Low Volume Gas Flow Meter

I've been looking for an inexpensive gas flow meter that doesn't cost an arm and a leg. The flow rate I'm trying to measure is low; in the mL/min range. Everything I've found so far either won't measure that low, doesn't do gas, or it's for lab use and costs many hundreds of dollars.

Can anyone point me in the right direction?

About 1 or 2 ml/min ? That is even hard for a soap film flow meter. These kind of things are for a laboratory, and they need the best accuracy. That is why the sensors are so expensive.

What kind of accuracy do you need ? Do you need just a rough indication or perhaps 10% accurate ? What kind of gasses ?

Perhaps the best sensor for such low rates, is a thermal differential sensor in a chip. I can find MEMS or MEMSIC flow sensors for low flow rates, but I can't find where to buy them or what the price is. It seems that I run into the same problem as you.

I want to monitor CO2 offgassing from my fermenter. Accuracy is not a major concern since this is purely a hobby endeavor and it won’t even be used for control. I think it’s probably more in the 10s of mL/min. It’s a bit hard to say since all I really know is that I’m getting a bubble every couple of seconds.

It may simply be that this is a “hard” sensor problem, and I won’t be able to find it at a price that is reasonable for me.

The Omron D6F-P0001A1 seems to be a normal flow sensor. You can find it at omron.com and you can buy it from mouser.com. I think it can only be used with dry air.

You could try this question on a forum for beer brewing.

Are the bubbles composed only of CO2 (or mostly)?

If so - and this may not be the answer you want, but it might be cheap to do - since you have mentioned that you can see the bubbles - then a camera could as well.

Place a camera above the vat to observe the bubbles. Then apply some machine vision algorithms to it - perhaps using Python and OpenCV (or something similar - RoboRealm would be a good choice if you are using Windows); you'd have to do some edge detection, and some kind of contrast filtering to only get the bubbles and nothing else - then some kind of blob measurement (and isolation, maybe) - so you can determine when a bubble occurs, just how much gas was in the bubble (when it "pops"). Assume a bubble is a half-sphere with a diameter that of the bubble.

Not a perfect nor accurate solution - but it would be relatively cheap.

The Omron sensor looks like it could work, thanks! I probably should try a brewing forum.

The computer vision technique is a very interesting idea, but the shape of the airlock would make defining the geometry of the bubble very difficult. I might be able to analyze the volume of the bubble cap, though. This is an intriguing suggestion!

A capacitive sensor has been mentioned in another thread. It might be possible to detect/count water/gas movement in the bottom bend of an air lock. Leo..