The sensor detects the rotation of the small star-shaped wheels, called scaling stars, within the meters, as part of the gravimetric testing process.
Up until now, Invensys had been using its own contrast sensor for this task. This was necessary 30 years ago because commercial sensors could not cope with all the possible sensing conditions. For example, the viewing window between the scaling star and the sensor can be made of glass or plastic. In addition, the scaling stars come in many shapes and colors.