Method for operating an electrostatic soot sensor

1. A method for operating an electrostatic soot sensor by means of a voltage supply, wherein the electrostatic soot sensor has a first electrode, a second electrode, and a guard electrode, wherein the first electrode and the second electrode are electrically insulated from one another by an insulating body, and the guard electrode is arranged between the first electrode and the second electrode, wherein the guard electrode is electrically insulated from the first electrode and the second electrode by the insulating body, the method comprising:

determining a dew point release;

applying a first electrical potential is applied to the first electrode by the voltage supply;

applying a second electrical potential to the second electrode by the voltage supply such that an electrical voltage arises between the first electrode and the second electrode;

applying a guard potential to the guard electrode by the voltage supply, wherein the applied guard potential is greater than the second electrical potential;

measuring a measuring current flowing between the first electrode and the second electrode with a current-measuring element;

disconnecting the first electrode from the first electrical potential to measure a leakage current flowing between the guard electrode and the second electrode; and

measuring the leakage current flowing between the guard electrode and the second electrode with the current-measuring element.

2. The method for operating an electrostatic soot sensor as claimed in claim 1 , further comprising:

filtering the leakage current measured by the current-measuring element using a low-pass filter.

3. The method for operating an electrostatic soot sensor as claimed in claim 1 , wherein the electrostatic soot sensor is arranged in an exhaust section of an internal combustion engine, and the leakage current is measured when the internal combustion engine has come to a standstill.

4. The method for operating an electrostatic soot sensor as claimed in claim 1 , wherein the electrostatic soot sensor is arranged in an exhaust section of an internal combustion engine, and the leakage current is measured when the internal combustion engine is operating in an overrun cut-off phase.

5. The method for operating an electrostatic soot sensor as claimed claim 1 , further comprising:

determining a soot content in an exhaust gas of an internal combustion engine by subtracting the leakage current from the measured measuring current.

6. The method for operating an electrostatic soot sensor as claimed in claim 1 , further comprising:

measuring a plurality of values of the leakage current;

storing the plurality of values of the leakage current in a memory element; and

identifying the electrostatic soot sensor as faulty if a value of the leakage current exceeds a previously defined limiting value.

7. The method for operating an electrostatic soot sensor as claimed in claim 1 , wherein the first electrode is connected to a ground potential (GND) after the first electrode has been disconnected from the first electrical potential.

8. The method for operating an electrostatic soot sensor as claimed in claim 2 , wherein the electrostatic soot sensor is arranged in an exhaust section of an internal combustion engine, and the leakage current is measured when the internal combustion engine has come to a standstill.

9. The method for operating an electrostatic soot sensor as claimed in claim 1 , wherein the guard electrode stabilises the electrical potentials to ensure that no leakage currents flow between the first electrode and the second electrode during the measuring operation.

10. The method for operating an electrostatic soot sensor as claimed in claim 1 , wherein the guard potential applied to the guard electrode is 0.5 V to 1 V.

11. The method for operating an electrostatic soot sensor as claimed in claim 1 , wherein the guard potential is greater than a ground potential (GND).

12. The method for operating an electrostatic soot sensor as claimed in claim 6 , further comprising:

repeating the measuring of the plurality of values of the leakage current to confirm that the electrostatic soot sensor as faulty.

13. The method for operating an electrostatic soot sensor as claimed in claim 1 ,

wherein the dew point release is measured using the guard electrode,

wherein a current is an indicator for the dew point release.

14. The method for operating an electrostatic soot sensor as claimed in claim 13 ,

wherein the current is driven via a moist insulating body to the guard electrode by a 1 kV voltage at the first electrode,

wherein a drying of the soot sensor is determined when this current drops by at least one power of ten after a start of the cold internal combustion engine.

15. The method for operating an electrostatic soot sensor as claimed in claim 1 , wherein the dew point release is determined by a current measurement between the first electrode 2 and the second electrode.

16. The method for operating an electrostatic soot sensor as claimed in claim 15 ,

wherein the current is driven via a moist insulating body to the guard electrode by a 1 kV voltage at the first electrode,

wherein a drying of the soot sensor is determined when this current drops by at least one power of ten after a start of the cold internal combustion engine.