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For this section of coursework I decided to undertake the task of building and testing a sensor. The sensor, which I built, was a thermocouple, I built this to take measurements of the temperature of a certain window.

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Sensors Project Introduction For this section of coursework I decided to undertake the task of building and testing a sensor. The sensor, which I built, was a thermocouple, I built this to take measurements of the temperature of a certain window. Aim My aim for this experiment to find how well a window conducts heat on both the outside and inside. Also I wished to find whether there was a correlation between the temperatures of the window at different points. I thought the side of the window, which would be at a higher temperature, would be the inside. I also felt due to the rule that hot air and fluids rise, I felt that the higher up the window the higher the temperature would be. Choice of Sensor For this experiment I could have chosen another option. I could have used a bead thermistor to do this. A bead thermistor is a semi conductor, so instead of resistance increasing with temperature it decreases. I did not use this because I have had previous experiences with thermal couple and I know the behaviour of one. I know that the Thermocouple has linear response, when measuring temperature. This means if the temperature doubles the EMF generated doubles. With a thermocouple you get the temperature is measured a lot quicker than a mercury thermometer, this was another reason why I used it to so I could measure more temperatures in the same amount if time. For my experiment I decided I needed the following equipment: * Copper and Constantian wire * Bunsen Burner * Beakers of water a differing temperatures * Heatproof mat, Tripod and Gauze * Mercury Thermometer * A Digital Voltmeter * A Window * Connecting Wires and Crocodile Clips A thermocouple can be made using two similar metal wires and a dissimilar metal wire connected together to form two junctions acting in opposition to each other. ...read more.


Sensitivity is concerned with the size of the output of an instrument, compared to its input. The sensitivity of a measuring instrument is the change of its output divided by the change in input. A temperature sensor whose output changes by 100 mV for a change of 2 K in its input has a sensitivity of 50 mV per Kelvin The more sensitive an instrument is, the greater the change of its reading for a given change of the variable causing the change. In an instrument in which the change of the reading is directly proportional to the change of the variable would, on a graph, cause a straight line through the origin. The gradient of the line is equal to the sensitivity, which is the same across the full range of the instrument because the line is straight. So the sensitivity of my thermocouple would be: EMF/temperature change For the thermocouple 4.2mV/100 oc = 0.042 mV/ oc As you can see this value is very small, it shows that the Thermocouple only gives off very small amounts of EMF. Once I had calibrated my thermocouple I was ready to begin my experiment. For my experiment I chose a window in my physics laboratory. In order to show the points on the window where I will be measuring I will draw the window and label it with a key. I measured the window and found it to be 95cm tall and 60cm wide. From this I could work out where on the window I would be taking my measurements. Once I had found all my points I stuck bits of sellotape to the window so I could clearly see where I had to take the measurements. When taking the measurements of the window it was very similar to the calibration. I had to put on of the junctions into a beaker of water with temperature of 5 oC, but the other junction went directly onto the window. ...read more.


Then is the risen air cools it contracts becomes dense and falls again to the bottom of the window. Here is a diagram. If I were to do this experiment again there would be a few things I would change. The first thing would be to do the whole experiment on the same day. I feel this is the biggest reason why the results for the top of the outside window were so. I would also choose a taller window. This would be better for trying to prove the relationship of as you get higher up the window the temperature would be higher. I would also try and use more accurate equipment, especially the digital voltmeter. This is due to the difference of temperature between 0.1mV. This would make the experiment more accurate. Also to make my results more accurate I could try to amplify my results this way you would be able to see a clear difference in voltages, not use 0.1mV. From this you could tell whether the changes are significant or just uncertainties. I could also try windows, which were situated in different places relevant to the sun, this would prove whether the sun's rays affect the temperature of the window. Unfortunately as I did not know the thickness of the window I could not find the thermal conductivity of the glass, but the temperatures from the inside to the outside was a difference of about 5 oC. I feel that this is a sensible figure considering the window was just a single panel and not double-glazed. I do feel that my experiment went quite well. The calibration proved successful as I got a straight line for my line of best fit. Also I feel that I got sensible results for the temperatures apart from I felt that the range was quite big. You can see that there is a trend of, the higher up the window the higher the temperature is, but as the potential difference measured were so small I could not be sure that this was not down to some uncertainties. Matthew Barrett ...read more.

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