Dual sensor circuit design

[miteehigh3]

I am in process of building a device that will require two sensors. The first sensor is sensitive to ethanol and also to carbon dioxide and the second sensor is sensitive to only carbon dioxide. The second sensor will be used to discriminate against the carbon dioxide that the first sensor is sensitive to.

Both sensors will produce a lower resistance to the individual components that they are sensitive to. How would I design a circuit that allows the carbon dioxide sensor (sensor 2) output to remove the effect from the first sensor (ethanol and carbon dioxide complex)?

Thank you for any help that you can provide.

 

[simonbramble]

If I were you, I would determine the output voltage that each sensor gives for a given exposure to carbon dioxide only. Configure 2 amplifiers (one per sensor) with different gains so that each amplifier gives the same output voltage for the same exposure to carbon dioxide. Then feed these into a differential amplifier (a standard op amp should do - LTC6240 is ideal). See FIG 4 here:
https://en.wikipedia.org/wiki/Differential_amplifier

You should then be getting zero voltage output for the same exposure to carbon dioxide. The differential amplifier should then output a voltage proportional to ethanol only (and each amp on the front end will give outputs of ethanol + carbon dioxide and Carbon dioxide only)

You might need to put each sensor into a bridge configuration to get an output voltage from them

 

[miteehigh3]

Thank you for your information. Much appreciated.