[NeXus-tech] Sample environment log data in ISIS NeXus files

[freddie.akeroyd at stfc.ac.uk]

Following on from our TC discussion this is what we do:

 

Sample environment data (e.g. temperature v time) is stored in a
standard NXlog group with a base offset time of "start of run". We also
want to store details of the kit that measured this temperature and
things like the requested setpoint, so the structure i use is as
follows:

 

 In  /item(class)/  notation measuring an item such as "guide_pressure"
would result in a group

 

    /raw_data_1(NXentry)/selog(IXselog)/guide_pressure(IXseblock)

 

Within the guide_pressure(IXseblock) group I have the following:

 

vi_name          # labview Vi used

read_control   # indicator  name for log values

set_control      # control name for setpoint

setpoint        # requested value

value     # "value" of block -probably last measured value

value_log   #  a usual NXlog of values

 

I don't currently compute an average or standard deviation for the NXlog
values yet as there is ambiguity about "average" e.g. average only when
beam is on or over whole run time? I could do both but then I may need
to invent some new field names in NXlog J  At the moment I leave all
this to the analysis program - there are separate NXlog groups detailing
beam on/off status etc. that can be used to extract a subset of values
to average over. 

 

I have a separate set of NXlog entries in
/raw_data_1(NXentry)/runlog(IXrunlog) - these are quantities
automatically monitored by the control program over time (e.g. frames,
beam status, proton charge delivered) and put here rather than in
"selog" to avoid any possible name clashes if a user decided to create
an "seblock" with the same name.

 

Freddie

 


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