A coursework on sensing temperature with voltage.

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Sensing coursework 2004

A coursework on sensing temperature with voltage.




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.


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. They do not really alter the results. Rather they tend to move the whole data and the values are not affected singularly. Good sensors should have as little systematic error as possible. However today there are ‘smart’ systems which process information to compensate for systematic error.

Handling data: The data gotten from a good sensor must be adequately processed often with appropriate averaging, analyzed and displayed effectively so that it is generally comprehensible.

Creativity: It should be creative, experimental, spontaneous even!

These factors were taken into consideration in creating this temperature system. The result is a reasonably balanced system with adequate resolution, very high sensitivity and appropriate range, little random error (which is almost totally wiped out by the graph and averaging a set of readings), analyzed and understandable data, and has a pretty wide range of applications making it handy to a fairly wide range of people.


The circuit is set up as shown

The water is boiled until it reaches a temperature of just above 90 degrees Celsius. The thermistor is inserted into the hot water and the voltage across it is measured for a temperature (t1) of 90 degrees. The varying voltage across the thermistor is measured as the temperature falls at 10-degree intervals. The experiment is repeated and a second set of readings obtained. An average set of readings is obtained and a voltage-temperature conversion graph is plotted.

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The readings obtained are as follows and the graph is attached.

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 ...

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