Patent ID: 8688391

Claim:
A method for determining the erosion of contacts of an electromagnetic switching device, comprising: measuring a mechanical variable, which characterizes a time profile of relative movement between the contacts, the relative movement between the contacts being caused by movement of an actuator, the mechanical variable being measured during a switch-on operation in which the contacts are closed; determining a time at which the contacts close by evaluating the time profile of the relative movement; using the time profile and the time at which the contacts close to monitoring a distance covered during the switch-on operation by either: determining a distance covered by the contacts from a beginning of the switch-on operation until the time at which the contacts close, or determining a distance covered by the actuator from the time at which the contacts close until an end position of the actuator; and comparing the distance covered with a stored reference value, wherein the mechanical variable is measured by a sensor, which is coupled mechanically to the actuator, and the sensor is selected from the group consisting of a velocity sensor, an acceleration sensor, and a displacement sensor.