Ozone-sensing

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Ton_vN
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Ozone-sensing

#1 Post by Ton_vN » 10 Sep 2021, 14:10

Being interested in sensing for air quality, recently found at the website https://aqicn.org/ under title Gaia-sensors this ozone-sensor:
https://aqicn.org/air/view/products/spe ... module.pdf
All sensors applied in these Gaia-sensors seem of a category 'available & manageable for DIY'.
Anybody with practical experience for this O3-sensor, especially in relation with ESP8266/ESPEasy?

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Re: Ozone-sensing

#2 Post by TD-er » 10 Sep 2021, 15:49

A quick glance at the datasheet you linked, suggests it may be very similar to the MH-Z19 plugin.
So a quick-and-easy test could be to alter the code of that plugin to match the suggested commands and reply of the ozone sensor.

I have not tried it myself, but it looks interesting.

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Re: Ozone-sensing

#3 Post by chemmex » 12 Sep 2021, 00:03

This is electrochemical type of sensor, it reacts to the change of gas concentration in nanoampere current range, so there is a potentiostat circuit which converts current to voltage. Winsen's analog front-end has serial output but there's also 0.4-2V analog output, so you may use ADC input to read concentration.
From my experience with electrochemical sensors, it is easy to interface them with the MCU, but getting calibrated results is quite a headache. They are cross-sensitive to other gases, but most difficult part is temperature and humidity sensitivity which is quite nonlinear. So to compensate baseline drift in outdoor conditions the sensor should be better placed in a thermal chamber and the air should be normalised before measurement.

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Re: Ozone-sensing

#4 Post by TD-er » 12 Sep 2021, 09:16

You would expect the Winsen's implementation to contain temp/hum sensor and a factory calibration inside their module to compensate for that.

However I have no idea how much aging (when used) and shelf life (not used) affect the calibration.
So I guess it will be more about getting some idea of the trend of the Ozone concentration than getting actual readings which you can compare with other (ozone) sensor readings.

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Re: Ozone-sensing

#5 Post by Ton_vN » 18 Sep 2021, 10:58

TDer

;-) DIY-assembly & -application remains a headache with these sensors due to the aspects of aging & calibration.

The views in the previous messages more or less confirm my idea (in that perspective) that the lease-approach by AQICN.org may have some merit.
They deliver a complete package consisting of PMS5003+Ozone-sensors, plus BME280 as THB-sensor, all assembled&integrated in a compatible housing, and as part of the lease after 2 years of use they 'refresh' the device. Not stated, but it is a guess that a form of calibration is happening before delivery.
The price for P&P is of such magnitude that it looks that also precautions are taken for safe transfer from supplier to user.

Notes:
Interesting aspect will be for transfer of the package how much Customs-value is stated, because it is lease, not purchase.
Looking further into the future, also 'termination&return-policy' is nowhere described.

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Re: Ozone-sensing

#6 Post by Ton_vN » 23 Sep 2021, 16:11

That the Ozone-sensor ZE25-O3 has similarity to CO2-sensor MHZ19 is not really surprising, because as alternative A13-configuration they offer a version with MHZ19B-sensor: then intentional commonality of interfacing is very useful/economic.

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Re: Ozone-sensing

#7 Post by Ton_vN » 11 Oct 2021, 14:14

ZE25-O3 is easily available at AliX. by several suppliers, for prices between Euro30 and Euro75 per device.
If DIY-assembly at least you have to invent housing & airflow and interfacing.
Some further research into the characteristics of ZE25-O3 reveals that besides an UART-interface it also has an analogue output.
For application of UART protocol provided in the datasheet: no discussion on resolution etc.
With the analogue signal a provisional, experimental DIY-setup is even easier:
;) you 'only' have to solve yourself the aspect of scaling/calibration ........
You pay a price, but advantage of the Gaia-sensor A13 is that they already took care of the effort mentioned above, incl. related companion sensors for dust, temperature, humidity and pressure.

Also ZE27-O3 exists, with almost identical info & layout, with UART-interface only [price seen of Euro 30/device].

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