Abstract: A switching signal, either for the switching off of the print head (20), or for a lowering of the operating frequency, or for a switching-on/switching-off control of a blower motor, is employed in connection with an installation of a temperature surveillance of a print head (20) or of a hammer block based on an electromagnetic coil construction. In order to achieve a more precise, a quicker and a more individual measurement determination, the electromagnetic coil (3), coordinated to each print element (1), is in each case switched during a current-passing pause to a primary constant current source generating a voltage (U.sub.p). A coil voltage drop (U.sub.s) at the electromagnetic coil (3) generates a reference signal (26) at the comparator (27) setting the temperature limit. The reference voltage (U.sub.ref) is received as a binary logic signal in an intermediate data memory storage (30).