A method for signal testing of at least a first and a second analogue input signal (210, 220) which are provided by an electrical device and which during normal operation of the device depend on one another such that a first output signal that can be determined from the at least one first and second analogue signals using a predetermined first rule is substantially constant over time, comprising the steps of: - defining a second rule for determining a second output signal from the at least one first and second analogue input signals (210, 220), which varies over time within a predetermined value range; - providing an analogue circuit arrangement implementing the second rule, which comprises at least a first signal input for the first and a second signal input for the second analogue input signals and an output for providing the output signal generated by the circuit arrangement on the basis of the second rule; comprising - a first circuit part adapted to add the positive voltage portions of the first and second input signals (210, 220); - a second circuit part adapted to add the negative voltage portions of the first and second input signals (210, 220); and - a third circuit part connected to the first and second circuit parts for determining the difference between the added positive and added negative voltage portions, the third circuit part providing the test signal as the output signal on the output side; - feeding the at least one first and second analogue input signals (210, 220) to the associated signal inputs (A, B) of the provided circuit arrangement; - evaluating the output signal of the provided circuit arrangement; - providing a positive test result of the signal test, if the output signal present at the output of the circuit arrangement is within the predetermined value range; and - providing a negative test result of the signal test, if the output signal present at the output of the circuit arrangement is at least temporarily outside the predetermined value range. - defining a second rule for determining a second output signal from the at least one first and second analogue input signals (210, 220), which varies over time within a predetermined value range; - providing an analogue circuit arrangement implementing the second rule, which comprises at least a first signal input for the first and a second signal input for the second analogue input signals and an output for providing the output signal generated by the circuit arrangement on the basis of the second rule; comprising - a first circuit part adapted to add the positive voltage portions of the first and second input signals (210, 220); - a second circuit part adapted to add the negative voltage portions of the first and second input signals (210, 220); and - a third circuit part connected to the first and second circuit parts for determining the difference between the added positive and added negative voltage portions, the third circuit part providing the test signal as the output signal on the output side; - a first circuit part adapted to add the positive voltage portions of the first and second input signals (210, 220); - a second circuit part adapted to add the negative voltage portions of the first and second input signals (210, 220); and - a third circuit part connected to the first and second circuit parts for determining the difference between the added positive and added negative voltage portions, the third circuit part providing the test signal as the output signal on the output side; - feeding the at least one first and second analogue input signals (210, 220) to the associated signal inputs (A, B) of the provided circuit arrangement; - evaluating the output signal of the provided circuit arrangement; - providing a positive test result of the signal test, if the output signal present at the output of the circuit arrangement is within the predetermined value range; and - providing a negative test result of the signal test, if the output signal present at the output of the circuit arrangement is at least temporarily outside the predetermined value range.