FI89835B - Method and device for determining the speed of a gas flowing in a pipe - Google Patents

Abstract

Acoustic flow measurement method and device for determining the flow speed of gases and/or gas derivatives. In a measuring pipe 1 two microphones 3a, 3b have been mounted at a given longitudinal distance L from each other with two loudspeakers 2a, 2b outside these, which supply sound to the measuring stretch L which is delimited by the microphones 3a, 3b, which sound is in the form of stationary broadband sequences in the direction of the flow Sd(tT) and against the flow Su(tT). The frequency range of the sequences Sd(tT) and Su(tT) is selected so that only a basic mode in the form of a flat wave front can advance without being suppressed. In addition the sequences Sd(tT) and Su(tT) are selected so that they are orthogonal to each other and have no common frequency components except for zero. The detector signals which are picked up by the microphones 3a, 3b are processed by a signal processing arrangement essentially in real time, which produces different kinds of correlation functions or Fourier transformations of the same. From these the system determines in addition different kinds of alternative algorithms by applying the transit time of the said sound in the measurement stretch L with the flow and against the flow and from these and from the cross section of the pipe and the density which was determined for the gas, determines the flow speed, volume flow and/or mass flow. <IMAGE>

Description

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Method and apparatus for determining the velocity of the gas flowing in a pipe Förfarande och anordning för bestämning av gaastigheten pä en gas som strömmar i ett rör 5

The invention relates to a method for measuring the flow rate, volume flow and / or mass flow of a gas flowing in a pipe, in which sound sensors are arranged in the flow pipe at a certain longitudinal distance 10 sound and flow rates are determined by the travel times of said sound upstream and downstream in the measurement range, the cross-sectional area of the pipe and the density of the gas to be measured.

The invention further relates to a device for measuring gas flow rate and / or quantities derived therefrom, such as volume flow and / or mass flow, which device comprises a measuring tube in which the flow to be measured flows and which device 20 comprises wideband, low frequency and only plane wavefront sound signals and transmitters power amplifiers, microphones and microphone signal amplifiers as sound detectors, and each device is equipped with calculation devices and software for calculating said flow rate or quantities from the sound detectors, the longitudinal distance of the flow tube, the cross-sectional area of the measuring tube and the flow density, the flow gas density upstream on the distance between the sound detectors.

It is known that the rate of propagation of an acoustic piston mode in a pipe does not depend on the flow profile or other profiles causing local sound velocity variations, but on the average flow rate integrated over the pipe cross-section and the resting B. velocity of the gas composition filled with the pipe. Robertson "Effect of arbitrary temperature and flow profiles on the speed of sound in a pipe" J. Acoust. Soc. Am., Vol 62, No. 4, pp. 813-818, October 2 fc $ ι; 5 i; 1977 and B. Robertson, "Flow and temperature profile independence of flow measurements using long acoustic waves," Transactions of the ASME, Vol 106, pp. 18-20, March 1984]. Accurate, profile-independent flow rate measurement is thus possible by measuring the travel times of the piston mode upstream and downstream 5 within a certain measurement interval, preferably using broadband sound, as disclosed in the applicant's FI patent No. 76885. In order for the higher wave modes interfering with the measurements to be attenuated already in the vicinity of the sound sources, the sound frequency must be sufficiently below a certain cut-off frequency depending on the shape and dimensions of the flow tube and the speed of sound propagation. For a round tube, this cutoff frequency 10 is

The cut-off frequency fe = (c - vwac) / (1.7 * D) (1) where c is the speed of sound in the resting gas, vmax is the maximum rated flow rate and D is the pipe diameter. It is known that flow rates can be calculated from formulas

Flow rate [m / s] v = 0.5 * L * (t / J -1 ^ 1) (2) 20 Volume flow [m ^ / s] Q = v * A (3)

Mass flow [kg / s] M = Q * p (4) where 25 v is the average flow rate L is the distance between the sound sensors in the longitudinal direction of the pipe 11 is the flow time of the sound downstream between L t2 is the flow time of the sound upstream between LQ is the volume flow 30 A is the cross-sectional area of the pipe M is the mass flow p is the gas density I: k 'J · 1 · ό i'j 3

Em. The FI patent discloses the measurement of transit times by correlation technology and the FI patent does not restrict the choice of broadband transmission or correlator type in any way. The subclaims describe the use of a polarity correlator, which can be implemented in full parallel. In practice, it has been found that achieving the required signal-to-noise ratio with the polarity correlation technique in generally noisy measurement conditions requires that audio transmissions be transmitted alternately upstream and downstream and that microphone signals be filtered to pick up only transmitted audio and eliminate interference. The sound transmitted in the form of frequency-scanning and the filter connected to follow it in principle also allow sound to be transmitted in both directions simultaneously, but at different instantaneous frequencies, so that the forward and counter-current signals of both sound sensors can be separated by a total of four sweepable filters. : o 916102.

