Hello everybody,

I read all posts that were about CO2/calibration etc but I still quite not get it...

I have the TGS4161 sensor. With GAIN = 1, I took some measurements in external environment and the value is approximately 1.4 - 1.5.. if we suppose that outside the medium concentration is 350ppm as you said, shouldn't the value of the reading function be 0.22 - 0.49 (V) as the specs say?

even if we find the voltage in this concentration or if the above result is correct, according to your directions we then have to set the GAIN enough for this voltage to reach ~3.3 V..
what is the formula we use to get ppm?

Thanks in advance
cheers,
Lefsp

edit: the value is now around 0.40 so I guess this is correct*
I set the gain to 7 and now normally I get 2.x - 3.2999, I will have to test it outside again

what is the formula you use to convert to ppm?



*I am really worried that there is something wrong with this Gas Board, sometimes the values go mad like -1 or 40 C temperatures (the normal is 20) for quite a long and it needs a reset to fix
the same that happened with co2 when it was showing wrong values in my first post
is this a hardware problem you think? does anybody else faced it?

Hi lefsp,

I'm not sure of having understood your problem. You mean that, after some time of taking CO2 and temperature measurements, you start to get senseless values and you have to reset the mote to get back to normal operation? That's pretty weird, could you post the code you are using?

Regarding the conversion into ppm, you have a graph of the electromotive force variation with gas concentration in the documentation of the board. You just have to subtract the voltage read from the voltage measured at 350ppm, divide by the gain set and translate that value to the graph to get the gas concentration.

Regards.

I still do not get good results

I measured the voltage with GAIN 1 in the atmosphere (lets say 350ppm) and it is around 380mV
If you say that the variation must be found in the graph then the maximun variation is around 90mv right?

that said the minimum that the sensor can measure is: 290mV

But I get values much less than this! how is it possible?

Hi lefsp,

yes, the maximum variation in the working range of the sensor is around 100mV, but this is for the working range of the sensor, between 350ppm and 10000ppm. This doesn't mean that the sensor stops working at this range, output will keep on decreasing, but accuracy and linearity won't be guaranteed out of this range (the sensor could be even damaged if it is exposed to a too high concentration).

Regards.