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calomega: calibrate omega zero-point

"calomega" is a program to calibrate the "omega" zero setting on the KappaCCD by analysis of a 360 degree phi scans of an ambi crystal at dx=80 and chi=90 degrees.

Please note: The "calomega" procedure is a routine that was written to trace very rare problems in a goniometer. Under normal circumstances it is not necessary to run it. Service people can perform the calibration using mechanical means easily; calomega is only used if we want to make sure an omega offset is not the cause of a strange collision.

The software omega calibration procedure is not as robust as the other calibrations. It is very difficult, because an offset in omega only affects positions of reflections by a very small amount. Luckily, of course, this also means that an omega offset will not affect your data quality. The only real reason why an omega calibration is necessary is to prevent collisions in the system. And that does not require a very accurate calibration; a few tenths of a degree is enough.

Usage

calomega [options] [make] [filenames]

Without any argument, the "calomega" program will analyze an image named "calomega01f.kcd" in the current directory. With the argument "make" it will make a 360 degree phi scan at dx=80 and chi=90 first, and then analyze this.

The program can analyze an image specified on the command line instead.

Possible options are:

frametime=f: Sets the time to spend per frame. In seconds. Default frametime=300 for Mo radiation, and frametime=100 for Cu radiation.

By studying the center of all quadruplets of reflection at two different distances, the absolute omega zero is determined, and if it is significantly offset, the program will print instructions on how to re-calibrate the omega on the server PC.

WARNINGS:

Calomega needs a good distortion correction and a good detector alignment to be able to work. Please run makedistor and makedetalign before running calomega.
Running "calomega" is harmless, but if mistakes are made during the actual recalibration on the server PC, the KappaCCD might be damaged.
If the offset printed by "calomega" is not absolutely reasonable, do not recalibrate the server PC, but warn your Bruker Nonius service contact instead.
It is advisable to check after a recalibration whether the result of a retest comes out correctly.

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