Any ideas on how this can be made. It has to weight less than o.5kg and measure wind speeds of 0-10knots, to an accuracy of +/-0.2. Any help would be much appreciated it’s for my school project. I can’t get to grips of how to make a mechanical input of the say a fan moving into an electrical output and the reading to be digital. Can any one help!! Thanks Rob

-- robert george (robert480@hotmail.com), December 06, 2001

Answers

The device you are building is called an Anemometer and I built one for my Physics 'A' level project, many years ago. The meter itself was made with three cups (which helps to ensure that it doesn't stall), attached to a small dynamo (I used the motor from a scalextric car). The 'digital' readout came from a galvanometer, showing a pulsing deflection. No doubt a modern meter could give you a much smoother display. The largest part of the project by far was the calibration. For this I constructed a wind tunnel, using an old cylinder vacuum cleaner and large cylinder made of cardboard. By powering the vacuum cleaner via a rheostat, the wind speed could be altered, so the calibration took place in two stages: 1 - calibrate the rheostat. Haing measured the cross sectional area of the tunnel, I needed only to find out the volume of air being pushed per unit time. For this I used a large bag of known volume and kept re-inflating it at different rhestat settings and timing its inflation. 2 - calibrate the anemometer. Now that the rheostat had been re- labelled in wind speed, it was simply a matter of producing a graph of wind speed against galvanometer deflection.

Remember, if your tunnel can't produce 10 knots of wind, get as many calibration points as you can and then extrapolate a formula from the graph you obtain.

Hope this is of some use, best of luck with the project!

-- Tony Gower-Mead (Hedgewolf71@aol.com), December 08, 2001.