Air quality sensor for PM2.5 and PM10?


(Hoon Park) #21

Well... I could not call every manufacturer to find it out. Since I do not know enough about air qualify measurement methods, I just called one manufacturer (see below). Based on their input, I just guessed similar looking sensors would be for indoor use only.

Here is what I did.

If you open the following web site:
http://aqicn.org/sensor/

You will find the following two LPO Optical PM Sensors on the web page:
(1) Shinyei PPD42NS
(2) Samyoung DSM501 (http://www.samyoungsnc.com/m2/sub31.php)

Samyoung DSM501 is a copy of Shinyei PPD42NS by a Korean manufacturer. So, I just called Samyoung and asked them if I could use 'Samyoung DSM501' for outdoor PM2.5 measurement.

Their answer was this device is indoor use only and I could not use it for outdoor due to the method the device using to measure PM2.5.


#22

If they say you could they would be responsible for the device to survive outdoor conditions. Now it's straightforward; it's up to you to build a decent case. If it dies, your case wasn't decent.

With a small remark that such a case would only protect the outside. I can image that true outdoor sensors would also have sealings inside the measuring tube. Probably that theoretically lowers the expected lifespan but taken the price tag into account it still pays off.


(Hoon Park) #23

It's not just a matter of casing. I've been told by the manufacturer the sensor itself needs major changes to be used outdoor.


#24

I assume, but I stand corrected if someone else knows more about it, that this is because you can't put a sensor like this in an entirely sealed case. It needs a tube to sense the air and even with an enclosure this tube is not really moist-resistant. In particular because of that lack of seals. To overcome this I'd say you need a relatively large box where the sensor can smell open air while it still thinks it's inside. Because the box will protect it from rain and wind.

But again, if it would be decently sealed including the inside it would survive longer. But that's not the case. Why don't you just try one? Even without LoRa you could test it with an arduino.


#25

If you have a look at the open source product AirBeam, you'll see that this outdoorunit uses a Shinyei PPD60PV.

(they first use the cheaper PPD42NS and the reason is noise detection)


(Hoon Park) #26

Thanks for sharing the info. It is good to know about AirBeam.


#27

Well that price tag does explain the AirBeam's pretty high price..


#28

I did some more research on the subject. It seems that the PPD42 simply is the way to go. The GPY2Y1010 doesn't seem very useful for this application. It's does not necessarily always give wrong readings, but it's considered unpredictable since the results are between reasonably good to almost random.

I also saw tests where the same was said about the PPD42. This is probably caused by the fact that it has two signal pins while an often used wiring only uses one of them. For setups using both channels very cool results were achieved.

What is particularly cool is that these also contain scientific references, dragging away the subject from pure 'hey you guys with resistors and soldering irons, you're just playing around and we don't believe your results'. For this reason I would also not recommend the copied DSM501A. Even if it would perform similar it might raise questions you prefer to avoid.
https://aireas.files.wordpress.com/2015/05/managementsamenvattingfase1aireaseindhoven-1.pdf
http://www.sciencedirect.com/science/article/pii/S0269749115000160
http://www.davidholstius.com/

Waag society also used this for their new experiment. The first smart citizens project primarily taught them how you shouldn't do this and based on this experience they made a new attempt. It's based on WiFi but they consider porting it to LoRa (anyone knows more about this?)
http://waag.org/en/blog/making-sense-making-sensor. Also check the github link for more detailed docs. It also contains temperature/humidity and nitrogen sensors.

For that nitrogen sensor they used a more expensive sensor. I couldn't find actual prices, but think about 50-100 euro because of calibration costs. Reasons I found so far to measure nitrogen is that it's an easy proxy for dust. Interpreting this nitrogen sensor is also the reason you need the temperature/humidity because changes effect its effectiveness. But given that the nitrogen measurement makes it much more expensive than this cheap dust sensor I think when you're on a budget it makes sense to drop both nitrogen and temp/humidity.

They base their concept on the dustduino.
https://publiclab.org/wiki/dustduino
http://geojournalism.org/2015/09/dustduino-cookbook-a-brief-introduction/

.. and this is what I'm currently porting to LoRa :slight_smile:

I'll add a lab post in the near future. An indoor version seems to work pretty nice.

Summary from all links mentioned above:
- calibration is a subject that has not been addressed yet. But if you calibrate them yourself using a few identical sensors and compare them to each other your get reasonable results
- do not try to make a low power device except if your find a way for 'free' air flow. If you don't, expect somewhere in the range of 100-150mA power consumption
- take the average of 1 hour readings as starting point. Everything shorter is too unreliable. With 1 hour it reaches acceptable accuracy.
- I can't recall where I read it, but while browsing I saw multiple reports that a relatively high number of sensors (perhaps 10% or so) of the individual sensors is simply unreliable. So order at least 3 to be able to compare them.


#29

did you read this


#30

Did you read this? :wink:

Since that ppd60 is about 20x more expensive compared to a ppd42 I think it's an acceptable trade off.


#31

true, but the ppd42 seems useless to me
' The Shinyei PPD42NS was one of the first sensors we evaluated' and they have the equipment to calibrate.. we don't

and uh.. 20x more expensive ??


#32

According to your September 13th post it costs 1800 yuan which is 250 euro. The PPD42 is 10 euro or so.

Regarding the first part of your post: please have a look at the links in my post from this morning. I consider myself not qualified to make the choice. But given the results in those links by people who look better qualified to this the results seem acceptable to me. As long as you don't expect real time result, and that's exactly in line with that aircasting link. Just imagine an average in the graph they use to show the PPD42's noise.


#33

The 'thing' with AirBeam is, that they developped special firmware, in cooporation with the factory.
So you'll never get the same results if you use the open source code.. :wink:


#34

I can source sensors from this company: https://www.nano-sense.com/en/P4000/p4000-fine-particles-probe.html
Performance on paper is comparable to the cheap Chinese sensors, but these sensors are actually tested and usable for professional purposes. Prices are below €200.


(Jose Marcelino) #35

I know the Alphasense OPC-N2 is used for example in outdoor sensors around Heathrow and now also in a commercial outdoor product, the AQMesh

Price is high though, about $500.

http://www.alphasense.com/index.php/products/optical-particle-counter/


#36

My tests with the PPD42 so far were just playing around with only one channel attached and measurements per minute. It looked reasonable yet it did show noise. Now I've attached the second channel and changed measurements to 5 minute average. And then I went cooking..

Not bad at first sight.


(Arjan) #37

Just two links I found through Slack:

(Also, a Dutch health institute claims most fine dust is inhaled in one's kitchen while, and long after, cooking...)


#38

The first sensor of the maaspoort meet! project stayed in my living room/kitchen for a while. I can confirm that the effect is horrible at least considering the particle count. Opening my oven after I forgot to turn it off with a baguette half an hour in it was worse than new year's eve..


#39

#40

Please note also the work at http://luftdaten.info/feinstaubsensor-bauen/ (they have a working sensor with ESP8266)

The LoRaWan integration is missing, but the subject matter expertise in inbuilt in this one.