DE1275917B - Device for detecting fish - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

Number:
File number:
Registration date:
Display day:

GOIs

German class: 74 d - 6/15

P 12 75 917.0-35 (S 82489)

17th November 1962

22nd August 1968

The invention relates to a device for detecting fish with an on board the Transmitting device attached to the ship for the emission of pressure wave impulses into the sea and for receiving the echoes reflected from the object and from the seabed and with a display device for these echoes, with a number of spaced apart transducers belonging to the system Receiving elements with associated separate receiving channels belongs to which a control device is connected, which is a preferred sending and / or receiving direction for the pressure wave pulses determine below the ship in relation to the seabed.

About the rolling and pounding of the ships that carry a device for detecting fish are to be taken into account, transmission and uses receiving elements capable of transmitting and receiving the energy over wide angles. However, this has the disadvantage that the echoes in a given area cannot be visually displayed always corresponds to the marking of fish vertically below the ship. Especially when trawling In deep seas, information is primarily provided about the height of the fish above the sea floor needed. However, the display achieved by a wide beam makes it impossible to between Fish that are vertically under the ship and fish that are to the side of the ship, but are in the same row to distinguish. The transmission or reception of a narrow beam would improve the accuracy in this regard in still water, but a swelling and Rough seas cause the ship to roll and pitch, which makes this device less so more effective than the ordinary wide beam device.

There is now a device of the type mentioned above is known in which several on the ship Transmitting and receiving transducers are arranged in such a way that such a transducer is approximately in the Center of the ship and the other two transducers on the left and right sides of the ship are. A special control device now alternately switches the left, middle and right transmission and receiving device, it being ensured that the transducer is always active on that side is according to which the ship is currently leaning in rough seas. For the activation of the converter device which causes a beam direction perpendicular to the sea floor, serves a special one System that registers the inclination of the ship.

Device for detecting fish

Applicant:

S. Smith & Sons (England) Limited, London

Representative:

Dr.-Ing. E. Liebau, patent attorney,

8902 Göggingen, v.-Eichendorff-Str. 10

Named as inventor:
William Halliday, London

The disadvantage of the known device is that several working practically independently of one another Transmitting and receiving devices must be available. Only the display device only needs to be present once. The number of necessary devices of the type mentioned is so The greater, the more precisely the ultrasound is exactly perpendicular to the at any inclination of the ship Desires to straighten the seabed. Accordingly, in a precisely working system, the known Kind of a very large number of transmitting and receiving devices are necessary. But there is It is remarkable that the performance of the system hardly with the increased number of such transmitting and receiving devices increases because only one such device is in operation at a time and all of them other devices are turned off.

Furthermore, a locating device working according to the echo sounder principle is known in which on one A number of transmitters and receivers are arranged in a circle. The device allows radiation in a certain direction by only using a few adjacent transmitting or receiving elements an electronic or mechanical switch. Due to the special use by delay elements it is achieved that despite the arrangement of the elements on a circle each a plane wave is emitted. In this way, this device allows any selection from a larger number of beam directions, but this selection does not take place automatically.

In this known device there is also a large number of transmitting and receiving elements necessary, each of which has a delay element associated with it, the delays of these elements

809 597/136

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must be set with great accuracy, a receiving energy converter is received, to obtain the required accuracy in directional such as storage devices, e.g. B. Cathode Ray Choice to obtain. This is due to the large number of tubes, one can get the required direction from it Delay elements cumbersome and time-consuming. The one through the reflection of the auxiliary impulse consuming. In addition, it is already received for a direction 5 information is used to each difficult to switch the required accuracy in this one of the storage devices alternately, to ensure complex device, let alone If z. B. Cathode ray tubes are used for switching from one direction to the other, the auxiliary pulse reflections become different. In addition, the known device moved the time bases of each cathode ray tube in the very complex and has a considerable amount of room to switch. The stored information requirement. the echoes from the main impulse will be later from all

