A device for measuring a periodic signal is disclosed. The device includes a light source for generating an optical input signal directed at an object being measured from an electrical input signal generated by a driver device on the basis of a first clock pulse, an optical receiver for detecting and converting the signal received, a central control and measuring device is designed to generate the first clock pulse for the driver device and to receive and process the electrical measuring signal, and a voltage-supply apparatus for supplying the driver device. The central control and measuring device are preferably designed to generate a second clock pulse for the voltage-supply apparatus and to filter the electrical measuring signal on the basis of the first and/or second clock pulse. The frequency of the second clock pulse is an even multiple of the frequency of the first clock pulse.