The sensor has only a first contact (1) and a second contact (2). In the first step of the method, current is passed through the sensor element (3) while simultaneously measuring the measured variable using a closed switch (4). In a second step, the measured value is then converted into a digital signal in an analogue/digital converter (5) and the digital signal is transformed into a digital output value in a digital switching mechanism (6) which is connected downstream of the analogue/digital converter (5). In a third step, the digital output value is serially sent via the first contact (1) and the second contact (2) with the switch (4) open or closed depending on the binary structure of the digital output value.