Rust sensor

The sensor (10) has a structure of measuring electrodes (3) attached on a substrate (1). An electrical resistance between the measuring electrodes is measured as a measure for soot concentration of an exhaust gas flow. The structure of measuring electrodes is divided into two regions, where no soot particles are deposited on the region. The soot particles from the exhaust gas flow are deposited on the region. The regions are simultaneously exposed incidentally in the exhaust gas flow in dominant condition. The structure of the measuring electrodes is made of thin-film electrodes. An independent claim is also included for an electrical switch for evaluating a soot sensor.