FR2519067A1 - CARRIER FREQUENCY REMOTE CONTROL METHOD AND DEVICE FOR SLAUGHTER AND UNLOADING MACHINES WITH MILLING CYLINDER - Google Patents

Abstract

THE INVENTION CONCERNS A CARRIER FREQUENCY REMOTE CONTROL PROCESS AND DEVICE. THE DEVICE INCLUDES TWO SWITCHES 4, 5 CONNECTED TO THE DIFFERENT MOTORS TO BE CONTROLLED 1, 2 BY A CABLE AT TWO ENDS OF WHICH ARE PLACED SEPARATOR UNITS 12, 7; A CONTROL UNIT 17 IS FURTHER PROVIDED FOR COOPERATING WITH TWO CONTROL UNITS 10, 15, TWO TRANSMITTERS 8, 14 AND WITH TWO RECEIVERS 9, 13 TO ENSURE THAT THE SIGNALS TO BE TRANSMITTED ARE CHECKED AND IDENTIFIED FROM THE RECEPTION SIDE AND THAT ONLY SIGNALS IDENTIFIED IN THIS MANNER SHALL BE TRANSMITTED TO RECEIVERS. APPLICATIONS TO MINING EXPLOITATIONS.

Description

19067

  The present invention relates to a method and a remote control device with a carrier frequency for slaughtering and loading machines with milling rolls. In underground operations and during mining operations carried out in coal mines, machines with milling cylinders are used to a large extent. Such machines are manufactured, for example, in the Soviet Union, Poland, the Czech Republic,

  German Democratic Republic and in Great Britain The

  common to all machines is that the

  machines are connected by means of combined

  to the mains, that is to say that it is provided inside the supply hose four supply conductors and three control conductors, whose diameters are different In running, the hose of feeding is constantly subjected to bending stress and it

  As a result, it is damaged after a short time.

  In most cases, the breakdowns of

  This is because of the frequent bending, the rather thin conductors which are arranged in the supply hose for the transmission of the control signals are damaged first. In this case, it is necessary to consider as a disadvantage that the breakage of the thin conductors can not be easily detected from the outside, which

complicates fault detection.

  Another disadvantage of these machines is that the succession of frequent repair operations that it is necessary to perform on the cable also reduces the duration of the working time Taking into account that the service life of the co-drivers Oreat fort is much longer than the service life of the weak current conductors used for the transmission of control signals, the disadvantage of the devices described above can not be

  eliminated only by removing weak current drivers.

  High current cables that are used with a voltage of the order of 1 kV increase the reliability of devices and reduce downtime caused by repairs. In installations operating with high current, the strong current network is often also used for the transmission of carrier frequency signals. The characteristic of conventional devices operating at high voltage and with a carrier frequency is that it is provided, at the limit points of the section used for the transmission of signals, wave suppressors which are also able to absorb the short circuit power of the network These wave suppressors have the function of reducing the attenuations occurring under the effect of impedance variations of the network manifesting itself

  outside the transmission channel.

  Since they operate with a duplex carrier frequency, carrier separation systems tend to be used for the separation of directions.

  the artificial impedance characterizing the transmission path.

  The condition of operation without reflection of

  However, hybrid systems consist of installing a

  corresponding waveband and an artificial impedance

  This implies mutually contradictory conditions.

  In addition, for each conventional device, a coupling capacitor,

  coupling and a carrier frequency transmission cable.

  The use of the aforementioned elements in practice introduces many disadvantages, also outside of the conductors, because the weight of each wave suppressor amounts to a few hundred kilos and simultaneously the assembly can practically not be achieved in places of volume extremely small amounts available in mines and

  under rather unfavorable operating conditions.

  Another disadvantage is that, in all the carrier-frequency devices, there must be a frequency transformation in both the transmitter and the receiver, which requires the use of two oscillators.

quartz or more.

  The object of the invention is to provide a carrier-frequency device for duplex operation for the remote control of felling and loading machines with milling cylinders, this device making it possible to eliminate the disadvantages of the known devices and which can also function properly in the adverse conditions existing in the mines, while not causing a modification and interruption of the existing network in the mine. In conventional devices, the data transmission is carried out in most cases by asynchronous modulation. Compared to this solution, the method according to the invention and the device for putting it into practice have essential differences as well.

  well as regards the arrangement that also the principle.

  By the use of a new element the carrier frequency separation unit - it is possible to suppress the following units for the transmission of duplex signals: the carrier frequency wave suppressors, the frequency hybrid systems carrier, coupling capacitors placed on the outside of the device, coupling filters and cables for

  low current and in addition one can use a single oscilla-

  The frequency transformation is also superfluous because the carrier frequency is provided by direct synchronous modulation and it is received by direct capture of the carrier frequency In order to improve the qualitative characteristics of data transmission which is extremely important in a mine from the point of view of the safety of persons and equipment, the device according to the invention has incorporated a coincidence acoustic protection circuit and an integration-action sampling circuit to determine

the duration of the signal.

