Method for testing a sensor

1. A method for testing a sensor with a primary inductor which is galvanically isolated from first and second secondary inductors which are respectively coupled inductively to the primary inductor, comprising:

calculating a sensor output signal from the secondary inductor, wherein the sensor output signal is dependent on a coupling between the primary inductor and the first secondary inductor as well as that between the primary inductor and the second secondary inductor; and

determining whether the sensor is operating in a faulty state by:

applying a constant current signal to the primary inductor and determining a first electrical variable, by measuring a voltage across the primary inductor; and

comparing the first electrical variable with a first limiting value, the first limiting value being a threshold amplitude that is between a normal amplitude of the measured voltage when the sensor is operating in a normal state, and a fault amplitude of the measured voltage when the sensor is operating in the faulty state.

2. The method as claimed in claim 1 , wherein the primary inductor is fed by an AC generator, wherein the first electrical variable is formed by an absolute value of the voltage occurring at the primary inductor, or

wherein the primary inductor is fed by an AC voltage generator, wherein the first electrical variable is formed by an absolute value of the current flowing through the primary inductor, or

the first electric variable is formed by a sum or a difference between the signals of the first and second secondary inductors.

3. The method as claimed in claim 1 , wherein a second electrical variable is compared with a second limiting value in order to determine whether the sensor is in a faulty state.

4. The method as claimed in claim 3 , wherein the first electrical variable is formed by the sum of the signals of the first and second secondary inductors, and the second electrical variable is formed by the difference between said signals, or vice versa.

5. The method as claimed in claim 1 , wherein the sensor output signal is used to check the plausibility of the information as to whether the sensor is in a faulty state.

6. The method as claimed in claim 5 , wherein in order to check the plausibility of the state of the sensor it is evaluated whether, within the possible values of the sensor output signal in a measuring range of the sensor, the sensor output signal corresponds to a value from an associated partial range of these values.

7. The method as claimed in claim 6 , wherein the partial range includes the center of the measuring range of the sensor, and preferably extends mirror-symmetrically with respect to the centre, wherein the partial range in particular takes up less than 40%, preferably less than 30%, of the measuring range.

8. A method for testing a sensor with a primary inductor which is galvanically isolated from first and second secondary inductors which are respectively coupled inductively to the primary inductor, comprising:

calculating a sensor output signal, wherein the sensor output signal is dependent on a coupling between the primary inductor and the first secondary inductor as well as that between the primary inductor and the second secondary inductor,

determining a first electrical variable, of an additional signal of the sensor, which is different from the sensor output signal, and

comparing the first electrical variable with a first limiting value in order to determine whether the sensor is in a faulty state,

wherein the first limiting value of at least one of the limiting values is formed by a value which is constant over the measuring range of the sensor and which lies between the value of the first electric variable in the case of a faulty state and all or the values of the electrical variable which are delimited by the partial range in the case of a non-faulty state.

9. The method as claimed in claim 1 , wherein the respective electrical variable is related to its maximum possible value within the measuring range of the sensor.

10. The method as claimed in claim 1 , wherein, in order to calculate the sensor output signal the signals of the first and second secondary inductors are subtracted from one another.

11. The method as claimed in claim 10 , wherein the sensor output signal is calculated in that the signals which are subtracted from one another form an AC voltage whose amplitude is rectified by means of a phase-sensitive rectifier, or in that the signals which are subtracted from one another are divided by their sum.

12. A device for carrying out a method as claimed in claim 1 .

13. A device comprising a memory and a processor, wherein the method as claimed in claim 1 stored in the form of a computer program in the memory, and the processor is designed to execute the method when the computer program is loaded into the processor from the memory.

14. A sensor comprising encoder, a primary inductor, which is galvanically isolated from first and second secondary inductors, and a device as claimed in claim 12 .

15. A sensor comprising encoder, a primary inductor, which is galvanically isolated from first and second secondary inductors, and a sensor as claimed in claim 13 .