The 48 hour burn in of both sensors has now been completed and I have been able to do some initial measurements of the sensors characteristics. So far both the sensors does seem to react to acetone but that is not rely surprising. The sensor resistance range (Rs) does vary a lot between them, the TGS822 has a span of 300Ω – 78 kΩ while the MQ-3 has a more narrow resistance span of 22.6 – 1.5 kΩ. Since I am interested in low concentrations of gas I want to have as wide range as possible and have therefor selected to go on working with the TGS822 sensor first.

One aspect of the sensors that makes the them a bit annoying to work with is that they have a warmup period of 3-5 minutes before the resistance has stabilized it self and they also take quite a long time to return back to the initial value after a measurement has been done. The time it takes for the sensor to reset is related to how high the gas concentration was.

Figaro TGS822

• Rs = 78 kΩ, 22 degrees C, 20% Humidity, normal air.
• Rs = 300 kΩ when blowing into the sensor.
• Rs = 300 kΩ after ail polish remover puff.

A good value for voltage divider resistor with the TGS822 should be 10k. A 10k resistor would give an output to the Arduino of just above 0.5 V at no gas detection up to a full 5 V for high gas concentrations.

Reset time, Resistance in kΩ/time after acetone puff.

• 32 kΩ after 7 minutes
• 41 kΩ after 10 minutes
• 51 kΩ after 13 minutes
• 54 kΩ after 15 minutes
• 58.4 kΩ after 18 minutes
• 62 kΩ after 21 minutes

MQ-3 sensor

• Rs = 22.6 kΩ, 22 degrees C, 20% Humidity, normal air.
• Rs = 15 kΩ when blowing into the sensor.
• Rs = 1.05 kΩ after ail polish remover puff.

Reset time, Resistance in kΩ/time after acetone puff.

• 10.5 kΩ after 8 minutes
• 14.5 kΩ after 16 minutes
• 17.9 kΩ after 26 minutes
• 18.9 kΩ after 31 minutes

Blowing at the sensor with clean air did not seem to have any effect on the reset time.