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Tony81269
USA
68 Posts |
 Posted - 08/17/2024 : 16:30:44
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| I haven't bought one of these GQ brand meters but I do have serious questions about calibration. I work in the Well Logging industry and I deal with the NRC on at least a yearly basis. Our survey meters have to be calibrated to certain standards in labs. There are specific requirements. For analog meters it is "Accurate to 20%, and must be calibrated on each scale twice, at approximately 1/3 and 2/3 of full scale deflection" an on digital models it is "must be calibrated at one point per decade over the range that will be used". Must be done every 6 months. So, I look at the description on Amazon and it says they will give you a certificate upon request and then they say something about having a third party to do it for extra money. I find this confusing. Is it really calibrated to NRC standards when you buy it? Or do you have to pay to have that done?The lack of information leads me to think these aren't really professional instruments. Anyone ever try to have one of these meters calibrated at a licensed place? Is that even possible? |
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| Reply #1
EmfDev
2250 Posts |
Posted - 08/19/2024 : 11:26:50
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| GQ Geiger counters are advertised for general use and not for professional use. However, some models like the GMC-800/500/+/600+ can be calibrated with 1-2% accuracy and certified with the NRC / NIST via 3rd party. |
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| Reply #2
Stargazer 40
USA
431 Posts |
Posted - 08/19/2024 : 17:16:51
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| Tony, I think EmfDev means that they build them and establish deadtime and tube voltage values that are within the range of the components as far as design, and if you want them further tweaked to certification standards then that's a step you can take because it's possible to effect the necessary accuracy of certification. |
Stargazer 40 |
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| Reply #3
Tony81269
USA
68 Posts |
Posted - 08/19/2024 : 17:57:42
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quote:
Originally posted by EmfDev
GQ Geiger counters are advertised for general use and not for professional use. However, some models like the GMC-800/500/+/600+ can be calibrated with 1-2% accuracy and certified with the NRC / NIST via 3rd party.
Actually, I've been talking to support and they tell me that yes they can be calibrated and certified by a third party. The showed me an example certificate that came from Applied Health Physics. Although you say they are marketed towards general and personal use, if you are saying that a meter can pass NIST/NRC standards with an accuracy of 1-2% then why couldn't you use it in a professional setting? That's a better accuracy statement than you can get from Ludlum. Speaking of Ludlum, I did several comparisons today between a Ludlum 3 (44-6) and the GMC-800. I was amazed at how close the two were. I was measuring little sources down to 5 uCi up to 300 mCi. At different distances. They all showed really close to the ludlum. So, why can't I use it in my profession? |
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| Reply #4
Tony81269
USA
68 Posts |
Posted - 08/19/2024 : 18:12:24
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quote:
Originally posted by Stargazer 40
Tony, I think EmfDev means that they build them and establish deadtime and tube voltage values that are within the range of the components as far as design, and if you want them further tweaked to certification standards then that's a step you can take because it's possible to effect the necessary accuracy of certification.
GMC-800 Reading at 6ft from 300 mCi Cs-137
Ludlum 3 (44-6) at 6ft from 300 mCi Cs-137 X10 selector
So, GMC-800 reading 15.76 mR/h and Ludlum 3 reading 16 mR/h. To me, that is really close considering the GMC has not had a NIST calibration.
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| Reply #5
Stargazer 40
USA
431 Posts |
Posted - 08/19/2024 : 18:36:51
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LIABILITY
Certification carries weight with decisions made as a result of measurements taken. It's that simple. Many people can drive cars or even fly airplanes. Without a drivers license or pilots license you simply aren't counted as qualified to do so. With ham radios, I can have a perfectly wonderful and useful radio that allows me to talk to people on say a federally managed fire. But the FCC can fine or put me in jail if that radio is not Part 90 of some FCC code certified. |
Stargazer 40 |
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| Reply #6
Tony81269
USA
68 Posts |
Posted - 08/19/2024 : 18:46:42
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quote:
Originally posted by Stargazer 40
LIABILITY
Certification carries weight with decisions made as a result of measurements taken. It's that simple. Many people can drive cars or even fly airplanes. Without a drivers license or pilots license you simply aren't counted as qualified to do so. With ham radios, I can have a perfectly wonderful and useful radio that allows me to talk to people on say a federally managed fire. But the FCC can fine or put me in jail if that radio is not Part 90 of some FCC code certified.
Yes, I certainly understand that. If we don't have our meters certificates then we get violations from the NRC. Too many violations and it costs money. After that, the program is shut down. This company says in many places that the meter meets the standards to be calibrated by NIST/NRC standards. I have emailed support and they say yes it can and gave me an example certificate from Applied Health Physics. So, I don't see a problem. I am going to try to get this this calibrated by Applied Health Physics. We will see how that goes |
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| Reply #7
Stargazer 40
USA
431 Posts |
Posted - 08/20/2024 : 04:33:05
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| To document that process would be really great! |
Stargazer 40 |
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| Reply #8
Tony81269
USA
68 Posts |
Posted - 08/20/2024 : 09:44:32
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quote:
Originally posted by Stargazer 40
To document that process would be really great!
Do you mean document the process that Applied Health Physics uses? Not exactly sure but they gave me a copy of one of their calibration certificates. Hope they don't get mad with me posting it here.Also I was told that it "will be calibrated at 1, 10, 20, 50, 100, and 200 mR/h" which seems a little different than this document shows
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| Reply #9
Stargazer 40
USA
431 Posts |
Posted - 08/20/2024 : 09:55:46
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| No, from contact to sending in to time it takes to any interaction with them to return time and payment types they use. Nice to have that process documented. They may contact GQ to get adjustment entry points. Be nice to know that has taken place if needed. |
Stargazer 40 |
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| Reply #10
Tony81269
USA
68 Posts |
Posted - 08/20/2024 : 12:36:08
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quote:
Originally posted by Stargazer 40
No, from contact to sending in to time it takes to any interaction with them to return time and payment types they use. Nice to have that process documented. They may contact GQ to get adjustment entry points. Be nice to know that has taken place if needed.
Oh! Sorry I misunderstood. From emails to GQ, they said if I sent it to them then it would be $130 and at least two weeks. They did go on to say that I could contact Applied Health Physics myself and save on the shipping and middle man. That was kind of cool to tell me that. I have some emails in to Applied health Physics and was told that their calibration tech was out of the office today. He's supposed to be back tomorrow. I will let you know what they tell me. the place is in Pennsylvania. https://ahprad.com/ |
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| Reply #11
Tony81269
USA
68 Posts |
Posted - 08/20/2024 : 14:51:19
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quote:
Originally posted by Stargazer 40
No, from contact to sending in to time it takes to any interaction with them to return time and payment types they use. Nice to have that process documented. They may contact GQ to get adjustment entry points. Be nice to know that has taken place if needed.
Also, I did contact the guy who calibrates our Ludlums and he said that he could probably do it but then when on to talk about not being able to get parts if they break and also talked about the plastic case not being very rugged. Then he tried to sell me some new Ludlums  |
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| Reply #12
Bobakman
USA
97 Posts |
Posted - 08/28/2024 : 08:53:45
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@Tony81269
I sent you a PM you should’ve got it in your email. Let me know if you did.
Bob
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“If you want to find the secrets of the universe, think in terms of energy, frequency and vibration.”
