DIP2000
user manual
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This section explains how to align the DIP2000 scanner to an X-ray
beam from a graphite monochromator. Alignment of the DIP2000 with mirror-mirror
optics is described in the manual of the Double mirrors X-ray Optical system.
However, many parts of this chapter, particularly concerning the software
and the beam stop alignment may also be of use to users having mirror optics.
Log in on the computer which is attached to the DIP2000 system. Check that enough disk space is available for your work with the command % df. Each (uncompressed) DIP2000 image takes up 12.5 Mb for 20 cm plate systems and 18Mb for 30 cm plate systems, so for 180 images of 1, one needs 2.25 Gb resp. 3.24 Gb disk space.
Set the default directory on a disk with sufficient space.
Start the DIP2000 program :
% xpress
The program starts by displaying a bar with control buttons at the top
of the screen (see fig. 4.1).
The left, green part is for the operation of the generator. This part has not yet been implemented.
The middle, blue part is for the two devices attached to the generator, device A and device B. Generally the DIP2000 is controlled as device A. Operation of the DIP2000 will therefore be done by pulling down the menu from the button marked "Device A".
Off-line operations like e.g. display and analysis of images can be done from the button marked with the pencil. The red right button is an emergency button for the DIP. Pressing this button will halt all DIP operations.
In the winterm window from which xpress has been started a list
of commands and replies will pass which echo the communication between
the controller and the Indy computer. This is called the LINEEYE output.
This may be useful to see whether something is happening and in some cases
for trouble shooting, because one can see which command has been executed
as the last one. An explanation of these commands can be found in appendix
1.
The data collection program on the DIP2000 is written with the OpenWindows window manager. This program has the following conventions :
Two kind of buttons can be distinguished : Rectangular boxes and (triangular)
arrows. The boxes allow for one choice only and should be clicked with
the left hand mouse button. The arrows are pointing to pull down
menus with several choices and these should be pulled down with the right
hand mouse button. Pushing the left hand mouse button means that one selects
the top choice of the pull down menu, which is not always what one wants.
An example : If one would push the right hand mouse button on
the Device A button, two possibilities appear : Manual Operation and Standard
Data Collection. The first one will pop up three windows (see below), the
second one will pop up one window. If one would use the
left mouse
button, the first choice would be taken automatically and the three windows
will appear on the screen.
Manual Control program description
For alignment and testing of the instrument the manual control level is used . Three screens will be popped up if you put the mouse at the [Device A] button and select the box "Initialize/Manual". :
The Setup window, which allows you to put all the axes to zero and to reset the readout of the axes
The Instrument Status screen which displays the current positions of the IP change axis, reading arm, and goniostat axes. If the controller has been reset or if the zero positions are lost, the display for axes will be shown in grey and no values will be visible.
The Manual Control window, which shows the possible options of the Manual control section.
These windows are shown here:
This window displays the several options for process selection : Setting up, Basic Operation, SC counting, Attachment and HV/PHA setting. These will be discussed separately below.
Initial values settings and optional offsets of zero must be set for each part of the instrument. Normally these should be zero. During read out of axes these offsets will be applied and each axes position , IP change axis, reading arm, and Phi axis will be corrected for. Also the HV/PHA setting of the scintillation counter will also be done. When the [Setup start] button is pressed, all processes will be executed in sequence. In order to execute only a specific process, select the process from the menu of this button by pressing the right mouse button and execute the preferred process. The sensitivity range of the scintillation counter can be set by changing the PHA mode.
Whenever the power of the system controller has been turned "on" or when the reset switch has been pushed, be sure to execute the setup process, by pressing the [Setup start] button.
This is used for alignment and testing and for independently controlling individual parts of the instrument. Be sure to "Quit" this basic operations screen before going to the operations in "DIP Measurement".
Beware ! Many tests can be done simultaneously, that should not be done simultaneously.
For alignment purposes, the only things needed are : Shutter control, positioning of the goniostat axes, positioning of the Image plates and read out of the scintillation counter. These are all in the top half of the Basic Operations screen, from commands a - g. The lower half is for extensive testing only and should be used with caution.
Put the mouse in the Manual Control window and select [Basic Operations], by clicking the left mouse button. This pops up the following screen. A description of the parameters of the different window follows below.
(a) Main shutter control
This opens and closes the main shutter of the generator. This has not been implemented yet.
