[Amps] Airflow meter

Dr. David Kirkby david.kirkby at onetel.net
Fri Apr 15 01:23:51 PDT 2011


On 04/13/11 07:24 PM, Jim Barber wrote:
> I wonder if a hand-held anemometer would have significant back pressure?

I would not think it be very significant myself.

> It's fairly easy to convert flow rate to volume if the duct size is known.
> Inexpensive units go for 20-30 USD on eBay.


My ex-boss (Prof. D. T. Delpy) used a technique for measuring air *velocity*, 
which I don't think is particularly relevant here, but I'll describe it since it 
is quite interesting. Although it used platinum wires, I suspect you could use 
copper, though I do see platinum would have some advantages.

It was used for measuring the speed babies breathed out air, so had to have 
negligible restriction on the airflow. Using a plastic bag would not have been 
very good for this purpose!

Going left to right there is:

Source of air --- > heater ---- > thermometer

1) The source of air. This was the babies mouth.

2) Heater. This is a thin platinum wire through which a short pulse of high 
current is passed. I've no idea of the temperature the wire reached, but it's 
not important to know the temperature.

3) Thermometer. This is another thin platinum wire, forming part of a platinum 
resistance thermometer. This responds very rapidly to temperature changes.

The time between heating the first platinum wire, and when the temperature 
increase was observed on the second is measured. Knowing the distance between 
the two wires and the time allows one to calculate the velocity.

> The "Bagometer" method is straightforward as well; just curious about
> alternatives.

Well, above is a curious alternative, though not very useful in this application.

I'd be surprised if this technique was not described in some medical journal by 
him, but a quick glance with Google Scholar was unable to unearth the paper.

-- 
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing in e-mail?

Dave



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