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# Test how the sensor I have chosen reacts to an external change and compare the properties of three different sensors.

Extracts from this document...

Introduction

Sensor Project

Preliminary Work

My aim is to test how the sensor I have chosen reacts to an external change and compare the properties of three different sensors. The sensors I have chosen to investigate are thermistors named sensor A, sensor B and sensor C. To compare the 3 sensors I shall be primarily looking at their sensitivity and what purpose each sensor would be best suited to after establishing this.

To do this I will have to set up a circuit shown above to produce a set of results calculating the resistance of the given sensor using the formula R = V/I as it varies with temperature.

My circuit consists of two 1.5V batteries in series with an ammeter (which will give me my current reading), thermistor and a variable resistor, which I have placed in the circuit to act as a potential divider. The use of a potential divider is to tap off a certain voltage so that the voltage I currently use does not over heat and potentially damage the sensors.

Middle

120

6.32

55

810

110

804

110

809

110

7.34

50

920

100

921

100

921

100

9.21

45

1000

100

1000

100

998

100

9.99

40

1060

90

1067

90

1073

90

11.85

35

1190

90

1180

90

1191

90

13.19

Sensor B

 Experiment 1 Experiment 2 Experiment 3 (°C) Temp (mV) Voltage (mA) Current (mV) Voltage (mA) Current (mV) Voltage (mA)

Conclusion

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1050

4.16

1070

4.16

1050

4.00

257.31

35

1160

3.87

1150

3.89

1160

3.90

297.60

Sensor C

 Experiment 1 Experiment 2 Experiment 3 (°C) Temp (mV) Voltage (mA) Current (mV) Voltage (mA) Current (mV) Voltage (mA) Current (Ohms) Average Resistance 85 2520 5.53 2520 5.50 2520 5.49 457.63 80 2550 5.18 2560 5.20 2550 5.21 491.34 75 2580 4.87 2590 4.95 2580 4.81 529.73 70 2590 4.51 2590 4.60 2600 4.50 571.64 65 2650 4.02 2650 4.00 2650 4.00 661.40 60 2690 3.90 2670 3.87 2680 3.89 689.54 55 2710 3.76 2710 3.78 2700 3.78 717.31 50 2750 3.29 2760 3.30 2750 3.32 833.50 45 2780 2.92 2780 2.94 2780 3.96 849.29 40 2800 2.68 2800 2.71 2800 2.70 1038.32 35 2810 2.60 2810 2.67 2820 2.63 1068.35

Evaluation

From my experiment I have obtained an accurate and very conclusive set of results. Following calculating the resistance from the averages of the repeated experiments (using the formula R=V/I) I placed my results in three separate temperature/resistance graphs. This enabled me to establish if there was a connection in the change in resistance to a change in the thermistors temperature. I noticed a few systematic errors from placing my results into a graph but most of the results followed a direct correlation and after adding a line of best fit this was much clearer. Sensor A, B and C all showed a decrease in resistance as temperature rose. The results I gained proved conclusively my prediction that the resistance of the thermistors dropped as temperature rose was correct.

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