A thermistor resistance goes up or down depending on the type. It usually signals a control device. My question is-As the resistance increases or decreases does it signal a sudden change in the control or does it give a variable change. And if it is a variable change how does it incrementally make a device work. Of course it usually is connected to a control board and works with the boards internal semiconductor devices.

 

Have a read through this Wikipedia entry: http://en.wikipedia.org/wiki/Thermistor