Over the mains carrier current remote control for central heating. The thermostat transmits a 100 KHz carrier over the mains wiring when it's too cold. The receiver detects the 100 KHz carrier and fires the boiler.
http://www.holmea.demon.co.uk/Thermostat/Stat.htm
Thermocouples find widespread use for temperature measurement in systems. During system design or testing, you must observe the system's response at different temperatures.
http://www.edn.com/contents/images/110801di.pdf
the temperature regulator(Thermostat) which used a thermistor for the temperature sensor.
http://www.hobby-elec.org/e_ckt25.htm