Finally, one of the aforementioned ahn storage devices is scanned at the same time,
borrowed device is known, which is also based on a preferred embodiment of the invention

a circle arranged several acoustic transducers contains means for delaying the echo signals in are generated by the respective activity of only a few 15 of each channel received by the receiving elements of the the transmission channel originates from a few neighboring converters, with the delays in the of a given ray in the form of a plane different channels are the same, furthermore in each Allow wave. Also the echo, which means in a channel, which is based on an echo signal from the sea sols directed beam is created, will respond to the storage mechanism for catch that the converters concerned are simultaneously storing the delayed signals in a 20 address, as does the case with a plane wave memory device associated with each channel is. This arrangement is about actuating and reproducing means for scanning correct sizing of delay elements that of the various storage devices, such that to achieve mentioned behavior, namely above all all echo signals, which in the same moments the emission of a plane wave. 25 relative to receiving from their united marine

The object of the invention is to add a basic echo signals stored together To be device of the type mentioned. Thus, all corresponding echo signals, create, by means of which in a particularly simple manner the received through the various elements and precisely the preferred transmission or reception direction and the echo signals from the seabed for the pressure wave impulses are independently 30 combined with each other additively, depending on these are not different echo signals from the respective fluctuating movements. In the Andes Can stabilize ship .. would take that the receiving elements in a straight line This object is arranged according to the invention, which in a given line solved that the control device of the moment, resulting from the lurching of the ship, Echoes thrown back from the sea floor are influenced and applied and the various channels depend on whether the sea floor is horizontal or which of them controls the times at which the echo signals all echo signals from objects perpendicularly signals received in the various channels originate below the receiving energy converter, will. additively joined together.

In the device according to the invention, the 40 echo signals from an object, which is in a delay in accordance with the measured direction at right angles to the line of the receiving sensor delay between the respective receiving elements, are received in phase and receive signals from two transmission and Receiving units are therefore regulated at different times relative to the directions and, in this way, continued seabed echo signals are stored. Thus, and in accordance with the circumstances prevailing in each case, these echo signals are not set additively by the scanning. In this way, device is assembled at any time,
a precise setting of the relative delays. The output of the playback means can be in the

and thus the effective direction of the beam. After all, this is type of record or temporary image it should also be pointed out that the reproduction of the invention exists.

If the seabed is very irregular and also tolerates rough operation, as it contains on fishermen's sharp points, the steering means act unboil, without their reliability regularly, because the preferred direction depends on the Spikes occurring in the closed-In one embodiment of the invention is a separate area that wobbles. However, transmitters are arranged to send out a wide beam of trawl fishing normally over one, the emitted pulses not passing through the seabed after such, so that regardless of this point on the seabed, no significant disadvantage is present.
Achieve lurching and pitching of the ship. In another preferred embodiment of the control means are provided in order to merely determine the presence of the echo signals received for control purposes from the separate receiving lines. This can be done in different ways the phases of the pulse transmission are used to the. You can z. B. send out an auxiliary pulse in front of each identical or corresponding element as a main pulse. This auxiliary pulse must stimulate the transmission beam to have a frequency different from the main pulse on a part of the ocean floor, which is a closed area, and for this reason a separate transmitter and 65 is directed.

Receiver required for this auxiliary pulse. By According to another embodiment of the invention

Checking the arrival times of the echo signal containing a detector capable of detecting an energy from Sea floor with different elements depending on momentum in a given direction

5 6

the reception of the energy pulse from the given sea to generate the echoes from the fish and send out a series of receivers from the seabed,
The echoes are connected by the receiver row of reception channels and with the corresponding catch and arrive in the control and delay transmission channels, each of which is linked to the corresponding reception channels. Transmission channel contains a time measuring device, each of these circuits generates a fixed verdict suitable for triggering the operation of a reference delay, which in the present embodiment is related to a signal that is received and carried through in the reception channel usually connected in each channel for 10 milliseconds. The seabed echo is reversed bypassing another signal which is attracted to the time base of the cathode ray of the reception of said signal in the first tube memory in the channel for the storage of the channel where it has been received, is delayed, and from the fish and from the seabed receiving means that trigger echoes on the return of the timing device.

in each transmission channel to their reference ratio 15. The control circuit 24 then automatically enters

appeal to the sending out of an energetic activity, as described below, to the

initiate impulse from the transmission channel. Time base 23 to excite and at the same time the

The invention will now be given by way of example with storage disks in the cathode ray tube memory

Described with reference to the drawings are scanned at the same time. The outputs of the output

the one in which 20 electrodes of the cathode ray tube memory are

F i g. 1 shows a graphical representation of a block in the adding device 20 added together

Scheme of a device for locating fish is, and from there the cathode ray tube 31 is fed,

F i g. 2 shows a detailed graphical representation on the luminescent screen 22 of which it is depicted

position of part of FIG. 1 is to be.

