Folks - Looking for some ideas re how you could make a simple air flow measuring device with Arduino that didn't necessarily need any calibration. Looking at a range of say 5 - 30 metres/second. Accuracy doesn't have to be too good, say +/- 2 m/s
Most sensors should be calibrated but if you don't care too much about the accuracy, you can generally get away with using the factory calibrarion. You simply need to find a transducer (designed for air flow in your application) that outputs a voltage between 0 and 5 volts. Then, with LIFA you simply read the voltage of the analog pin and convert the voltage to the appropriate engineering units.
I was rather hoping that some clever guy had worked out some method to do this other than using off the shelf meters. I've been looking at a couple of methods, one using pairs of ultrasonic transducers either side of the pipe and another measuring the change of temperature of a heated filament in the pipe.
Most Air Velocity sensors are designed for industrial applications and most likely won't fit your budget. However, You could build a DIY air velocity sensor using two pressure taps and a differential pressure transducer. See the following link for theory.
For differential pressure you could use two barometric pressure sensors such as the following.
Differential pressure would certainly be a way to go... I'm trying to see if there is something I can do external to the pipe being monitored. So the ultrasonic idea seemed to have merit...
CFM implies fairly large volumes of air flow and suggest the use of an orifice and a differential pressure measurement.
See: <http://www.efunda.com/formulae/fluids/calc_orifice_flowmeter.cfm> for an example that uses an orifice plate and a differential pressure measurement. See <http://www.phidgets.com/products.php?category=3> for a differential air pressure sensor.
here as an article on this topic using AMS 5915 differential pressure sensor and Arduino. This pressure sensor comes with 2 nozzles and its output is digital.