Dear All,

We are using Nucleonic Level Transmitters which use Geiger Muller Tubes as level detectors.

We are facing problems with these tubes, as they get leak and fails frequently.

The ionization voltages (which are supposed to be around 500 to 580) are sometimes less.

Our installations are water proof, dustproof, moisture free.

Please somebody who are familiar in this field, suggest some ideas to overcome the problem.

Our make of the transmitters is TRACERCO.

With Best Regards,

Ravichandran
Indorama Petrochem.

 

GM tubes are among the most durable of sensors. When I was at Texas Nuclear, we regularly used GM tubes for point level switches in some of the dirtiest, most hazardous and difficult applications, where heat, vibration and temperature change were endemic. We had very few failures.

Based on my experience, you need to look for another supplier of GM tubes. You are buying poor quality sensors.

Walt Boyes
Editor in Chief
Control magazine
www.controlglobal.com
blog:Sound OFF!! http://waltboyes.livejournal.com
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Reaching way back to Cold War Civil Defense times regarding GM tubes and mixing in some forgotten lore from when gas regulator tubes were common, there are a few things that might help:

Vibration is bad for these tubes physically. They generally have glass to metal seals which are only good if the metal is not deformed. Temperature extremes and changes are hard on the seals also. The gas is subject to getting "poisoned" by outgassing from the elements. These work by keeping the tube on the verge of ionization so that ionizing particles cause an avalanche. Once ionized the tube will conduct unless the voltage is brought below an extinction potential. If the voltage applied is too high for the series resistance employed to drop the voltage to extinction, the tube may stay conducting. This is bad because it's not detecting, and the current can heat the elements which helps with outgassing. This is old, rather imprecise, technology with a whole raft of variables. There is a rather large, by todays standards, normal distribution of parameters on the tubes and many factors that affect reliability. The manufacture of GM tubes is not easy, there was at least a 2 or 3 to 1 spread in reliability between vendors back when many thousands of these were purchased for Civil Defense shelters and the tube industry was mainstream then. The last high volume tube is the CRT, there is almost zero tube manufacturing here, I don't doubt that a lot of knowhow is forgotten. The gas itself wears out. I don't recall anymore what the mechanism was, but I have enjoyed relating some of the obsolete, almost totally useless knowledge I possess in abundance and I'll take to the grave. In general, remember that this is a fragile thin glass envelope with a gas filling whose composition must stay consistant, but doesn't and the thing is sensitive to shock, temperature. etc. Oh, and hopefully, the occasional ionizing particle on it's way through. These were high rel devices in their day, too bad there isn't a really good semiconductor replacement. You may just have to live with 1960's reliability.

Regards
cww

 

Thank you very much sir, on your elaberated reply.
I will try look in to the vibration and heat factors.

regardrs
Ravichanran

 

Generally GM tube is used with load resistor and preamplifier ckt, but it is advisable to put 1M ohm in series with anode terminal. This protects from discharging high voltage (charge voltage across shielded cable) through GM tube.