F i g. 3 shows an explanatory waveform; and FIG. 25 It is estimated that coincident signals which

F i g. 4 is a block diagram of a part of a further adding device 20 supplied and additively

ren device for locating fish shows. are added together where they reinforce each other

In Fig. 1, a transmit energy transducer 10 will produce a powerful resultant in imaging by a trigger oscillator 11 in a known manner, while other signals are relatively excited to provide pulses of ultrasonic driftwaves into the 30 insignificant records.
See from one not shown in the drawings. In this embodiment the only shown ships are to be sent. The ultrasonic transmitter sends echo signals, which in the adding device emit the pressure waves in a wide beam so that they are coincident when the sea floor is horizontal that the closest point on the sea floor is zontal, echo signals from targets in or near the pressure waves, regardless of the normal 35 vertical below the energy converter, such as rolling and pitching of the ship, is achieved. will be described below.

For the reception of the echo signals that return from the horizontal ship and over a hori-fish and from the seabed, a zontal seabed is provided to reach all echoes from series of energy transmitters or separate receivers in or near the vertical at the same time the catching elements, of which only two 40 recipients. Each echo signal is given a delay at 12 and 13 shown. It is initially approximated to 10 milliseconds and then it is assumed that the receiving energy converters are in the same position on its connected memory in a linear array and that plate at the beginning of the scanning over the memory this array extends across the ship.
and is horizontal when the ship is horizontal. 45 Thus, in simultaneous playback of the

Each receiver has a special received signal, the total echo signals additively

collecting channel, behind which a control and totaling together and thereby reinforce each other,

delay circuit and a storage device which The case will now be considered in which the

can simply be a cathode ray tube memory, echoes from targets that are noticeably off the vertical

is arranged. The control and delay circuit 50 are removed, the energy converter on one side

for the first recipient 12 is indicated at 16, the ship's order in which to reach it. Consequently

that with the cathode ray tube memory 17 and are these echo signals with respect to the beginnings

correspondingly at 14 and 15 for the «th receiver of the scans via the respective memory

13 is connected. plate gradually farther from the beginning of the scan

The output electrodes 18 and 19 of the two 55 away.

Cathode ray tube memories 15 and 17 are connected to When all of the storage disks are scanned, output electrodes of the other, not shown, are reproduced by the stored echo signals in the order of the cathode ray tube memory of an adder, and they are therefore not connected to device 20, the output of which is mutually amplified to another, to produce a powerful pictorial cathode ray tube, which is connected to a 60 representation.

Fluorescent screen 22 for the pictorial display of the If now the ship relative to the horizontal

Echo signals is provided. lurches, the echoes reach from the targets

A time base circle 23 for the cathode ray tube originate in or near the vertical, the receiving

21 is controlled by a control circuit 24, which is sent to the energy converter in the order in which it is, but the

Control and delay circuits in the individual 65 ground echoes also accomplish this, and therefore

Channels of the receiver is switched, controlled. the relationship between their storage positions remains

When working the device is an ultrasound and the beginnings of their respective scans

pressure wave pulse from the ultrasonic transmitter 10 into the undisturbed, whereby the preferred receiving direction

direction remains in the vertical. The effective scanning beam width is of course dependent on the Number of recipients and their distance from each other, which is understandable.

When the ocean floor is sloping, the preferred direction is centered on a line, soft perpendicular to the sea floor and through the row of receivers.

A detailed description of the

A voltage increase is generated by the multivibrator 31, as indicated by the curve / in FIG. 3 is shown.
Corresponding voltage peaks, such as e _n , graze

5 generated from the ground echo which is received by the other transmitting and receiving elements; however, the monostable multivibrator only responds to the first one, which in this case is the voltage peak C ₁ . This becomes order of F i g by a small amount. 1 is now referenced back to io (L milliseconds, curve g in FIG. 3) by an on FIG. 2 given, which delays a block circuit of a fixed pulse delay circuit 32 to receive channel, namely the channel for the energy, a delayed voltage rise, as shown in converter no. 1 together with a device general curve g of FIG. 3 is shown to generate. According to my for all receiving channels, represents. Passage through the isolator circuit 33 solves this

The control and delay circuit 16 of FIG. 1 15 time base circuit 29 again for the cathode in Fig. 2 through an amplifier 25, a radiation tube memory 17. It becomes a

second delayed breakover voltage of 10 milliseconds generated (not shown).