Nikola Tesla |
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| Reply #13
Tony81269
USA
68 Posts |
Posted - 08/29/2024 : 17:15:19
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quote:
Originally posted by Bobakman
@Tony81269
I sent you a PM you should’ve got it in your email. Let me know if you did.
Bob
Not sure if I'm set up to get emails from people on here. I'll look at my settings. If you want to know anything just ask right here. I'll tell you |
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| Reply #14
Tony81269
USA
68 Posts |
Posted - 08/29/2024 : 17:46:08
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quote:
Originally posted by Tony81269
quote:
Originally posted by Bobakman
@Tony81269
I sent you a PM you should’ve got it in your email. Let me know if you did.
Bob
Not sure if I'm set up to get emails from people on here. I'll look at my settings. If you want to know anything just ask right here. I'll tell you
I looked and my setting say I can get emails but I don't see any from you or from this website |
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| Reply #15
Bobakman
USA
97 Posts |
Posted - 08/29/2024 : 21:12:33
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Ok NP I know a guy in Houston Texas.
Below is his eBay page get in touch with him message him on Ebay and he can set you up with a good deal on a reconditioned Ludlum for a lot less than a brand new one.He has guy that calibrates them for him as well. This forum wouldn't let me attach his eBay link directly
Simply replace the 2 astrisks with 2 "t"'s, and it'll take you right there.
Bob
h**p://ebay.com/str/mybrainfart |
“If you want to find the secrets of the universe, think in terms of energy, frequency and vibration.”
Nikola Tesla |
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| Reply #16
Stargazer 40
USA
431 Posts |
Posted - 08/30/2024 : 14:31:34
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quote:
Originally posted by Tony81269
GMC-800 Reading at 6ft from 300 mCi Cs-137
So, GMC-800 reading 15.76 mR/h and Ludlum 3 reading 16 mR/h. To me, that is really close considering the GMC has not had a NIST calibration.
That was 300 mCi and not uCi? I have two 10uCi source and two 5 uCi sources and these are more than enough together to peg every meter I have but the CDV-717 Survey meter. Is this a downhole tool source you screw into the tool?
I tried to do some math to get to your ~16mR/h with a 300mCi source:
To estimate the reading on a Geiger-Müller (GM) meter in milliroentgens per hour (mR/h) when 18 inches away from a 300 millicurie (mCi) source, we can use the inverse square law for radiation. This law states that the intensity of radiation decreases with the square of the distance from the source.
Here’s a simplified calculation:
Determine the dose rate at 1 meter (100 cm):
For a point source, the dose rate ( D ) in mR/h at 1 meter from a 1 mCi source is approximately 0.5 mR/h.
For a 300 mCi source, the dose rate at 1 meter would be 300 times 0.5 = 150 mR/h.
Adjust for the distance:
The distance in inches is 18 inches, which is approximately 45.72 cm.
Using the inverse square law: D_2 = D_1 times ({d_1}/{d_2})^2
Here, D_1 = 150 mR/h, d_1 = 100 cm, and d_2 = 45.72 cm.
So, D_2 = 150 times {100}/{45.72}^2 approx 717 mR/h.
Therefore, the GM meter would read approximately 717 mR/h when 18 inches away from a 300 mCi source.
Then let’s adjust the calculation for a 300 microcurie (µCi) source instead of a 300 millicurie (mCi) source.
Determine the dose rate at 1 meter (100 cm):
For a point source, the dose rate ( D ) in mR/h at 1 meter from a 1 µCi source is approximately 0.0005 mR/h.
For a 300 µCi source, the dose rate at 1 meter would be 300 times 0.0005 = 0.15 mR/h.
Adjust for the distance:
The distance in inches is 18 inches, which is approximately 45.72 cm.
Using the inverse square law: D_2 = D_1 times ({d_1}/{d_2})^2
Here, D_1 = 0.15 mR/h, d_1 = 100 cm, and d_2 = 45.72 cm.
So, D_2 = 0.15 times ({100}/{45.72})^2 approx 0.717 mR/h.
Therefore, the GM meter would read approximately 0.717 mR/h when 18 inches away from a 300 µCi source.
Neither is 16 mR/h but the 717 mR/h seems more appropriate for the 300mCi source from my experience.
Got to be variable here not accounted for but seems awful strong source for only 16 mR/h exposure.
Math was courtesy of CoPilot GPT4 by Microsoft.
Both meters say the same thing so that in itself says math is properly characterizing the exposure rate.
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Stargazer 40 |
Edited by - Stargazer 40 on 08/30/2024 14:41:38 |
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| Reply #17
Stargazer 40
USA
431 Posts |
Posted - 08/30/2024 : 14:48:31
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oops, that was six feet from source. Whole different problem.
And for CS-137 the answer is much closer to what you got
For Cesium-137 (Cs-137), the specific gamma-ray constant (#915;) is approximately 0.33 R·m²/hr·Ci1.
Let’s use this value to calculate the dose rate at 6 feet from a 300 mCi Cs-137 source.
First, convert the activity to curies (Ci):
300 mCi=0.3 Ci
Next, calculate the dose rate at 1 meter (3.28 feet):
I1#8203;=#915;×Activity=0.33×0.3=0.099 R/hr
Convert R/hr to mR/hr:
0.099 R/hr=99 mR/hr
Now, apply the inverse square law to find the dose rate at 6 feet (1.83 meters):
I2#8203;=99(63.28#8203;)2#8776;30 mR/hr
So, a GM meter would read approximately 30 mR/hr when 6 feet away from a 300 mCi Cs-137 source.
Again from CoPilot GPT4 |
Stargazer 40 |
Edited by - Stargazer 40 on 08/30/2024 14:49:59 |
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| Reply #18
Tony81269
USA
68 Posts |
Posted - 08/30/2024 : 19:14:47
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quote:
Originally posted by Stargazer 40
oops, that was six feet from source. Whole different problem.
And for CS-137 the answer is much closer to what you got
For Cesium-137 (Cs-137), the specific gamma-ray constant (#915;) is approximately 0.33 R·m²/hr·Ci1.
Let’s use this value to calculate the dose rate at 6 feet from a 300 mCi Cs-137 source.
First, convert the activity to curies (Ci):
300 mCi=0.3 Ci
Next, calculate the dose rate at 1 meter (3.28 feet):
I1#8203;=#915;×Activity=0.33×0.3=0.099 R/hr
Convert R/hr to mR/hr:
0.099 R/hr=99 mR/hr
Now, apply the inverse square law to find the dose rate at 6 feet (1.83 meters):
I2#8203;=99(63.28#8203;)2#8776;30 mR/hr
So, a GM meter would read approximately 30 mR/hr when 6 feet away from a 300 mCi Cs-137 source.
Again from CoPilot GPT4
I understand the inverse square law. I actually applied it to some of my tests. At six feet away from the 300 milicurie source it was reading something a long the lines of 15.78. If you do the math and want to see what it should be at 19 feet, your will get approx 1.57mr/h. I have pictures of both the ludlum and the GMC reading 1.58mr/h.
Now, here is something that I failed to mention. It was a 300mCi in 2006. My calculations put that at roughly 197mCi right now.
I'm fairly good at some of this stuff but when it comes to what a dose rate should be right in front of a certain size source without taking any measurements, I get a little lost. Most if this is never used in real life for us |
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| Reply #19
Tony81269
USA
68 Posts |
Posted - 08/30/2024 : 19:20:58
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You know what? I'm not exactly sure when that source was born. Let me get back to you on that.