(b) Beam shutter control
This opens and closes the shutter of the DIP2000. The DIP2000 shutter will open when the [Open] button is pressed and, after the time designated in the time space, close again. When the time space is left blank or 0 is input, the open time is unlimited and the shutter will not close until the [Close] button is pressed.
(c) Beam stop
This opens and closes the X-ray by moving the beamstop aside. (Early series vertical phi axis systems only).
(d) IP change axis operation
Rotates the IP change axis through the angle, which is given at the line Setting angle (deg). For 0 degrees, IP1 is the "readout/erase side" and IP2 is the "exposure side". For - 180 degrees, IP1 is the "exposure side" and IP2 is the "readout/erase side". At -90 degrees, the scintillation counter is at the primary beam position and neither IP1 or IP2 is at the "readout/erase side" or "exposure side". The positioning will be done after the [Start] button has been pressed.
(e) Reading arm operation
Moves the arm for IP reading to the designated position. Beware ! The readout value of the readout arm is relative to the IP change arm value. Be cautious when changing this value.
(f) Phi axis operation
Executes Phi axis positioning and oscillation. The Setting angle is active for positioning. If Oscillation is selected the Range and Speed have to filled in.
(g) Weissenberg
Moves and oscillates the Phi and IP change axes to execute Weissenberg operation.
(h) Reading arm operation mode
Used for setting the operation mode of the arm for IP reading. Internal means that the reading arm operation will be controlled by the program, External means that it is fully under user control. BEWARE ! This is only to be used by service engineers, when the covers of the scanner are removed.
(i) IP rotation
Used to set the rotation mode for IP1 and IP2 to ON or OFF
(j) Solenoid for IP lock
Used to turn the solenoid ON or OFF in order to lock the rotation of each IP. Do not do this while IP1 or IP2 is rotating!
(k) Halogen lamp
Turns the halogen lamp ON or OFF for IP erasure.
(l) IP erase
Performs the erasure for the IP on the "reading/erase side". Set the moving speed for the halogen lamp arm in the speed space. The angle to move is about 45, so a speed of 1/sec will erase the plate in roughly 45 seconds.
(m) IP reading
Performs reading of the IP on the "readout/erase side". Data which is read will be stored in the designated file. X-Y conversion will not be done, so the file will be stored in r- format.
(n) Mask
Opens and closes the cover plate between the "reading/erase region" and the "exposure region" in the scanner box. This works on first series DIP2000 systems only.
Using a scintillation counter, the X-ray intensity is measured. The rate meter near the DIP2000 scanner will indicate the countrate of the primary beam. It can be scaled to the read out of the ratemeter by turning the "rate" knob on the controller.
On the monitor display it can be shown as follows:
In the "Manual Control A" window, press [SC counting]. This will pop up a window "SC counting A". The data from the counter can be written to a file. If you want this, set "Save the data" is set to [yes] , fill in the filename and click [Exec]. This will save the data in the designated file when measurement is completed. If you do not want to save the data, click the [No] button after "Write to a file" and click [Exec].
Pushing the [Exec] button will pop up two windows:
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 |
"SC counting A" and "Graph Control". Click the [Reset] button in the Graph Control window, to display the countrate in the "SC counting" graph window.
With the buttons in the "Graph control" window, the graph can be modified to ones own needs. To close the windows, click [Suspend] in the first "SC counting A" window, followed by [Quit].
This window is used for setting the optimum high voltage of the scintillation counter system and the baseline and window values for the pulse height analyzer. This should be done with a beam which is as monochromatic as possible, so before alignment you are in a catch-22 situation.
Clicking the HV/PHA setting button will pop up the following window. By selecting one of the upper two buttons, HV and PHA, one can select the setting of either of these.
The HV or PHA will be varied and the number of counts is plotted as a function of these. The final values should be put in the setup window.
Rough alignment of the DIP2000 scanner
Make sure the X-ray generator is levelled by using a spirit level.
Level the main body of the DIP2000. Align the height of the connector with the focus of the X-ray generator. Use the remote controller (if present) to adjust the height of the 3 legs on the base. Knob nr. 1 operates the leg closest to the table edge, knob nr. 2 operates the leg closest to the back of the table and knob nr. 3 operates the leg closest to the X-ray port.
Put the main body of the DIP2000 scanner on the X-ray generator and make sure the take off angle is 6 degrees.
Put the DIP2000 in the "zero" position, so that the collimator axis is along the undiffracted X-ray beam. Use the following settings :
Crystal to plate distance : 200 mm
Theta : 0
2thetam : 0, with the adjustment in the middle of the scale.
