Abstract: A method for operating an ultrasonic measuring device for measuring a property of a medium includes: an arrangement of at least two pair of ultrasonic transducers for emitting and receiving ultrasonic signals across a signal path through a fluid; a holding apparatus having a wall in contact with the medium and a flat wall section for holding the ultrasonic transducers; an electronic circuit configured to operate the ultrasonic transducers and to provide measured values of the property, wherein the ultrasonic transducers form Lamb oscillations in the respectively associated wall, wherein at least two pair of the at least two pair of ultrasonic transducers each excite and capture different modes of Lamb oscillations, wherein the different modes are excited in groups, wherein a time delay between temporally adjacent emissions of ultrasonic signals is shorter than a shortest propagation time of the ultrasonic signals between associated ultrasonic transducers.

Abstract: A traffic signalling apparatus wherein LEDs are employed to present various displays and the LEDs are secured with their sidewalls in a tubular holding device such that a good heat discharge from the LEDs to the holding device is guaranteed. The holding device is securely fixated in a front plate of the signalling apparatus, preferably detachably. An optical imaging device is additionally provided in order to achieve an emission characteristic which is optimized for traffic participants.