But the part about the reading at 6ft and 19ft is true. I did the math after I had taken the measurements and was surprised. I should have done it before the 19ft |
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| Reply #20
Tony81269
USA
68 Posts |
Posted - 08/30/2024 : 19:34:31
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quote:
Originally posted by Tony81269
You know what? I'm not exactly sure when that source was born. Let me get back to you on that.
But the part about the reading at 6ft and 19ft is true. I did the math after I had taken the measurements and was surprised. I should have done it before the 19ft
Ok, I looked up that source and it was 300mCi in 2011, so I calculate it is now 222.6 mCI.
So the inverse law reading 15.78mr/hr at 6ft would put me at 1.57mr/h at 19ft.
Also, source on ground with tape measure
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Edited by - Tony81269 on 08/30/2024 19:35:40 |
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| Reply #21
Tony81269
USA
68 Posts |
Posted - 08/30/2024 : 19:56:30
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Also, just to say how the calibration process is going - They got my meter Tuesday. I got a call from the guy saying he was going on vacation and I won't get it for awhile. The price is $77 plus you pay shipping both ways. I would say this would probably be about a 2 week process unless they're on vacation
After the thing comes back calibrated, I will do similar tests and see if there is any big difference
I don't know how this is calibrated at GQ. There are 6 points to calibrate. The CPM numbers from the factory look like stock numbers that are probably the same from meter to meter. Is this calibration linear? If so, why 6 points? |
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| Reply #22
Tony81269
USA
68 Posts |
Posted - 08/30/2024 : 20:16:01
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Also, yes I can do math for Inverse Square law and a couple of other things. But honestly for Well Logging work is all we need to know is what the restricted area around where you are working is. Most people just use a survey meter. Some use pre-made charts. Well Loggers aren't exactly math wizards.
There is a website with many different kinds of calculators. I use it to check if my math is right on certain things - www.radprocalculator.com/Gamma.aspx
They also have a downloadable version. It has Inverse, Decay, Activity to dose and vice versa. Some others as well. You should check it out |
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| Reply #23
Tony81269
USA
68 Posts |
Posted - 08/30/2024 : 21:07:25
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quote:
Originally posted by Bobakman
Ok NP I know a guy in Houston Texas.
Below is his eBay page get in touch with him message him on Ebay and he can set you up with a good deal on a reconditioned Ludlum for a lot less than a brand new one.He has guy that calibrates them for him as well. This forum wouldn't let me attach his eBay link directly
Simply replace the 2 astrisks with 2 "t"'s, and it'll take you right there.
Bob
h**p://ebay.com/str/mybrainfart
I appreciate it but I'm just seeing how this thing will function in a real world situation. Can it actually be NRC calibrated. Is it accurate? If you drop it will it fall into 100 pieces? We have tons of Ludlums that we get calibrated every 6 months. Company doesn't want to spend money just because some of these meters are old. As long as they are reasonably accurate, I can't make the case on buying any more. Now if the gQ meters turned out to be well made then I could make the arguent to buy some more |
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| Reply #24
Stargazer 40
USA
431 Posts |
Posted - 08/31/2024 : 03:30:15
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Nuclear physics in college was a long, long time ago. Don't remember a lab like optical physics where we played with these things. My calibration work on these GQ meters (plus some other Russian GM kits and Mazur) have been wonderfully enlightening. I am very interested in the differences you get when this is NRC calibrated. The GM tubes are pretty well understood. That the GMC-800 is so close to the Ludlum says any factory calibration will likely not be far off. But the cert will be the important part as discussed previously. Thanks for digging in on this.
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Stargazer 40 |
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| Reply #25
Tony81269
USA
68 Posts |
Posted - 08/31/2024 : 11:19:32
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quote:
Originally posted by Stargazer 40
Nuclear physics in college was a long, long time ago. Don't remember a lab like optical physics where we played with these things. My calibration work on these GQ meters (plus some other Russian GM kits and Mazur) have been wonderfully enlightening. I am very interested in the differences you get when this is NRC calibrated. The GM tubes are pretty well understood. That the GMC-800 is so close to the Ludlum says any factory calibration will likely not be far off. But the cert will be the important part as discussed previously. Thanks for digging in on this.
You know the requirements from the NRC on any meters including digital ones are not that difficult. Now it may be different for Well Loggers than for Power plant workers - idk. The accuracy requirement for analog meters like the Ludlum is 20%. To me, that's a very large tolerance. It really does look like depending on what job you have is how a digital meter needs to be calibrate. One regulation says "must be calibrated at one point per decade over the range that will be used" but I do not see very much on what the accuracy should be. My job falls under NRC 10 CFR 39. It explains for analog meters but all it says for digital is "at appropriate points."
The method that GQ's third party (applied health physics) uses is really simple. I'm going to attach the method below. They were given this by GQ. Now, the GMC-800 has 6 calibration points. The people doing the calibration simply put the meter in some standard position from a know source that can be traced to NIST. They go 1, 10, 20, 50, 100, 200 mR/h and get the CPM for each of those. That's about all there is. No messing with voltages or deadtime - at least it doesn't mention anything on this paper. I do not understand if this is a linear calibration or if they have some curve fit stuff going on. All I know is if I get a sheet back that says it can read those 6 points at 1-2% accuracy, the NRC will have no problem with it. Well Loggers survey meters are only required to go up to 50mR/h.
I do wonder something though. I didn't try this when I had the meter but we have some 5Ci AM-241BE neutron sources. Now Americium is an Alpha emitter and this thing will obviously not read neutrons however a Ludlum will detect quite a bit of gamma rays coming off this neutron source. I'm assuming this one will too. It has to because the Ludlum 3 with a 44-6 probe is beta/gamma. We pick up quite a few mR/h of gamma coming from that neutron source. Anyway, here's the calibration procedure that cam from GQ and sent to Applied Health Physics
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| Reply #26
Tony81269
USA
68 Posts |
Posted - 08/31/2024 : 12:28:58
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quote:
Originally posted by Bobakman
Ok NP I know a guy in Houston Texas.
Below is his eBay page get in touch with him message him on Ebay and he can set you up with a good deal on a reconditioned Ludlum for a lot less than a brand new one.He has guy that calibrates them for him as well. This forum wouldn't let me attach his eBay link directly
Simply replace the 2 astrisks with 2 "t"'s, and it'll take you right there.
