TGS 2442

HELLO guys.

I have tgs 2442 CO sensor and then I was able to read its raw value from analogue read. My problem emerge when converting this analogue value into ppm value. let me explain a little bit. my circuit quite similar like this link

http://www.habitatmap.org/habitatmap_docs/HowToBuildAnAirCastingAirMonitor.pdf on page 5,

i only change its digital pin from 5-6 (in example ) to 9-10 digital pin with the same resistor value(39Kohm). it ran almost a week and resulting with stable 340 raw reading. with 7-9 Volt supply.

and I very confused right about the equation right now since I dont any standard gas or even CO gas analyzer to do calibration process n order to Resistance value at 100 ppm or else.

So, can somebody share with me the right program or step/procedur to do this without calibration. I only able to retrieve this from datasheet... for now i just use percentage as a replacement (340 - 910) => (0-100%)

RL = 39Kohm analogue read = 340

Vout = ( analogue read x 5.0 ) / 1024 Rs= ((Vc x RL) /Vout ) - RL

COppm = 100/Rs

please help me out...ASAP

since I dont any standard gas or even CO gas analyzer to do calibration process

Then sorry but you can not calibrate the sensor and you will not be able to get it to give you an absolute reading.

Calibration involves putting it in a known gas concentration and seeing the reading. Then using that to calculate an unknown concentration from a reading. Without a known gas concentration this is impossible.

thanks for fast reply,

but can you explain little more why I cant get the actual ppm reading without calibration. I only know that as we dont know the actual concentration of CO, then it is impossible to the R0 ( 100 ppm ) right..

please explain i need to know why its impossible ?

The act of calibration is seeing what your measuring equipment gives for a known input. If you do not have a known input therefore by definition you can not calibrate.

http://en.wikipedia.org/wiki/Calibration

with that problem..im guessing I just convert those raw value of minimum and maximum (340-910) into percentage via map function, since I run this circuit in a home made bottle full of smoke source.

its the a least thing I could do right now.. =(