A second output is provided at amplifier 25 see which leads to delay circuit 26, where a delay of 10 milliseconds is created, the is equal to the time base generated by the time base circuit 29. From the exit of the Delay circuit 26 runs the signal over the forms. Further isolators 33, not shown, are, 25 »read / write switch to the control grid of the one for each cathode ray tube memory cathode ray tube memory 17. It is provided intended. that the »read / write switch from the

In addition, a read amplifier 34 is shown, the delay time deflection 23 is controlled so that it is connected to the output element of the memory plate 19 of the initially delayed received signals on the cathode ray tube memory 17, as well as memory 17 during the first or memory tilting like a Y amplifier 35, which switches between the adder and later a constant bright voltage for device 20 and the Γ deflection coils of the image, the reproduction and visual representation during tube 21 is switched. of delayed tilting.

delay circuit 26, a "read-write switch" 27, a time and amplitude gate 28 and a time base 29 for the cathode ray tube memory 17 educated.

The control circuit 24 of FIG. 1 is shown in FIG. 2 through a mixer and isolator 30, a monostable Multivibrator 31, a fixed pulse delay circuit 32 and an isolator 33

The at points a _v b _v c _v d _v e, f and g in

Thus, the signals from curve U _{1 are} during the

F i g. 2 occurring signals and voltages are in 35 write or storage phase, as indicated by the curve d _x

Fig. 3 represented by curves. In all of these shown in Fig. 3, stored. Of this

Curves other than d _t represents the ordinate the curve is shown to be tilting the beam

Voltage and the abscissa represents time. At the straight line begins at one edge of the storage disk and

Curve d _± represents the ordinate of the stored charge just at the opposite edge of the storage and the abscissa the distance through the storage disk ends. The fish echo is during the tilt

plate 19 in the tube 17. 36 at 36 'and the seabed echo at 37'

In Fig. 2 the output of the receiver 12 is stored.

amplified by the amplifier 25. The received signals from the other receivers are

Assume that the received signal is sent out in the same way to the memory

the echo signal 36 from the fish and the 45 plates of the cathode ray tube memory of the respective

Sea floor echo 37 (curve a _t in FIG. 3) consists, stored channels.

which appears at the output of amplifier 25. Thus all echo signals of the fish are in the same

The signals directly control the time and amplitude subdivided periods of time from their respective

tudentor, which works in a known way to generate seabed echo signals at appropriate points

the steep seabed stored on the front flanks of their respective storage disks,

echo signal of relatively wide amplitude to be selected, assuming that the seabed and the

len and on the excitation of part of this signal, the row of receivers is horizontal when the ship,

exceeds a given amplitude value, if one that carries it is horizontal, the

Tripping voltage derived from the curve b _t in FIG. 3 a preferred vertical arrangement

is shown, to provide the timing circle 29 55 direction. The curves a _n , b _n , C _n and d _n of

pass through, causing a 10 millisecond F i g. 3 are curves corresponding to a _v b _v C ₁ and d _±

Breakover voltage, as shown by curve C ₁ , will cause the η-th receiver energy converter in the series. The output of the gate 28 is also the
Mixer and isolator 30 supplied where it is connected to the
Outputs of the corresponding time and amplitude 60
tudentore is mixed in the other channels.
The curve b ₁ in FIG. As can be seen, the voltage shown in FIG. 3 has a level that is little
is behind the beginning of the seabed echo.

The mixer and isolator responds solely to the voltage rise b _t and generates a voltage spike, as in curve ^ ₁ of FIG. 3 is shown
which triggers the monostable multivibrator 31.

Ship opposite the horizontal

if that
lurches.

It can be seen from curve d " that, despite the rolling, the echo signals 36" and 37 "corresponding to 36 and 37 of curve a _± are stored at locations 36 '" and 37 "' corresponding to 36 'and 37' of curve d _x .

The delay time base 23 is controlled by the voltage rise of curve g (FIG. 3). This increase is by a fixed amount of L milliseconds after the first trigger signal O ₁

delayed for each storage time deflection circuit 29. who receives the seabed echo, its oscillation delay L is chosen so that the entire movement pulse is transmitted last. The timing is completely stored under normal conditions so that the preferred direction of transmission is enabled. vertical direction is obtained.

