Abstract: A transmitting/receiving circuit for an acoustic transducer (W1, W2) wherein the transmitting transducer (W1) is sequentially controlled by different modulated carrier frequencies (f1, f2), where the control is first matched to the inherent frequency (f1) of the transducer (W1) and afterwards the control of the transducer (W1) is by a frequency (f2) outside of the inherent frequency. During a signal reception by the receiving transducer (W2), a lock-out of a phase-locking circuit (PLL) is detected, where with an object to be measured is in a near range an active lock-out due to the frequency shift of the reception signal outside a frequency bandwidth of the phase-locking circuit is detected, and where with an object to be measured is in a far range, a passive lock-out is detected due to the fact that the reception signal amplitude falls below a noise level.

Abstract: A method for operating a transmitting/receiving circuit for ultrasonic signals includes the steps of producing a carrier frequency by a voltage-controlled oscillator having an output frequency controlled in accordance with a temperature dependency of an inherent frequency of the transducer, modulating the carrier frequency, applying the modulated carrier frequency in a transmitting mode to energize an ultrasonic transducer to produce ultrasonic transmission signals, switching from the transmitting mode to a receiving mode, applying output signals from the transducer representative of received ultrasonic signals to a phase-locked-loop circuit using the voltage-controlled oscillator whereby the phase-lock-loop circuit is automatically matched to a frequency of the received signals.

Abstract: An apparatus for detecting the distance of an object from a signal transmitter during radiation of a transmitter signal uses a first capacitor which is initially short-circuited by means of a first switch and subsequently is charged from a constant current source following an opening of the switch. Upon a reception of an echo signal, the charge of the first capacitor is transferred to a second capacitor by closing a second switch at the time of the echo signal reception. The charge on the second capacitor, which is proportional to the elapsed time between transmitted and received signals, is delivered to an output via a low pass filter with the output signal representing a distance measuring signal.

Abstract: A method for measuring the running time of a signal transmitted by a transmitter and received by a receiver is devised, where the signal is transmitted and received by the same transducer. For transmitting the transmitter is driven by an electrical pulse train, and in receiving the received signal is converted back into an electrical signal. In receiving triggering is done on the trailing edge of the envelope of the received signal. At the transmitting side the transducer after its incitement is driven by a pulse train being in phase opposition to the original inciting signal and having a larger amplitude than the original inciting signal which results in a higher steepness of the envelope. At the receiving side the maximum amplitude is measured, and the triggering point of time is determined when the actually measured value of the envelope falls below a certain percentage value of the maximum value.