Bob
h**p://ebay.com/str/mybrainfart
I looked through your friends ebay store. We wouldn't be interested in any ludlum 3's or other alpha/beta/gamma types. I did see he has a model 12-4 neutron detector. We aren't required to have neutron detectors but I would like one anyway. A couple things about this one is the price is $4000. I do not know what a new one would cost. Maybe I should find out. Another thing is that is says it is new/2024 and that it is seller refurbished. That seems strange to me. Not saying it isn't true but where would you get an almost brand new 12-4 that you had to refurbish. I would really have to know the story behind that one. Not saying this guy is shady or anything at all. And finally there are my bosses that will say "why would we pay for something we don't really need?". As future RSO I would like to have one because we do have Ambe sources but are not required to have meters that measure neutrons |
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| Reply #27
Stargazer 40
USA
431 Posts |
Posted - 09/01/2024 : 03:16:29
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| The AM-241BE source is interesting. Americium kicks out alpha and gamma and then the alpha interacts with the Beryllium to kick out neutrons. Never gave any though to the standard Neutron-Density tool that was primary porosity tool and gas indicator with cross-over, but fun to see interaction of these sources and their actual activity levels. Have used smoke detector AM-241 sources to test the GQ alpha meters and some Russian pancake tubes, most notably an SI-8B (Russian kit GM meter), SBT-11a (GMC-600) and the LND 7313 (GMC-600+). |
Stargazer 40 |
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| Reply #28
Stargazer 40
USA
431 Posts |
Posted - 09/01/2024 : 04:28:19
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No idea of the certifier's setup but CoPilot GPT4 says your meter is reading a little low compared to theoretical. To get perfect reading for your estimated source strength at 19 feet it should be 2.20 mR/h. Here's calcs for your measure and that would provide calibration counts for the GQ table:
To determine the distances required to achieve specific exposure rates from a 222.6 mCi Cs-137 source, we can use the inverse square law for radiation. The exposure rate constant for Cs-137 is approximately 0.33 mR/hr per mCi at 1 meter.
Given a 222.6 mCi Cs-137 source, we can calculate the distances for the desired exposure rates:
1. 10 µSv/h (1 mR/h): d = sqrt {0.33 * 222.6}/{1}} approx 8.57 meters or 28.1 feet
2. 15.8 uSv/h (1.58 mR/h) d = sqrt {0.33 * 222.6}/{1.58}} approx 6.82 meters or 22.4 feet
3. 22.0 uSv/h (2.20 mR/h) d = sqrt {0.33 * 222.6}/{2.20}} approx 5.78 meters or 19.0 feet
4. 100 µSv/h (10 mR/h): d = sqrt {0.33 * 222.6}/{10}} approx 2.71 meters or 8.9 feet
5. 200 µSv/h (20 mR/h): d = sqrt {0.33 * 222.6}/{20}} approx 1.92 meters or 6.3 feet
6. 500 µSv/h (50 mR/h): d = sqrt {0.33 * 222.6}/{50}} approx 1.21 meters or 4.0 feet
7. 1000 µSv/h (100 mR/h): d = sqrt {0.33 * 222.6}/{100}} approx .86 meters or 2.8 feet
8. 2000 µSv/h (200 mR/h): d = sqrt {0.33 * 222.6}/{200}} approx .61 meters or 2.0 feet
9. These calculations assume no shielding and ideal conditions.
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Stargazer 40 |
Edited by - Stargazer 40 on 09/01/2024 04:31:49 |
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| Reply #29
Tony81269
USA
68 Posts |
Posted - 09/01/2024 : 08:36:46
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quote:
Originally posted by Stargazer 40
No idea of the certifier's setup but CoPilot GPT4 says your meter is reading a little low compared to theoretical. To get perfect reading for your estimated source strength at 19 feet it should be 2.20 mR/h. Here's calcs for your measure and that would provide calibration counts for the GQ table:
To determine the distances required to achieve specific exposure rates from a 222.6 mCi Cs-137 source, we can use the inverse square law for radiation. The exposure rate constant for Cs-137 is approximately 0.33 mR/hr per mCi at 1 meter.
Given a 222.6 mCi Cs-137 source, we can calculate the distances for the desired exposure rates:
1. 10 µSv/h (1 mR/h): d = sqrt {0.33 * 222.6}/{1}} approx 8.57 meters or 28.1 feet
2. 15.8 uSv/h (1.58 mR/h) d = sqrt {0.33 * 222.6}/{1.58}} approx 6.82 meters or 22.4 feet
3. 22.0 uSv/h (2.20 mR/h) d = sqrt {0.33 * 222.6}/{2.20}} approx 5.78 meters or 19.0 feet
4. 100 µSv/h (10 mR/h): d = sqrt {0.33 * 222.6}/{10}} approx 2.71 meters or 8.9 feet
5. 200 µSv/h (20 mR/h): d = sqrt {0.33 * 222.6}/{20}} approx 1.92 meters or 6.3 feet
6. 500 µSv/h (50 mR/h): d = sqrt {0.33 * 222.6}/{50}} approx 1.21 meters or 4.0 feet
7. 1000 µSv/h (100 mR/h): d = sqrt {0.33 * 222.6}/{100}} approx .86 meters or 2.8 feet
8. 2000 µSv/h (200 mR/h): d = sqrt {0.33 * 222.6}/{200}} approx .61 meters or 2.0 feet
9. These calculations assume no shielding and ideal conditions.
Yeah, I just looked that up on the radpro calculator and it is saying it should be 2.1 mr/h. The things is I was getting 1.58 on the GMC-800 and 1.55 on the Ludlum 3. The activity off 222.6 mCi should be correct based on the dates we have on spreadsheets. I wonder if there is some minor shielding happening. Or it could just be that I didn't have everything exactly at 19 feet. It had to be within an inch. When I get the meter back I will make checks at many different distances and if it's not reading what it mathematically should then I will try to find a plausible explanation. Below is how our "bullplug" is. These are two different pictures of the bullplug pointing two ways. The top one shows the actual little cs137 pill circled and the bottom one shows where that little pill will be at when the bullplug is together, That's what I meant about soe minor shielding but I doubt it would cause that much.
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| Reply #30
Tony81269
USA
68 Posts |
Posted - 09/01/2024 : 11:17:30
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quote:
Originally posted by Stargazer 40
No idea of the certifier's setup but CoPilot GPT4 says your meter is reading a little low compared to theoretical. To get perfect reading for your estimated source strength at 19 feet it should be 2.20 mR/h. Here's calcs for your measure and that would provide calibration counts for the GQ table:
To determine the distances required to achieve specific exposure rates from a 222.6 mCi Cs-137 source, we can use the inverse square law for radiation. The exposure rate constant for Cs-137 is approximately 0.33 mR/hr per mCi at 1 meter.
Given a 222.6 mCi Cs-137 source, we can calculate the distances for the desired exposure rates:
1. 10 µSv/h (1 mR/h): d = sqrt {0.33 * 222.6}/{1}} approx 8.57 meters or 28.1 feet
2. 15.8 uSv/h (1.58 mR/h) d = sqrt {0.33 * 222.6}/{1.58}} approx 6.82 meters or 22.4 feet
3. 22.0 uSv/h (2.20 mR/h) d = sqrt {0.33 * 222.6}/{2.20}} approx 5.78 meters or 19.0 feet
4. 100 µSv/h (10 mR/h): d = sqrt {0.33 * 222.6}/{10}} approx 2.71 meters or 8.9 feet
5. 200 µSv/h (20 mR/h): d = sqrt {0.33 * 222.6}/{20}} approx 1.92 meters or 6.3 feet
6. 500 µSv/h (50 mR/h): d = sqrt {0.33 * 222.6}/{50}} approx 1.21 meters or 4.0 feet
7. 1000 µSv/h (100 mR/h): d = sqrt {0.33 * 222.6}/{100}} approx .86 meters or 2.8 feet
8. 2000 µSv/h (200 mR/h): d = sqrt {0.33 * 222.6}/{200}} approx .61 meters or 2.0 feet
9. These calculations assume no shielding and ideal conditions.
A guy from work says the difference in the math and reality may be related to the double stainless encapsulation of the ceramic pellet. So when you buy these from the manufacturer are they considered 300mCi before being encapsulated or after? I don't know the answer to that one. The same guy who knows more about this than me says that 300 mCi source you buy may have some tolerance on it's exact activity. He points out that on our neutron sources they actually just put 5-6 Ci on the sheet you get from the manufacturer. I will look at some of the original sheets we got from them on Tuesday. I will see if they give a tolerance on that activity level.