A disadvantage of the prior art discussed above is that the frequency sweep is in principle non-stationary, in which case the necessary filters are also time-dependent. This causes dispersion, i.e. the delay of the filters is frequency dependent, which further causes an easy error in determining the running time, unless the sweep is selected correctly, the sweep is selected too fast or the start and end of the sweep are omitted from the measurement. These disadvantages can be avoided if stationary, broadband transmissions are used instead of frequency scanning, in which all frequencies ring at a constant amplitude at all times. At the same time, this means that sound is transmitted in both directions at the same time. For example, current DSP technology enables versatile real-time processing of audio frequency signals 25 and offers several possibilities for determining transit time information in a noisy environment.

In order to eliminate the above-mentioned drawbacks and to achieve later goals, the method of the invention is mainly characterized in that said sound is transmitted to the flow tube in the measuring interval simultaneously in both directions as stationary, periodic sequences, downstream sequence Sd (t, T), and downstream where T is the length of the period and t κ 9 9 / '· - 4 is the relative time measured from the beginning of each period, and that said sequences Srf (t, T), Su (t, T) and are orthogonal to each other, i.e. they have no common , non - zero frequency components.

The device according to the invention, in turn, is mainly characterized in that the sound transmitted via said loudspeakers consists of wideband, sequential, simultaneously downstream and countercurrently transmitted sequences T in the downstream sequence Sd (t, T) and the countercurrent sequence SM (t, T), which sequences Sd (t, T), Su (t, T) and are arranged to be orthogonal to each other, i.e. they do not contain common non-zero frequency components.

In the following, the theoretical background of the invention and some application examples of the invention will be described in detail with reference to the figures of the accompanying drawing, in which Fig. 1 is a block diagram and a lower curve of a correlation peak of odd frequencies thought to be measured upstream, Fig. 4 shows an embodiment corresponding to Fig. 3, in which its Hilbert transform is chosen instead of the second correlated sequence, Fig. 5 shows phase-difference curves with even and odd frequencies reflection echoes, and Figure 6 shows the cumulative distributions corresponding to Figure 5.

5 t: c:

Figure 1 shows a general block diagram of a system by which the invention can be advantageously implemented. The flow to be measured, e.g. the natural gas flow, travels at speed v in a flow pipe 1 with sound sources 2a and 2b, preferably speakers generating sound sequences in flow pipe 1. Between sound sources 2a 5 and 2b sound transducers 6a and 6b are arranged. A determine the scaling factor of the flowmeter. Fig. 1 4a and 4b are power amplifiers, 5a and 5b are signal amplifiers, 6 is a real-time processor, preferably a digital signal processor with the necessary analog inputs and outputs, which can implement procedures based on FFT algorithms or FIR filter-10 algorithms, 7 is a system through which communication between the real-time processor 6, the display device 8 and the separate PC workstation 9 is implemented.

In determining the travel time of stationary, wideband sound for flow measurement purposes, it is essential that the sounds transmitted simultaneously from the speakers 2a and 2b in both directions do not interfere with each other and that the measurement is also as insensitive as possible to the noise of the pipe 1. Consider the periodic but otherwise arbitrary sound sequences of the speakers 2a and 2b for a given measurement period T. It is known that such signals consist of discrete, evenly spaced, multiple frequency components AWJ * cos (m * 2 * 7r * t / T + 0 /> J) of the fundamental frequency / = 1 / T, which are orthogonal to each other, i.e. over a period the calculated correlation functions disappear when m and n are different large (Equation 5).