  The method according to the invention for providing a remote control with carrier frequency and in duplex operation can be characterized in that, thanks to the use of appropriate separating elements, it is also possible to ensure precise transmission of the signals also in the case of networks with high variable loads and without the need for stop-and-go

  hybrid system with carrier frequency.

  One of the characteristics of the process according to the invention consists in that the signals to be transmitted are controlled and identified from the side and exclusively

  the identified signals are transmitted to the receiver.

  In the device according to the invention, there are provided motors and switches and the elements necessary for the transmission of the carrier frequency signals. The subject of the invention is also a device for remote control using a carrier frequency

  duplexes, in particular for slaughtering machines and load-

  The device according to the invention can be characterized in that the first switch is connected to a second switch arranged in the form of a main circuit breaker and which is also connected. to the network and in addition to engines; the two ends of the cable connecting the motors to the first switch are respectively connected to a splitter unit. The common point of the motors and the network cable is connected to the first input of a control unit; its first output is connected via a regulator and an accumulator to the first input of a transmitter; the second input of the aforementioned transmitter is connected, via a transmitter control unit, to the input of the first separator unit while the output is connected, via a receiver and a digital receiver at the second input of the control unit and the second output is connected through the second input of the horn control unit; the output of the second splitter unit connected to a high current cable is connected, via another receiver and a digital receiver, to the first input of the control unit while the input-of the separating unit is connected to the output of an emitter; the first input of the aforementioned transmitter is connected indirectly, and the second input via another transmitter control unit, to the first input of the control unit whose second input is connected to the network by via the connecting cable and the second switch arranged under

shape of a main circuit breaker.

  Another advantageous embodiment can be characterized in that the common point of the horn and the transmitter control unit is connected to the input of an admittance measuring apparatus while the first output of the aforesaid admittance measuring apparatus is connected to the first input of the transmitter control unit

  and that the second exit is connected to the horn.

  In an advantageous embodiment of the device

  according to the invention, the separating units are

  killed by two series circuits connected in parallel, the

  series circuits each consisting of an oscillating circuit

  parallel and oscillating-series circuit, the windings of the oscillating circuits being each provided with a winding

  secondary insulation and a secondary winding of

  tation. Another embodiment of the device according to the invention is characterized in that the admittance measuring apparatus contains an acoustic frequency generator

  whose output is connected through a transfor-

  the rectifier circuit and the power supply unit

  interior of the admittance measuring device while

  that the output of the rectifier is connected to an input-

  a bridge circuit whose other input is connected, via another rectifier and a current transformer, to one of the inputs of the admittance measuring apparatus and that the Another output of the admittance measuring apparatus is connected via a stage of

  output and a comparator, at the output of the bridge circuit.

  It is further considered advantageous that the carrier frequency receivers each contain a coincidence acoustic protection circuit, which consists of a circuit arranged for transmitting the received signal or a differential frequency setting circuit which is connected to the output of the circuit cited in

  first, in which case one of the entrances to the establishment circuit

  differential frequency is connected to a receiver oscillator while the output of the differential frequency setting circuit is connected to one of the inputs of the frequency comparator whose other input is connected

  via a divider to the receiver oscillator.

  In accordance with another advantageous mode of

  According to the invention, the receivers each comprise a processing circuit, these processing circuits being connected to the coincidence acoustic protection circuits.

  each processing circuit contains a delay circuit

  whose entrance is the entrance to the processing circuit.

  while its output is connected to one of the inputs of a gate circuit and a counter, the other input of the gate circuit being connected through the output of the receiver oscillator to the counter input, the output of the aforementioned counter constituting the output of the

processing circuit.

  Other advantages and characteristics of the invention

  will be highlighted in the following description, given

  by way of non-limiting example, with reference to the appended drawings in which: FIG. 1 is a block diagram of the device according to the invention, FIG. 2 is a more detailed block diagram of the separating unit constituting the FIG. 3 is a detailed diagram of the bridge circuit of the admittance measuring apparatus, FIG. 4 is a block diagram of the admittance measuring apparatus, FIG. acoustic protection circuit of coincidence,

  Fig. 6 shows the processing circuit.

