In this investigation I want to look into how a thermistor works, then experiment to find how temperature change affects its resistance. The main aim of this investigation is to design and build, using a thermistor, a temperature sensing circuit.

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Thermistor Investigation

Aim:

In this investigation I want to look into how a thermistor works, then experiment to find how temperature change affects its resistance. The main aim of this investigation is to design and build, using a thermistor, a temperature sensing circuit. This will be for use in a computer system.

Because of the recent advances in the speeds of PCs there has been a big problem in to deal with the extra heat that their faster CPUs (central processing units) produce. Most manufactures have simply increased the surface area of heat sinks used and fitted larger and more powerful fans but even these are sometimes not enough. If the same air is being forced through a heat sink over and over again it becomes quite warm and unable to remove more heat from the CPU so its temperature will rise. To solve this problem case fans are needed to refresh the air in the case but these can be noisy.

Because the amount of heat produced varies and there is a big difference between the heat made on idle and when the CPU is under load (it can vary from 30w to 100w in some cases). This means the extra case cooling would only be needed when the CPU is under load and reaches a certain temperature.

Noise is that last thing you want when trying to concentrate at a computer so by only having the case fans on when needed to remove the hot air from the case I keep the computer as quite as possible whilst keeping the CPU at safe temperatures.

Preliminary:

How a thermistor works:

Commonly, thermistors are made of semiconductor materials such as silicon, because this has a tendency to conducts better at higher temperatures, the resistance goes down as the temperature gets higher and the resistance will go up as it gets colder.

Plan:

My preliminary investigation will involve gathering test data about the resistance of the thermistor I want to use at different temperatures. To do this I would wire up the thermistor and plug it into a multimeter and use it to test for resistance. This is a lot simpler than setting up a powered circuit and measuring the volts and amps to determine the resistance. It also reduces that chance of the current through the thermistor heating it up and altering the results or even blowing the thermistor and finally makes it safer because mixing mains power and water isn’t good practice.

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I will set up the experiment as shown in fig. 1

I will fix the temperature sensor from a multimeter to the thermistor with insulations tape to hold them close together. This will limit the temperature variation between the two. I will then pour a small amount of hot (80°C) water into a beaker and place the instrument into the water. I am using a small amount of water because it will cool faster so I don’t have to wait as long for the results, also I am not being exactly precise with the amount of water because ...

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