New Station Kenley Surrey

I think the problem is not in the SBM-20. It is enough sensitive. Is there strong electromagnetic fields around your home? This cyclicity is very strange. But really - measure the voltage that goes to the tube and check how must it be for SBM-19.

The display cabinet where my Geiger Counter is stored has LED strip lighting. It seems when I turn on the lighting the count goes up. I turn the lighting on around 17:00hrs and off around 23:00hrs. I tested it this morning by putting the lights on around 05:40 for 15min before I went to work and there is a small increase at this time and I also turned the lights off early tonight around 21:00hrs . The LED lights I think are dimmed by PWM so could this be interfering with my tube/counter.

Maybe I can try moving the tube away from the lights? I have moved it outside but the reading shot up maybe due to a long cable length.

Hm... as you know the light (even led) is electromagnetic waves... if they can increase CPM, that's mean something with the tube gone wrong or problem with signal amplifier in the counter (in my opinion). In fact radiation also is electromagnetic wave but with different wave lenght. For example - when I put the tube over my laptop and srart some game the cpm goes terribly hight probably because of hight level of processors work, not because of real radiation. Another example - when I connect the counter on battery and I touching tube everything is ok, but when I switch it on ftdi connector only and touching tube the cpm gone crazy. If the counter is connected correctly and they ( led's electromagnetic waves) change tube's measurements, then tube is defective I think. Isn't that sbm-19 tube hypersensitive? Try with another one tube (sbm-19 and sbm-20) without any led, oled etc. and take a look on results. Very strange, indeed

My guess is the EMF from the PWM is affecting the counter circuit, not the light falling on the tube. For such a small enclosure the strip lighting current ought to be small enough to use a bigger resistor instead of PWM to get the brightness you want. But didn't you say the 7 segment LED display is also dimmable? That 2-level PWM circuit may affect the counts too.

The LED strip lighting is in a very large 8ftx8ft display cabinet, my Geiger Counter is inside the cabinet and is therefore surrounded by LED strip lights on all sides. My previous tube the SBM20 I presume was probably not sensitive enough to be affected by the PWM LED strips but maybe the SBM19 is.

The 7 segment LED displays are PWM controlled but also turn off when no one is in the room or near the cabinet so most of the time they are off. The CPM increase only seems to happen in the evening when its dark.

As an experiment I did not turn the LED strip lights on last night and the CPM count did not rise. See my charts My charts with LED strips turned off 21 Jan PM

If I get time today I will move the SBM20 tube into my garage that is next to the room where my Geiger counter is situated. There is a solid brick wall between the 2 rooms so it should cut out any noise from the LED strips.

Someone needs to put this station in experiment mode or up the warning level. We don't need alerts every minute if they are erroneous. If you're unable to do it in your mode of submission maybe mw0uzo can handle it.