T

2 Λ £ Λ = Am * An * 6mjt * cos (m * 2n * -j) (5)

The main idea of the invention is to transmit downstream and upstream of the speakers 2a and 2b to the measuring tube 1 such wideband and continuous audio sequences, S 1 (t, T) and Su (t, T), which do not contain any common frequency components and are thus orthogonal, i.e. their the correlation function identically disappears: k Q Γ s 6 ~ rc * (0) = JS pj) * Su (t-QJ) * dt SO (6) o Then the signals of the microphones 3a and 3b, let D ^ (t, T) be L the signal of the left end microphone 3a and the signal of the right end microphone 5 3b of the DÄ (t, T) range, except for background noise, can be unambiguously decomposed into mutually orthogonal upstream and downstream components: DL (t, T) = DjJf, T) + DJtJ) DR ( t, T) = D ^ tJ) + D ^ tJ) U) This main idea of the invention makes it possible to solve many problems that degrade the signal-to-noise ratio and leads to a number of different implementation options. Over a period of more than 10 minutes, only the smaller part of the external pipe noise hits these discrete frequency components, the more periods over which the situation is considered. In averaging over N periods, the periodic signal increases in direct proportion to N, while the non-eccentric noise increases in proportion to the square root of N.

15

The phase angles of the discrete frequency components can in principle be chosen freely. In order to minimize the effect of the non-linearity of the speakers 2a and 2b or similar sound sources and for example due to the safety regulations of the natural gas pipelines, momentary sound power peaks should be avoided. This goal is well achieved 20 if said phase angles are chosen randomly. The frequency range used is limited at the upper end by the so-called a cut-off frequency [formula (1)] at which, in addition to the piston mode, the first unattenuated higher mode appears, which has a different propagation speed and thus interferes with the accurate determination of the propagation speed of the piston mode. At the lower end, the mains frequency of the AC network and the frequencies lower than its first supercar 25 should often be cut off.

li W '%:' Ί; r 7 The division of the remaining frequencies between the upstream and downstream audio sequences can be done in different ways. The simplest is to choose even frequencies for one sequence and odd frequencies for another. This selection results in each sequence consisting of two half-cycles, of which the half-cycles of the even frequencies 5 are identical to each other, as shown in the upper graph of Figure 2, and the half-cycles of the odd-numbered frequencies are also identical to each other, as shown in the lower graph of Figure 2. Thus, the upstream and downstream sounds can be simply distinguished from each other by adding an even number of half-cycles together a second time as such and a second time 10 by first changing the sign of every other half-cycle. Another option is to draw the available frequencies irregularly but evenly into the upstream and downstream sequences.

The travel times of the measurement sound in the measurement interval L upstream and downstream can be determined from the same measurement data in several different ways. The basic options are to form a filtered correlation function of the signals of the microphones 3a and 3b as a function of the time difference or to consider the the phase shift of successive frequency components of the signals as a function of frequency. The fast Fourier transforms of digital signal processors with FFT algorithms allow the signal to be processed in time and frequency space 20 on exactly the same devices as needed, interfering only with the real-time program.

Determining the travel time of the measurement sound from the correlation functions is as follows. The most ideal situation for determining the center of the correlation peak is when there is only one peak in the whole correlation function, i.e. the amplitudes of the other possible peaks are so small that their distortion in the region of the main peak is below the allowed level. The origin of the interference peaks may be in the wrong direction of the propagating background noise, from which the correlation filter has left the selected frequency components in the main peak or the sensor connections and connections that cause the 30 interfering echo peaks. If the interference peaks cannot be attenuated small enough, their location and area of influence must be sought to get the main peak out of range. The location of the echoes can be influenced by the connections of the sensors 3a and 3b

b 9 Π 9 S

8 placement and the area of influence so that the frequency dependence of the amplitudes of the frequency components is made uniform while avoiding sharp points of discontinuity. Three different correlation functions can be formed from the signals of the microphones 3a and 3b

n * T

C (0) = -L · f Averm [DL (t, Dl * Averm [DR (t-Q, T,)} * dt n * TJ0

n * T

CW = - ^ f Fd * Averm [DL (t, Dl * Averm [DR (t-Q, T)] * dt n * T o

n * T

/ AverJDu.ftT)] -AverJDJyt-O.T)], dt (8)

n * T o n * T

Ce (0) = J- / Fu * Averm [DL (t, Dl * Averm [DR (tQ, Dl * dt n * T o «* r -LiAw'JPJtm'fimJPJt-VH '* n * T0 5 where Fd and Fu denote filter operators that extract only the downstream or countercurrent portion of the detector signals, Averm means averaging over m periods and averaging n correlation functions by integrating over n periods.The first correlation function is the simplest and contains essentially two peaks, and the other with a negative delay value of 10 corresponding to the flow of sound upstream and downstream.This is also the most sensitive to interference.Each of the following filtered correlation functions contains essentially only one peak, the other corresponding to the flow of sound only downstream and the other only upstream, Figure 3 shows the upstream downstream. a correlation peak consisting of even frequencies and correlates consisting of odd frequencies considered to be measured downstream 15 below The small side peaks are caused by negative reflections from the speaker branches.

