Welcome to the Cumulus Support forum.

Latest Cumulus MX release 3.14.0 (build 3159) - 04 December 2021

Legacy Cumulus 1 release v1.9.4 (build 1099) - 28 November 2014 (a patch is available for 1.9.4 build 1099 that extends the date range of drop-down menus to 2030)

Download the Software (Cumulus MX / Cumulus 1 and other related items) from the Wiki

If you are interested in supporting Cumulus then maybe you would like to contribute to the maintenance of the Wiki? This need not take hours of your time - just a half hour here and there can make a big difference, particularly if many people are doing this. Any contributions are very welcome, whether they involve new content or editing of existing content. It will be very helpful to current and future users of Cumulus software if the Wiki is kept well-maintained and current. If you are interested then please contact forum user saratogaWX and ask for a Wiki account.

Ecowitt WH41 air quality sensor mystery

GW1000 WiFi gateway
Post Reply
User avatar
KarlS
Posts: 116
Joined: Tue 30 Nov 2010 3:01 pm
Weather Station: Ecowitt GW1003 w/AQ
Operating System: Buster Lite on Pi4
Location: Bridge Lake, BC, Canada
Contact:

Ecowitt WH41 air quality sensor mystery

Post by KarlS »

I'm very much aware that low cost air quality sensors like the WH41 have their limitations. But still ...

Here is the situation: for a few nights now I have observed unusually high AQ readings while the air quality was actually fine. I'm now trying to figure out what the reasons for these mis-readings are. First off: it's not the battery (fully charged) and not the humidity (around 70%, no snow or flurries).

211124 AQ.jpg

The Ecowitt web site states:
When the Dew Point is close to the outdoor temperature (T - D < = 2C), the PM2.5 reading will be very high (which is not the real condition). If mind, please don't purchase.
Possible, but this can't be the (only) reason, since the temperature/dew point difference was below 2°C most of yesterday morning and the AQ readings were not affected (the light green shaded areas are below 2°C difference).

Another reason – or a combination with the above – could be the temperature. False readings only occurred at temperatures below -6.5°C. But shouldn't an AQ sensor specifically built for outdoors work at these temperatures. What will happen when it hits -30°C in a few weeks' time?
And why is it happening only at night? :groan: I've been brainstoring with my wife and we now believe it's a Sasquatch (the North American version of a Yeti) lying down for the night under the sensor. Maybe some of you can find a better explanation ...

On a related issue, it would be nice to be able to set a spike limit for AQ sensors to catch errors like these:

AQ spikes.png
You do not have the required permissions to view the files attached to this post.

User avatar
HansR
Posts: 2661
Joined: Sat 20 Oct 2012 6:53 am
Weather Station: GW1100 (WS80/WH40)
Operating System: Raspberry OS/Buster/Bullseye
Location: Wagenborgen (NL)
Contact:

Re: Ecowitt WH41 air quality sensor mystery

Post by HansR »

Would people be burning their stoves at night? Smoke from wood fires are known (under favorite wind conditions) to give high levels of PM.
Hans

https://meteo-wagenborgen.nl
https://meteo-wagenborgen.nl/CMX4/index.html
Cumulus build 3149 ● Ecowitt GW1100/WS80/WH40 ● RPi 3B+ ● Raspbian 5.10.52-v7+ ● Mono 6.12.0.122

User avatar
KarlS
Posts: 116
Joined: Tue 30 Nov 2010 3:01 pm
Weather Station: Ecowitt GW1003 w/AQ
Operating System: Buster Lite on Pi4
Location: Bridge Lake, BC, Canada
Contact:

Re: Ecowitt WH41 air quality sensor mystery

Post by KarlS »

HansR wrote:
Wed 24 Nov 2021 6:46 pm
Would people be burning their stoves at night? Smoke from wood fires are known (under favorite wind conditions) to give high levels of PM.
Sure there are wood fires, but that would be much more of a problem during the day. In the evening you usually let your woodstove burn down, except it is REALLY cold. If it was wood fires I would expect a peak between 6 and 8 AM.
Last edited by KarlS on Wed 24 Nov 2021 7:28 pm, edited 1 time in total.

User avatar
dazza1223
Posts: 657
Joined: Sun 25 Jan 2015 8:41 pm
Weather Station: Davis Vantage Pro 2 plus
Operating System: Raspberry pi 4 (4gb)
Location: Worthing
Contact:

Re: Ecowitt WH41 air quality sensor mystery

Post by dazza1223 »

yeah tbt i got mine today and im sending it back as it crap i got the davis air link one for out side but this one is something like a toy :D :D :D
Have fun and keep learning

dazza :D

https://www.davisworthing.co.uk

Image

Phil23
Posts: 803
Joined: Sat 16 Jul 2016 11:59 pm
Weather Station: Davis VP2+ & GW1000 (Standalone)
Operating System: Win10 Pro / rPi Buster
Location: Australia

Re: Ecowitt WH41 air quality sensor mystery

Post by Phil23 »

Like Hans mentioned it might be directed smoke.

I was about to draw a parallel to the spike I was seeing until I saw your time scale.
Mine I believe were light leaking into the sensor chamber.

Take a look at my post on WXforums

My spike moved from morning to afternoon when I spun the sensor 180°.

Also worth noting, is that the sensor that's pictured early in the thread is different to what I see in mine.
Not sure what sort of time span that involved.

Edit:- you need to scroll back to see my early posts with graphs of the spikes.
:Now: :Today/Yesterday:

Image

Main Station Davis VP2+ Running Via Win10 Pro.
Secondary Stations, Ecowitt HP2551/GW1000 Via rPi 3 & 4 Running Buster GUI.
:Local Inverell Ecowitt Station: :Remote Ashford Ecowitt Station:

cliftonweather
Posts: 11
Joined: Sat 14 Nov 2009 12:34 pm
Weather Station: Vantage pro

Re: Ecowitt WH41 air quality sensor mystery

Post by cliftonweather »

I think you also need to look at wind speed & pressure, I find my sensor (homemade using a SDS011) does exactly what yours is doing some nights, usually when the wind is light or there is an inversion. I can only assume that any particulate matter, possibly from wood burning stoves, gets trapped at lower levels and slowly drifts to your location overnight or an increase in water droplets would have a similar effect, a slight increase in wind and the values drop.

Post Reply