Abstract: A single-shot element, an interruption element and a valuation device are arranged for indicating signal pulses having a duration which exceeds a limit value and to suppress disturbing pulses having durations which are less than the limit value. Upon each leading edge of any pulse, the single-shot element begins to generate a control pulse which ends either due to an interruption or when its duration reaches the limit value. The interruption element interrupts the control pulses by means of the trailing edges of the disturbing pulses. While uninterrupted control pulses cause, the valuation device to generate indication signals which indicate a signal pulses.