Communications – electrical: acoustic wave systems and devices – Echo systems – Distance or direction finding
Patent
1994-06-01
1996-04-23
Pihulic, Daniel T.
Communications, electrical: acoustic wave systems and devices
Echo systems
Distance or direction finding
367 97, G01S 1508
Patent
active
055110410
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a process for setting the transmission frequency of a distance measuring instrument operating according to the echo-sounding principle, including at least one electro-acoustic transducer for emitting sonic or ultrasonic pulses and for converting received sonic or ultrasonic signals into electric received signals, a frequency-adjustable oscillator for generating an electric signal having the transmission frequency of the sonic or ultrasonic pulses which are to be transmitted for activating the electro-acoustic transducer, and an evaluation circuit for determining the travelling time of the sonic or ultrasonic pulses as a measure of the distance of a target object, the optimum transmission frequency being determined and tuned in the oscillator by analysing received signals obtained at different transmission frequencies.
A process of this nature is known from the PCT publication WO 90/08966. In contrast to other known processes in which the transmission frequency is adjusted to the resonance frequency of the electro-acoustic transducer, or is controlled as a function of the temperature of the transducer according to a known predetermined temperature characteristic curve for the electro-acoustic transducer, this process has the advantage that the entire measuring sequence comprising a transmitter, an interface with an acoustic space, a path to and from the reflective target object together with a receiver is involved in determining the transmission frequency. The solutions described in this publication are confined, however, to certain special cases. Thus, for determining echoes in the decaying range of the electro-acoustic transducer the most favourable higher or lower harmonic frequency for operating the system is to be determined by analysing the performance of the transducer and the receiver at the higher or lower harmonic frequencies within a predetermined frequency range; alternatively, when measuring echoes at low signal-to-noise ratios, the parameters characterising the background noise are to be determined and the pulse form and carrier frequency are to be adjusted in accordance with these parameters. No concrete solutions are disclosed, however, as to how the analyses are to be performed or how the parameters are to be determined, or how the transmission frequency can be determined as a function of the results obtained.
The present invention has as an object the provision of a process of the nature described above, which in a simple manner and using minimal circuitry permits an analysis of received signals, immediately providing the optimum transmission frequency.
This is attained according to the invention in that during the analysis of the received signals in each reception interval following the emission of a sonic or ultrasonic pulse the amplitude-time profile of the received signals is formed and integrated, that the integrated values obtained for different transmission frequencies are stored and that the transmission frequency of the oscillator is tuned to that frequency at which the maximum integrated value is attained.
In the process according to the invention the fact may advantageously be utilised that it is increasingly becoming the practice in recently adopted processes of distance measuring according to the echo-sounding principle to form the amplitude-time-profile of the received signals and to process these in order to determine the required echo and to determine its travelling time. Apparatus available for this purpose may also be utilised for the direct analysis of the received signals using the method according to the invention. The only additional measures are confined to integrating the amplitude-time-profiles for signals received at different transmission frequencies, and determining the transmission frequency at which the maximum integrated value is obtained. These measures require no additional circuitry if effected by suitably programming the computer forming the evaluation circuitry in the normal measuring procedure. This is readily feasible since th
REFERENCES:
patent: 4901245 (1990-02-01), Olson et al.
patent: 4905208 (1990-02-01), Dick
Endress & Hauser GmbH & Co.
Pihulic Daniel T.
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