A level :: Design and Technology

A level ObjectiveThe challenging task that I have finalised and undertaken for thiscoursework is to build and tally a sensor. I decided to build a sensor,which would automatically change the speed of a fan by using athermistor. The main documental of the experiment was to monitor andrecord the voltage change as the temperature changes. Specifically, aspredicting that when the temperature increases the voltage wouldincrease and thus the fan speed would increase too, thus causing acooling effect to the environment.Data InformationThermistors argon thermally sensitive resistors and have, according to graphic symbol, a negative (NTC), or positive (PTC) resistance/temperaturecoefficient. A thermistor is a type of resistor whose resistancechanges significantly when its temperature changes.A negative temperature coefficient thermistor has a resistance thatdecreases with increase of temperature. This is the most common type.This is the type of resistor that I shall be evaluating and will b eusing in my experiment.A positive temperature coefficient thermistor has a resistance thatincreases with increase of temperature. The resistance of a semiconductor device generally decreases with increase of temperature.Semiconductors are therefore use to manufacture NTC thermistors.When the temperature of a semiconductor is increased, the keep down ofcharge carriers increases as more valence electrons promote sufficientenergy to break free from atoms to become conduction electrons. Thenumber of charge carriers increases as the temperature is increased sothe resistance of the semiconductor falls. Semiconductors are used tomake a wide range of electronic devices including electronic chips,light emitting diodes and solid-state lasers. Communications, commerceand entertainment have been revolutionised as a result ofsemiconductor devices. In galvanizingal terms, materials are classed aseither conductors or insulators or semiconductors.Semiconductors are solid materials with conducti vities in between thein truth high conductivity of metals and the very low conductivities ofinsulators. There are a variety of types of semiconductor, includingmetal oxides as well as elements like silicon and germanium. Ininsulators, essentially all the electrons are tightly bound to atomsor ions, and none are free to move under an external electric field.In effect, these materials do not conduct electrical energy at all. Inmetallic conductors, essentially all the atoms are ionised, providingfree electrons, which move freely through the ions and can move underan external electric field. These conduction electrons glue the ionstogether, and provide non-directional bonding which holds the materialtogether. They become shared amongst all the atoms in the materialinstead of remaining attached to one atom.Semiconductors differ from two insulators and metallic conductors.Only a small proportion of atoms are ionised, so that although thereare conduction electrons they are relatively smal l in number and the