Opened 13 years ago

Closed 13 years ago

#102 closed bug (fixed)

Using the detector pixel size from the data file, not from a global constant

Reported by: srkline Owned by: srkline
Priority: minor Milestone: SANSReduction_5.1_Release
Component: SANS Reduction Keywords:
Cc: Blocking:
Task:

Description

-- from John's e-mail --
Hi Steve,

I thought you may want to start thinking on what is the best way to

fix an upcoming pixel size problem. All the data taken on the Ordela
detectors (since 1998) currently uses a 5.00 mm pixel size, which is
recorded in the raw data header, and used by IGOR data reduction. Current
measurements indicate the pixel size is actually 5.12 mm. I plan on
contacting Ordela with our calibration measurements shortly , to see
whether the 5.12 mm agrees with their specifications.

Once we change the instr.cfg file, future data will have the

correct pixel size, the problem comes when users view old data sets. I
believe our users will need to be able to patch the header to raw data to
correct the pixel size, either within the data reduction program or if with
an other special patch program. There maybe other better (easier, most
robust, ..) ways to handle this.


Ideally, the proper value should be in each data file (verify this), and used from the data file (change this, and verify)

Change History (4)

comment:1 Changed 13 years ago by srkline

DetCorr?() already uses the values from the header ( rw[10] and rw[13] )

Averaging routines and Kappa (ABS scaling - solid angle) use the global variable.

all should be converted to use whatever is in the raw data file.

comment:2 Changed 13 years ago by srkline

Upon closer inspection of what the detector calibration constants actually mean and how they are derived (they are fitted!) - I'm not so sure that Sx and Sy are really the pixel size in real-space.

??

comment:3 Changed 13 years ago by srkline

After talking to John, the Sx and Sy in the non-linear corrections are really the pixel dimensions, especially if the other two parameters have been set to give a linear response.

In addition, Paul has gotten verification from Ordela that the pitch is 0.200" +/- 0.001" (non-cumulative). That makes the real pixels size 5.08 mm. This will need to be added to instr.cfg, and reduction software will need to be modified to always read from the data file, not from globals.

A utility (patch) feature could be added to convert older data sets to have the proper pixel size.

comment:4 Changed 13 years ago by srkline

  • Resolution set to fixed
  • Status changed from new to closed

Fixed in changeset 247:

Changes made to read the physical detector pixel size X and Y from the file header, not from globals defined in _Utils.ipf. Now proper values must be input from instr.cfg, or patched after the fact.

Added utility procedures to write updated values (batch patch) directly to file headers, and a utility to read out the c
urrent values stored in the headers. These are available as Macros from the SANSBeta menu.

Made the corresponding changes in the FACILITY_... files for future use.

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