Also, I keep seeing you mention CoPilot GPT4. When I search it looks like some form of AI. Do you just ask questions about all the math involved with radiation? It looks kind of cool but I would second guess my math, then second guess the copilot, then I would look at Radpro Calculator. I don't really trust my math and not really sure about the other two |
Edited by - Tony81269 on 09/01/2024 16:19:28 |
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| Reply #31
Stargazer 40
USA
431 Posts |
Posted - 09/02/2024 : 04:16:00
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In earlier reviews of the GMC-800 there was a question about why GQ went to six calibration points instead of the three they have been using. Now that we see this certification form it's pretty obvious that these points pretty much cover the bases as to needed coverage for most uses. These aren't survey meters that would have much higher exposure coverage.
I think given what you show in the pics above that the pill is likely about in the middle of the large threads. You have circled the retaining lug. At the same time, a half inch or inch would well be within a margin of statistical error.
I am most interested in the CPM for each of the exposure amounts on the form. Thanks for sharing those when this gets back from testing (if you don't get the form back then they can be read from the calibration points in the config section). Then of course how it compares to the Ludlum after calibration, especially the high end. |
Stargazer 40 |
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| Reply #32
Tony81269
USA
68 Posts |
Posted - 09/02/2024 : 10:43:38
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quote:
Originally posted by Stargazer 40
In earlier reviews of the GMC-800 there was a question about why GQ went to six calibration points instead of the three they have been using. Now that we see this certification form it's pretty obvious that these points pretty much cover the bases as to needed coverage for most uses. These aren't survey meters that would have much higher exposure coverage.
I think given what you show in the pics above that the pill is likely about in the middle of the large threads. You have circled the retaining lug. At the same time, a half inch or inch would well be within a margin of statistical error.
I am most interested in the CPM for each of the exposure amounts on the form. Thanks for sharing those when this gets back from testing (if you don't get the form back then they can be read from the calibration points in the config section). Then of course how it compares to the Ludlum after calibration, especially the high end.
Yes, I will post whatever they send but I suspect it will only show what it should be reading in mR/h and what it now is reading in the same. But Yes I will take pictures of each point that will show the dose and CPM. If these meters are made and had some kind of factory calibration, those numbers might be close enough to put in other meters.
Idk...I realize that everyone is interested in calibration. I'm sure there might be digital ways or ways to use small uCi check sources and maybe mathematically determine something. All I know from the people in these labs is they actually have a source that will read 200mR/h. Most normal people would not have this kind of thing. We used to calibrate our own Ludlums many years ago and they taught me how they do it. We have a 150 mCi source that's in a shielded box. There's a window on the front of the box and also three plates that could be put into different configurations. You would but the meter on a table at specific distances and then go through and open the front window and there were instructions on which plates to put in on several different step. One step might just have 1 plate and then another have all three plates. We had spreadsheets that we were to record what mR/h at the different distances and with whatever combination of plates were used. I remember doing it a couple of times and then we started sending them to outside labs,When we did it ourselves, the Ludlum three just have a little calibration pot and you just tweaked it to get things closer to what it should be. We never did anything with voltages or deadtime. I would say if you someone wanted to have your meter calibrated to NIST/NRC standards then outside labs coud get you between 1-2% accuracy. Now if you just like tweaking on survey meters then go for that as well |
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| Reply #33
Tony81269
USA
68 Posts |
Posted - 09/02/2024 : 11:00:19
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quote:
Originally posted by Stargazer 40
In earlier reviews of the GMC-800 there was a question about why GQ went to six calibration points instead of the three they have been using. Now that we see this certification form it's pretty obvious that these points pretty much cover the bases as to needed coverage for most uses. These aren't survey meters that would have much higher exposure coverage.
I think given what you show in the pics above that the pill is likely about in the middle of the large threads. You have circled the retaining lug. At the same time, a half inch or inch would well be within a margin of statistical error.
I am most interested in the CPM for each of the exposure amounts on the form. Thanks for sharing those when this gets back from testing (if you don't get the form back then they can be read from the calibration points in the config section). Then of course how it compares to the Ludlum after calibration, especially the high end.
Also, are these meter supposed to be linear? I truly don't know. If it were then you would only need a two point calibration - a low and high and whatever CPM you get at those two points. I suspect they are not because of the 6 points. I think they are creating some curve based on dose and CPM. The software reads the CPM and outputs mr/h based on the calibration curve. idk?? |
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| Reply #34
Stargazer 40
USA
431 Posts |
Posted - 09/02/2024 : 14:39:05
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| OR it could be six points because that's what the NRC certificate needs to say to imply it's fully calibrated. Deadtime is real and the meter processor can do the calculations based on counts and deadtime for that tube and increase the exposure from the lower CPM deadtime creates. But you can also do a linear interpolation between each of the actual readings with six calibrations that cover the range of the tube. I estimate at 2000uSv point 6 that the CPM needs to be raised about 33% because of deadtime of 90 usec for the J321 tube. Your analog meters can't do deadtime calcs. So the six points of calibration for the Ludlum is likely just interpolating between them OR each range on the switch (.1X, 1X, 10X, 100X) is calibrated separately as four point instead of six for this GMC-800. So likely the GMC doesn't have deadtime computed by processor because many calibration points describe the curve. If your numbers are little changed from factory, then likely deadtime being incorporated. If the CPM is falling off of linear then deadtime is not computed, ie., the lower CPM because of deadtime misses needs to indicate higher exposure rate. |
Stargazer 40 |
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| Reply #35
Tony81269
USA
68 Posts |
Posted - 09/03/2024 : 12:12:14
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quote:
Originally posted by Stargazer 40
OR it could be six points because that's what the NRC certificate needs to say to imply it's fully calibrated. Deadtime is real and the meter processor can do the calculations based on counts and deadtime for that tube and increase the exposure from the lower CPM deadtime creates. But you can also do a linear interpolation between each of the actual readings with six calibrations that cover the range of the tube. I estimate at 2000uSv point 6 that the CPM needs to be raised about 33% because of deadtime of 90 usec for the J321 tube. Your analog meters can't do deadtime calcs. So the six points of calibration for the Ludlum is likely just interpolating between them OR each range on the switch (.1X, 1X, 10X, 100X) is calibrated separately as four point instead of six for this GMC-800. So likely the GMC doesn't have deadtime computed by processor because many calibration points describe the curve. If your numbers are little changed from factory, then likely deadtime being incorporated. If the CPM is falling off of linear then deadtime is not computed, ie., the lower CPM because of deadtime misses needs to indicate higher exposure rate.
Interesting, I don't know much about deadtime other than the definition. Yes, it is real. They set our logging tool gamma detectors at a certain level. They are also used in logging for Uranium. Not really finding uranium but using a deadtime and k-factor to determine ore grade. I have loads of papers on it I should read one of these days. |
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| Reply #36
Bobakman
USA
97 Posts |
Posted - 09/03/2024 : 13:11:07
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quote:
Originally posted by Tony81269
quote:
Originally posted by Bobakman
Ok NP I know a guy in Houston Texas.
