When we have a particualr sensor we have to make sure that it is suitable for the use we have designed it for. The three main things we need to look at are:
resolution – the smallest change it can detect
sensitivity – output/input
response time – how long it takes to reach the ‘right’ reading when we change the input
Depending on the use we need different values for these. A light sensor on a street lamp can have a response time measured in minutes because the sun sets quite slowly. A speed camera however needs to respond almost instantly.
There is more to a good sensor that these three: http://ocw.mit.edu/courses/mechanical-engineering/2-693-principles-of-oceanographic-instrument-systems-sensors-and-measurements-13-998-spring-2004/readings/lec2_irish.pdf but they are the three main points.