Temperature detecting circuit

Claim 1

A temperature detecting circuit comprising a three-wire temperature sensor module including a first, a second and a third terminal, a temperature responsive resistance, a first cable lead connected across said first terminal and one end of said temperature responsive resistance, a second cable lead connected across said second terminal and said one terminal of the temperature responsive resistance, and a third cable lead connected across said third terminal and the other end of said temperature responsive resistance, a first and a second power terminal across which a reference voltage is supplied, said first terminal being connected to said first power terminal, a first resistance connected across said third terminal and said second power terminal, a second and a third resistance connected in series across said second terminal and said second power terminal, the respective resistance values of said first, second and third resistances being such that a current flowing through said second cable lead is substantially equal to that of said third cable lead, a potential devider being connected across said first and second power terminals and having a movable contact, and a summing amplifying means for summing a first voltage appearing at a junction between said third terminal and said first resistance, a second voltage appearing at a junction between said second and third resistances and a third voltage appearing on said movable contact of the potential divider and for generating an output signal, said potential devider being designed so that a variation of said third voltage can be rendered equal to a variation of said first voltage corresponding to the resistance value of said temperature responsive resistance sensing a temperature.