| T O P I C R E V I E W |
| Geo-Johnny |
Posted - 09/22/2019 : 02:17:29
Everyone knows the "Nuclear Radiation Safety Guide" Card, which is enclosed with the GQ Geiger counters ...
The question now is, what values would the Safety Guide contain if the GMC500+ had ONLY the second counter tube (SI3BG) in operation?
The reason for my question is that I can not come to a correct conclusion with the conversion rates. The set default value CPM 25 = 4.85uSv/h (0.194) can not be correct if the second counter tube is used stand alone. According to the data sheet of this SI3BG tube, I always come to a conversion rate between 0.709 and 0.887. Or am I wrong? In any case, the conversion rate of the M4011 counter tube is clear to me, but suspicious in some other counter tubes. |
| 13 L A T E S T R E P L I E S (Newest First) |
| Geo-Johnny |
Posted - 09/25/2019 : 10:42:41
I am considering whether the automatic voltage setting would work reliably even with my model of the GMC500+ for the LND712 counter tube? Because EmfDev has told me that I have installed on my device which the old 1G resistor after each factory reset the command <SETHVCALIB1> on the terminal.
Now I'm not sure if I should perhaps take the connection for the LND712 counter tube on tube 2, especially since the space next to it for the connection socket would be ideal? On the other hand, the tube 1 would be better, because you can set two calbration points in the menu.
The decision is difficult. I will test the whole thing with a free wiring and then decide for tube 1 or 2 before I make a hole in the case. |
| Geo-Johnny |
Posted - 09/24/2019 : 07:54:49
Good Arguments Stargazer_40, I will follow your advice. The ordered hollow plug socket has arrived and I am already looking for a suitable mounting position. Unfortunately, I still do not have the LND712 counter tube. |
| Stargazer 40 |
Posted - 09/24/2019 : 05:44:24
@ullix - I post a number of tests in this thread that you should get some relevant numbers from.
https://www.gqelectronicsllc.com/forum/topic.asp?TOPIC_ID=5416&SearchTerms=lnd712 |
| Stargazer 40 |
Posted - 09/24/2019 : 05:27:11
Working voltage for SI3BG is 380-460V. Recommended voltage for LND712 is 500V, but plateau goes up to 650V. There shouldn't be any problem with even 700V from the power supply being applied to the SI3BG, you just are well outside the plateau region for the tube. Again this is the problem with the tube 2 location being used for both the LND712 and the original SI3BG in a switchable configuration. It would be better placed in the circuit with the M4011 (provides AVA, tube 2 doesn't), and that approach provides an additional supporting argument for having the power supply software configurable to switch between two preset voltages(added) and conversion factors as described in my calibration thread for using the M4011 as a Background/Survey meter or as a Sample/Food Testing meter. In my older 500+ (V1) I manually adjusted the voltage up to 500V and removed the SI3BG entirely.
I think the SI3BG tube is still a good mate for the M4011. It provides incident Survey meter application much like my CDV-717 ionization meter. At 10CPM it is measuring about 9uSv/h. Assuming it gets there and DT added, it can measure 500mSv/h and that is 'First Responder depart the area immediately' level, which is something to know when entering an area in an incident. |
| Geo-Johnny |
Posted - 09/24/2019 : 01:41:02
Sorry guys, an other importent question:
The maximum voltage for the M4011 counter tube is 700 volts. Does anyone know how many volts the SI3BG tube can withstand? Because if I switch back from the LND712 counter tube on one of the two internal tubes by pulling the plug, there are suddenly 500 volts on the internal counter tube. The M4011 can handle this without any problems, I am not sure about the SI3BG due to lack of information. |
| ullix |
Posted - 09/24/2019 : 00:31:53
GeigerLog has now received support for the Gamma-Scout breed of Geiger counters. Those counters all hold a LND712 tube ("Halogen filled Geiger-Müller tube with mica end window [LND 712 or equivalent]").
According to the tube's specs ( https://www.lndinc.com/products/geiger-mueller-tubes/712/ ) its sensitivity is 0.009 µSv/h/CPM, i.e. about 30% less sensitive than a M4011 (0.0065 µSv/h/CPM).
This may be not a completely fair comparison, because the Gamma-Scout tube has a certification for Cs173 - you can even get an ISO 9000 certificate! - while the M4011 certification was never published, perhaps even never done?
However, the LND tube is smaller in volume and smaller in inner-surface, so a reduced sensitivity is to be expected.
Then what is the benefit over the M4011 in a GMC counter? I don't see any.
The window, you may say. But look at the dimensions: it is a very small window. I am not even sure that this window over-compensates the general lower sensitivity due to its smaller size? Does anyone have data to show otherwise?
By the way: I don't have much data about Gamma-Scout and GeigerLog. Anyone having such a counter and can share data collected with GeigerLog? I am interested to see!
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| Geo-Johnny |
Posted - 09/23/2019 : 13:37:54
@ Stargazer_40 thanks. With the conversion rate for the SI3BG counter tube in standalone mode, we both come up with the same result. This counter tube is likely to be used only near reactors, presumably in power plants, nuclear-powered submarines or in the manufacture of nuclear weapons. Otherwise, I would not know a useful application of this tube.
I ordered the LND712 counter tube for around $ 100, but it has not arrived yet. I want to use it the way you do. However I would like to use a 3,5mm hollow plug socket with integrated switch, which shuts off the internal counter tube at the anode, as soon as the plug is inserted. An approximately 30 cm long shielded cable is to establish the connection, but the anode takes over the shielding and the counting cathode side runs over the inner conductor. The anode resistor comes directly to the LND712 tube. I hope with the anode shielding to minimize the HV problems. Which of the two internal counter tubes will be switched off, I have to think twice. I think 30 to 50cm shielded cable should be enough, because with Alpha measurements you have to be close to the source anyway. Anyway, I will report here in the forum on the implementation.
@EmfDev thank you, you know what I mean. Out of the box, the user should be warned of the possible high levels of radiation in stand-alone operation of counter tube 2 by default values at the alarm threshold and on the display. If the user later sets the thresholds even higher, it is all his own business. But from the factory a warning should be made, because that is the real meaning of a Geiger counter. |
| Stargazer 40 |
Posted - 09/23/2019 : 10:53:53
In Reply#17 of this thread I got .881 CPM/uSv/h for gamma only response for the SI3BG and that's what I use when only tube 2 is on.
https://www.gqelectronicsllc.com/forum/topic.asp?TOPIC_ID=5554 |
| Stargazer 40 |
Posted - 09/23/2019 : 10:18:44
Moving from the SI3BG tube to the LND712 is going in the opposite direction from a kind of mid range sensitivity and low sensitivity gamma/xray meter to a mid sensitivity and alpha detector windowed tube. If you had an LND 712 wand on a cable like mine that when added to the meter on the SI3BG power supply side without AVA you would still have high count voltage issues. It would be better to add it to the M4011 side with plug in connection and a menu switch to select which tube the power supply connects to (or use the DIY add somehow separated from the primary). |
| EmfDev |
Posted - 09/23/2019 : 09:59:51
Thank you for your suggestion Geo-Johnny, Ill discuss it with the team.
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| Geo-Johnny |
Posted - 09/23/2019 : 01:01:36
Thank you ullix, I see, I still have a lot to learn. My head is already buzzing with reading, because the topic about the second counter tube is very complex. My English is not the best and I have to translate a lot. Anyway, I'd like to miss a LND712 counter tube on the GMC500 + instead of the SI3BG tube, much as Stargazer_40 did. That's why I was interested in the way the SI3BG works in advance. |
| ullix |
Posted - 09/22/2019 : 23:25:26
The 2nd tube's calibration is wayyy off the mark. See the lengthy discussion here: http://www.gqelectronicsllc.com/forum/topic.asp?TOPIC_ID=5369
One conclusion is in Reply #10.
quote:
With Thorium = 0.468, and K40 = 0.494, I'd finally put the calibration factor for the 2nd tube, the SI3BG, to 0.48 µSv/h/CPM. Which makes it 74 fold less sensitive than the M4011!
If your data show otherwise, please show the data!
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| Geo-Johnny |
Posted - 09/22/2019 : 05:20:06
No matter how high the conversion rate for the second counter tube (SI3BG) actually is, a safety change of the current firmware of the GMC500+ should be made with the next revision!!! Because if ONLY the second counter tube is selected for the measurement, the threshold value for the alarm should be automatically set to uSv/h or CPM 1 default! In any case, the threshold in CPM(default 100) is much too high, since you are already in the dangerous range from 1 or 2 CPM. Also the thresholds on the display for MEDIUM and HIGH should be changed automatically. For example, Default MEDIUM = 1CPM, Default HIGH = 2CPM. |
