Weird measurements

Hi everyone,

Does anyone know how two sensor (literally 1 metre apart) have a measurement deviation of 30 %?

Kind regards,

Screenshot 2023-05-05 162805

What type of sensors? Are the readings flat on both? If only 1m apart what is the difference in location? Lots to think about.

I’m using two identical sensor, both with SDS011 and DHT22 sensors.
Location difference: the one is 1 metre above the other.

The only difference is the refresh rate of the sensors. But should that make such a difference?

It would be helpful to understand the exact values and average values. The sensor specification states a variation of 15% +/- 10ug/m^3 is possible at 50% humidity. I came up against this when trying to assess if two new SDS011s were performing within the specification or not.
I too have a difference in my collocated sensors. I believe this is due to an ageing effect in one of my sensors. I will report this more fully in a separate post.

1 Like

@Ben21 I have sensors since some years, one in the courtyard and one in the living room. They give me an idea about the air quality. As well I teached in a school how to build this sensors. I am aware about the deviation of this sensors. After using SDS011 I changed to PMS7003 because I found them less sensitive to humidity.

But, what are we talking about? If you say 30% it might be 1ppm on one sensor, 1.3 on the other. Or 10 to 13, 50 to 65, 100 to 130? I think that’s nothing which would make a big difference in air quality. One meter different hight could explain that, but even if there is no influence from the hight, the basic air quality is quite clear.

Actually there are some scientific studies I have read (sorry, I forgot where) which results are, that the measurements by this simple sensors as a cloud of sensors are of high scientific value. That is my basic understanding.

Of course, we should be aware, that a sensor can brake, get’s old, is installed in a wrong position, to get the best possible data this sensors can deliver.

Correct me if I am wrong.

1 Like

Please give me the coordinates. I will check the graphics and archives.

Map Sensor.Community

I can see no sensor now and yesterday only 1.

I just checked, now both should be there…
(Please don’t look at the PM values, they’re fine → the problem is the rel. humidity…)

Are they DHT22 Sensors?
Please replace them with BME280 or SHT30. The DHTs are crap…

Yes, DHT22. So I know what to do now… Thank you @pjg!