After the storage is complete, the 5 die curves and U ₁ of Fig. 3 which triggered the span delay time base, and in the same voltages Z ₁ and Ic ₁ in Fig. 3. 4, the trigger pulse g triggers the storage because the charge change occurs simultaneously in all channels in the keyed approximation time base 29, charging circuit 39 and the output of the oscillator, whereby the storage disks in all storage 41 occurs. The curves / _n and k n show which are scanned at the same time. It is also prior to the tensions in the η-th channel when we see that the ship is lurching as a result of the tilting of the delay time. It has been shown that the base 23 is a control signal via the line 38 at the time τ between the keying of the charging circuits in "read-write" switches 27 in all channels of the two channels equal to the time r between the transmission. This causes this switch to be the solution of the two transmitter oscillators.
a fixed light or write voltage to the control unit 15 When the ship sails over a sloping sea grid of all cathode ray tube storage systems, the preferred emission rate changes

Thus the reading is effected and the alignment is automatic from the vertical to the normal signal from the stores are in the paint to the sea floor.

Adding device 20 put together and after If the change in charge in circle 39 of

Passage through the F-amplifier 35 the display ao is progressively changed channel to channel, gives way tube 21 fed. the preferred direction from normal to

By progressively changing the delayed seabed.

wrestling generated by delay circuit 26 Where the arrangement of FIG. 4 the arrangement

the preferred of FIG. 1 may vary from channel to channel. 2, there is a preferred outward direction over a horizontal seabed 25 direction and a preferred receiving direction than can be manufactured vertically. tion, which of course is usually accurate

In Fig. 4 is a block diagram of an arrangement according to one another.

reproduced, which alternately or additionally It can, however, be provided that a preferred

to the above-described arrangement for the related direction of transmission by means of the description a preferred radiation direction device is present with reference to FIG. 4, can be turned. The F i g. 1, 2 and 4 indicate that reception is over a wide angle identical parts with the same reference numerals. he follows.

In Fig. 4, a charging circuit 39 is through the To achieve this, a separate receiver can

Waveform b ₁ blanked in such a way that charging with the energy converter or an energy conversion begins _{with a positive increase in O 1.} The delayed voltage rise g is also used in the selected energy converter or a group of charging circuit 39 to block the phase of the energy converters that are used to control external charging and a discharge phase from the direction of discharge can be used to initiate a charge change of the same image. recording device or a recorder register

To the charging circuit 39, an amplitude gate 40 shear device or both can be connected.
40 connected, and when the charge returns to zero The image recorder and the screech return, the gate 40 provides a trigger signal to operate in the same way as the transmitter oscillator 41, which receives a pulse from the ultra-cathode ray tube memory shown in FIG. 2 illustrated sound vibrations are supplied to the energy converter 12 by executing the seabed echo. The energy converter 12 thus acts in this 45 solution and delay of the received echoes embodiment both as a reception as well as when it is used accordingly. A suitable transmission energy converter. The clerk registrar is in the UK

As described above, each receive channel is described in patent specification 852566. A detailed to a corresponding charging circuit 39, a description of a suitable tripping and ver amplitude gate 40 and a transmitter oscillator 41 ge 50 delay circuit with cathode ray tube memories switches. Consider now the case in which and with a record mentioned last The ship lies horizontally and the direction of the seabed is shown in British patents 785 001, is also horizontal. In this case received 839 131 described.

all energy converters the seabed echo the same - although in the described embodiments

timely, and therefore charge and discharge 55 men the pulses for scanning and recording corresponds to the blanked charging circuits, whereby voltage are used, these are also used for all transmitter oscillators 41 are triggered at the same time control of the recording or for pulse output, in order to transmit a preferred vertical direction or both are used. It can lead to this keep. Purpose alternately an auxiliary sounding, which with

It is now assumed that the ship is echoing at a different frequency from the main and in this case the charging current will start working, be applied. The circles of the sea according to the order in which the seabed echo signals from the received energy echo is received by the energy converters, converters of the auxiliary echo sounding are received, to charge. The moment of reversal of can then be used to control the storage and Charge to discharge, however, is the same for 65 reproduction of the echo signals in the main echo all Channels, making the energy converter, which plumbing used to be a preferred receives the seabed echo last to maintain its direction of reception. The auxiliary echo sounding Vibration pulse is sent out first and the first, can alternatively or additionally to control the

Pulse transmission in main echo sounding can be used to determine a preferred transmission direction to obtain.

