Patent ID: 7994796

Claim:
A circuit arrangement for monitoring the function of a fill level measuring apparatus, comprising: a first piezo-electric vibration device as a transmitting device; a second piezo-electric vibration device as a receiving device; an oscillator circuit having an input and output respectively connected to the first and second piezo-electric vibration devices; first, second, and third switches; a first connecting line connecting a first connection of the second piezo-electric device to the first switch; a second connecting line connecting a second connection of the second piezo-electric device to the third switch; a third connecting line connecting a first connection of the first piezo-electric device to the second switch; and a monitoring circuit, wherein: the first and second switches connect the first and second piezo-electric vibration devices in parallel and the third switch disconnects from ground and connects the first and second piezo-electric vibration devices to a capacitance measuring apparatus during a temporary monitoring mode, a capacitance value (c) is supplied by the monitoring circuit as an indicator of the function of the first and second piezo-electric vibration devices and/or of at least one of the first, second, and third connecting lines.