How to do optical analysis for gas sensor

[istemihan]

Hi, I am a newby here, just registered today. I am not sure if this website is the right place for my question, however I am desperate to do anything right now.

Question is this. I am assigned to develope a gas sensor module. This gas sensor works with IR(infrared) sensor and an accor(contains all the wavelengt of blackbody spectrum). The light is sent by the accor and an IR detector receives only a light has exact wavelength. But this system has to be in a very reflective tunnel. on the one end of the reflective tunnel, accor is placed and on the other one, IR receiver.

So do you know any simulation program which could help me to simulate density and the spectrum of light on all points in he tunnel? If you could help or suggest me anything I will very appreciate it. Thank you already.

 

[IRstuff]

What's an accor?

Any optical design software will be gross overkill for what you claim to be doing. Why do you care what's happening in between? How did you filter out the one wavelength?

TTFN
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[istemihan]

Hi, Thanks for the reply.

Accor could be an incandescent or a bulb. Sorry for mistranslation. So you say it is unnecessary to simulate it. But, in one scenerio, we might have to use mirror and change the direction of the beam. It could be Z shape or W shape. In that case, do we still not need simulation?

I was thinking that could be uncesessary if we calibrate the sensor well and do calculations precisely by reference receiver though. However, my employee loves details.

Filters are embedded on the receiver. We are thinking of thermopiles to use as you can see in the picture attached. Red and green screens are filters upon the thermpiles. One is 3.91 um pass filter as reference and other is 4.26 um pass filter for CO2 detection.

 

[IRstuff]

Are they separate detectors as well? How do you calibrate them against each other?

What kind of openings are there to introduce the gas? Are there lenses or optics anywhere? Otherwise, since you do have a reference, then you don't really care much about the particulars of the optical system, since you are ultimately going to take the ratio of the CO2 to reference? Note that even in such a short path, the atmosphere itself has CO2 to start with, so you will need a double reference, once with no extra gas, and once with.

TTFN
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[istemihan]

Yes you can think them as seperated receivers, but their grounds are common. Actually, you will see the datasheet of a simple dual thermopiles, you will understand the concept:

http://www.heimannsensor.com/Datasheet-3a-Dual_Quad_rev2.pdf

Calibration will be done in a clean room or a clean tube or something like that for referance detector. Once you know the dynamic behavior of the referance you can calculate the other detectors real loss and so the density of the initial gass. The explanation for calculation is a little complex but I can say that it is related to gas density and temperature of the envronment.

Gass will be introduced via holes on the tunnel. You can understand the concenp by looking this simple drawing attached. Actually, we are on the beginnig of the design process so we do not know if we will need mirrors or lenses. Actually, thats why I want to listen from experienced engineers. What do you say? We need the simulation or don't?

Best Regards.

 

[IRstuff]

Perhaps you should look at:

http://www.ti.com/lsds/ti/analog/webench/sensors-overview.page

and

http://www.ti.com/lit/an/snaa207/snaa207.pdf

TTFN
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