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A coursework on sensing temperature with voltage.

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Introduction

Sensing coursework 2004

A coursework on sensing temperature with voltage.

BY

NNEKA EZEIGWE

SENSING COURSEWORK.

AIM: To devise a means of sensing temperature through a potential divider circuit with a thermistor.

MATERIALS/APPARATUS NEEDED: Thermometer, Thermistor, Beaker, Electric kettle, Power supply, Multimeter, Resistance box.

For the experiment to be successful a lot of things have to be considered and the first thing to consider when working with sensors is the properties of sensors.

PROPERTIES OF A GOOD SENSOR

High resolution: resolution refers to the smallest change a sensor can detect in the quantity it is measuring. This quality is highly related to precision.

Sensitivity: This refers to the ratio of the change of output to the change of input. Sometimes however it is necessary to compromise on sensitivity so as to increase the range. However a good sensor should have reasonable sensitivity and range.

Noise, random error and fluctuations: This is bound to occur as the input signal may fluctuate or the sensor itself may produce some noise. Small unsystematic variations occur in all experimental data. Taking an average however reduces the effect of this.

Systematic error: Systematic error is very hard to detect and includes things like zero error, which are constant throughout the experiment.

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Middle

       38.1

The volume of water used for this experiment was kept at 250cm³

The experiment was completed over two days.

On the first day 15th October 2004, the temperature in the physics laboratory (P1) where the experiment took place was 19.8°C

On the second day 19th October 2004, the temperature in P1 was 20.1°C.

The results of this experiment are reasonably accurate because there are few factors that affect it and they tend to remain fairly constant throughout the experiment for example the impurities present in the water and the prevailing atmospheric pressure could affect the boiling point of the water though this is relatively insignificant.

The readings in this experiment are accurate to one decimal point and readings are repeated to reduce the effect of random error and to eliminate erratic error. It is always better to take the average of two or more readings because then we increase the degree of accuracy and precision and what we get is closer to the truth.

There is no constant value for the sensitivity of the thermistor in this experiment because the graph produced is a curve rather than a straight line. This means that the gradient is constantly changing and as the gradient changes, sensitivity is altered.

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Conclusion

Data handling: I tried to handle the data I obtained as effectively as possible. I used graphs and tables to present the result and how to read and interpret the graph are explained adequately so it is generally comprehensible and easy to use.

Creativity: My sensor falls short in this respect because it is a rather basic potential divider circuit and measures temperature, which is not uncommon. However, it is very useful and that is what is really important from my point of view. Temperature measurement has a wide variety of applications. It can be used to determine the optimum temperature of a baby’s bath, baby’s food, minimum and maximum temperatures reached in a day and many other useful applications.

IMPROVEMENTS THAT COULD BE MADE TO MY SENSOR.

        My sensor could be improved in a number of ways. Firstly, I could have measured the change in resistance with temperature and not voltage. This is because using resistance as my variable would have given me a much clearer linear logarithmic graph making deducing values much easier and reliable.

        Also, most textbooks relate the change in resistance of thermistors with temperature and not the change in voltage that occurs as a consequence of the change in resistance. Therefore, I would have had more formulae at my disposal.

Nneka Ezeigwe. 1434

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