Monochromator crystal :
Set the attenuator holder in front of the Image plate and put the
aluminium absorption plate (0.5mm) in the slit holder.
Put a 0.9mm collimator in the collimator holder.
Set the X-ray generator to low power, e.g. 20 kV and 5mA.
Use the Basic Operations window to put the scintillation counter of the DIP2000 in line with the beam by putting the IP change arm at -90.
If the Basic Operations window is not yet on the screen this can be
obtained as follows :
In the "DIP2000 system status list" window, the read out of the
IP change arm will now be set to -90.000 deg.
Open the main shutter on the X-ray generator.
Open the DIP2000 shutter as follows : In the "Basic operations" menu, input "0 sec." for the time value in "Beam shutter control", then press [Open]. This will leave the shutter open.
Align the DIP scanner with respect to the generator by adjusting the height, the position and the theta rotation of the DIP scanner by maximizing the number of counts on the scintillation counter. The number of counts can be seen on the computer screen by using the SC counting option and it can be followed with the rate meter on top of the scanner. The sensitivity of the rate meter can be adjusted with the knob on the controller. It can also be changed with an order of magnitude by setting the PHA mode in the DIP2000 setup window to Diffx0.1 instead of Diffx1.0. This can be done as follows :
Use the right mouse button to select the PHA mode : Diffx1.0, Diffx0.1 or INT, the latter meaning integral, without discrimination by window or base level. Select Diffx0.1.
Put the mouse on Setup start and use the right mouse to select HV/PHA. This way the High Voltage and Pulse Height Analyzer mode is updated, without changing the goniostat or IP axes. This should be done, otherwise the scintillation counter is no longer at the direct beam position and then the direct beam hits the plate.
If the maximum has been reached, and the DIP2000 is well aligned at theta=0, the shape of the beam should be nice and round and should be centred at the position of the crystal. This can be checked with the fluorescent screen at the crystal position. The true position of the crystal can be marked with a pencil dot on this screen by putting the tapered jig in the collimator holder and carefully touching the flu-screen. The point where the jig hits the screen, should also be the place where the beam is hitting the screen. If the beam is not nice and round, adjust the height and position of the DIP2000 scanner to obtain the desired shape.
The monochromator crystal can be put in the right position by performing
"beam division" using the monochromator crystal. An outline of the monochromator
is to put in a figure below.
The above described operation is used to align the crystal as parallel
as possible with the beam. The shape of the beam should now be a half moon
and should touch the position of the crystal. This can be checked with
the fluorescent screen at the crystal position.
Record the Theta-m value of the monochromator crystal.
For the fine alignment the Theta-m, 2Theta-m, and tilt of the monochromator crystal are adjusted using the ratemeter to monitor the intensity.
(1) Align with the target of the X-ray generator and set 2theta-m and
Theta-m.
Starting from the 2Theta-m position during direct beam adjustment,
align with the target and move 2Theta-m by the angles below.
Starting from the Theta-m position during direct beam adjustment, align
with the target and move Theta-m by the angles below.
| Anode material | Mo | Cu |
| Theta | 6.09 | 13.29 |
| 2Theta | 12.18 | 26.58 |
(2) Open the shutter and align Theta-m, 2Theta-m, and the Chi rotation
of the crystal by maximizing the output on the ratemeter as follows :
(3) Change the collimator to 0.5 and 0.3mm and align 2Theta-m, Theta-m
and the tilt.
(4) Close the DIP2000 shutter by pressing the [Close]button following
the line "Beam shutter control" in the Basic Operations menu
The beam shape can be checked with the fluorescent screen. (For this the shutter should be open)
A final check of the beam (also for future reference) can be made by making a direct beam exposure with the plate at an offset. Leave the Basic Operations for this and go to the Data Collection mode. Make a 1 second still at e.g. 10 degrees IP position. The peak height and Full Width at Half maximum can be checked with the profile option in the display program.
Use the pinhole on the goniometerhead to determine the exact position of the crystal. First centre the pinhole using the microscope or CCD camera. The centre should be at the position where the X-ray beam goes through the hole and where the intensity at phi=0 and phi=180 is equal. The height of the crystal can be determined by adjusting the height of the pinhole and maximizing the intensity.
Centre the position of the microscope so that the hole of the pinhole is at the centre of the crosswires.
Reinstall the beam stop.
Attach the jig with the tapered end in place of the collimator and
adjust so the centre of the beam stopper is at the centre of the jig.