## Calibrating a Figaro TGS822 sensor, by drawing…

After consulting with the boys and girls at chemicalforums.com about how to produce an ethanol gas with a 300 ppm without having to buy a lot of fancy gear and thus finding out that it was more difficult then I initially thought I have reluctantly decided that I don’t think I will be able to pull it of. There for I have decided to work with what I got. What I got is air and a datasheet.

The data sheet provided by Figaro for the TGS822 only goes down to 50ppm, however the graph looks pretty logarithmic linear to me so I decided to add the 10-50ppm part my self making a bold assumption that it will be logarithmic linear in that interval as well.

From the data sheet we get the relation between RL and RS which is a voltage divider circuit.

From the graph in the data sheet we can also see that the resistance of the sensor in air is RS (air) = R0 * 19.

If we combine these two facts we can express R0 as a relation of RS (air) and the value of RS (air) can be deduced by reading the voltage of the sensor and using the voltage divider formula.

RS (air) / 19 = R0 in my case RS (air) = 78kΩ. => R0 = 4105Ω

When we have R0 we can make a table to relate resistance (RS) to ppm by reading the scaling factor of RS/R0 from the graph for different gas concentrations.

 Rs in air = 78000 Ro = 4105,26315789474 ppm Scaling factor Rs = Ro * Scaling factor 0 19 78000 10 15 61578,947368421 10 10 41052,6315789474 20 9 36947,3684210526 20 7 28736,8421052632 30 6 24631,5789473684 30 5,7 23400 40 4,7 19294,7368421053 50 4 16421,0526315789 60 3,5 14368,4210526316 70 3,2 13136,8421052632 80 3 12315,7894736842 90 2,7 11084,2105263158 100 2,5 10263,1578947368 150 2 8210,5263157895 200 1,6 6568,4210526316 300 1,2 4926,3157894737 400 0,9 3694,7368421053 500 0,75 3078,9473684211 600 0,67 2750,5263157895 700 0,58 2381,052631579 800 0,52 2134,7368421053 900 0,47 1929,4736842105 1000 0,4 1642,1052631579 2000 0,2 821,0526315789 3000 0,15 615,7894736842 4000 0,1 410,5263157895

The TGS822 sensor is affected by both temperatures and humidity and it should be complemented with a thermistor and hygrometer so that it is possible to compensate for temperature and humidity. I don’t have any thermistor or hygrometer yet but if we use the ”calculate R0 from RS (air)” every time we start the sensor then perhaps we will also compensate for temperature and humidity, this is something further experimenting will tell.

Annons

### 8 svar till ”Calibrating a Figaro TGS822 sensor, by drawing…”

1. […] the TGS822 was what was written in the datasheet. I wrote a post a little while back called ”Calibrating a Figaro TGS822 sensor, by drawing…” so take a look at that if you want to know more about my thoughts on how to use the info in […]

Gilla

2. […] LCD display, and two sensors – one for acetone, and another for temperature and pressure. By carefully calibrating a TGS822 sensor, [Jens] was able to measure the acetone content of an exhaled breath along with temperature and […]

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3. […] plus twin sensors – individual for acetone, plus additional for temperature further force. By carefully calibrating a TGS822 sensor, [Jens] was talented to mete the acetone capacity of an exhaled breeze accompanying among […]

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4. […] LCD display, and two sensors – one for acetone, and another for temperature and pressure. By carefully calibrating a TGS822 sensor, [Jens] was able to measure the acetone content of an exhaled breath along with temperature and […]

Gilla

5. […] and two sensors – one for acetone, and another for temperature and humidity. pressure. By carefully calibrating a TGS822 sensor, [Jens] was able to measure the acetone content of an exhaled breath along with temperature and […]

Gilla

6. Where do you get a Rs/Ro in air of 19? Is it not 10.9?

Gilla

1. Haha nevermind! My mistake…

Gilla

7. Dear Jens,

I am trying to figure out how you get Rs(air)=78000ohms. Could you please provide more descriptive calculations or place where I can find this information?

Gilla

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