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Subsections
The six-position sample changer can be used to collect room temperature data
on up to six different samples under control of the data
collection program, ICP.
The steps to be followed
for automatic usage are outlined below and then will be discussed subsequently
in more detail.
Note that the function
key references (e.g. F17) refer to the labels on the
console computer, not to the the letters on the keys.
- 1.
- Mount the sample changer and connect the motor controller.
- 2.
- Ensure the changer works and the correct sample is rotated into
position (NEXT).
- 3.
- Define parameters for run in ``Prepare mode.''
- 4.
- Set the data collection time using Automon.
- 5.
- Copy and edit the parameters for additional runs.
- 6.
- Set up a run sequence (RS=...).
- 7.
- Switch to control mode (F17) and check the run sequence
timing (HOWLONG/RS).
- 8.
- Check and log the neutron monitor (MRAT) as well as
document the sample on: a sample tag, the white board and in the log book.
- 9.
- Start the run sequence (RS).
- 1.
- Physically move the sample changer into position and connect the two
motor controller cables marked ``Sample Changer'' A and B.
They are polarized so that they can only be connected in one way.
- 2.
- Load your samples into the changer, paying careful attention to the
position number of each sample. A good practice is to fill out a sample
tag for each sample before you load the samples and then mark down the
position number on the sample tag.
- 3.
- Check that the sample changer advances properly by typing NEXT.
Note that it takes about 1 minute for the sample changer to completely advance
and the Motor 15 display to be set correctly. If the display is not
correctly synchronized with the actual position, the display can be reset
using the INI15=# command, where # is 1,2,3,4,5 or 6.
- 4.
- In ``Prepare Mode,'' define a run to be measured
in what is called an ``increment buffer'' (see Figure 14).
Each ``buffer'' line defines the parameters for a single diffactometer scan.
For convenience, you may wish to use the buffer numbers that correspond to
the positions of your samples in the sample changer.
Figure 14:
Defining a single run in ``Prepare Mode.''
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For use with the sample changer, a temperature controller,
you will typically need to set the following fields in the buffer:
Comment, T0, Monit, Prefac. and M-typ,
which are used as follows:
- Comment
- This sets a 1-line file header and the name of the data collection file. Be
sure to use letters and numbers (A-Z and 0-9) and no other characters
for the first five letters of the Comment as this is used for the file name.
If an invalid name is used the file will be named DEFLTxxx.BT1, where xxx is
a number in the range 001 to 999.
- T0
- This specifies the nominal temperature for data collection. T0 should be
0, when temperature control is not being used. This causes the
Wait, Err, Inc-T, and Hld0 values to be ignored.
- M-typ
- Is either ``NEUT'' or ``TIME''. NEUT is used for most data collection, where
the data collection time is adjusted to match the neutron flux on the sample.
- Prefac
- Each data point is measured ``Prefac'' times and if Prefac is 4 or greater,
the measurements are checked for statistical agreement, so that significant
noise spikes can be discarded. A rule of thumb is that Prefac should be 4 for
runs of 6 hours or less. It may be desirable to increase Prefac by 1 for
each additional 6 hours of length, but 4 is a good default value regardless
of the data collection time.
- Monit
- This value, along with Prefac, determines the length of the data
collection period. If M-typ=TIME, this specifes a count time in seconds. Most
commonly, M-typ=NEUT and Monit is set using the AUTOMON (AMON) feature.
It is very unlikely that you will want change the default values
for some fields:
A3-beg, A3-end, Inc-3, A4-beg, A4-end, Inc-4 and #pts. The Col field informs
ICP of the in-pile collimation (15' or 7'). The default, 15' is usually
correct. Note that the A4-*, #pts and Col values are reset every time
a buffer is edited. There is one exception to this. If you are setting up
runs while the instrument is collecting data and
plan to use a
different monochromator than the one that is currently in use, you may need to
change the A4-beg and A4-end values to match the monochromator you plan to use.
Use 3-13 degrees for Cu311 and Si531 and 1.3-11.3 degrees
for Ge311. Note that the
A- command in control mode turns off the automatic resetting of A4-beg
and A4-end.
Note that the field Hld should always be 0.
Hld creates a delay that
is executed at each data point. This is never of use at BT-1.
- 5.
- Determine the data collection time using the Automon feature. The
appropriate monitor value is computed so that the current run
will finish at a specified time.
Automon is initiated by moving the cursor to the AMON field and pressing
Enter. The screen shown in Figure 15 then appears.
Figure 15:
Using Automon to compute a run length.
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The number of days and the end time for
the run are entered in the Automon page.
Use 1 for delta-days if the run will go
past midnight even if the run length is only a few hours. A run starting
at 21:00 (9 pm) and ending at 9:00 (9 am) the next morning, would be entered as
delta-days=1 and Time=9:00. The computed Monit value is set when Automon
completes.
- 6.
- Complete buffers for all the samples you want to measure. If many parameters
are similar, it may be useful to
duplicate the run information for other temperatures that you will wish to
run. This is done either by highlighting the buffer to be copied and
then pressing the F14 key (actually the F6 key), which will copy the
information to all
other buffers, or (preferably) the buffer can be copied selectively by
pressing the F18 key (actually F10) to enter the ``Buffer Ops'' mode where
a buffer can be copied by entering a command such as COPY 2,3
(see Figure 16).
Figure 16:
Copying a buffer in ``Buffer Ops'' mode.
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This
copies the parameters in buffer #2 into buffer #3. Exit ``Buffer Ops'' mode
by pressing the F20 key (actually F12).
Each buffer can then be quickly modified to
change the appropriate fields.
- 7.
- Once a series of runs has been defined, a ``run sequence'' can be defined
by pressing the F19 key (actually the F11 key). This brings up the menu
shown in Figure 17. If a previous sequence is present, it can be
cleared by typing DEL and return.
Figure 17:
Entering a ``Run Sequence'' for the sample changer.
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Commands are added to the run sequence by typing RI#, where
# is the
buffer number of the run in the list. Commands may be entered one a time
or several commands may be entered at once, separated by semicolons (;).
Be sure to use a NEXT command between each RI# command so that
the sample changer will be advanced to the next sample.
The run sequence RI1;NEXT;RI2;NEXT;RI3 buffer 1 to be collected and
the sample changer will be advanced and buffer 2 will be collected. The
sample changer will be advanced again and buffer 3 will be collected.
To skip a sample position, two next commands can be used:
RI1;NEXT;NEXT;RI3 and it is also possible to collect multiple
data sets on a sample: RI1;RI1;NEXT;RI2;NEXT;RI3.
Exit the RS menu with the F20 key (actually F12).
- 8.
- Switch to control mode by pressing the F17 (actually F9) key.
The length of a run sequence can be estimated using the HOWLONG/RS
command (see Figure 18).
Figure 18:
Using the HOWLONG/RS command to determine the expected run time for a ``run sequence.''
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- 9.
- Before starting the run be sure to:
- (a)
- be sure the shutter is open
- (b)
- measure the monitor using the MRAT command
- (c)
- enter the sample composition and contact info on the white board
- (d)
- put the sample tag in the holder on the white board
- (e)
- enter the sample information in the log book.
- 10.
- The run sequence is started with a RS
command, as shown in Figure 19.
Figure 19:
Starting a ``run sequence'' with the RS command.
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Note that it is possible to modify the run sequence or change
the measurement parameters for the runs that have not been started in another
(ExtraICP) window while the data collection is in progress.
Next: Retrieving and Processing BT-1
Up: A User's Guide to
Previous: Using a ``Displex'' closed-cycle
Brian Toby
4/22/1999