Patent ID: 8870451

Claim:
A circuit device for an electrical heater of a vehicle seat, the heater having a heating resistor connected to a supply voltage via a power path and connected to a seat ground cable in a region of the vehicle seat, the circuit device comprising: a temperature-dependent sensor resistor positioned in the vehicle seat; a control unit positioned outside of the vehicle seat, the control unit being connected to a control unit ground that is positioned remotely from the vehicle seat, to activate the heating resistor and to determine a seat temperature; a series circuit comprising the sensor resistor and a further resistor to connect the heating resistor to the supply voltage, such that the heating resistor can be connected to the supply voltage either via the series circuit or via the power path; and a measuring signal cable through which the control unit measures a voltage drop at the sensor resistor when the heating resistor is disconnected from the supply voltage, the control unit storing the voltage drop as a voltage measurement, wherein the control unit measures a potential difference between a potential of the seat ground cable and a potential of the control unit ground, and the control unit takes the potential difference into account in order to correct the voltage measurement, produce a corrected voltage measurement, and determine the seat temperature from the corrected voltage measurement.