Below is his eBay page get in touch with him message him on Ebay and he can set you up with a good deal on a reconditioned Ludlum for a lot less than a brand new one.He has guy that calibrates them for him as well. This forum wouldn't let me attach his eBay link directly
Simply replace the 2 astrisks with 2 "t"'s, and it'll take you right there.
Bob
h**p://ebay.com/str/mybrainfart
I looked through your friends ebay store. We wouldn't be interested in any ludlum 3's or other alpha/beta/gamma types. I did see he has a model 12-4 neutron detector. We aren't required to have neutron detectors but I would like one anyway. A couple things about this one is the price is $4000. I do not know what a new one would cost. Maybe I should find out. Another thing is that is says it is new/2024 and that it is seller refurbished. That seems strange to me. Not saying it isn't true but where would you get an almost brand new 12-4 that you had to refurbish. I would really have to know the story behind that one. Not saying this guy is shady or anything at all. And finally there are my bosses that will say "why would we pay for something we don't really need?". As future RSO I would like to have one because we do have Ambe sources but are not required to have meters that measure neutrons
Understand. You would need to contact him he is a pretty straight forward guy and will be more than happy to answer any questions that you have.
Bob |
“If you want to find the secrets of the universe, think in terms of energy, frequency and vibration.”
Nikola Tesla |
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| Reply #37
Tony81269
USA
68 Posts |
Posted - 09/03/2024 : 16:22:04
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quote:
Originally posted by Stargazer 40
OR it could be six points because that's what the NRC certificate needs to say to imply it's fully calibrated. Deadtime is real and the meter processor can do the calculations based on counts and deadtime for that tube and increase the exposure from the lower CPM deadtime creates. But you can also do a linear interpolation between each of the actual readings with six calibrations that cover the range of the tube. I estimate at 2000uSv point 6 that the CPM needs to be raised about 33% because of deadtime of 90 usec for the J321 tube. Your analog meters can't do deadtime calcs. So the six points of calibration for the Ludlum is likely just interpolating between them OR each range on the switch (.1X, 1X, 10X, 100X) is calibrated separately as four point instead of six for this GMC-800. So likely the GMC doesn't have deadtime computed by processor because many calibration points describe the curve. If your numbers are little changed from factory, then likely deadtime being incorporated. If the CPM is falling off of linear then deadtime is not computed, ie., the lower CPM because of deadtime misses needs to indicate higher exposure rate.
We have something very much like this at work. We don't use it anymore. The procedure was similar but we had a tape measure and placed the meter at different distances
www.youtube.com/watch?v=k9hyMk6U_Mw |
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| Reply #38
Stargazer 40
USA
431 Posts |
Posted - 09/11/2024 : 06:54:27
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| Do they still have your meter? Or is guy taking a long vacation? |
Stargazer 40 |
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| Reply #39
Stargazer 40
USA
431 Posts |
Posted - 09/11/2024 : 07:00:39
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quote:
Originally posted by EmfDev
GQ Geiger counters are advertised for general use and not for professional use. However, some models like the GMC-800/500/+/600+ can be calibrated with 1-2% accuracy and certified with the NRC / NIST via 3rd party.
EmfDev, do current versions of 500/600 firmware include the same six point calibration as the GMC-800 or is there a different procedure for having them certified with NRC? Is deadtime a part if that or is it assumed to be correct and only the calibration points altered during the calibration process? |
Stargazer 40 |
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| Reply #40
Tony81269
USA
68 Posts |
Posted - 09/12/2024 : 17:14:36
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quote:
Originally posted by Stargazer 40
Do they still have your meter? Or is guy taking a long vacation?
I got a call from him today and he said that meter was spot on. Took my credit card stuff and said it would either ship out today or Monday. So, fedex express usually takes a couple of days so I really don't think I'll get it till next week sometime. I don't want to say this guy is slow or anything. If he had a vacation planned then stuff happens. I might have some other guys send to him and see how long it takes. I think in a normal situation this could be a two or three week deal |
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| Reply #41
Stargazer 40
USA
431 Posts |
Posted - 09/15/2024 : 04:15:55
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| Thanks. It doesn't sound like he made any adjustments to the calibration points to get it to be 'spot on' or did he say after adjustments it was 'spot on'? |
Stargazer 40 |
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| Reply #42
Tony81269
USA
68 Posts |
Posted - 09/15/2024 : 12:52:00
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quote:
Originally posted by Stargazer 40
Thanks. It doesn't sound like he made any adjustments to the calibration points to get it to be 'spot on' or did he say after adjustments it was 'spot on'?
I am pretty sure he meant that after he calibrated the meter it was "spot on"
It will likely be this week sometime and I will post a copy of his calibration sheet. I will also post the numbers that were entered into all 6 calibration points.
After that, I will do some more accuracy tests. Maybe try to be a little more scientific about it, including source decay and all that good stuff.
I'm not sure if I did already but I will post how the calibration was done at GQ. It may be tomorrow till I can get to that |
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| Reply #43
Tony81269
USA
68 Posts |
Posted - 09/15/2024 : 13:05:44
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quote:
Originally posted by Stargazer 40
Thanks. It doesn't sound like he made any adjustments to the calibration points to get it to be 'spot on' or did he say after adjustments it was 'spot on'?
I am attaching what GQ gave me as their factory calibration for my meter. I can guarantee the one from the lab will look nothing like this
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| Reply #44
ullix
Germany
1171 Posts |
Posted - 09/16/2024 : 00:44:24
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A "Certificate of Calibration" ? Well, this is hilarious. Doesn't GQ feel embarrassed by presenting such a gibberish as "Certificate"? Let alone as "Calibration"?
There is not even a single line which qualifies as calibration!
At best this is a QA check at the end of production. The sloppiness is already visible in the making of this form, as under the heading "Energy MeV" none(!) of the 3 entries has anything to do with energy!
Further, when you do have a CPM value of 50, then as a trivial consequence of the Poisson law is the Readout Deviation 15%. This is not a separate check!
And then note that the background is given as a range of 15 to 50 CPM. This implies that the AM241 measured count rate of 50 is within the background. In other words: they have not gotten any signal at all!
This thingy of paper is the ultimate of BS!
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| Reply #45
Stargazer 40
USA
431 Posts |
Posted - 09/16/2024 : 04:02:14
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If you look at the 'Type' line it says pretty clearly 'QA/Production'. Doesn't say anything about NRC calibration and obviously is only meant to show it passed basic operational testing prior to being shipped. All the stuff reported here is most likely conforming to design standards. Since they don't make this a part of what's delivered (I didn't get this form with my GMC-800) I can only assume it was supplied as a result of a request?
If GQ had done an NRC type calibration it would look a lot different. But as ullix has stated in another thread, all the calibration points are linear out of the box. GQ felt the GM tube was 'close enough' to linear that they didn't need to add more detailed numbers for the vast majority of those purchasing this device. And they provide access to a means to meet NRC calibration certification and even recommend a third party to do it. They have no involvement in that but have provided the user a meter that can be NRC certified. I have calculated the numbers that should be in each of the calibration spots taking into account DT. I'll post those after Tony posts the actuals from his meter. That should lead to a very interesting discussion. |
Stargazer 40 |
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| Reply #46
Tony81269
USA
68 Posts |
Posted - 09/16/2024 : 10:09:53
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quote:
Originally posted by ullix
A "Certificate of Calibration" ? Well, this is hilarious. Doesn't GQ feel embarrassed by presenting such a gibberish as "Certificate"? Let alone as "Calibration"?
