This was really interesting, thanks Dave
![Clapping :clap:](https://www.eevblog.com/forum/Smileys/default/clap.gif)
. I design these type of instruments for a living, but not for Ex certification. Our stuff, as far as I know, doesn't usually go down into mines. I design hand-held particle counters and gas meters
![DMM :-DMM](https://www.eevblog.com/forum/Smileys/default/smiliey_dmm.gif)
. I found it interesting they used that DB25 connector to the battery compartment. They must be doing some form of parallel communication with that compartment to use that type of connector
![Confused :-//](https://www.eevblog.com/forum/Smileys/default/confused0024.gif)
? I've also never ripped open one of those sensors, well, because the ones I use are typically over $200 US. Some of them use a UV lamp and photo-ionization to detect gases (like volatile organics), but that doesn't seem to be the case for any of those sensors ... electrochemical maybe? And as for that gunk in the sensor, I had the same reaction as you ...
![WTF? :wtf:](https://www.eevblog.com/forum/Smileys/default/wtf2.gif)