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# Exploring the characteristics of a sensor

Extracts from this document...

Introduction

Exploring the characteristics of a sensor

AIM:

The aim of my experiment is to measure the resistance of a thermistor at temperatures which are acceptable by the human body. I can then use this information to create a sensor that can be placed in a bath to record the temperature. This will be beneficial to people who cannot feel the temperature of bath water such as a person who has suffered from a stroke.

RESEARCH

To be able to do my experiment successfully I needed to find out a suitable temperature range to test on.  I found out that the human body tolerates temperatures from 25˚C to 45˚C.

I also decided to research thermistors. There are two kinds of thermistors; these depend on the sign of the resistance. If the resistance is positive, the resistance increases with the temperature and is called positive temperature coefficient (PTC) thermistor. If the sign is negative, the resistance decreases as the temperature increases. This is called a negative temperature coefficient (NTC) thermistor.

VARIABLES

For my experiment to be a success I must make it a fair test.

Middle

– This will be connected in my circuit so I can measure the temperature of my circuit. The kind of thermistor I use will be kept the same to ensure a fair test1M wire – this will be connected to the meter bridgeGalvanometer – this measures the potential difference in my circuit. When the galvanometer is at 0 it means the two resistances are equal to each otherPower supply – I will use the same power supply at the same voltage to make it a fair test. Resistor – The resistor I use will be dependent on the reading from the multi meterThermometer – I will use a thermometer to measure the temperature of the water in the beaker. I will make sure the water is at the correct temperature before conducting my experimentWater – the water will be heated up using a Bunsen burner, I will then allow it to cool until it reaches the temperature I wish to measure. The amount of water I use will also be kept the sameBeaker – I will use a beaker to contain the water.

Conclusion

>

41

61.0

39.0

0.95

30˚C

69

64

63

31

36

37

65.3

34.6

0.79

35˚C

71

70

72

29

30

28

71.0

29.0

0.61

40˚C

75

73

74

25

27

26

74.0

26.0

0.52

45˚C

79

78

79

21

22

21

78.6

21.3

0.40

50˚C

82

83

82

18

17

18

82.3

17.6

0.32

So I predict that as heat enters the thermistor the electrons subsequently can move around and become free, the current will then increase as the electrons flow around the circuit and the resistance will decrease as more energy is supplied to it. The Voltage should not increase or decrease by more than 0.2V and I expect that the current will increase proportionally until the experiments end.

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