Said second physical value represents a second detectable item of information in addition to the first physical value representing the data, independently of said first physical value .

To that end, a test valuator device (3) is used which, when an electrical checking signal is applied, generates a non-electrical physical value which is of the same type as the physical value to be measured by the sensor (2).

The physical value is determined by comparing the influence of changes in the at least two modes resulting from the influence of the physical value (such as ΔI).