At Maker Faire Milwaukee this past weekend, [basement tech] was showing off his latest build, a PID ... sensor stuck through the grill gives the reading of the air inside, and an Arduino nearby ...

Assume that the process variable is temperature, and to measure the process variable a temperature sensor is used ... To implement a PID controller in an Arduino sketch, five parameters must be known: ...

It is a common situation in electronics to have a control loop, that is some sort of feedback that drives the input to a system such as a motor or a heater based upon a sensor to measure something ...