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 2.GQ Geiger Muller Counter
 GMC500+ vs Data Loger Pro
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sannexus

Japan
6 Posts

Posted - 05/20/2018 :  01:15:05  Show Profile  Reply with Quote
Just been using GMC500+ with Data logger in the last few hours and noticed that data logger consistently shows lower ÁSv/h than that are displayed on GMC500+ by 2-3ÁSv/h.
Is there any reason why and what should I trust?
thank you

sannexus
Reply #1

ullix

Germany
213 Posts

Posted - 05/20/2018 :  03:55:00  Show Profile  Reply with Quote
A DIFFERENCE of 2-3ÁSv/h is quite a chunk. What does the "calibration" of the counter say? Readout via GQ Data Terminal or GeigerLog.

On a 500 (non-plus, i.e. single tube) this is :
Device Calibration Points:
   Calibration Point 1:     60 CPM =   0.39 ÁSv/h (0.006500 ÁSv/h / CPM)
   Calibration Point 2:    240 CPM =   1.56 ÁSv/h (0.006500 ÁSv/h / CPM)
   Calibration Point 3:   1000 CPM =   6.50 ÁSv/h (0.006500 ÁSv/h / CPM)


Does the CPMs you see, multiplied with 0.0065, get to the values you see?
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Reply #2

EmfDev

106 Posts

Posted - 05/21/2018 :  09:46:26  Show Profile  Reply with Quote
ullix is correct. The calibration settings should match between the Data logger and the GMC500+ unit.
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Reply #3

sannexus

Japan
6 Posts

Posted - 05/21/2018 :  16:24:14  Show Profile  Reply with Quote
Sorry, my writing was wrong, I just realised.
Data logger shows 0.02-0.04#181;Sv higher than the what GMC-500+ shows.
The Calibration ref is:
#1 60 . 0.3#181;Sv
#2 240 1.2#181;Sv
#3 . 1000 . 5#181;Sv
#4 . 2000 . 10#181;Sv
#5 . 4000 . 20
on Data Logger PRO.
The counter is 500+
Should I be changing the above figure?

But also the other thing is I have 2 other geiger counters,
PKC-107 and MKS-05.
GMC-500+ actually does show the result a little higher, side by side, like 0.01-0.04#181;Sv.
And in someway what Data logger display and 2 other shows about the same result and the GMC-500+ higher.
So it kind of hard to decide which number to trust.
Any advice?

sannexus
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Reply #4

ullix

Germany
213 Posts

Posted - 05/22/2018 :  00:17:20  Show Profile  Reply with Quote
@EmfDev: Are there 5 "calibration" points in the 500+, not 3? You recently provided "the latest configuration data structure in C code on GMC-500 and GMC-600", and there are still only 3, and no space for an extra 2? What gives?
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Reply #5

ullix

Germany
213 Posts

Posted - 05/22/2018 :  00:40:15  Show Profile  Reply with Quote
@sannexus: just to clear up: what you labeled "ÁSv" should all be labeled "ÁSv/h" , i.e. microSievert per hour. The difference between Dose and Dose Rate!

Your 5 "calibration ref" points all code for identical 0.005 (ÁSv/h)/CPM (like for ref #2: 1.2/240 = 0.005)

On a 500 non-plus (i.e. single tube) this value is 0.0065 (ÁSv/h)/CPM.

In other words, due to its 2nd tube the 500plus gets ~30% more counts from a given source than a 500non-plus. Hence you multiply with a smaller number to end with the same Dose Rate in ÁSv/h.

As you did, the dose rate (ÁSv/h) is the thing to be compared between the counters. They should show "roughly" the same Dose Rate, but there are multiple things which impact the readout, so an agreement within +/-20% I would consider as good, even +/30% wouldn't worry me.
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Reply #6

EmfDev

106 Posts

Posted - 05/22/2018 :  10:55:15  Show Profile  Reply with Quote
@sannexus, you need to check your gmc-500+ for the calibration values. Then change the logger pro values to match the geiger counter. The defaults should be:

#1. CPM: 60.........uSv: 0.39
#2. CPM: 10000......uSv: 65.00

You only need to change 2 of them for 500+

@ullix, There are still 3 calibration values for the 500+, 2 for 1 tube and 1 for the other.
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Reply #7

sannexus

Japan
6 Posts

Posted - 05/22/2018 :  20:44:09  Show Profile  Reply with Quote
Hello,
By plugging the unit to a PC and reading the unit with Data Viewer, I see that unit is set to
#1 60 CPM 0.39#181;Sv
#2 10000 CPM 65#181;Sv
#3 25 CPM 4.85#181;Sv

sannexus
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Reply #8

EmfDev

106 Posts

Posted - 05/23/2018 :  08:56:04  Show Profile  Reply with Quote
I think that's correct from the unit.

If you change the values on the data logger, will it match the displayed uSv/h?
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Reply #9

sannexus

Japan
6 Posts

Posted - 05/25/2018 :  00:05:38  Show Profile  Reply with Quote
Thank you everyone.
I might adjust the calibration #1 to read 60cpm 0.33 so that all 3 geiger counter I have gives roughly the same reading.

Any thought on this, anyone?

sannexus
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Reply #10

EmfDev

106 Posts

Posted - 05/25/2018 :  09:37:20  Show Profile  Reply with Quote
That works. If you want them to be similar reading.
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Reply #11

ullix

Germany
213 Posts

Posted - 05/26/2018 :  00:50:41  Show Profile  Reply with Quote
As it is neither known how GQ arrived at their calibration values, nor is it known how the manufacturer of your other counters arrived at their respective calibration values, the difference between 0.39 and 0.33 - about 20% - is well within the uncertainties of all those "calibrations". Making these devices report the same ÁSv/h is surely a good enough reason to adapt the setting.

However, I don't believe you can achieve your goal by only changing the 60cpm value to 0.33. My take about the algorithm implemented in the firmware of the counters is such that every CPM between zero and 60 is translated to ÁSv/h by the factor of 60/0.33 = 0.0055 ÁSv/h/CPM, while everything between 61 and 10000 is using the factor 65/10000 = 0.0065 ÁSv/h/CPM (presently the GQ default).

Thus, at 60 CPM you would get 0.33 ÁSv/h, and would expect at 61 to get 0.33 *(61/60) = 0.34 ÁSv/h.
Yet, you will be getting 61*0.0065 = 0.40 ÁSv/h.

This can easily be tested with a source delivering more than 60CPM. If you have no other source get some KCl from you local garden supplier and measure as described in my Potty Training https://sourceforge.net/projects/geigerlog/files/GeigerLog-Potty%20Training%20for%20Your%20Geiger%20Counter-v1.0.pdf/download , which should give you something up to 160CPM.

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