air pollution particulate sensor package

is the baseline. He could probably count individual particles"

That may solve a problem but it creates another.

Then the mirror has to be cleaned.

Now if this thing is allowed to have moving parts we can deal with that. In fact even a lens would have to be cleaned sooner or later but a mirror wou ld of course be worse. Emitting surface, detecting surface and then reflect ing surface. Bad enough without that reflector.

But then, that is all up to the designer. Maybe it would be better. We are still a bit scant on details until - well - whatever.

According to my reference, its serpentine ( blue, mostly ) asbestos which is the bad one, chrysotile ( white ) asbestos is relatively safe. Can you quote a source for the data ?

Hello Sir, Thanks for the detailed description, it appears that this is a large project, and would need considerable time, effort and money. There are two aspects -- detection and measurement. The first is straightforward -- a simple phototransistoe, would work as a detector - like in a smoke detector. Measurement is tough, since then your device has to be calibrated against a test bench. What is the test-bench ?

Please don't spend the time. I found a used one on eBay and I'm sure it will come with a manual.

I'll see if I can take it apart and get the actual circuit.

I'm interested to find the size range. I'll compare it with the Dylos and see if that helps.

I know the stench of burning pcb. It goes everywhere. Unfortunately, I also know the source. It is usually something I did.

It is interesting that it responds to the particles from an overheated pcb. I don't know what the size range would be, but that may be something I could try when the unit arrives and I can compare it with the Dylos.

Thanks for the time and effort you put in to answer my questions.

Very interesting. I'm sorry I didn't catch you in time to save you the effort. But now I am really interested in taking the thing apart to find out how it works. Thanks to Phil's work, we have a pretty good idea what to expect in the circuits. If those are present, it's a good lead to what's inside the box.

I'll take some pictures if I can get in without destroying it.

Thanks again. Just for fun, I uploaded 3 files showing the operation of the Dylos.

This shows a normal count in my apartment. The two counters agree to about

Here shows a higher count in a stairwell. Still very good agreement.

Here is a prototype particle filter I am working on. About 40dB reduction in particle count. That's pretty good for 0.5 to 2.5 micron particles. They are very hard to filter without a HEPA, which is very expensive for good air flow.

PS, I'm mainly interested in the left column, which shows particle count for sizes between 0.5 and 2.5 micron.

The right column shows particle sizes above 2.5 micron. I'm not so much interested in these because they don't have the same tendency to lodge in the lungs. They also tend to run about one-tenth the number of the smaller particles, so if you know one, you automatically know the other. Within statistical error, of course:)

I have no idea what the particle count would be for sizes below 0.5 micron.

There seems to be little information on the health effects, or what size ranges are filtered by ordinary PM 100 air filters. The 3M description covers a very broad range:

The health effects seem to be ill-defined. Here is an excerpt from a student lesson:

distributed in the cells. They do not appear to be encapsulated by macrophages and seem to be entering cells and transported throughout the body by other, yet unknown, mechanisms. This has significant implications for the potential health effects caused by particles in this size range."

These issues are very significant for the design of particle filters to improve indoor air quality.

Thanks for prodding me--looks like I was completely off track.

The Wikipedia page talks about chrysotile and serpentine being the same thing, and amosite and crocidolite (which I'd never heard of) as the nasty carcinogenic ones.

Of course even completely inert mineral needles will cause fibrosis if you inhale enough of them.

Whether that's enough to justify forcing millions of drivers to use inferior brake pads is a policy question. (Nowadays brake pads have to warm up to achieve their maximum effect, whereas asbestos ones didn't.)

Cheers

Phil Hobbs

That's a perennial problem with optical sensors. I once talked with a guy who made optical sensors for cracks in railway rails. Trains are _dirty_, and the only way they were able to keep their optics clean was to continuously blow compressed air out of the optical port.

Cheers

Phil Hobbs

Serpentine is California's State Rock. It's pretty, green with white streaks.

Mirror? A laser or LED shoots out light and a photodiode catches light scattered by particles. Shine a laser pointer across the room and see the dust or smoke particles... no mirror involved.

Photoelectric smoke detectors work like that.

Oh good, I was going to say that besides optical you could also pass the air though a filter and then see/weight what the filter collects it's not that fast though.

George H.

Nice pictures and especially I like the domain name! Could the metal tunnel be an electrometer circuit ? The center plate might be connected to the LMC6001, which is quite common in aerosol electrometers. What's inside the black box marked with 'CAM-003' ?

Yes, it could but I have no clue how one would measure dust accumulation using an electrometer. Besides, the forward mounts for the insulate plate uses nylon insulators, which are hygroscopic, and would leak badly if uses as an electrometer. Yet, there's a very low input current op amp on the board. If some spare time finds me, I'll investigate the patents and maybe try to reverse engineer the PCB.

I don't know. I have to go back inside anyway. I just noticed on one of my photos that I forgot to reinsert all the connectors. Argh.

Get a hybrid. Generally, the brakes last over 100K miles before needing replacement. They are only used to stop the car from below 9 MPH or so.

Jon

So, a far better way is to shoot a narrow beam of light down a dark tube, and have a sensor slightly off to the side of the beam, looking toward the source. The forward scattering of light is vastly stronger than the backwards reflection. But, it is very dependent on the particle size and species. So, you need a calibration factor for the type. This is how photoelectric smoke detectors work, and with a collimated laser that is pulsed, you can get a lot of light to work with.

Jon

If you want to count particles, you need a VERY small beam spot, so you focus a beam down to a needle point, and also focus the detector on the same spot, usually at right angles. Then, you can put this in a chamber with a mild vacuum pump, and have the air sample introduced through micro-sized tubing, like big hypodermic tube. This can focus a jet of sample air into the focal region of the source and detector. You will get microsecond pulses as the particles zip by.

Jon

You might look for "aerosol charger" related to some work we did about 40 years ago. You need a radioactive source, although the ones in home smoke detectors are probably usable. The beta particles (excited electrons) ionize the air sample, which charges the particles. These are then trapped in a filter, and the charge bleeds off to an electrometer. We smoked the filters with a soot source to make the filter more conductive, then had to insulate the filter from the vacuum system so the only path was through the electrometer. This was a bit tricky, we used a thin mylar film, IIRC. You have to use a specific electrometer op amp and one of those Victoreen glass-encased gigiOhm resistors.

Jon

You can create uniform 1 um particles with di-octyl pthalate, kind of a relative of the stuff that makes the hot butter smell at the movie theater popcorn machine. Then, you need a particle counter, as we have discussed. if you know particle size and the count in some measured air sample, then you can compute the particle density in the ambient air, by count, mass/volume and other measures.

There are other schemes for generating known particle density.

All this should be readily searchable in the air pollution literature from 40 years ago.

Jon