A field transmitter F, a control device B is in the form of a separately portable unit linked to a field transmitter S1 by radio over short ranges. This eliminates the need to make a direct visit to an inaccessible field transmitter S1 for control purposes. In addition, one control device B can be used to control a plurality of field transmitters S1, S2, S3, A1, A2 by radio. In situ control, which is normally permanently integrated into the field transmitters S1, S2, S3, A1, A2, can be dispensed with.