Instead of directly correlating the microphone signal of each, upstream or downstream to the selected frequencies, each signal of the microphones 20a and 3b can be correlated separately to a constant phase reference sequence with the desired amplitude distribution, Rrf (t, T) and RM (t, T) derived from the corresponding transmission sequences Sd (t, T) and Su (t, T) of li b '«<' 7- ϋ 9 or from the microphone sequences measured in the zero-flow situation and producing the following correlation functions

T

cjfi, D = fRJM) * DL (t-e, D * dt t m CJQJ) = fR £, T) * DR (t-Q, T) * dt o

T

C J0,7) = fRu (t, 7) * DL (t-QJ) * dt tm C ^, 7) = [Ru (t, T) * DR (tQ, T) * dt o where the time of sound in the measurement interval L downstream is determined as the time difference between the centers of the peaks of the correlation functions £ χ ^ (θ, Τ) and CRd (Θ, Τ) and upstream as the time difference between the centers of the peaks of the correlation functions CLu (6, T) and C ^ U (6, T). For this, either two FIR filter pairs (finite impulse response) can be used, one of which is the downstream reference sequence and the other the countercurrent reference sequence, respectively, or the operation can be performed in frequency space-10 sa as the following multiplications of the components of Fourier transform vectors ^ (ω /) = Λ + Ζ) ι (ω /) (l0b) where * as superscript means complex conjugate, and inversely converting the input vectors into time-space correlation functions. Again, it is possible to make averages similar to those made for the correlation functions.

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Instead of the usual correlation function, which ideally produces completely symmetric peaks, in all the above cases, instead of another sequence to be correlated, a Hilbert transform can be chosen, whereby the correlation peaks become completely antisymmetric. The center of these zero plane 5 intersections may be more accurately determined than the center of the symmetrical peaks. This case is illustrated in Figure 4, which, except for symmetry, otherwise corresponds to the case shown in Figure 3.

Determining the travel time as a frequency dependence of the phase angle is as follows.

10 If the correlation function contains essentially only one peak, the phase angle of its Fourier transform increases or decreases linearly as a function of frequency, the slope being proportional to the peak displacement from the origin, because the time displacement Θ is realized in frequency space by multiplying by exp (2ffi * <a7 * 0). An estimate of the travel time of the measurement sound in the measurement interval L is now obtained by averaging the phase angle differences calculated over 15 consecutive frequency steps of the same parity between 17 ... l2:, * ~,, * Σ argus [D ^ M) iD ^ o),))] 2π /,, - < U) θ- =? Λ- ,, * Σ argutiPi ^ u, .j) * /> * (<*> i + 1) ^ (ω,) * 0Λι (ω /)]

In the formulas (11), Fourier transforms of the signals of the microphones 3a and 3b have always been used as frequency vectors. As discussed above in connection with the correlation functions, also in formula (11) the vector derived from the signal of the second detector 3a, 3b can always be replaced by a Fourier transform of the reference sequences Rd (t, T) and R „(t, T) to give the next four time shifts? dRd, dLu and QRu. Travel times downstream are obtained as the difference between the first two and travel time upstream is obtained as the difference between the latter two. In all the above cases, the successive phase angle differences can alternatively be formed as a cumulative function, and the time shifts can be determined as the slope of this regression line.

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If there are other peaks in the correlation function, modulation occurs in both the phase difference distribution and the cumulative function. However, the right line is not dropped if the phase angle difference truly remains between -7Γ ... + 7Γ. The risk of exceeding or falling below these limits is reduced if the mean of the phase angle diff-5 rents remains close to zero. For this reason, it is worth comparing the actual travel time with, for example, the travel time of the zero flow situation of the reference pipe 1, in which case only the travel time difference caused by the flow rate v is shown as a small deviation from zero of the average phase difference distribution. Figure 5 shows the phase difference graphs 10 for both even and odd frequencies in the case where the modulation is due to reflection echoes alone. Figure 6 shows the corresponding cumulative distributions.

