The disclosed seat belt tensioner for a seat belt system may comprise a seat belt spindle, a gearwheel connected to the seat belt spindle, and a latching pawl for locking the seat belt spindle in the tensioned position by engaging in the teeth of the gearwheel. The apertures each have a periphery, and each of the apertures has at least one protrusion extending inwardly from the periphery. Pressure within the workpiece is monitored and the resulting pressure information is used for maintaining a condition that exhibits the hollow cathode effect. In order to form the guard ring, a guard ring opening etching stop film is formed on a fuse line.