and 2q. Conceptually, this is the same as step 3., except that the angle is affected by the leveling of the base, so be sure that the base remains level. Remove vertical slit, and make sure edge of collimator is vertical; use a square on the anvil guide blocks to make sure. Use motors 4 for Z (with 5 and 6 tracking), and 3 for 2q. When steps 3. and 4. are completed, you know that the dovetail is parallel to the beam when 2q is equal to 0.
5. Align collimator. Insert horizontal slit and move the CSA to the position where it will be used. The x-rays should now go through both the collimator and the horizontal slit. If they do not, then the line passing between them is not parallel to the dovetail. The only way presently to make this adjustment is to loosen the screws holding the slit assembly and move them by hand. It helps to clamp a guide block before you loosen the screws and use shims to control movement. Adjust the collimator, then repeat step 4. If you feel that this is unnecessary, move 2q until the x-rays pass through collimator and slit and set this value at zero. Record the value on the mechanical indicator (typically about .561). This slight error means that when 2q is zero, the dovetail is not quite horizontal, and if the CSA is moved, there will be alignment errors; as you will not move the CSA from now on, this should not be a problem.
6. Zero 2q. When the Base is aligned, fix motors 4, 5, 6, 7, and 8 and set the base motor enable switches to OFF. In this way you know that the base cannot be accidentally moved, and if the Camac and/or computer power are lost, they are at zero. Using the RB (reset base) command, set all base motors to zero. Using the ZE command, record the position of the automatic zero for 2q. (it is about 10 degrees). In the future, if 2q zero is lost, the ZE command will automatically find this position, and 2q can be reset.
7. Adjust Incident Light Slits With the diffracted beam slits and collimator in place, insert the 100 micron incident light slits in their holders one at a time and drive the motors in Y and Z until you find the center of the beam. After the slits are adjusted, reset their motors to zero using RS (reset slits). The slit motors should be left on, because if they are off, they can be manually turned. If they are accidentally moved with the computer, they can be returned to the zero position with the ZS (zero slits) command.
After the Base is aligned, the Pedestal (and the press which is mounted on the Pedestal) can be moved until the center of the sample assembly is located at the intersection of the 2q axis and X-ray beam. The Pedestal contains four motor adjustments: X, Y, Z, and a rotational adjustment about a vertical through the center of the sample. The most important part of this alignment to be done at this time is Y and rotation. Drive Z until the sample location appears to be about right, relative to the collimator tip. Adjust PY (Pedestal Y, motor 10) and PO (Pedestal rotation, motor 12) until the collimator appears to be centered in the gap between the anvil guide blocks. Drive 2q so the collimator is not in the way (~20 degrees). Remove the horizontal incident light slit and widen the horizontal BLA slit to about 10 mm and look for a large spot on the fluorescent screen. Rotate the pedestal until the beam is eclipsed; note that angle. Widen the beam to make sure the eclipse is real. Rotate the pedestal the other way until the beam is eclipsed again; the correct position will be halfway between these two eclipsed positions.
Return the beam width to its original value of .2 mm, and drive the pedestal in Y until the beam is cutoff; repeat in the reverse direction. Again, the center position is the correct one. Fix motor 12 (pedestal rotation) and turn on its brake, you will not need it again. You will, however, be using motor 10 later. The final alignment of the pedestal is accomplished with a test sample. When this is completed, reset the pedestal motors to zero (RP). The pedestal can always be driven to this position with the zero pedestal (ZP) command.