There is not even a single line which qualifies as calibration!
At best this is a QA check at the end of production. The sloppiness is already visible in the making of this form, as under the heading "Energy MeV" none(!) of the 3 entries has anything to do with energy!
Further, when you do have a CPM value of 50, then as a trivial consequence of the Poisson law is the Readout Deviation 15%. This is not a separate check!
And then note that the background is given as a range of 15 to 50 CPM. This implies that the AM241 measured count rate of 50 is within the background. In other words: they have not gotten any signal at all!
This thingy of paper is the ultimate of BS!
Yes, I requested this because if you read the fine print on Amazon or wherever, it tells you that they can give you a GQ calibration certificate upon request but they also tell you that calibration is not nist/nrc.
I also thought it was all strange as well. Everything you said. I also wondered why they would use Am-241. Most calibrations are done with Cs-137.
But the thing is, no matter how they actually did their calibration, it matches up pretty close to reality. |
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| Reply #47
GTS
USA
38 Posts |
Posted - 09/16/2024 : 17:01:47
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| More fuel to the BS bonfire. If I am not mistaken, Am-241 is mostly an alpha emitter with a little gamma so the GMC-800 is not going to detect this source very well given its geiger tube type. The clicks should be just above background with that slight gamma emanation. |
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| Reply #48
Tony81269
USA
68 Posts |
Posted - 09/16/2024 : 19:17:12
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quote:
Originally posted by GTS
More fuel to the BS bonfire. If I am not mistaken, Am-241 is mostly an alpha emitter with a little gamma so the GMC-800 is not going to detect this source very well given its geiger tube type. The clicks should be just above background with that slight gamma emanation.
very true. I hadn't even considered that. This may not have been calibrated to Am-241 but rather a measurement taken of this little check source to determine accuracy tolerance. Idk
I'm not going to jump all over GQ. The meter they sold me was fairly accurate compared to a Ludlum. I do wonder if they calibrated a few of these and determined some standard numbers. Those numbers would have just been entered into the meter calibration points of all new builds. Then they would make a final check of each meter to make sure that it fit into the tolerance.
At this point, I may just email support and ask them. They have been very open with me so far about everything they do
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| Reply #49
ullix
Germany
1171 Posts |
Posted - 09/17/2024 : 01:45:20
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Am-241 is a bit of an unexpected radioactive source, but as this Pseudo-Certificate has absolutely nothing to do with "Calibration" I guess this is just used for convenience to create "some counts".
Am-241 is used in ionizing smoke detectors. Those devices look like this:
Putting one of them on the top side of a GMC-300 counter I get some CPM=100, strongly position dependent, like shown in this GeigerLog run:
Am-241 is an alpha emitter. It is this property, which is used in smoke detectors. The decay is rather complex, having multiple alpha energies, even fission, and it also comes with multiple gamma emission. The gammas are of low-energy (<100keV), about on a par with medial-X-ray energies.
If you want to use then at home you can buy such encapsulated units on AliExpress for $3.40
https://www.aliexpress.com/item/1005007315035011.html
But I very much suggest to keep them assembled to avoid releasing Am-241 to your environment! I would not want having any radioactive emitters, and in particular alpha emitters, floating in the air I breathe!!!
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Edited by - ullix on 09/17/2024 01:56:27 |
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| Reply #50
Tony81269
USA
68 Posts |
Posted - 09/17/2024 : 15:17:30
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quote:
Originally posted by ullix
Am-241 is a bit of an unexpected radioactive source, but as this Pseudo-Certificate has absolutely nothing to do with "Calibration" I guess this is just used for convenience to create "some counts".
Am-241 is used in ionizing smoke detectors. Those devices look like this:
Putting one of them on the top side of a GMC-300 counter I get some CPM=100, strongly position dependent, like shown in this GeigerLog run:
Am-241 is an alpha emitter. It is this property, which is used in smoke detectors. The decay is rather complex, having multiple alpha energies, even fission, and it also comes with multiple gamma emission. The gammas are of low-energy (<100keV), about on a par with medial-X-ray energies.
If you want to use then at home you can buy such encapsulated units on AliExpress for $3.40
https://www.aliexpress.com/item/1005007315035011.html
But I very much suggest to keep them assembled to avoid releasing Am-241 to your environment! I would not want having any radioactive emitters, and in particular alpha emitters, floating in the air I breathe!!!
Yeah it's interesting that Alpha can't penetrate your skin, but if you inhale or ingest them then your going to have some issues.
You can buy check sources of all kinds from Direct Scientific but the prices are kind of high for a normal person. Now, if you enjoy messing with radiation then I suppose it's not so bad. I don't know where we get them from but we have a bunch of check sources in our electronics lab. They are in a thick safe and nothing in there but gamma. I took my Ludlum and went through there one day and there was a lid with about 5 cobalt-60 check sources. They were putting off quite a bit so I put them in a lead container. Even though these things are little, I would recommend being as safe as you can |
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| Reply #51
Tony81269
USA
68 Posts |
Posted - 09/17/2024 : 15:42:35
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quote:
Originally posted by Stargazer 40
If you look at the 'Type' line it says pretty clearly 'QA/Production'. Doesn't say anything about NRC calibration and obviously is only meant to show it passed basic operational testing prior to being shipped. All the stuff reported here is most likely conforming to design standards. Since they don't make this a part of what's delivered (I didn't get this form with my GMC-800) I can only assume it was supplied as a result of a request?
If GQ had done an NRC type calibration it would look a lot different. But as ullix has stated in another thread, all the calibration points are linear out of the box. GQ felt the GM tube was 'close enough' to linear that they didn't need to add more detailed numbers for the vast majority of those purchasing this device. And they provide access to a means to meet NRC calibration certification and even recommend a third party to do it. They have no involvement in that but have provided the user a meter that can be NRC certified. I have calculated the numbers that should be in each of the calibration spots taking into account DT. I'll post those after Tony posts the actuals from his meter. That should lead to a very interesting discussion.
I am still waiting on my meter to get back from AHP. I also talked to GQ support about how they "calibrate" their meters. Here's the deal, this is an inexpensive Geiger counter that can offer you some protection, peace of mind, or just some fun looking for radioactive stuff. It is not meant as a professional instrument (at least not yet) although they do claim that it can be calibrated to NRC standards and have good accuracy. I'm fixing to find that out.
The way they got their calibration numbers was exactly as I thought. They had a few of them actually calibrated and then came up with some standard numbers to put into new builds. Then they will check them for some tolerance to decide if the pass or fail. That's basically what that "certificate" was from GQ. Just a QA/QC document. The calibration is "mostly" linear but they do use 6 points for that line. Honestly for a $100 meter, there is nothing wrong with the way they did this. 99% of their customers are not concerned with calibration.
I remember one time, I bought a YSI conductivity meter to measure fluid. This was about a $3,000 instrument at the time and I remember them asking me at checkout if I wanted to buy some calibration fluid. I asked them aren't these calibrated before being sold and they told me they were "pretty close". I ended up buying some of it because I wanted my meter to be more than close. I felt like for $3000 and a brand name that had been around for a long time, they should have provided me with a calibrated fluid meter. GQ is a little different story.
