thermocouple
Concise Oxford English Dictionary © 2008 Oxford University Press:
thermocouple/ˈθəːməʊkʌp(ə)l/
▶noun a device for measuring or sensing a temperature difference, consisting of two wires of different metals connected at two points, between which a voltage is developed in proportion to any temperature difference.
'thermocouple' also found in these Oxford entries:

