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To conduct an experiment that proves that asensor is affected by temperature. In my experiment I will investigatethe effects of temperature on the resistance of a thermistor. I willuse a range of temperatures to see how it affects the resistanc...

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Introduction

Alasdair Naisbitt

Sensing Coursework

Aim: To conduct an experiment that proves that a sensor is affected by temperature. In my experiment I will investigate the effects of temperature on the resistance of a thermistor. I will use a range of temperatures to see how it affects the resistance of the thermistor.

Safety: The main safety point in this experiment is that there is a high element of risk associated with the high water temperatures that will be reached during the course of the experiment. Common sense should be used at all times during the experiment by making sure to not put your hands in the Bunsen burner or pick up the beaker after it has been heated.

Electricity is also a key safety aspect. There should be no loose live wires and a qualified person must check all electrical equipment before use.

The combination of water and electricity can be dangerous so any spillages should be cleaned up as soon as possible. Lab rules should be followed at all times.

Preliminary Experiments: I have chosen to investigate the effects of temperature on a thermistor. However to make my experiment quicker, I needed to do some preliminary work. There are two types of thermistor – positive temperature coefficient and negative temperature coefficient.

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Middle

90

35

90

66

100

20

100

65

The results for the negative coefficient were taken to the nearest 5 ohms because accuracy was not important.

Sensor Terms

Sensor: Sensors are systems that measure or respond to changes in their surroundings. In this case the thermistor responds to changes in temperature by increasing/decreasing resistance.

A sensor is a device designed to produce an electrical signal in response to a change in its surroundings, either caused by a change in a specific physical variable or by the movement of surrounding objects.

Sensitivity: The ratio of output for a given 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.

In an instrument in which the change of the reading is directly proportional to the change of the variable causing the reading, a graph of the reading (on the y-axis) against the variable (on the x-axis) would be 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.

In a system or an instrument in which the change of reading is not proportional to the change of the variable causing the reading, the graph would be a curve.

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Conclusion

Poor connections in my circuit could have increased resistance so any of my results could have been anomalies.

Resolution: From my plotted graph of Average Resistance against Temperature, I obtained my resolution results by drawing lines from my error bars across to the line of best fit and then down to the x-axis. I then measured the distance between the vertical lines. My results are shown below:

Temperature (ºC)

Resolution (Ω/º)

10

4

20

4

30

5

40

6

50

3

60

4

70

8

80

4

90

5

Conclusion: From my results I can state that as temperature increases, average resistance decreases. I can also state that I have no anomalies in my average resistance because the line of best-fit travels through every error bar on my graph.

When the temperature is low, the average resistance is very high and has large error bars. The results were very far apart and so producing an element of inaccuracy to my experiment.

From my results for resolution, I can conclude that my results show that as temperature increases, so does resolution.

I think that overall the experiment was conducted and executed well with no apparent disastrous inconveniences. There was however, a very small problem, which I encountered during the course of the experiment. The original thermistor that I began to use for my preliminary experiment decided to cease to function. This resulted in a loss of time, as I had to repeat my preliminary experiment so that any results conducted were not fair.

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