So, I wouldn't jump on GQ about any of this calibration stuff. The meter seems to be worth the $100 I paid. I'm surprised they didn't charge more |
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| Reply #52
EmfDev
2250 Posts |
Posted - 09/18/2024 : 10:07:24
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| @Tony81269 Once you receive your counter, we advice that you go to the calibration menu and make a record of the CPM : µSv/h for each of the 6 calibration points as a factory reset will clear the values. |
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| Reply #53
Tony81269
USA
68 Posts |
Posted - 09/18/2024 : 10:48:32
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quote:
Originally posted by EmfDev
@Tony81269 Once you receive your counter, we advice that you go to the calibration menu and make a record of the CPM : µSv/h for each of the 6 calibration points as a factory reset will clear the values.
Yes, very good idea! |
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| Reply #54
Tony81269
USA
68 Posts |
Posted - 09/19/2024 : 12:32:04
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quote:
Originally posted by Stargazer 40
If you look at the 'Type' line it says pretty clearly 'QA/Production'. Doesn't say anything about NRC calibration and obviously is only meant to show it passed basic operational testing prior to being shipped. All the stuff reported here is most likely conforming to design standards. Since they don't make this a part of what's delivered (I didn't get this form with my GMC-800) I can only assume it was supplied as a result of a request?
If GQ had done an NRC type calibration it would look a lot different. But as ullix has stated in another thread, all the calibration points are linear out of the box. GQ felt the GM tube was 'close enough' to linear that they didn't need to add more detailed numbers for the vast majority of those purchasing this device. And they provide access to a means to meet NRC calibration certification and even recommend a third party to do it. They have no involvement in that but have provided the user a meter that can be NRC certified. I have calculated the numbers that should be in each of the calibration spots taking into account DT. I'll post those after Tony posts the actuals from his meter. That should lead to a very interesting discussion.
Ok guys, I got my meter back from Applied Health Physics. Attached is the calibration sheet. In my next post I will show the calibration points on the meter and CPM values
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| Reply #55
Tony81269
USA
68 Posts |
Posted - 09/19/2024 : 12:57:56
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quote:
Originally posted by Tony81269
quote:
Originally posted by Stargazer 40
If you look at the 'Type' line it says pretty clearly 'QA/Production'. Doesn't say anything about NRC calibration and obviously is only meant to show it passed basic operational testing prior to being shipped. All the stuff reported here is most likely conforming to design standards. Since they don't make this a part of what's delivered (I didn't get this form with my GMC-800) I can only assume it was supplied as a result of a request?
If GQ had done an NRC type calibration it would look a lot different. But as ullix has stated in another thread, all the calibration points are linear out of the box. GQ felt the GM tube was 'close enough' to linear that they didn't need to add more detailed numbers for the vast majority of those purchasing this device. And they provide access to a means to meet NRC calibration certification and even recommend a third party to do it. They have no involvement in that but have provided the user a meter that can be NRC certified. I have calculated the numbers that should be in each of the calibration spots taking into account DT. I'll post those after Tony posts the actuals from his meter. That should lead to a very interesting discussion.
Ok guys, I got my meter back from Applied Health Physics. Attached is the calibration sheet. In my next post I will show the calibration points on the meter and CPM values
Ok here are the actual CPM per 6 points. All of them start with zero except for point 6 and it starts with a one.
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Edited by - Tony81269 on 09/19/2024 15:25:10 |
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| Reply #56
Stargazer 40
USA
431 Posts |
Posted - 09/20/2024 : 04:27:02
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Here are the numbers I calculated using DT delay of 90 usec and the initial input of 1538 CPM
Cal 1 - .998 to 1535 Tony 960 Chg 1.6X
Cal 2 - .988 to 15198 Tony 8991 1.7X
Cal 3 - .976 to 30039 Tony 17115 1.8X
Cal 4 - .940 to 72274 Tony 40079 1.8X
Cal 5 - .880 to 135268 Tony 78848 1.7X
Cal 6 - .760 to 233739 Tony 144614 1.6X
So my initial number is high by 1.6X, and average is going to be that my readings are 1.7X higher. DT is not in the shipped meter numbers and the 90 usec DT delay is a pretty good number for the tube. Just have to drop the initial number and this is a good match. I'll do that in a heartbeat.
Thank you for sharing! |
Stargazer 40 |
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| Reply #57
Tony81269
USA
68 Posts |
Posted - 09/20/2024 : 05:16:46
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quote:
Originally posted by Stargazer 40
Here are the numbers I calculated using DT delay of 90 usec and the initial input of 1538 CPM
Cal 1 - .998 to 1535 Tony 960 Chg 1.6X
Cal 2 - .988 to 15198 Tony 8991 1.7X
Cal 3 - .976 to 30039 Tony 17115 1.8X
Cal 4 - .940 to 72274 Tony 40079 1.8X
Cal 5 - .880 to 135268 Tony 78848 1.7X
Cal 6 - .760 to 233739 Tony 144614 1.6X
So my initial number is high by 1.6X, and average is going to be that my readings are 1.7X higher. DT is not in the shipped meter numbers and the 90 usec DT delay is a pretty good number for the tube. Just have to drop the initial number and this is a good match. I'll do that in a heartbeat.
Thank you for sharing!
Looks like you got them pretty much spot on other than your initial number. Awesome! |
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| Reply #58
Stargazer 40
USA
431 Posts |
Posted - 09/20/2024 : 06:39:51
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| It would be kinda fun to set up a meter with your numbers and send it in for calibration. Would it come back with anything changed saying the tubes and electronics are pretty consistent. If so, GQ could ship all GMC-800 meters with a much better calibration set. (Or just send it in as is and see how it comes back. Both ways would work.) |
Stargazer 40 |
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| Reply #59
Tony81269
USA
68 Posts |
Posted - 09/20/2024 : 08:38:27
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quote:
Originally posted by Stargazer 40
It would be kinda fun to set up a meter with your numbers and send it in for calibration. Would it come back with anything changed saying the tubes and electronics are pretty consistent. If so, GQ could ship all GMC-800 meters with a much better calibration set. (Or just send it in as is and see how it comes back. Both ways would work.)
I sent GQ all this data last night. They can compare it with what they have gotten before. They are actually quite open and willing to talk about stuff like this.
From my understanding is that is what GQ has already done. They took a handful and had them calibrated. Then they determined standard numbers to be used in all newly manufactured ones. Then they would go through a final QA/QC to see if they match up closely to the original. So, every meter that you buy will most likely have the same set of calibration numbers already in there. If something were off with the tube or components of the meter then they would hopefully catch it in QC |
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| Reply #60
Tony81269
USA
68 Posts |
Posted - 09/20/2024 : 17:44:29
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quote:
Originally posted by Stargazer 40
It would be kinda fun to set up a meter with your numbers and send it in for calibration. Would it come back with anything changed saying the tubes and electronics are pretty consistent. If so, GQ could ship all GMC-800 meters with a much better calibration set. (Or just send it in as is and see how it comes back. Both ways would work.)
I have started testing the accuracy of this calibrated meter. I won't be able to get to any larger sources until next week at work. I did start a new topic for this in the forum called "GMC-800 Accuracy NIST/NRC Calibrated" |
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NRC Calibration Question