The applicability of the phase angle method requires that the correlation function have a distinct principal peak and that the phase angle of its Fourier transform at each individual frequency is reasonably close to the value corresponding to the travel time of this peak.

The following claims set forth within the scope of the inventive idea, the various details of the invention may vary and differ from those set forth above by way of example only.

Claims (12)

12 S Q> 'λ · - A method for measuring the flow rate, volume flow and / or mass flow of a gas flowing in a pipe, the method comprising fitting sound sensors (3a, 3b) to a flow pipe (1) 5 at a certain longitudinal distance between the measuring pipe (1) and the measuring distance (3a, 3b) L) from outside the flow pipe (1) is supplied with sound sources (2a, 2b) long-wave, only in the basic mode, as a plane wave front in the flow pipe (1) upstream and downstream and flow rates are determined from the travel times of said sound 10 downstream and downstream of the pipe (L) (A) and the density (p) of the gas to be measured, characterized in that said sound is transmitted to the flow tube (1) in the measurement interval (L) simultaneously in both directions as stationary, periodic sequences, downstream sequence Sd (t, T) and countercurrent sequence Su (t), Where T is the length of the period and t is the relative time measured from the beginning of each of the 15 cycles, and that said sequences Sd (t, T) and Sy (t, T) are orthogonal to each other, i.e. they have no common, non-zero frequency components. A method according to claim 1, characterized in that the mutually orthogonal sound sequences Sd (t, T) and Su (t, T) are formed such that, with respect to their fundamental frequency corresponding to their repetition period, the sequence Sd (t, T) / Su (t, T) contains only even and the sequence Sy (t, T) / Sd (t, T) to be transmitted in the other direction only odd frequency components. Method according to claim 1 or 2, characterized in that the travel time of said sound in the measurement interval (L) upstream and downstream is determined in time space by the correlation functions formed by the left sensor signal DL (t, T) and the right sensor signal DÄ (t, T). as the offset values of the center of the peaks from the origin or as the difference between two such offsets, forming one correlation function from the signal of each sensor (3a, 3b) as such, first averaging over several (m) periods T by summing or averaging the correlation function over several (n) periods ; ?, c 'v. w' by determining, and determining the transit times of the correlation function H * TC „(0) = - ^ 1 * f Averm [DL (t, T>] * Averm [DR (te, T)] * dt n * T o as the time offsets of the two main peaks from the origin. Method according to claim 1 or 2, characterized in that the travel time of said sound in the measurement interval (L) upstream and downstream is determined in time space by correlation functions formed from the left sensor signal D1 (t, T) and the right sensor signal DÄ (t, T). as the offset values of the center of the peaks contained in it from the origin or as the difference between two such offsets, 10 generating the signal from each sensor as such, first averaging over several periods (m) or integrating the correlation function over several (n) periods, integrating two different correlation functions; with the downstream filter Fd and the other Cu (0) filtered with the countercurrent filter Fu, and determining the travel times of the two correlation functions n * T Q0) = -i- / Fd * Averm [DL (t, 7)] * Averm [DR (tB, T)] * dt non * T cw (0) = -L f Fu * Averm [DL (t, T)] ^ verw [Z) Ä (f-0,0)] * dt n * T o 15 as the time shifts of the only major peaks from the origin. Method according to claim 1 or 2, characterized in that the travel time of said sound in the measurement interval (L) upstream and downstream is determined by forming in time space the left sensor signal DL (t, T) and the right S 9 Π? 5 14 sensor signals DÄ (t, T) always from one detector signal as such or averaging over several (m) periods, and from one of the two fixed-phase, memory-read reference sequences, Rrf (t, T) or Ru (t, T), which is derived from the corresponding transmission sequences or zero-current detection-5 ris sequences, possibly over several more periods by integrating a total of four correlation functions CLd (t), CRd (t), CLu ^ J'a cäu (1) η · Τ CJB) = -L · f R ^ t, T) * Averml (DL (t-ByT)] * dt n * T o H * T Λ · Τ CJB) = -L · f Ru (t, D * Averm [DL (t-Btiy \ * dt n * l J0 n * T CÄ (0) = -L f Ru (tJ) * Averm [DR (t-ByT) \ * dt and determining the travel time downstream as the time difference and travel time of the centers of the correlation functions C ^ B) and CRJB) 10 upstream as the time difference