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Introduction

SENSORS COURSEWORK PLAN: We were asked to investigate the properties of a sensor. The sensor I have chosen is a potentiometer. A potentiometer is a device which taps off a fraction of its input to provide a controlled output. It consists of a sliding contact which moves across wire coils to cause a change in resistance. Equal movements of the sliding contact give equal changes in output. We are actually using the potentiometer as a variable resistor so that instead of tapping of a proportion of the potential difference it taps off a part of the resistance. We are using a rotary potentiometer for our experiments. This means that the slider moves in a circular motion across the contacts. For us to be able to conduct tests we must be able to accurately measure how much we have moved the contacts so that we can compare it with the change in resistance. We have decided to measure the movement in degrees. This means we had to fix an arm to the moving contact of the potentiometer so that we could see the moving part of the potentiometer. Then we had to draw a circle on some card and mark of the degrees using a protractor. We then mounted the potentiometer on the card so that it was held firmly in place. This meant that now we could see how many degrees movement gives a certain out put. ...read more.

Middle

1.1 1.06 5.7 5.377 250 1 1.1 1 1.03 5.7 5.533 255 1 1.1 1 1.03 5.7 5.533 260 0.9 1 1 0.96 5.7 5.937 265 0.9 1 0.9 0.93 5.7 6.129 270 0.9 1 0.9 0.93 5.7 6.192 275 0.9 0.9 0.9 0.9 5.7 6.333 280 0.9 0.9 0.9 0.9 5.7 6.333 285 0.9 0.9 0.9 0.9 5.7 6.333 290 0.8 0.9 0.8 0.83 5.7 6.867 In order to make these results easier to interpret I plotted them on a line graph of resistance against movement. This allowed me to see any relationships between the two far more easily. ANALYSIS: The first thing we checked for was systematic errors. We could find no zero error as the instrument was pretty accurate. Also we could detect no random fluctuations in the equipment. From the graph we can see that there is a relationship between the amount of movement and the resistance. As the amount of degrees moved increased the resistance increased. The increase in resistance was caused by the fact that as the contact was moved more of the coils were exposed and there were more of them for the current to travel through. In a series circuit such as the one we used resistance increases as the length of a resistor increases (in this case the coils). So for example if the length of the resistor is doubled then the resistance is doubled. This happened to a degree in our experiment. ...read more.

Conclusion

They were almost certainly down to human error in either, the moving of the arm on the potentiometer or reading the figures from the ammeter. Also these anomalous results seem to appear in groups, which is probably due to the fact that when one false reading was made this caused a few other readings to be slightly out. If I were to conduct this experiment again there would be quite a lot I would change. Firstly I would have to find a better way of measuring the angle that the contact had been moved. I felt that the method we used was adequate but it was quite inaccurate because there were a number of stages where human error could play a part. Firstly when marking the degrees on the card it would have been quite easy to put the mark in slightly the wrong place. Also it would be quite easy to move the arm to far or not far enough which would cause misleading results. Another problem area was the method we used to secure the potentiometer. We clamped it to the table so that it didn't move whilst the slider was being moved, however it was easily possible that it could have slipped causing a deceptive set of results. One way to eliminate these errors as much as possible would have been to take more sets of results before taking an average. This investigation could be extended to look at linear potentiometers and potentiometers of different power ratings to see how the properties of different types of potentiometer would compare to one another. ...read more.

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