How Indoor Air Quality Works

[Carl Fredrik Ahl]

Hi,

I know that indoor air quality sensors works by measuring the amount of oxygen, carbon monoxide and carbon dioxide. I know that oxygen and carbon monoxide is measured by consuming it and get the electric current from that consumption to see the quantity of the gases and that carbon dioxide is measured with an infrared sensor.

 

I wonder how the sensor can consume oxygen and carbon monoxide and then get the electric current. I also wonder how the infrared sensor gets the amount of carbon dioxide. Does it calculate how much infrared light is reflectes back to the sensor?

[swansont]

11 minutes ago, Carl Fredrik Ahl said:

Hi,

I know that indoor air quality sensors works by measuring the amount of oxygen, carbon monoxide and carbon dioxide. I know that oxygen and carbon monoxide is measured by consuming it and get the electric current from that consumption to see the quantity of the gases and that carbon dioxide is measured with an infrared sensor.

 

I wonder how the sensor can consume oxygen and carbon monoxide and then get the electric current. I also wonder how the infrared sensor gets the amount of carbon dioxide. Does it calculate how much infrared light is reflectes back to the sensor?

"Consume" in this case is having the molecule in question undergo a chemical reaction. It's done in a fuel cell, and there is a current associated with the reaction, similar to a battery reaction. the materials, and the reactions, are designed to be specific to the molecule. The fuel for the O2 sensor does not react to CO, and vice-versa.

The CO2 sensor is based on attenuation of IR light. CO2 has certain absorption bands in the IR. If you have a dual detector, you can compare an attenuated signal with an unattenuated one, and the loss is proportional to the CO2 concentration.

 

 

[Carl Fredrik Ahl]

On 11/26/2018 at 4:50 PM, swansont said:

"Consume" in this case is having the molecule in question undergo a chemical reaction. It's done in a fuel cell, and there is a current associated with the reaction, similar to a battery reaction. the materials, and the reactions, are designed to be specific to the molecule. The fuel for the O2 sensor does not react to CO, and vice-versa.

The CO2 sensor is based on attenuation of IR light. CO2 has certain absorption bands in the IR. If you have a dual detector, you can compare an attenuated signal with an unattenuated one, and the loss is proportional to the CO2 concentration.

 

 

Thx for the answer, can you plz explain how this fuel cell works more specific and how the co2 absorption bands works more specific.

[swansont]

12 minutes ago, Carl Fredrik Ahl said:

Thx for the answer, can you plz explain how this fuel cell works more specific

You should be able to google this, but...
https://www.systechillinois.com/en/support/technologies/electrochemical-sensor

12 minutes ago, Carl Fredrik Ahl said:

and how the co2 absorption bands works more specific.

Any gas molecule will absorb light that's resonant with a transition in that molecule; the electron energy states are quantized, so there is a specific energy difference between allowed states. Light that has that amount of energy is likely to be absorbed. For CO2, there are several transitions in the infrared, which are particularly well-known because it's why CO2 is a greenhouse has. So you pick one of the transitions, probably one that does not correspond to where water also absorbs, and use that the detect how much CO2 is present.

[Carl Fredrik Ahl]

14 hours ago, swansont said:

You should be able to google this, but...
https://www.systechillinois.com/en/support/technologies/electrochemical-sensor

Any gas molecule will absorb light that's resonant with a transition in that molecule; the electron energy states are quantized, so there is a specific energy difference between allowed states. Light that has that amount of energy is likely to be absorbed. For CO2, there are several transitions in the infrared, which are particularly well-known because it's why CO2 is a greenhouse has. So you pick one of the transitions, probably one that does not correspond to where water also absorbs, and use that the detect how much CO2 is present.

Thx for the answer. I looked on the link that you gave me, but I don't understand why it's not enough to only use the lead anode that get oxidesed.

So when the sensor have sent out the infrared and the C02 absorbs it, how does it get the information back? And how does it know how much C02 is in the air by doing so?

[swansont]

3 hours ago, Carl Fredrik Ahl said:

Thx for the answer. I looked on the link that you gave me, but I don't understand why it's not enough to only use the lead anode that get oxidesed.

You need to generate a current.

3 hours ago, Carl Fredrik Ahl said:

So when the sensor have sent out the infrared and the C02 absorbs it, how does it get the information back? And how does it know how much C02 is in the air by doing so?

There is a photodetector that has an output signal (voltage or current) that you measure. If it goes down, it's because there is CO2 absorbing the light, and the amount of the dip is proportional to the CO2 concentration. The values are calibrated at some point with known CO2 sources.

[Carl Fredrik Ahl]

10 minutes ago, swansont said:

You need to generate a current.

There is a photodetector that has an output signal (voltage or current) that you measure. If it goes down, it's because there is CO2 absorbing the light, and the amount of the dip is proportional to the CO2 concentration. The values are calibrated at some point with known CO2 sources.

How does the other components generate the current? Doesn't the oxygen generate current while taking electrons from the lead?

Can you please show an image or paint one where it's showed how the photodetector operates?

Edited November 28, 2018 by Carl Fredrik Ahl

[swansont]

23 minutes ago, Carl Fredrik Ahl said:

How does the other components generate the current? Doesn't the oxygen generate current while taking electrons from the lead?

Not in a simple oxidation. You just form the new molecule, and the electrons are shared. You need to have a setup where there is a current, and where you can measure it.

23 minutes ago, Carl Fredrik Ahl said:

Can you please show an image or paint one where it's showed how the photodetector operates?

Use a search engine. This information exists already.

[Carl Fredrik Ahl]

15 minutes ago, swansont said:

Not in a simple oxidation. You just form the new molecule, and the electrons are shared. You need to have a setup where there is a current, and where you can measure it.

Can you explain in more detail how this works please?

 

16 minutes ago, swansont said:

Use a search engine. This information exists already.

Ok.