A level

A level

Objective

The challenging task that I have finalised and undertaken for this

coursework is to build and test a sensor. I decided to build a sensor,

which would automatically change the speed of a fan by using a

thermistor. The main objective of the experiment was to monitor and

record the voltage change as the temperature changes. Specifically, as

predicting that when the temperature increases the voltage would

increase and thus the fan speed would increase too, thus causing a

cooling effect to the environment.

Data Information

Thermistors are thermally sensitive resistors and have, according to

type, a negative (NTC), or positive (PTC) resistance/temperature

coefficient. A thermistor is a type of resistor whose resistance

changes significantly when its temperature changes.

A negative temperature coefficient thermistor has a resistance that

decreases with increase of temperature. This is the most common type.

This is the type of resistor that I shall be evaluating and will be

using in my experiment.

A positive temperature coefficient thermistor has a resistance that

increases with increase of temperature. The resistance of a

semiconductor generally decreases with increase of temperature.

Semiconductors are therefore used to manufacture NTC thermistors.

When the temperature of a semiconductor is increased, the number of

charge carriers increases as more valence electrons gain sufficient

energy to break free from atoms to become conduction electrons. The

number of charge carriers increases as the temperature is increased so

the resistance of the semiconductor falls. Semiconductors are used to

make a wide range of electronic devices including electronic chips,

light emitting diodes and solid-state lasers. Communications, commerce

and entertainment have been revolutionised as a result of

semiconductor devices. In electrical terms, materials are classed as

either conductors or insulators or semiconductors.

Semiconductors are solid materials with conductivities in between the

very high conductivity of metals and the very low conductivities of

insulators. There are a variety of types of semiconductor, including

metal oxides as well as elements like silicon and germanium. In

insulators, essentially all the electrons are tightly bound to atoms

or ions, and none are free to move under an external electric field.

In effect, these materials do not conduct electricity at all. In

metallic conductors, essentially all the atoms are ionised, providing

free electrons, which move freely through the ions and can move under

an external electric field. These conduction electrons 'glue' the ions

together, and provide non-directional bonding which holds the material

together. They become shared amongst all the atoms in the material

instead of remaining attached to one atom.

Semiconductors differ from both insulators and metallic conductors.

Only a small proportion of atoms are ionised, so that although there

are conduction electrons they are relatively small in number and the