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Making a Sensor

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David Bumby 6499 Making a Sensor I first came up with the idea to come up with an electrical sensor for measuring wind speed when I saw a program on TV explaining Meteorological Methods of recording the weather throughout the ages. I aim for it to be a simple method of recording air movement. My first idea was to measure wind speed using a "vane" on a spindle, which would rotate because of the wind to give me a reading of how fast the wind is going. I initially thought that I would be able to do this with a "light gate". I would set-up the apparatus so that every time the vane would spin it would break the "light gate's" beam. I would measure the amount of times that light beam is broken a minute; therefore working out the speed of the air-stream I would have hoped to wire this to a computer through, an interfacing program, which would record all the data for me (it would also increase the accuracy of my results). But unfortunately I did not have a light gate at my disposal, neither did I have computer, with the necessary capabilities or applications. I decided as a source of my "wind" I would use a hair dryer but the problem with this, as my air stream: is that I wouldn't be able to vary the wind speed greatly. ...read more.


I did this by measuring the distance from the centre of the vane to the ground and then calibrated it against the distance from the centre of the nozzle and then to the ground. Unfortunately setting it up in this manner the flow of air is not concentrated into the vane, it spreads out from the source. The further away you are the more spread out it is. Therefore it does not produce a totally accurate reading, but it still obeys certain rules. The air flow hits the vane and we only need to consider the area of the vane. For example. a : b (linear ratio) then it implies that a2: b2 (area ratio) is correct. See diagram. If this correct then it is also true for the (volume ratio) a3 : b3 because as the air is blown from the source it spreads out in a cone. The fact that the air blows in a cone becomes slightly irrelevant because the airflow is always going to be striking the same area; because the vane doesn't change in size it is always going to be 64cm2. So we can use it according to the area ratio. The 8cmx8cmx8cm open-faced cube only becomes affected by the fact that the "wind" blows in a cone, when the distance changes between the vane and the wind source. When the distance is doubled the amount of air hitting the vane is multiplied by a quarter. ...read more.


* Probably the most important thing to do next time (If I was to redo this experiment) would be actually record the wind speed from certain distances. So I could try to find a relationship between the resistance and the wind-speed. This would allow me to see whether any of my previous calculations above are correct. Percentage Errors We can see how inaccurate the apparatus was by performing a few percentage error calculations. As you can see the percentage errors are so small that it is probably justified not to take them into account, but I did only take two sets of results, so it could be more if I had time to take more results. Distance Average Current (200?A) Distance from the mean Percentage Error 110 23.35 0.05 0.21413% 100 23.35 0.05 0.21413% 90 23.35 0.05 0.21413% 80 23.4 0.1 0.42735% 70 23.45 0.05 0.21322% 60 23.45 0.05 0.21322% 50 23.55 0.05 0.21231% 45 23.5 0 0.00000% 40 23.7 0.1 0.42194% 35 23.9 0 0.00000% 30 24.1 0.4 1.65975% 25 24.7 0.1 0.40486% 20 25.65 0.55 2.14425% 15 26.3 0.3 1.14068% 10 27.2 0 0.00000% Distance Average Resistance in Ohms Distance from the mean Percentage Error 110 106.43 0.00776824 0.00730% 100 106.4240123 0.013755915 0.01293% 90 106.2103371 0.227431129 0.21413% 80 105.9848416 0.429286011 0.40504% 70 105.5437352 0.866521186 0.82101% 60 105.9710857 0.439170758 0.41443% 50 105.3083303 0.627479264 0.59585% 45 104.6808511 0.827623512 0.79062% 40 104.6449936 0.879303214 0.84027% 35 103.7656904 0 0.00000% 30 102.9205125 1.281168205 1.24481% 25 100.811369 0.408143194 0.40486% 20 96.33222834 1.675739789 1.73954% 15 94.11654135 0.883458647 0.93869% 10 91.17647059 0 0.00000% ...read more.

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