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2.GQ Geiger Muller Counter

Checking GMC-320S accuracy after long storage

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smanna

USA
1 Posts

Posted - 11/21/2025 : 23:21:49

Hi everyone,
I recently pulled my GMC-320S out of storage after not using it for almost two years, and I’m noticing that the CPM readings seem slightly higher than what I used to get in the same environment. Before I assume the tube is drifting, is there a reliable method to verify whether the CPM readings are still accurate?

For example:

Is there a recommended low-cost check source or calibration reference for home users?

Does long-term storage affect the M4011 tube’s baseline readings?

Should I perform any internal reset or firmware check before testing accuracy?

Thanks in advance for any guidance!

https://geometrydashwave.io

Reply #1

ullix

Germany
1234 Posts

Posted - 11/22/2025 : 05:14:27

Storage should not not have an impact. But giving ageing electronics and ageing tube -- who knows!

A non-inteact tube may have its inner colorful shiny surface changed into something of whitisch cloudiness. Then the tube may have a crack and air had come in. But then should not work at all.

A full reset can't do harm. In addition, I would also take the batterie out for some 10 sec and restart.

With this device expect avg CPM=15 ... 25. Some radioactive sources at home may be kitchen/bathroom tiles, countertops from stone. All because of Potassium. For more see my Potty Training
https://sourceforge.net/projects/geigerlog/files/Articles/

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