Creating GEM Data Files During an Experiment

BEGIN 

When you type begin in an OpenGenie window on the instrument control PC, (or click on Begin Run) the counts from the neutron detectors start to be recorded in the memory of the data acquisition electronics (accessible to OpenGenie on the instrument control PC by typing set/file $dae). At this stage the data are not stored in any computer file on any disk. If you type abort (or click on Abort Run) the accumulation of data is stopped and no computer file is created. Thus the data already accumulated at that time are lost. 

END 

When you type end in an OpenGenie window on the instrument control PC, (or click on End Run) named like GEM34567.RAW is stored on the disk of the instrument computer, assuming that 34567 is the number of the run that was being performed. At the same time the run number is automatically increased by one (you can see it change on the dashboard). This ensures that every run is given a unique run number, and has the consequence that there is only one version of each .RAW file. When you type end the computer also automatically starts new log files for the new run number. The log files contains records of all commands issued on the instrument and of all sample environment parameters which are being logged (such as sample temperature). The log files are named GEM25576_Vacuum2.txt for example (this is a log of the pressures logged for vacuum2).

SAVE Files 

It is possible to save the data at an intermediate point during a run, without incrementing the run number. This is done by typing update and then store in an OpenGenie window on the instrument control PC (or click on Save Run). In this case a file named GEM31200.S02, for example, is created. The run number is not increased, and thus more than one version of the save file may exist for each run number. Each save file contains all the neutron counts that have been accumulated since the command begin was issued.

Location of Data Files

Whilst datafiles are being accumulated they are stored on the instrument control PC (called NDXGEM) in c:\data . Shortly after ending the run, the datafiles are moved to a safe archive location. At present, this has the result that there is a short period of time when the datafiles are unavailable. If you want to find the location of a GEM .RAW file, say GEM20000.RAW, then type gempath 20000 in an OpenGenie window - this will redefine the x:\ drive to stand for the location of the file.

Older data files, for run 16504 and before, are stored on the VMS system - see here.

Journal Files 

When a run is ENDed, information about the run is stored in a journal file named GEM_DATA:JOURNAL.TXT . This file contains the run number, the user’s name, the run title, the run start time, and the amount of beam used in units of micro-Amp-Hours. At the end of each ISIS operating cycle, the GEM instrument scientists produce a unique journal file for that cycle, named GEM_DATA:JOUR002.TXT , for example. (Cycles are numbered according to a convention where, for example, cycle 002 is the second cycle in the operating/financial year 2000.) Several commands have been set up to give GEM users easy access to the information in the journal files, as follows:

Last updated on 15 Dec 2005 by Alex Hannon (a.c.hannon@rl.ac.uk)