Friday, November 2, 2012

ISEM DMA acquisition problems

ISEM DMA modes do not work. Image acquisition otherwise hopelessly slow.

  • verify Hsync, Vsync, Pixel clock outputs from Zeiss PC, these look good.
  • Pull multichannel receiver out of rack, verify signals arrive on board, they do.\
  • Shut down PC and reseat PCI cards (Zeiss control and Omicron data acq)
    • this was suggested as a possible fix for detector contrast problem
  • Now try ISEM DMA
    • now it works. no obvious problem fixed???
    • put back in rack, still works
ISEM tests

  • image acq will be painfully slow. Test with spectra at, for example, 1 ms acq time. cannot see Si KLL on Si, for example
  • with CRR 3 and 25 ms/pixel, can start to see spectra (10 kV max current)
  • with 200 ms, not bad
  • image time line by line ~ 2-3x raw image time (zeiss) for fast scans, overhead may reduce
    • optimal image (no OH) at 0.2 sec, for 2x512x384, around 20 hours...
  • there is a line scan mode, can do point by point or line by line, but cannot get line data, only peak/back. No chance for own processing.
    • for Au on Si, large backscatter and noise effects, swamps real contrast
To try
  • can take reduced image for test
  • can modify data 'schema' to get access to raw images peak/back acquired line by line, for post process later
  • can try multipoint acq to get family of spectra, but OH and data format may be a pain.
  • need to test data export, image dynamic range may be reduced either to 256 or 100 values (bad)

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