A relay device according to an embodiment of the present invention comprises: a relay unit in which a switch operates according to a voltage applied to a coil; a first control unit that controls a voltage applied to the coil by turning on and off a first switching element according to a first control signal; a first discharge unit and a second discharge unit that discharge a back electromotive force generated in the coil when the relay unit is turned off; and a second control unit including a second switching element, and controlling the back electromotive force to be discharged through the first discharge unit or the second discharge unit by turning on and off the switching element according to a second control signal.

A magneto-inductive flow measuring device including a coil arrangement and a circuit for controlling a supply voltage of the coil arrangement. The circuit is designed to provide the supply voltage of the coil arrangement with a voltage curve sequenced as follows: A) the voltage rises from a starting voltage I up to an overvoltage II; B) in given cases, the voltage is held at the overvoltage II; C) the voltage falls from the overvoltage II down to a holding voltage V. The circuit controls the fall of the voltage from the overvoltage down to the holding voltage by tuning the voltage to at least two or more predetermined, intermediate, desired values III, IV.