between the centers of the principal peaks of the correlation functions CLu (t) and CÄW (t), respectively. Method according to one of Claims 1 to 5, characterized in that Hilbert transforms are used as correlation functions instead of substantially symmetric peak-containing correlation functions, and the meanings of the substantially antisymmetric correlation functions thus obtained are determined preferably as time values where the function changes most sharply. Method according to Claim 1 or 2, characterized in that the travel times of the sound upstream and downstream are determined in frequency space by first forming Fourier transforms of the sound sensor sequences as complex frequency vectors ϋ ^ (ω;), Diu (<o;), T> Rd (< u> j) and DÄU (o>;) and DÄW (o>}) and determine the travel time of the sound downstream Bd and the travel time upstream Bu essentially S 9 Γ 7 '5 15 from the formulas T h θ, = -— jr — ττΣ orguslDjt ^) * Da <j (ω *)] 2tci, T k β .--— ΤΓΤτΣ ®A (“i. |) 2π * (Ζ2- / 1) ti of which in the upper formula the index 1 is only even and in the lower formula only odd frequency values . 5 Method according to Claim 1 or 2, characterized in that the travel times of the sound upstream and downstream are determined in frequency space by first forming Fourier transforms of the sound sensor sequences as complex frequency vectors DLd (w;), ϋ ^ (ω j), ϋΛ ^ (ω}) and ϋΛΐί (ω 7) and Fourier transforms of fixed-phase reference sequences derived from 10 transmission sequences or zero-transducer sound sensor sequences as complex frequency vectors Rd ((i) j) and Ru (<ii j), and determine the time travel of the sound downstream of% d and travel ®Rd ~ ®Ld = 15 where QLd, ΘRd, QLu and ΘRu are determined essentially by the formulas T ^ eu = * 2_ <1 J, T ^ * 2 “M <i T ^ θι * = -Γ-Τ-Σ * ί £ (ωΜ) * Λ; (ω,) * Ζ> (ω,)] h ~ li *, τ 11 Θλ s Τ ^ ΓΣΛΓ ^ [Λ1, (ω | .1) * ^ (ωίΜ) * Λ; (ωί ) * Ζ) Αί (ωρ] * 2 ~ * 1 * ι b 9 B 3 S 16 in which in the two upper formulas the index 1 is only even and in two ale in one formula only odd frequency values. An apparatus for measuring a gas flow rate and / or quantities derived therefrom, such as volumetric flow and / or mass flow, comprising a measuring tube (1) in which the flow to be measured flows, and comprising broadband, low frequency planar wave only propagating in the basic mode. the loudspeakers (2a, 2b) and their power amplifiers (4a, 4b), the microphones (3a, 3b) and the microphone signal amplifiers (5a, 5b) as sound detectors, and each of the 10 devices is equipped with calculation devices and programs for determining the flow rate or quantities; to calculate the sound between the sound detectors (3a, 3b), the longitudinal distance (L) of the flow tube (1), the cross-sectional area (A) of the measuring tube, the flow-gas density (p) and the travel time of the audio signals downstream (t;) and upstream (t2) in the distance (L) between the detectors (3a, 3b), characterized in that the sound transmitted via said speakers (2a, 2b) is composed of the wideband, concurrent, sequences transmitted simultaneously in the period T upstream and downstream, the downstream sequence Sd (t, T) and the countercurrent sequence Su (t, T), which sequences Sd (t, T) and Su (t, T) are arranged orthogonally to each other therefore, they do not contain common non-zero frequency components. 20 Device according to Claim 9, characterized in that the sound transmitted in the second direction contains only even and the sound transmitted in the second direction contains only odd frequency components. Device according to Claim 9, characterized in that the sound transmitted in the second direction contains only even and the sound transmitted in the second direction contains only odd frequency components. Device according to Claim 9 or 10, characterized in that the device comprises a real-time signal processor (6) for producing the input sequences of the audio sources to be transmitted and for processing the responses produced by the audio detectors (3a, 3b). Device according to Claim 9 or 10, characterized in that the device comprises a real-time signal processor (6) for producing the input sequences of the audio sources to be transmitted and for processing the responses produced by the audio detectors (3a, 3b). Device according to claim 11, characterized in that the device further comprises a system processor (7) which takes care of communication with said real-time signal processor (6), a possible digital display device li S 9 i '~' i 17 Device according to claim 11, characterized in that the device further comprises a system processor (7) which takes care of communication between said real-time signal processor (6), a possible digital display device (8) and an external computer (9) used as an interface. 15 18 b 9 '' / ·> ^