Although a simple linear series has been described for the application of the scan, the Series usually two-dimensional in order to stabilize the beam while rolling and To get stomping.

Claims (12)

Claims: IO 1. Device for detecting fish with a mounted on board the ship Transmitting device for the emission of pressure wave impulses into the sea and for the reception of the echoes reflected from the object and from the sea floor and with a display device for these echoes, with a number of spaced-apart transducers belonging to the system Receiving elements with associated separate receiving channels belongs to which a control device is connected, which opposes a preferred transmission and / or reception direction for the pressure wave pulses below the ship determine the seabed, characterized in that the control device is influenced by the echoes reflected from the seabed and the various Channels depending on the times controls at which the echo signals in the different Channels are received. 2. Apparatus according to claim 1, capable of relative a preferred direction of reception to determine the sea floor, characterized in that each receiving channel means (28, 29), which respond to the reception of seabed echo signals to actuate a Address signal storage device (15), a delay device (26) through which the received echo signals are transmitted before storage, a display device that Means (23, 27) for triggering the storage devices simultaneously in the various Channels to reproduce the stored signals and a circuit (20) for adding up the signals from the storage devices for use in an image display device (21). 3. Apparatus according to claim 2, characterized in that the storage devices contain cathode tube stores (15 and 17). 4. Apparatus according to claim 2 or 3, characterized in that the various Delay devices generated delays are equal to each other. 5. Apparatus according to claim 2, 3 or 4, characterized in that the display device a cathode ray tube (21). 6. The device according to claim 1 for the mood of a preferred transmission direction relative to the sea bed, characterized in that each receiving channel is coupled to a corresponding transmission channel (25, 28, 39, 40, 41) with a connected transmission element (12), each Transmit channel includes a timing device (39) reversed from a reference state by the seabed echo signal (e ") received in the channel and by another signal which is by a fixed period (L) relative to the moment of reception of the seabed echo signal (e,) is triggered in the first channel where it is received, and in that means (40) responsive to the retraction of the timing device to its reference state to initiate the transmission of a pulse from each transmitter element in the channel are provided. 7. Apparatus according to claim 6, characterized in that the timing device is a Charge and discharge circuit (39) is. 8. Apparatus according to claim 7, characterized in that the amounts of charge and Discharge of the charging and discharging circuits are the same. 9. Apparatus according to claim 6, 7 or 8, characterized in that the transmitting and receiving element forms a single element (12) in each channel which unites the two. 10. Device according to any one of claims 6 to 9, characterized in that the Display device to a selected receiving element or to a selected group of receiving elements is connected so that the receiving angle is much wider than that Outside angle is. 11. Device for detecting fish according to claim 1, characterized in that each channel (14, 16 or 25 and 28) has a separate delay direction (15, 17 or 39), a common control circuit (24 or 30, 31 , 32) emits a control signal (g) under the influence of one of the seabed echoes received from the channels, which is either the first seabed echo or has another predetermined ordinal number, and that each delay device (15, 17 or 39) causes a delay, which depends on the time span between the reception of the seabed echo by the corresponding channel and the transmission of the control signal (g), the delay caused being the shorter the later the respective seabed echo is received by the corresponding channel, in such a way that the delay devices ( 15, 17 or 39) either delay the input of the echo signals from the corresponding channels into the display device in order to correspond To combine the echoes in the display, or to delay pulses transmitted into the water by different transmitters (12) with respect to one another. 12. A device for detecting fish with a transmitter mounted on board the ship for sending pressure wave pulses in a given direction depending on the reception of a pressure wave pulse from the given direction, provided with a number of receiving elements coupled with transmission channels, characterized in that each transmission channel has a timing device (39), the function of which is triggered from a reference state by a signal (b) which is received in the coupled receiving channel, and which is reversed by a further signal (g) which is used for a correct length of time with respect to the moment of its reception (e _x ) in the first channel that receives it, as well as means (40) which respond to the return of the timing device in each transmission channel to its reference state, to the transmission of a pressure 14 initiate wave pulse (k) from the transmission channel. Publications considered: German AuslegeschriftenNr. 1037 929.1038 460, 863 For this purpose 2 sheets of drawings 809 597/136 8.68 © Bundesdruckerei Berlin