GQ Electronics Technical Support Forum


GQ Electronics Technical Support Forum
Home | Profile | Register | Active Topics | Members | Search | FAQ
Username:
Password:
Save Password
Forgot your Password?

 All Forums
 GQ Electronics Forums
 GQ Geiger Muller Counter
 GMC-300: CPM to uSv/h & mR/h conversion
 New Topic  Reply to Topic
 Printer Friendly
Author Previous Topic Topic Next Topic  

CPM

7 Posts

Posted - 11/17/2012 :  12:18:59  Show Profile  Reply with Quote
I took some measurements yesterday and I saw a similar calibration/conversion issue that ska had seen in his topic
with TOPIC_ID=3669 http://www.gqelectronicsllc.com/forum/topic.asp?TOPIC_ID=3669


Edited by - CPM on 12/15/2012 00:13:47
Reply #1

CPM

7 Posts

Posted - 11/17/2012 :  15:11:37  Show Profile  Reply with Quote
I guess, this might be because the GMC-300 could have been factory calibrated at three different points, possibly with different sources...if this is the case, now the question is: How can we avoid having such a significant jump (especially, a drop) in uSv/hr & mR/hr reading as a function of CPM?

I love my GMC-300 by the way... It is a well-made device.

Edited by - CPM on 12/15/2012 00:20:53
Go to Top of Page
Reply #2

ZLM

1047 Posts

Posted - 11/18/2012 :  23:42:33  Show Profile  Reply with Quote
The GMC-300 is able to calibrate to different range. This is useful when you working on a different radiation range and need a accurate reading.

The default calibration covers 0-1000 CPM. This covers most regular mornitoring level for a accurate reading(<1000CPM). From 1001 and up, the value will be estiminated from the lower calibrated data. This is why the jump point is at the 1000CPM.

Here is a calibration example:

If you are measuring high range (>1000CPM) and you need a accurate reading. Then you need change those calibration data.

But before you do that, you need to know what CPM range you want to calibrate. We know the CPM to uSv/h and mR/h convertion is not a simple liner convertion, so we are unable to calibrate the unit from 0 to infinity for a high accurate reading in full range. So, we must define a calibration range for a better convertion. Assume you are going to use it in a range 2000CPM to 3000CPM, then you may set the calibration data points as :

#1, CPM = 1000, uSv/h = 9.00 (the value we know at the 1000CPM)
#2, CPM = 2000, uSv/h = XXXX (the value you know at the 2000CPM)
#3, CPM = 3000, uSv/h = XXXX (the value you know at the 3000CPM)

With those calibration data, the range calibetated are : 0-1000CPM, 1001-2000CPM and 2001-3000CPM.

When CPM with in 0-1000, it uses #1 conversion rate.
When CPM with in 1001=2000, it uses #2 conversion rate.
When CPM with in 2001=3000, it uses #3 conversion rate.

If you have a better calibration way, please let us know.
Go to Top of Page
Reply #3

CPM

7 Posts

Posted - 11/19/2012 :  11:25:03  Show Profile  Reply with Quote
Yeah, that makes sense... This scheme is better than the ones that use only one conversion ratio for all regimes. At least, this method gives users more flexibility.

There are more elaborate calibration methods out there, but either they are not worth the trouble (for general use) or they are very application and source specific. I think this 3 point calibration is good enough. Thanks for the clarification.

Edited by - CPM on 11/22/2012 10:35:11
Go to Top of Page
Reply #4

and_kom

Ukraine
24 Posts

Posted - 11/22/2012 :  14:17:15  Show Profile  Reply with Quote
FYI, during Chernobyl Zone trip I've noticed that at high radioactive spots GMC-300 was showing less uSv/h (mR/h) reading than regular dosimeters.
At very high radioactive spots (about 1-2 mSv) GMC-300 stopped emitting sound and maybe counting (seems due to high current consumption by GMC-300 circuit).

Young and radioactive
Go to Top of Page
Reply #5

ZLM

1047 Posts

Posted - 11/22/2012 :  18:36:11  Show Profile  Reply with Quote
"emitting sound" takes lot of power. When at high frequncy sound, it takes much more power than counting and saving feature.

