Importance

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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.

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First Claim