Control Mode: Controlling the Instrument

  Selecting the Control Mode item in the main menu or pressing F17 in Prepare Mode brings you into the control mode, which is indicated by the prompt *. In this mode you have control over the instrument. This is the place to issue count or drive commands as well as to set the temperature and start a run. For a complete list of the allowed commands refer to the Appendix. ICP also provides online help; just type HELP for the complete command list or type HELP <command> for help on a particular command. A possible screen is shown in Fig. 7.

  

Figure 7: The screen in Control Mode.

pcol means print the current collimation and ini3=3 defines the current position of motor 3 ($\phi$) as 3 degrees; ri3 starts execution of data collection using the information in buffer 3. You are not restricted to uppercase commands; ICP will accept upper and lowercase characters.

The status line is important since it displays the status of some program controlling flags. Here is the list of these flags and their meaning, from left to right:

S

This flag tells you whether the statistics check is enabled or not. If S+ and prefactors > 3 the program will check the intensity data for statistical consistency. Use of statistic checks is encouraged, except perhaps for samples on a sample spinner.

T

Temperature control. If set to T+ and a temperature controller is connected, you are able to change and/or monitor temperature during scans. The command tdev will automatically be called up if T+ is entered without first using tdev to declare a temperature device. T# indicates that the option to use a database curve was selected in tdev. T* indicates that the ``careful-approach'' algorithm will be used.

H

Magnetic field control. If set to H+ and a magnet controller is connected, you are able to change and/or monitor field during scans.

W

The W stands for Write Log. If W+ the screen output is written to a file whose name is formed by the date. The file type is .log. If W$-$ the screen output is sent to the terminal only. (Data that is already stored in a file when a buffer or find-peak is executed is not included in the log file.)

R

R+/$-$ denotes whether a specified motor will be rocked during counting when a buffer is executed on BT-1.

A

On BT-1, A+ indicates that the automatic specification of scan ranges for motor 4 according to monochromator type is in effect. In this case, the starting position and increments for motor 4 are automatically filled in when an increment buffer is selected for editing. A$-$ denotes that this feature is disabled.

F:

F: is followed by a list of the motors that are currently ``fixed'' on the instrument. A fixed motor is not moved by a buffer execution. It may, however, be moved with a drive command. The command PFIX will print out a list of the fixed motor(s) at any time. Motor 3, the $\phi$ axis (sample table), is usually fixed on BT-1.

To change the status of one of these flags, type the flag character followed by a plus (+) or a minus (-) sign.

From Control Mode, you can press F17 to switch back to Prepare Mode. If you came from that mode you could also hit F20 and ``return'' from whence you came. F20 will always bring you back to the point from which you came.

Motors and Angles

  The most important aspect to know here is the angle numbering convention. The following motors are available on BT-1:

 

Motor Description Assigned No. Notes

$$\phi)$$ 3 seldom driven

$$\theta$$ 4

Sample changer 15 always drive in + direction

Note that the other computer controlled motors on BT-1 are used for aligning the instrument. They should not be changed except by an instrument scientist.

ICP allows use of two different types of angles, software and hardware angles, which differ by a zeropoint correction. It is our practice at BT-1 to always keep the zeropoint correction as zero so that both sets of angles are the same.

Dn

Absolute Drive: D4=5.6 Drive angle no. 4 to 5.6 degrees.

DnI

Incremental Drive: D4I=2.75 Drive angle no. 4 2.75 degrees further than it is now.

FIXn

Keep an angle fixed: FIX3 will fix the sample table. The FIXn command will NOT prevent you from manually driving that angle, e.g., with a Dn= command.

RELn

Release a fixed angle.

SETn

Change the zeropoint: SET3=134.69 Change the zero-point of angle no. 3 in such a way that the software angle of the current position reads 134.69. Please do NOT use this command at BT-1.

INIn

Initialize an angle: INI4=0. Make the motor controller believe that the hardware angle of the current position is 0.0 degrees. This command should be used after the fpd command is used to scan the direct beam.

NEXT

Move to next sample position on BT-1 when the sample changer is used.

Whenever a drive command is issued, the target angle is checked for hardware angle limits. If the target hardware angle is above or below the current hardware limits the drive will be refused. The lower and upper limits can be changed by Ln = f and Un = f respectively, with n as the angle number and f the hardware value for the limit.

It is possible to check the current position by issuing print commands:

PSA

Print software angles. This command will print the software value of all angles served by the instrument.

PHA

Print hardware angles. This command will print the hardware value of all angles served by the instrument. The values printed here must coincide with the motor controller displays.

PA

Print software and hardware angles.

PL

Print lower limits.

PU

Print upper limits.

PZ

Print zero adjustment values.

All the commands described above require a privileged terminal, e.g., you cannot access motors from your office.

Counting

  To issue a count command from Control Mode use:

CT=f Depending on the sign of f count will select the base:

f < 0 issue count with time for f seconds.

f > 0 issue count with monitor preset to f (no prefactors here).

CO is a synonym for CT.

After the count has completed, the intensity or intensities will be displayed on the terminal. That data cannot be stored in a file.

To find out the monitor rate use:

MRAT=f

The time parameter f is optional and defaults to 5 seconds.

MRAT/S=f

Perform an MRAT and save results for use with HOWLONG commands.

Initiating Runs

As previously described, there are three commands that can be used to start data collection. They are listed here for convenience.

RI

Run increment buffer or buffers. For example, ri4 will initiate data collection using the parameters defined in buffer 4. ri6-8 will execute buffers 6, 7, and 8.

RS

Execute the sequence of commands that were previously defined by the rs= command or by using the F19 option in Prepare Mode. Be sure to check this sequence using the prs (print run sequence) and drs (dry run sequence) commands.

RSF

The command rsf <filename> causes execution of the commands contained in the named file. These can be checked using the prsf (e.g., prsf myruns.com) and drsf commands.

Additional Features

ICP offers some additional features, which allow the experimenter to pause or stop the experiment or to enable special features on some of the instruments.

Hold

ICP will enter a hold state, for example, when changing samples using the automatic sample changer or when changing temperatures between data sets. This causes the computer to wait before beginning data collection. For temperature changes, the length of the hold-time is determined by the Wait field in the run buffer. As soon as the system goes into the hold state the status will show this by displaying a ***HOLD*** message. You can `wake' the system again by hitting Control-A which will abort the current hold and start the data-acquisition immediately.

Pause

If for instance you have to close the beam during an experiment, and you want the data-acquisition to pause until the beam is open again, you can make ICP pause itself by pressing Control-P. ICP will collect data for the current point and then pause. This state will be reflected in the status line by ***PAUSE***. To resume, hit Control-A.

Emergency Abort

If you have to stop a motor from moving, a counter from counting, or both together regardless of the circumstances, hit Control-A and the program returns to the command prompt ('*') in Control Mode. If you do this during data acquisition, your data file will be updated through the previous point.

Finish-Up

If you would like to terminate a buffer execution early but in a normal fashion, type Control-F. This will cause the current point to be finished and the scan terminated. The data file will be updated and control will pass to the next command in the run sequence or run sequence file.