Need air flow sensor for air flow measurement system

• Sep 9, 2006

• #1

E

ex4

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wind flow sensor

Hello,
i need to build a fully electronic air flow measurement system with speed from 0-45m/s, so anybody can help me about the design??
i want to connect it to my AVR ATMEGA16
i've search for commercial sensor but he price is nuts
thanks

 

• Sep 9, 2006

• #2

K

kender

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Re: Air Flow Sensor

Wow! That's a one fine project!

Look at the:
- Pitot tube
- Hot-wire anemometer
- (Ultra)Sonic anemometer

All of the above devices have no moving parts, so they can potetntially be made cheap.

 

• Sep 9, 2006

• #3

A

aland

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Re: Air Flow Sensor

Easiest is to use a couple of transistors, one placed in the Airflow and one shielded to pick up environmental temerature.

This will give a differential voltage due to self heating, that will be directly proportional to square of wind speed. Transistors are *real* cheap and not prone to physical damage.

Amplify with an op amp and feed into your chips ADC. Do all calibration in software.

 

• Sep 9, 2006

• #4

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ex4

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Re: Air Flow Sensor

Aland, do you have any schematic using that system??

Added after 56 minutes:

hey, i got this circuit from EDN, bu i'm confused about setting the maximum air flow measured, since i need more than 45m/s.
anybody can explained to me how??

 

• Sep 9, 2006

• #5

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SolarTorch

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Re: Air Flow Sensor

Hope the following paper can be useful for you.


"3D Out-of-Plane Flow Sensor Array with Integrated Circuits"

**broken link removed**

 

• Sep 9, 2006

• #6

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ex4

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Re: Air Flow Sensor

wow, that's mighty high tech :|:|
not a simple as i thought

 

• Sep 9, 2006

• #7

A

aland

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Re: Air Flow Sensor

It looks like that circuit is generating a wind speed to frequency output.

I'd tap off the output of the first Op Amp. Else I'd go looking for a simpler schematic that generates voltage output directly.

As a plus on this schematic if the sensor is a reasonable distance from your uC a frequency output is less subject to noise or attenuation.

I searched the site you mentioned using 'anemometer' and got this one thats linear (no calculating or lookup tables in your software)

their actual article is hxxp://www.edn.com/article/ca243221.html?ref=nbsa&text=anemometer

 

• Sep 10, 2006

• #8

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Re: Air Flow Sensor

Hi EX4 , have you considered using a PC powresupply muffin fan as a wind speed sensor?
with minor alterations it is capable of outputting a digital signal proportional to the wind speed.

 

• Sep 10, 2006

• #9

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newelltech

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Re: Air Flow Sensor

willib said:

Hi EX4 , have you considered using a PC powresupply muffin fan as a wind speed sensor?
with minor alterations it is capable of outputting a digital signal proportional to the wind speed.

Click to expand...

Excellent suggestion. Some of the newer fans have a built-in tachometer output, so no alteration would be needed. The only problem is that it's mechanical and would need more maintenance (bearings, etc) to keep it's accuracy.

 

• Sep 11, 2006

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Re: Air Flow Sensor

The alterations i've done were to remove the armature while keeping the circuit board and the hall switch intact , and connecting a two 10k resistors across the spots where the coils were connected.
this elininates the cogging caused by the magnets attrattion to the armeture , enabling it to spin freely , and if you can find one with ball bearings ( a lot of them are) then maintenance isnt a problem
also it even works on 5V so the output signal is essentially digital

 

• Sep 11, 2006

• #11

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ex4

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Re: Air Flow Sensor

well aland, my schematic from EDN just the ancestor of that one you got there
my question is, how can i make it to measure more than 30m/s???
and about the muffin power supply,i'm not so in fond of it :|
since i'm avoiding physical kind of design in the sensor part

 

• Sep 11, 2006

• #12

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aland

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Re: Air Flow Sensor

Looking at the circuit, set VR2 to its maximum,then adjust VR1 to zero the output, then calibrate R2 back to give an output with the range you want. If needed increase the value of VR2 (but I wouldn't go over 10K). Q3 and VR2 determines how much extra current is injected to heat Q1.

Just keep in mind the larger wind speed measured the less resolution you'll be able to measure.

The whole circuit would cost about $5 bucks to build - with PCB, so I'd play with it.

 

• Sep 11, 2006

• #13

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ex4

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Re: Air Flow Sensor

well, that's explain everything
now i'm convince in building it, i like the simplicity of the circuit
and most of all it works very well considering the component.

 

• Oct 13, 2006

• #14

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Re: Air Flow Sensor

if u dont need accurate method then here is one....
connect a small fan to a toy DC motor...due to shaft rotation a dc voltage will be developed....construct a table ...by comparing it with known values (previously tabulated ones) u can get it....