I have chosen to construct and test an anemometer. An anemometer is a sensor that is able to measure wind speed. Some anemometers measure wind speed and temperature, which I had initially planned to do. I decided this would be too complicated and not viable with the time and resources available. Background information: An anemometer is a type of flow sensor; flow sensors are used to measure the rate of flow for many applications for example in chemical industries to measure the rate of flow of liquid or gas in a pipe.
An anemometer is specific to measuring wind speed, or the speed of the movement of air. The type of anemometer that I have constructed does not depend on a certain wind direction so in essence it is just a device for measuring the speed of the wind, and not the velocity. This is because no directional information is gained from the results. An anemometer works by ‘catching’ the wind in ‘cups’ that are attached to a central axis. The wind causes the cups to move around the axis at varying speeds, which is dependent upon the speed of the wind.
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Complex sensors could be added to the wind-catching ‘cups’ to sense at what point the cups are accelerating the most, but as the cups are all attached to the same axis, they would all accelerate. Instead, the sensors could be added to cups to detect which cups are catching most wind, enabling wind direction to be calculated. Again this is far too complicated with respect to the available resources. There were several ways that I devised to measure the wind speed and temperature before deciding upon a final solution. These are listed below. To measure wind speed: 1.
Attach a magnet to each of the cups, and record on an ammeter creation of a current as the magnets pass a coil of wire. 2. Do the same as before, but have the magnets pass a reed switch, which would close the circuit in the switch creating a circuit which could be recorded. 3. Attach a motor to the central axis of the cups, and measure the voltage created from the motor using a multimeter. I chose idea 3 as I found this to be most suitable. I tried each idea, and found that for idea 1, the current created by a magnet passing a coil of wire was not large enough to be successfully registered by a sensitive instrument.
Only a few thousands of an amp were being created. This is not practical, as the needle moves around the same amount when it is moved or knocked, not practical as the anemometer would be used outside, where a perfectly still flat surface would not be present. I discounted idea 2, as the speed that the cups passed the reed switch was too fast for the reed switch to open and then close completely before the next cup passed. This is because the magnet, moving at the same speed as the cup was not near enough to the switch to have an effect for a long enough period of time.
Devised method to measure wind temperature: By devising a ‘hot wire anemometer’ I would have been able to compare the effects of wind speed upon temperature; in effect this would have been an analysis of ‘wind chill’. An increased wind speed has a dramatic affect upon the temperature of the air. To measure the temperature of ‘the wind’ I would have used heated resistance wire, the hotter the wire, the greater the resistance of the wire. This is because of the electron activity in the wire, the increased energy states of the electrons.
A hotter wire has a greater resistance than a cool wire. Therefore, when the wind passed the wire, the temperature of the wire would decrease, in turn decreasing resistance. The faster the wind speed, the more the wire would have been cooled, therefore the more the resistance of the wire would have decreased. To make this a successful analysis, I would have had to determine the type of relationship between wind speed and resistance, be it linear or non-linear to enable me to determine the relationship between wind speed and temperature.
This would have been overcomplicated. The wind speed meter that I have constructed has an inherent error present in its operation, which I will analyse in this write up. Therefore I would not have been able to use the meter I have made, as the error present in the wind speed readings would have been carried forward into the calculations attempting to determine the relationship between wind speed and resistance, corrupting the final conclusion – the relationship between wind speed and temperature.
To overcome this I could have used a wind speed meter that I knew was accurate which would have enabled me to make a more accurate conclusion, although errors in the measurement of wind temperature would still have been present. The use of a datum in my experiment will enable me to make a valid analysis of my results as I will have an accurate value with which I can compare with my experimental results, enabling me to identify, and analyse any discrepancies. I will not use a datum during the process of calibrating the sensor, as this is not necessary.
I will only need to compare the experimental results to analyse the accuracy of the system. Care will have to be taken throughout the calibration process and the recording of results. The anemometer will rotate at a fast rate, and would cause damage if it hit the user’s eye, especially as the cups are pointed. As the calibration is to be conducted in the dark room, and the length of the arm that the cups are mounted on may be underestimated, the user must take precaution.During.