I’m interested in obtaining a multichannel gas sensor v2 for environmental monitoring. However, it is not clear to me how should I calibrate the sensor.
The wiki contains some general calibration curves, and shows the effect of humidity and temperature, but this is not enough.
Therefore I’d like to ask the following questions:
Is the software already takes into account the calibration curves?
Regarding temperature/humidity curves, does the software is ready to accept temperature/humidity data in order to better calibrate the sensors? In that regard, could one just simply add a temperature/humidity sensor (e.g. BME680) to obtain more precise readings? (e.g. via the WIO terminal?)
If there is no embedded calibration software, do you have the data from the calibration curves in a table?
We also consulted sensor manufacturers about calibration.There is no specific calibration table for the sensor, only a curve of temperature and results obtained from multiple experiments.The manufacturer told me that this curve is linear.But I can’t give you the exact slope, because it depends on the pressure and altitude in different regions. If you want to use it in real products, please do many experiments and do calibration yourself.
This is not for a commercial product, it is for educational purposes.
I don’t have the means to do the experiments, I really needed that chart, because if it is going to change with temperature and humidity, as seen in the figures, you need to include that in the calibration so you have a decent offset of the bias.
Can you explain me how are you calibrating the sensor in the software?
What is this voltage number that the program outputs? I need to know how it correlates with the calibration plots from the wiki…the ppm numbers are too high!
No. I’m taking my measurements in a very low pollution area. I just need to know what to do to calibrate the sensor, if anything. And I need to know the meaning of the voltage.
I had a discussion with SEEED. Unfortunately, in the case of the multichannel sensor they don’t know what they produce. Their sketch means nothing, except the voltage values. These big readings are NOT ppm or ppb. There was absolutely unadequate email conversation between me and the SEEED service engineer (for example he said, that these “ppm” of hundreds are normal LOL! It is not normal! It is deadly! I had a conversation with WINSON, the company which produces the four sensors of the multichannel sensor. Because the WIKI of the SEEED is not full (NO2 calibration curve is missing), and they said nothing about that, I asked WINSON to send me the curve. After that I wrote a sketch which reads the CO and NO2 sensors and I have made the calibration of the sensors. Actually, the sensors are enough accurate (more than I expected before the tests). If someone is interested about how to read REAL ppm from the sensors, please write me to vcoder(at)abv.bg. SEEED, take this on mind! You sell not so cheap sensor! Please inform yourself, correct your WIKI and show to your customers how to operate with that sensor!
So Having many YEARS of experience with Process Gases and the devices use to test, calibrate and sample their respective gas types.
One must learn first you are either using it to Sample a Know gas and it’s presence(presence detector) or obtaining a Sample for Gas Quality and Purity as well as LEVEL(PPM & PPT)these days. This is all done via separate and distinctive procedures. There is NO such thing as a PLUG and PLAY or a One Size fits-all gas sensor. PERIOD.
Anyone embarking on this path better know and understand, any Sensor should be (ZERO) calibrated as Well as (SPAN) calibrated.
if you follow those processes you will be successful in obtaining accurate Data and valid test results.
ALL sensors have a “dry-down” time
Normal for some sensors, and at which point a Zero Gas calibration should be conducted first. (sample a Nitrogen Gas, as Purge gas)
after Obtaining a Closest to Zero result note the output. it won’t be ZERO. (first offset reading)
Next would be the (SPAN) calibration , sampling a known PPM Sample calibration gas. NOTING the Output.
You do this at different temps and flow rates and pressures then you have your calibration curve to apply to all of your DATA and do the CURVE fitting your self, or you just rent a GAS chromatograph
These are Educational Sensors meant to teach and create lower accuracy basic readings, some are only presence detectors. It’s up to you to do the extended research , even in the OP’s first post you can see after he was put in touch with the Manufacturer , he got educated on how to use it and his assumptions were just that.
Seeed is Awesome for even bringing this stuff no matter how sparse the Documentation is or how lacking a big SPOON for some aspiring makers the WIKI has.
I note and Notice the OP doesn’t provide any follow up info or share his findings instead he wants you to email him… B.S. imo. We are all here to share the info we gleen, Hence “discussion forum”
AMA on it I’ll do my best to get you straightened out.
IMO this is a Expanding and fast growing field look at the environment ever so changing. Good Science is always needed. and hard work too.
imo. We are all here to share the info we gleen, Hence “discussion forum”
PJ 