Chris Jones <
lugnut808@spam.yahoo.com> wrote:
On 16/03/2024 6:09 am, Phil Hobbs wrote:
Chris Jones <lugnut808@spam.yahoo.com> wrote:
Hi Phil,
You might find this interesting:
Design of a low-cost, open source, condensation particle
counter("OpenCPC") - EAC 2023
https://www.youtube.com/watch?v=1mmV81vFGys
Any ideas on ways to make it easier to build, or to count a higher
fraction of the incoming particles?
The end application is fit-testing of respirators, similar to the TSI
Portacount but cheaper.
BTW I already recommended your book to them, and pointed out that you do >>> consulting...
Condensation nucleus counters are old friends from my crud detection days
30 years back.
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.
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
I think they are using isopropanol, I guess because it is more widely available.
Dunno how well that would work.
I'm pleasantly surprised that they are getting a huge signal compared to
the background and noise.
CNCs turn everything into 1-2 micron boulders, which is the point of the exercise.
I'm waiting (and pestering them gently) until they upload their design
files, as it's meant to be open-source.
--
Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics
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