ping Phil Hobbs

Condensation nucleus counters are old friends from my crud detection days

They work by pulling air through a saturated vapor of n-butanol and then into a regular dark field particle counter. That’s why the sample volume is smaller—you have to limit the alcohol consumption.

The cool thing about them is that the particle radius grows linearly with time, up to a micron or so. The rate of collection per area is constant until the growing droplet starts depleting the local concentration of butanol.

That lets you detect particles down to 10 nm or so, but obliterates any size information.

Cheers

Phil Hobbs

Their design is a bit unusual in that they do not illuminate the whole stream of particles, the laser beam is smaller, and this means that they miss some particles and the fraction that they miss is size-dependent.

I think they are using isopropanol, I guess because it is more widely available.

I'm pleasantly surprised that they are getting a huge signal compared to the background and noise.

I'm waiting (and pestering them gently) until they upload their design files, as it's meant to be open-source.

All laser particle counters are like that. For a given particle size, operating in the shot noise limit, you can interrogate a fixed volume per joule of laser energy.

You can apportion that as a big beam and slow motion, or a smaller beam and higher air speed, but you get the same volumetric rate until you find yourself limited by some other noise source. Johnson, amplifier, and 1/f are the usual culprits.

Cheers

Phil Hobbs

Dunno how well that would work.

CNCs turn everything into 1-2 micron boulders, which is the point of the exercise.