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I chose to do my sensors project about sliding potentiometers because they are very common in every day life, and I thought it may be interesting to discover how they work.

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Introduction

Physics coursework

Introduction

I chose to do my sensors project about sliding potentiometers because they are very common in every day life, and I thought it may be interesting to discover how they work. There are potentiometers on lots of everyday household appliances, sliding and rotary potentiometer on hi-fis to change the volume or tuning, washing machines and dishwashers to change settings and other electrical equipment and machine. As the world becomes more computer reliant sensors will be used more often, especially potentiometers as they are easy to operate. Rotary and sliding potentiometers both work in a similar fashion. As the slider gets moved along, the voltage increases as the potential difference changes. A rotary potentiometer works the same way, but is twisted round, so rather than measuring displacement, degrees are considered. I will take this simple idea and look into true values and patterns.

Plan

image00.png

Fig 1.  Circuit diagram of  the circuit to be built.(Not to scale)

I am going to build the diagram as shown above and slide the potentiometer along and see what the different readings of the voltmeter are.

The equipment I shall be using is:

  • Wires x 4
  • A 59mm sliding potentiometer (5kB)
  • A digital voltmeter, Rapid 212 DMM. Reading error: 0.005V
  • 30cm Ruler. Accuracy: 0.5mm
  • Stopwatch, Unilab Accuracy: 0.005 secs
  • Power Pack (1kWIN L.V power supply (J0032)). Reading error 0.005V

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Middle

(3) Voltage (V)

(4) Voltage (V)

Average Voltage (V)

0

0

0

0

0

0

1

0.64

0.64

0.64

0.66

0.65

2

1.46

1.46

1.39

1.49

1.45

3

2.35

2.35

2.16

2.31

2.27

4

3.21

3.21

3.12

3.11

3.14

5

4.05

4.05

3.97

3.98

4.01

5.9

4.56

4.56

4.56

4.56

4.56

The graph of these results is attached: Graph 1.

From my results I can see that as the displacement increases, the voltage increases fairly uniformly. To make my results more accurate I decided to do the experiment using 0.5cm intervals. This way I can be certain about the pattern and have a more accurate line of best fit.

The Experiment

As well as measuring in 0.5cm intervals I will also measure the response time as it is vital to know if this sensor is going to be used in an electrical appliance, how long it will take for the displacement to be measured.

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Conclusion

From the graph 2 I have worked out that the resolution is 0.146. This is the smallest change on voltmeter in terms of displacement.

By looking at the gradient of the calibration curve I worked out that the sensitivity was 0.814. There is constant high sensitivity.

The response time was worked out by measuring how long it took for the voltmeter to stay on a constant level. I did a number of tests, and although it is hard to measure accurately as it is such a short time scale, these were my results:

Response time (secs)

0.97

0.78

1.43

0.66

0.66

1.29

1.31

1.12

0.83

1.19

As there is a fairly large difference between the results it is hard to get an accurate result as an average. The actual average response time is 0.9858 secs. However this is too accurate and I think that 1 sec (2 sig. fig.) is a better value.

From all these results I can conclude that for a knob on a hi-fi a sliding potentiometer is ideal, it has a short response time, highly sensitive, and very easy to use. The only downfall is that the displacement is limited, but the volume and such like is limited also, so this is not a problem.

        A sliding potentiometer is ideal for hi-fi knobs.

If I was to do this experiment again I would try out different lengths of potentiometers to check my percentage of displacement, voltage graph was correct.

Resources: (1) Advancing physics AS , Jon Ogborn

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This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.

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