On Thu, 16 Aug 2018 23:10:13 -0700, mike wrote:
Based on your experience, I think I know how it works.
I know how it is suppose to work. That's in the literature for the
various sensors found in the mess of links I provided. What I don't
know is what this particular device can do. It is not a scientific
instrument, show no sign of calibration or testing, and seems to be
made for the paranoia market.
The question is not how, but what is this particular model
Nikken 1394 actually measuring
in terms of particle dimensions.
Phil Hobbs explained most of that. However, it looks like all you
want is a number. I don't have specs on the specific model light
scattering box inside the unit, but I think this one is close:
https://www.digikey.com/product-detail/en/sharp-socle-technology/GP2Y1010AU0F/1855-1012-ND/720164
https://media.digikey.com/pdf/Data%20Sheets/Sharp%20PDFs/GP2Y1010AU0F.pdf
The data sheet does not specify the range of detectable particle
sized, but does mumble:
GP2Y1010AU0F is a dust sensor by optical sensing system.
An infrared emitting diode (IRED) and an phototransistor
are diagonally arranged into this device.
It detects the reflected light of dust in air.
Especially, it is effective to detect very fine particle
like the cigarette smoke.
In addition it can distinguish smoke from house dust
by pulse pattern of output voltage.
Ok, so it can detect cigarette smoke and house dust. Digging through
a handy table of dust particle sizes at:
https://www.engineeringtoolbox.com/particle-sizes-d_934.html
I find: microns
Burning Wood 0.2 - 3.0
Fly Ash 1 - 1000
Combustion 0.01 - 0.1
Household dust 0.05 - 100
Smoke from Natural Materials 0.01 - 0.1
Nothing found for cancer sticks (cigarettes).
House dust and fly ash have too wide a range of particle sizes to be
useful. That leaves burning wood, combustion products, and smoke from
natural materials as useful ranges. Therefore, I would guess(tm) that
the Nikken can detect particles from 0.01 to something less than 3.0
microns. That fits nicely with most of the smoke produced by the
fires. Normally, I would verify this by simply hanging a sheet of
sticky paper out the window for a while to collect the local dust and
ash. Then, a microscope and reticule to determine the particle size
from the fires. Fortunately, the EPA has saved me the effort:
https://www3.epa.gov/ttnamti1/files/ambient/smoke/wildgd.pdf
Particulate matter in wood smoke has a size range near
the wavelength of visible light (0.4 - 0.7 micrometers)
That's well within my guess(tm) as to the detection range of the
instrument, so it should detect smoke from the fire.
There's quite a bit of information in the above EPA document on what
constitutes harmful concentrations of smoke. Methinks that's what you
should be interested in calculating, not the number or size of the
particles. The document probably explains it better than I can.
My symptoms suggest that it does a poor job on forest fire smoke
from 200 miles away.
Most areas have air quality monitoring stations with associated web
pages. This is the one for my area:
http://air.mbuapcd.org
https://sites.google.com/firenet.gov/wfaqrp-airfire-tools/
You should be able to find the approximate smoke concentration on such
a site.
Is your experience different?
I don't know. We had a few bad days were there was quite a bit of
haze from the fires. However, I didn't bother checking the
concentration with the Nikken for that fire, or any previous fires.
Is mine broke?
I don't think so. It responded normally (2000 particles/liter) when
you went outside. You might want to try my favorite test. Find a
cloth sofa or padded seat. Fire up the Nikken meter. It should read
low on the graph. Now, beat on the sofa cushions once or twice. The
meter should indicate full scale. It's quite sensitive to house dust.
Or just not suited for very small particles?
No. The particle sizes calculated by Phil Hobbs is the minimum
particle size. There is no maximum expect perhaps limited by the
input air filter. I think it's the box to the right of the fan:
http://802.11junk.com/jeffl/Nikken%201394%20Air%20Quality%20Monitor/Nikken-AQM-03.jpg
held in with one obvious screw (but I'm not sure). Blow with clean
and dry compressed air. If there's a big pile of dust inside, the IR
sensor box is probably also full of dust.
Thanks for the links. I'm sure that's all good stuff, but does it
answer the question, "what can I expect from the Nikken?"
I can't answer that directly. What I've tried to do is use data from
a similar IR dust sensor to deduce what the Nikken might do. Without
data on the sensor used, I can't do much. I was hoping that you would
dig through the mess of links and do your own research. I can only do
so much.
Should I take it apart in anticipation that cleaning it will help
measure small particles? If I can't, I should just not try to use
it for that.
Unless you're prepared to go through some kind of calibration
procedure, the best I can suggest is to have me run some kind of
detection test and compare results on your unit. I could set fire to
various common objects and hope that the type and quantity of smoke
produces is identical.
The Dylos seems to read closer to what the Air Quality websites
publish. I built a battery pack for it, so now it's portable.
Well, if you have two units, and one of them is suspect, take the
suspect unit apart as I previously suggested.
Good luck.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558