Hi everyone,
I’m hoping someone here has run into this before because I’m honestly a bit stuck and not sure what I’m doing wrong.
I’ve been using my GMC-500+ for about a year now, mostly for background radiation monitoring at home. It’s been pretty stable the whole time — usually hovering around 0.10–0.18 µSv/h with very occasional small spikes, which I assumed were normal.
A couple of days ago, I updated the firmware to the latest version from the website (I followed the instructions carefully, used the official tool, and the update seemed to complete without any errors). Ever since then, my readings have been acting really strange.
Here’s what’s happening:
I’m now seeing frequent spikes up to 0.50–0.80 µSv/h, sometimes even hitting 1.2 µSv/h for a second or two
These spikes happen indoors, in the exact same location where readings used to be stable
The graph looks way more “noisy” than before — lots of sudden jumps instead of a smooth trend
If I leave the device untouched, it still fluctuates a lot, so I don’t think it’s movement-related
What I’ve already tried:
Power cycling multiple times
Letting it run for several hours to “settle”
Moving it to a different room (same behavior)
Taking it outside briefly — still seeing more fluctuation than I remember before
Resetting to factory settings
I’m starting to wonder:
Did the firmware change how the data is averaged or displayed?
Could this be some kind of calibration issue introduced by the update?
Is it possible the tube or hardware got affected somehow during the process?
Or… am I just overthinking normal statistical variation that I didn’t notice before?
One thing that concerns me is that the spikes feel too frequent compared to what I was used to. Before, I might see a noticeable jump once in a while — now it’s happening every few minutes.
If anyone else has updated recently and noticed similar behavior, I’d really appreciate hearing your experience. Also, if there’s a way to roll back firmware safely, I’d consider trying that just to compare.
Thanks in advance for any help — I’m still learning how to interpret these readings properly, so any insight would mean a lot. |
Unexpected spikes and unstable readings on GMC-500
Posted - 03/25/2026 : 00:52:07
