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VOC Sensor Update (TGS8100)
Hi Guys,

Sadly, after 4 months of testing, i am not able to create a procedure for calibrating the TGS8100.
With CO2 measurement, when you leave the sensor in your house and ventilate well, the indoor CO2 equates to the outdoor CO2 at least to a very big degree.
With the TGS8100, this is not the case, maybe due to the gases it measures. 
When it was indoor for few days, with nobody at home - the values were just dropping down, so the gases increase.
As soon as i got back and opened the door - the values jumped up again. Which was quite interesting.
Yet, still i was not able to get it to work better than +/- 20%. Then i took all 6 sensors out and they became quite weird.
Typically they increase their resistance in free air, reaching 300 kom maximum as per spec. And basically you measure the relation of the maximum resistance in free air, to the resistnace in indoor air (typically 30-40k), and based on this there is a chart to derive ppm. Yet 3 of the 6 sensors went quite higher, and sadly even a bit disproportional. So I am not really sure how to interpet this. I am going to contact the manufacturer next week. I highly doubt that they are going to tell me something useful.
So all in all, while it was interesting testing them out and trying to make sense of the results, it looks like this is going to be a waste of time and money

On the picture below you can see how their resistance changes. The two higher slopes on the left, are two days where the sensors were indoor, and the window of the room was open the whole day.
The next two are two days where i put them all outside. You can see how the light green one, jumps to almost 1200k the sencond day, while it was just max 700 the first day.

Interestingly - the other 3 are looking good, though - the second day out their readings were 10% higher than the first day.

So this is definitely nothing that i had expected, so unless i get some useful hint from the manufacturer i plan to cancel the VOC sensor research
And rather focus on battery operated sensors, noise or something else new Smile

[Image: 27258123-488631dc-53fa-11e7-961b-eaf19381c206.png]

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