Patent ID: 7317316

Claim:
Apparatus for measuring insulation resistance of a fuel cell system with respect to an electrical ground point, said apparatus comprising: a resistor arrangement formed by a series connection of reference resistors between two load-current lines of the fuel cell system; a reference voltage source which is coupled between the ground point and a node between the reference resistors, said reference voltage source including at least first and second reference voltages and first and second switches which are actuable alternatively to apply either said first reference voltage or said second reference voltage, respectively to said node via an output of said reference voltage source; a voltage-sensing device, which acquires the voltage between at least one of the load-current lines and the ground point; and an evaluation unit that is connected to the voltage-sensing device and determines the insulation resistance on the basis of a first voltage value between a first of the load-current lines and the ground point while the first reference voltage of the reference voltage source is applied to said node, and on the basis of a second voltage value between the first load-current line and the ground point while the second reference voltage of the reference voltage source is applied to said node.