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# Aim To build and test a temperature sensor and analysing its suitability as a bath water thermometer.

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Introduction

Physics Sensing Coursework - Temperature sensor Aim To build and test a temperature sensor and analysing its suitability as a bath water thermometer. Introduction In making a temperature sensor the circuit and individual components need to be thought about. Also I need to find a way of measuring my sensor to calibrate its voltage output with the temperature it's measuring. First of all I require a component in my circuit which will change its electrical properties in the changing of temperature. This component is called a thermistor and there are two types; * The positive temperature coefficient thermistor or PTC thermistor has an increased resistance as temperature increases. ...read more.

Middle

For this circuit I will use a simple NTC thermistor which changes variably, not suddenly, with change of temperature. This works by having the thermistor made of a semiconductor and works because raising the temperature of a semiconductor increases the number of electrons able to move about and carry charge, the more charge carriers that are available, the more current a material can conduct and so resistance decreases. Another component I could use for this is a thermocouple. This is made by twisting two wires of differing metals (best is an antimony-bismuth thermocouple) together and having junctions, where the wires are twisted more, placed in a high heat, the following junction cold and this produces a voltage output. ...read more.

Conclusion

The Wheatstone bridge cicuit would look like this; In this circuit all resistors are of equal resistance and so as in the potential divider as the temperature changes and the thermistor resistance changes so does the voltage output. The main difference between the two is that the Wheatstone bridge helps to eliminate noise as fluctuations from the power supply affect both sidesof the bridge. Having done some preliminary testing I found the school power packs to have few fluctuations that shouldn't be worried over. Because the potential divider has less wires and is much simpler and the power pack doesn't affect the results I will use the potential divider circuit in my system. Appartus Water bath Wires 12V power pack Digital multimeter NTC thermistor (about 47k?) 47k? resistor Temperature probe Data logger Diagram ...read more.

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