It is good to hear the sound at the low counting level. But it is better to turn off the sound if you are measuring high level. so that to save the power to counting and other features working correctly.

Go to Top of Page
Reply #6

and_kom

Ukraine
24 Posts

Posted - 12/28/2012 :  09:07:33  Show Profile  Reply with Quote
What if there will be more than 3000 CPM?
What is the default conversion rate?

Young and radioactive
Go to Top of Page
Reply #7

ZLM

1047 Posts

Posted - 12/28/2012 :  22:45:08  Show Profile  Reply with Quote
It selects the last rate used.
Go to Top of Page
Reply #8

and_kom

Ukraine
24 Posts

Posted - 01/03/2013 :  11:08:02  Show Profile  Reply with Quote
I did the following testing to better understand the conversion algorithm and got confusing results.

Calibration data used:

Calibrate 1: 5 CPM = 0 uSv/h
Calibrate 2: 10 CPM = 0.1 uSv/h
Calibrate 3: 20 CPM = 0.75 uSv/h

Results:

CPM uSv/h
0 0
1 0
2 0
3 0
4 0
---------
5 0
6 0.12
7 0.14
8 0.16
9 0.18
---------
10 0.10 - ???
11 0.72 - ???
12 0.78
13 0.85
14 0.91
15 0.98
16 1.04
17 1.11
18 1.17
19 1.24
---------
20 0.75 - ???
21 0.07 - ???
22 0.07
23 0.08
24 0.08

Could you give better explanation of the formula used and why there are significant uSv/h drops after 9, 11, 19 and 20 CPM?

Btw, in the Calibrate 3 menu CPM decrease step is 100, but increase is 232. Also in the same menu uSv increase/decrease steps are 1.00 uSv/h. So I was unable to set accurate values.

Young and radioactive

Edited by - and_kom on 01/03/2013 11:11:12
Go to Top of Page
Reply #9

ZLM

1047 Posts

Posted - 01/05/2013 :  01:22:47  Show Profile  Reply with Quote
I think it worked this way:

0-5 CPM. Use Calibrate 1.
6-10 CPM. Use Calibrate 2
11-20 CPM. Use Calibrate 3
>20 use some thing default.

The value inconsistent/jump can be eliminated by increase the 3rd calibration range. Example,

Calibrate 1: CPM = 60, uSv/h = 0.3
Calibrate 2: CPM = 240, uSv/h = 1.2
Calibrate 3: CPM = 1000, uSv/h = 5.0


I believe this is the best calibration for the general testing and it should be used as factory default. so that to avoid the confusion on the calibration settings and keep the conversion value linear.
Go to Top of Page
Reply #10

and_kom

Ukraine
24 Posts

Posted - 01/09/2013 :  10:17:46  Show Profile  Reply with Quote
For users who use SBM-20 instead of stock m4011 tube: conversion ratio for this tube is 175 (uSv/h = CPM / 175), so
calibrate settings should be:

Calibrate 1: CPM = 60, uSv/h = 0.34
Calibrate 2: CPM = 350, uSv/h = 2.00
Calibrate 3: CPM = 32000, uSv/h = 182.85

FYI in SW version 2.21 max CPM value is 32768 then if you try to increment you will get negative value.

Young and radioactive

Edited by - and_kom on 01/09/2013 10:18:17
Go to Top of Page
Reply #11

Distelzombie

Germany
165 Posts

Posted - 08/03/2016 :  01:07:16  Show Profile  Reply with Quote
Oh interesting. Thanks that you dug it up, dude.

GMC-300E+ V4.20 with sbt-11 alpha tube

My statements are to be taken as stuff-a-hobbyist-says.
Go to Top of Page
  Previous Topic Topic Next Topic  
 New Topic  Reply to Topic
 Printer Friendly
Jump To:
GQ Electronics Technical Support Forum © Copyright since 2011 Go To Top Of Page
Generated in 0.08 sec. Snitz Forums 2000