DE3726670A1 - Separation measurement apparatus which operates on the principle of ultrasound propagation-time measurement - Google Patents

Abstract

The patent describes a method using which the signal propagation time of an ultrasound pulse, as is used for non-touching separation measurement, is determined exactly. For this purpose, an ultrasound pulse is transmitted which consists of a plurality of frequencies, the ratios between which are odd-numbered multiples. By breaking the echo down into its frequency components and determining the phase angle of the signals with respect to one another, it is possible to determine the phase angle of the complete signal, as a result of which a separation sensor constructed in this manner achieves a resolution which is less than the wavelength of the highest frequency used.

Description

State of the art

Ultrasonic distance measuring devices, such as those used in industry today already used many times, have a resolution and a Measuring accuracy that is two to five times as large as the waves length of the frequency used. State of the art is through Rectification and smoothing to form the envelope of the echo. The envelope signal is minimized with a comparator height queried. A strong echo therefore switches the comparator inevitably earlier than a weak echo from the same Distance, which causes measurement errors.

To avoid these disadvantages, the echo is invented evaluated in its entire course. Since the temporal If the beginning of an echo cannot be determined exactly, it can be used an error occurs from just one frequency, which is exactly one Vibration length corresponds. According to the invention is therefore a Ultrasonic signal is used, which consists of at least two frequencies exists that are in an odd ratio to each other.

The echo shown in Figure 1 consists of two frequencies in a ratio of 1 to 1.6. Fig. 2 and Fig. 3: The two frequencies shown ( Fig. 2 and 3) only have the same phase relationship to each other every 5 or 8 vibrations. The evaluation can be carried out in the manner described below: The echo signal ( Figure 1) is broken down into its frequency components ( Figures 2 and 3). The sinusoidal signals determined (Figure 2 and 3) are converted into rectangular signals (Figure 4 and 5), from whose falling or rising edge needle pulses are formed (Figure 6 and 7). An AND link is used to determine whether needle signals are occurring in the signals ( Figures 6 and 7) at the same time. The result of the AND operation is shown in Figure 8. The technical circuit is shown in Figure 10.

Ultrasonic receiver ( 1 ), amplifier ( 2 ), filter ( 3 ) ( 4 ), comparator for forming the square wave signals ( 5 ), ( 6 ) with subsequent differentiators for needle pulse formation, and gate ( 7 ).

The needle pulse obtained in this way can be used to measure the running time be used.

Claims (6)

1. Distance measuring device, which is based on the principle of an ultrasonic transit time measurement, characterized in that an ultrasonic signal is emitted which consists of a sum of frequencies, whereby a typical signal curve is formed and the typical echo is thus broken down into its frequency components and the time ver is used for transit time measurement, at which the waveforms of all frequencies used simultaneously pass through the sine angle 0 degrees and this point in time is determined by the fact that the signals are converted by comparators into rectangular pulses, from whose falling or rising flank needle pulses are formed and the simultaneous occurrence the needle pulse is determined by an AND gate, whereby the distance measurement in its resolution is smaller than the wavelength of the largest frequency used. 2. Distance measuring device according to claim 1, characterized in that several ultrasonic receivers ver are used that selectively receive only one frequency at a time, which saves the filters. 3. Distance measuring device according to claim 1 and 2, characterized in that the echo curve from a transient recorder, whose sampling rate is a multiple of the ultrasound Frequency is recorded and then by a computer is examined for its phase position and its typical course, whereby the distance measurement in its resolution is smaller than that Wavelength of the largest frequency used and noise immunity increases significantly compared to external noise.   4. Distance measuring device according to claim 1 to 3, characterized in that the calculator the frequencies and phases were determined by a Laplace transformation and the point in time used for runtime measurement, on which the signal curves of certain Frequencies simultaneously determined sine angles, e.g. B. 0 degrees to run. 5. Distance measuring device according to claim 1 to 4, characterized in that the calculator the echo time by determines an auto-correlation calculation. 6. Distance measuring device according to claim 1 to 5, characterized in that the transient recorder is a car correlation register is connected upstream and the output signal of the autocorelation register is saved in the transient recorder becomes what relieves the computer of the calculation of the correlation.