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 Get Device uSv/h via USB Communication		  New Topic  Reply to Topic
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wikilicious

USA
19 Posts
Posted - 04/14/2024 :  17:24:58  Show Profile  Reply with Quote
I'm interested in calculating the uSv/h value displayed on the device screen from the USB communication protocol <GETCPM>> & <GETCFG>> for the PyGMC Python package - https://github.com/Wikilicious/pygmc

I'm not interested in calibrating the device with a known source...
I'm interested in how does the device use the calibration config to display uSv/h.
i.e. How do I compute the displayed uSv/h on the device without a <GETUSVH>> command?

Here is what I was using:
uSv/h = (CPM / CalibrationCPM_0) * Calibration_uSv_0


Some devices such as GMC-300S have identical calibration ratios for all three calibrations... however other devices such as GMC-600+ do not. The calibration procedure in the user guide https://www.gqelectronicsllc.com/GMC-600UserGuide.pdf did not offer a hint to how the calibration config is used.
Edited by - wikilicious on 04/14/2024 17:26:26
Reply #1

EmfDev

2150 Posts
Posted - 04/15/2024 :  10:11:34  Show Profile  Reply with Quote
for calibration 0 that is correct. For the others, it is not straightforward.
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Reply #2

wikilicious

USA
19 Posts
Posted - 04/15/2024 :  18:36:09  Show Profile  Reply with Quote
I made an assumption that all calibrations are linear and the calibration config points' just changes the slope & intercept.

I then gathered some empirical data... posted here: https://github.com/Wikilicious/pygmc/issues/97

Not straightforward; however, pygmc is now exactly matching what is being displayed on the device. (On GMC-300S at least - via fuzzing)


I did notice some nuances... and accounted for them... yet still see there could be more nuances.

Since "not straightforward" is acceptable... can you share more details? Are there nuances in different revisions? Different devices? Did I miss something?
Edited by - wikilicious on 04/16/2024 17:54:57
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Reply #3

wikilicious

USA
19 Posts
Posted - 04/16/2024 :  08:43:27  Show Profile  Reply with Quote
For others landing here while searching for calibrating GQ GMC's...
The impression I got from plotting a range of CPM and changing the calibration is that the calibration points are used to represent different response curves at different CPM ranges.

Calibration_CPM0 is treated as the max CPM that Calibration_uSv0 is valid for. i.e. uSv = <CPM> * (Calibration_uSv0 / Calibration_CPM0)

Once the CPM exceeds Calibration_CPM0, it switches to using Calibration_CPM1 & Calibration_uSv1... however, with a different equation than above. It becomes a simple y = mx + b equation where the slope and intercept are calculated from Calibration0 & Calibration1.

Once the CPM exceeds Calibration_CPM1, it switches to Calibration_CPM2 with the same process as above - using Calibration1 & Calibration2 to get the slope and intercept.

If the CPM exceeds the largest calibration point, the device extrapolates from the last largest calibration point.


It appears that the calibration points are intended to be increasing in CPM and quirks/nuances arise if they are not in increasing order.
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Reply #4

EmfDev

2150 Posts
Posted - 04/16/2024 :  09:53:51  Show Profile  Reply with Quote
You are right. Use the line between 2 calibration points to calculate the uSv/h.
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