| T O P I C R E V I E W |
| skylerclooney |
Posted - 09/05/2025 : 19:43:48
Hi everyone,
I’m Skyler and new here on the GQ forum. I’ve been using a GQ GMC-500+ Geiger Muller Counter for a few weeks, and I’m running into a problem I can’t figure out.
When I compare the readings from my unit with another counter, mine consistently shows values that are about 20–25% higher. I’ve tried resetting the device, updating the firmware, and even checking in different environments, but the discrepancy remains. I also noticed that sometimes the CPM spikes briefly without any apparent radiation source nearby.
Could this be a calibration issue, or something else I might be missing? Do I need to adjust settings manually, or is there a recommended procedure to check accuracy?
Any advice would be greatly appreciated. |
| 1 L A T E S T R E P L I E S (Newest First) |
| ullix |
Posted - 09/06/2025 : 00:19:09
The "spikes" are probably the result of an inappropriate setting in the counter's firmware. See in particular my Reply #7 in https://www.gqelectronicsllc.com/forum/topic.asp?TOPIC_ID=10932
Among possible settings, the default value of FET=3 is the worst setting! Switch FET off by setting it to FET=60!
If FET is off, and you still get spikes, they might be real - a consequences of the random nature of radioactivity. You can verify ok or not by running a Poisson check in GeigerLog https://sourceforge.net/projects/geigerlog/
Comparing different counter readings can be tricky. To which other counter(s) are you comparing your GMC-500 readings? Which Geiger tubes are those using?
This same question had been asked very recently, answer in Reply#1 in https://www.gqelectronicsllc.com/forum/topic.asp?TOPIC_ID=10933 .
You did not mention your radio source. Chances are it has significant beta radiation?
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