[ale] Sensor nuts

[Alex Carver]

The somewhat less expensive solution if you're willing to rent is a
particulate filter and analysis package.  You are sent a small vacuum
pump with a filter on the end of the hose.  It draws in air which
becomes trapped on the filter.  Then you ship the filter away and later
you get a report on the particulates.  It's not instant but it's accurate.

As for fans, what you're looking for is a known volume of air to go
through the sensor.  All of the various standards specify number of
particles per unit volume of air.  The sensor has to be built to deal
with moving air for it to work.  Most laser sensors do use a forced air
system and the laser spot is small enough to capture various particles.

Unfortunately for the Sharp sensor, forced air would probably cause more
issues than it solves.  it still can't resolve small particles and
forcing air through that particular sensor might actually push the
detection limit higher (meaning it starts to miss 1, 2, 5 micron
particles entirely).  Since it's using diffuse light illumination a high
speed particle will be missed.  You're still better off with the first
link I sent, it's just a $50 sensor but it will give you more data.

On 2016-06-08 12:43, Chris Fowler wrote:
> You came to the conclusion I did initially.  I even searched to see if I could 
> rent a 5K device.  It is still on my radar.
> 
> forced air is an interesting comment.  The application notes for the Sharp do 
> not talk about forcing air.  I thought about running a small fan at 5v at 
> reduced speed to imitate breathing via nostrils.  That would create some movement.
> 
> I'm redoing a bathroom and about a week ago an idea popped in my head suggesting 
> a powered respirator.  Masks suck.  I sweat wearing one.
> 
> 
> 
> 
> 
> --------------------------------------------------------------------------------
> 
>     *From: *"Alex Carver" <agcarver+ale at acarver.net>
>     *To: *ale at ale.org
>     *Sent: *Wednesday, June 8, 2016 3:03:11 PM
>     *Subject: *Re: [ale] Sensor nuts
> 
>     It's an interesting device but I think it's lacking for what you're
>     really attempting to do.  The data sheet from Sharp does not make any
>     claims about the final particle size that it can potentially detect (not
>     measure, that's an important distinction).  It mentions just "smoke" in
>     the datasheet which is probalby going to be around 1 micron diameter for
>     average smoke.  However, there are a range of particulates in the air
>     that are smaller than 1 micron (the EPA tracks PM10 and PM2.5 which is
>     10 microns and smaller and 2.5 microns and smaller).
> 
>     For a short list:  Household dust has an expected range of 0.05 - 100
>     microns, atmospheric dust (important if windows are open) ranges 0.001 -
>     40, wood smoke is 0.2 - 3, rosin smoke (from solder) is 0.01 - 1,
>     tobacco smoke is 0.01 - 4, and anything combustion related including
>     cars is 0.01 - 2.5.
> 
>     The problem with this detector is that it can't distinguish size, only
>     density.  So 10 particles at 10 microns diameter is the same as 1
>     particle of 100 microns or 100 particles of 1 micron (roughly).  It's a
>     reflectance measurement so it relies on the total cross section of all
>     particles in its field of view and makes an aggregate measurement.
> 
>     This sensor will basically be able to tell you "this room is % dusty"
>     but it can't say "there's lots of floating hair combined with very fine
>     pollen or soot" or "your chimney flue is not open enough and causing
>     some smoke to back up into the house".  It's also not a forced air
>     sensor so sampling is not going to be right since it will depend on dust
>     settling into the detector opening.
> 
>     What you actually need is a forced air, laser based sensor that can
>     distinguish sizes.  There are many around that could work within a
>     budget and give you some better numbers.    Here is one I found with a
>     quick search of "laser particulate sensor":
> 
>     http://www.dfrobot.com/index.php?route=product/product&product_id=1272&search=SEN0177&description=true
> 
> 
> 
>     Or you can get more commercial versions that have more bins for the
>     particle sizes:
> 
>     http://www.nano-sense.com/en/P4000/p4000-fine-particles-probe.html
> 
>     http://www.sens2b-sensors.com/en/item/pm2-5-laser-particle-sensor-module-for-air-purifier-application
> 
>     Just keep searching for other options but make sure it bins into various
>     sizes instead of lumping everything into a single measurement.
> 
> 
> 
> _______________________________________________
> Ale mailing list
> Ale at ale.org
> http://mail.ale.org/mailman/listinfo/ale
> See JOBS, ANNOUNCE and SCHOOLS lists at
> http://mail.ale.org/mailman/listinfo
>