The electromagnet has an exciter coil (41) wound on a coil body (90) and surrounded by a housing cover (11). A pole core (30) extends into the coil body. A pole plate (44) extends radially in front of the end face of the coil body between the pole core and the housing cover. The pole core has a partially circulating recess (50) on its outer side which radially faces the pole plate. The pole plate has a partially circulating recess (49) on its inner side which radially faces the pole core. The pole core and pole plate can be rotated against each other to change the covering of both recesses.
