# how to get a flow rate of a gas CO

#### kamel2913

Joined Mar 6, 2015
43
Hi guys,

I'm working on a project and I'm using a MQ7 CO gas sensor to mesure car CO gas emission, the output of this sensor is in PPM, I'm updating the measure of the car emission every 4 to 6 seconds, and I'm getting a chart like this (see the chart attach), ok now I want to get from this chart the rate flow (every second) and the whole quantity of emission, I want to get it as precis as possible.

To get the flow, there're two ideas in my mind and they both gives me a diffrent results, either I do the output of the sensor (Y(i)) divided by the time between this value (d(i))and the previous value (d(i-1)) or should I do the value of the output minus the previous value of the output divided by the time between the two value.

so in nutshell :

either I do this : Y(i)/[(d(i)-d(i-1))]

or : [Y(i)-Y(i-1)]/[(d(i)-d(i-1))]

if there're any other physical equation or way to get this I will be very happy to learn!

Thank you so much for your time & sorry for my English.

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#### MrChips

Joined Oct 2, 2009
27,088
Neither of your ideas will work. In order to measure flow you need a flowmeter.

#### kamel2913

Joined Mar 6, 2015
43
Neither of your ideas will work. In order to measure flow you need a flowmeter.
Hi, thanks for your reply, fo you have in mind any sensor refrence that can help me?

#### Hymie

Joined Mar 30, 2018
1,090
As you can imagine, measuring the flow rate of extremely hot gases is not easy.

This link shows Daimler-Chrysler using a bag volume method, even so this must be quite tricky given the large flow volumes and temperatures involved.

https://www.sae.org/publications/technical-papers/content/2005-01-0686/

I have used such a method to determine the flow rate of an electrical enclosure ventilation fan.
In its simplest form, the volume of a light-weight plastic bag is measured, the bag is then attached such that all the fan exhaust air is inflating the bag. The flow rate is then the bag volume divided by the time taken to fully inflate the bag.

Of course this method (plastic bags) could not be used on hot vehicle exhaust gases.

I suggest you consider measurement of the engine air intake and investigate factors that would need to be applied to correct for the increased gas temperature and fuel intake, in order to estimate the exhaust flow rate.

#### kamel2913

Joined Mar 6, 2015
43
As you can imagine, measuring the flow rate of extremely hot gases is not easy.

This link shows Daimler-Chrysler using a bag volume method, even so this must be quite tricky given the large flow volumes and temperatures involved.

https://www.sae.org/publications/technical-papers/content/2005-01-0686/

I have used such a method to determine the flow rate of an electrical enclosure ventilation fan.
In its simplest form, the volume of a light-weight plastic bag is measured, the bag is then attached such that all the fan exhaust air is inflating the bag. The flow rate is then the bag volume divided by the time taken to fully inflate the bag.

Of course this method (plastic bags) could not be used on hot vehicle exhaust gases.

I suggest you consider measurement of the engine air intake and investigate factors that would need to be applied to correct for the increased gas temperature and fuel intake, in order to estimate the exhaust flow rate.
Hi Hymie, Many thanks for your time and answer, I see, may I ask you if it's wrong to calculate the concentration produced per second instead of the rate flow, and that by summing up all the increase PPM in the chart ( chart in the bleu) than divided it by the green period, so I will get how much PPM produced per second, I don't have much knowledge in chemistry and physics, so I'm sorry if my question appear a little bit stupid.

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#### jpanhalt

Joined Jan 18, 2008
11,088
Can you clarify the temperature and relative humidity of the gas mixture you are measuring? Mention has been made of hot exhaust gas. That sensor is not usually used in that environment.

At nominal temperatures with gases of relatively known composition, you can use a hot wire to measure flow rate.

#### kamel2913

Joined Mar 6, 2015
43
Can you clarify the temperature and relative humidity of the gas mixture you are measuring? Mention has been made of hot exhaust gas. That sensor is not usually used in that environment.

View attachment 156722

At nominal temperatures with gases of relatively known composition, you can use a hot wire to measure flow rate.
Hi there, ok Thank you so muh, I think I have found the sensor I need it's a hot wire FS5.0.1L.195, that would work for me I think.

#### BR-549

Joined Sep 22, 2013
4,928
Where do you have the CO sensor mounted......have you measured the temp of the sensor? Does temp very with motion?

#### kamel2913

Joined Mar 6, 2015
43
Where do you have the CO sensor mounted......have you measured the temp of the sensor? Does temp very with motion?
in the Car's Exhaust system , yes the temp change when there're a lot of smoke.

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#### BR-549

Joined Sep 22, 2013
4,928

#### Hymie

Joined Mar 30, 2018
1,090
You might find once the hot wire flow sensor is covered in exhaust crud, that it no longer works.