Electrostatic soot sensor

1. An electrostatic soot sensor comprising:

a voltage supply;

a first electrode;

a second electrode;

a guard electrode; and

an insulating body isolating the first electrode and the second electrode from one another;

wherein the guard electrode is arranged between the first electrode and the second electrode and the guard electrode is electrically insulated from the first electrode and the second electrode by the insulating body;

wherein a first electrical potential is applied to the first electrode by the voltage supply and a second electrical potential is applied to the second electrode by the voltage supply, with a resulting electrical voltage between the first electrode and the second electrode; and

a guard potential is applied to the guard electrode by the voltage supply, wherein the guard potential corresponds to a first guard potential in the warm-up phase of the soot sensor and to a second guard potential in the measuring phase of the soot sensor.

2. The electrostatic soot sensor as claimed in claim 1 , wherein the voltage supply switches the guard potential present at the guard electrode from the first guard potential to the second guard potential when a dew point release is reached.

3. The electrostatic soot sensor as claimed in claim 1 , wherein an absolute value of the first guard potential is closer to an absolute value of an electrical potential present at the higher of the first electrode or the second electrode than the absolute value of the second guard potential.

4. A method for operating an electrostatic soot sensor having a voltage supply, a first electrode, a second electrode, and a guard electrode, the method comprising:

applying a first electrical potential to the first electrode with the voltage supply;

applying a second electrical potential to the second electrode with the voltage supply;

wherein an electrical voltage arises between the first electrode and the second electrode; and

applying a guard potential to the guard electrode with the voltage supply;

wherein the guard potential corresponds to a first guard potential in the warm-up phase of the soot sensor and corresponds to a second guard potential in the measuring phase of the soot sensor.

5. The method for operating an electrostatic soot sensor as claimed in claim 4 , further comprising switching the guard potential from the first guard potential to the second guard potential when a dew point release is reached.

6. The method for operating an electrostatic soot sensor as claimed in claim 4 , wherein an absolute value of the first guard potential is closer to a higher of two absolute values of the electrical potential at the first electrode or at the second electrode than the absolute value of the second guard potential.

7. The electrostatic soot sensor as claimed in claim 1 , further comprising a processor programmed to evaluate a current gradient in a dropping branch of a normal curve or of a fault curve, and on the basis of the current gradient differentiates between a faultless and a faulty soot sensor.

8. The method for operating an electrostatic soot sensor as claimed in claim 4 , further comprising evaluating a current gradient in a dropping branch of a normal curve or of a fault curve; and

based on the current gradient, differentiating between a faultless and a faulty soot sensor.

9. The method for operating an electrostatic soot sensor as claimed in claim 4 , wherein the first electrode and the second electrode are electrically insulated from one another by an insulating body;

the guard electrode is arranged between the first electrode and the second electrode; and

the guard electrode is electrically insulated from the first electrode and the second electrode by the insulating body.