Sometimes it is necessary to increase the current in a circuit. This is especially important if a sensor is being used as an input. Sensors are often used to switch on other devices. For example, a temperature sensor may to used to detect fire and then to turn on a water sprinkler system to put the fire out. Look at the example below.
When the rise in temperature (caused by the fire) is detected the sensor circuit (including an operational amplifier) allows a small amount of current to flow through it. However, the current is too small to activate the sprinkler system. The current must be increased for this to happen. An operational amplifier is used to increase the current (called GAIN). Then the sprinkler system is turned on putting out the fire.

The diagram below clearly shows how a small current (sometimes called a signal) is amplified by the Operational Amplifier to produce a larger current (signal)

QUESTION:
1. Name five different sensors and explain how each one could be used. For example, a temperature sensor could be used to detect a fire in a fire prevention system.