[throwaway8451]

These measurement devices have a limited lifetime and I think it is really the intake of dust and dirt that limits how long they can be used. That's why they're not running continously but for some seconds every few minutes (because flowing air will carry dust much more easily). If it's clogged up with dust or dirt, it really might be at end of life. I keep the electronics and sensor of mine in a closed box if I am not operating it.

[gsich]

Yes. But I can't see that, the sensor will still output values regardless of being clogged up. Not sure if I can open the device without destroying it, haven't tried. The power runs all the time as long as the USB cable is connected, but it's only a Serial-USB converter.