Sensors

What is a sensor and what does it do?
Wiki: "A sensor is a converter that measures a physical quantity and converts it into a signal which can be read by an observer or by an (today mostly electronic) instrument..."

In this part of the website, I will explain more about different sensors. How do you connect them to a sensor interface like Ipson or Arduino. How to tweak the active and passive sensors, so they give the most optimum value.