  The mode of operation of the device according to the invention will be explained in the following with reference to the figures. The engines 1 and 2 of the machines comprising the milling cylinder are connected, via the shielded power supply hoses used in mines, to the isolated central point of the power supply network 3; the connection is provided via a switch 4 arranged in the form of a circuit breaker.

  machine and a switch 5 arranged in the form of a disjunction

  The two switches 4, 5 are mounted in the control cabin and the motors 1, 2 can even be placed at a distance of 1 m COO meters from the control cabin. The present invention aims to cover this distance away without the use of low current conductors because the switch 4 must be actuated from the motors Through the use of the device according to the invention which is shown schematically in FIG. 1, the problem is solved in the following way. The carrier frequency transmission is ensured up to a maximum of 1140 V by the separating units 7 and 12, which ensure, on the one hand, that the power supply network high current 3 is isolated in correspondence with the high voltage signals and secondly that a selective coupling element ensures the transmission of the duplex carrier frequency signals Transmitters 8 and 14 emitting with separate frequencies in both directions are connected to separating units Emitters are ordered

by quartz oscillators.

  For reception of the carrier frequency signals, receivers 9 and 13 are provided, while transmitters 8 and 14 are respectively controlled by an emitter control circuit.

  detected appear at the receivers demodulator outputs.

  9 and 13, these outputs being each connected to the input of a digital receiver 11, 16 Digital receivers

  provide classification and signal processing.

  The transmitter control units 10 and 15 control the transmitters 8 and 14 and a corresponding coding is also

  performed in these circuits Each transmitter-transmitter

  receiver 8, 9 and transceiver 13, 14 is connected to

  two sides to the control element of the operating machine.

  This is to say that the connection is ensured on one side with the control unit 6 and on the other side with the control unit 17. The control unit 6 is provided on the side. switch contains the instruction relay, the

  vacuum contactors and SSR relays (solid state

  by which the control unit 6 is able to intervene in the actuation circuit of the switches

4 and 5.

  Among other things, the role of the control unit 17 also consists in producing, during the period when the motors 1 and 2 receive a supply voltage, a signal appearing at one of the outputs of the control unit and which is applied the regulator 18, so that it ensures the charging of an accumulator 19 during this time period The regulator 18 is provided with a circuit for regulating the accumulator voltage, which allows

  avoid the risk of overloading The transmitter 14 and the receiver

  13 of the motors 1, 2 are provided, via the transmitter control unit 15, with an admittance measuring circuit which controls and controls

the operation of the horn 21.

  Using the system described above, the tele-

  command is performed under the action of the remote control command signal as follows

  The operator presses the push-button "Enclen-

  The control signal 17 is supplied from the output of the control unit 17 to the transmitter control unit 15. which conditions the activation order for the carrier frequency transmitter 14 so that the subsequent transmission of the control signal can take place

  through the driver Simultaneously, however,

  a signal is transmitted on the one hand to the admittance measuring apparatus 20 and on the other hand to the horn 21; using this signal, it is possible to check the operating ability of the horn 21, ie if it is

  able to function acoustically when needed.

  When the horn is in a correct condition, the carrier frequency transmitter 14 sends the coded signal, through the splitter unit 12,

  strong current and the separating unit 7 placed on the side-

  reception, at the receiver 9 and the coded signals leaving the receiver 9 reach the digital receiver 11 In the digital receiver, the coded signals are analyzed; after completion of the analysis, the digital receiver 11 applies the control signal corresponding to the input of the

  control 6 and then the control unit 6 ensures the engagement

  Then, the carrier frequency channel sends the coded signals corresponding to the uninterrupted switch-on command to a time division multiplexing system. The digital receiver, which is provided on the supply side performing a code analysis, transmits the signal corresponding to the signal. switching command to the control unit 6 until, during the transmission cycles, i.e. during each 0.1 second cycle, it is able to detect all

  the conditions corresponding to the order of engagement.

  When the start command is absent from the first or second cycle or when an incorrect command is received,

  switch 4 is immediately opened.

  When producing the switching order, the carrier frequency remote control device according to the invention takes into account all the safety conditions.

  prescribed for a mining operation An important part

  under these conditions is that, when supplying the interlocking order, all the parts of the transmission channel, on both transmission sides of the carrier frequency, and the units placed in connection, are are in a correct state Stop priority in case of danger is guaranteed in relation to all other commands and coded information.

  thus the particularly effective safety conditions.

  FIG. 2 shows a block diagram of the separating units 7 and 12. The frequencies of the emitters 8 and 14 provided at the two ends of the strong current cable used for the transmission of the carrier frequency have been designated by f A i and f A 2 The mode of operation of the coupling and separation unit will be explained with reference to the separating unit 7, this explanation being

  obviously also applicable to the separating unit 12.

  The part of the separating unit 7 and located on the transmitter side consists of the oscillating-parallel circuit 22

  and oscillating circuit-series 23; the oscillating circuit-

  series 23 is tuned to the transmitter-side frequency f 'ie the oscillating-series circuit 23 has a minimum impedance for the frequency f Al' The parallel oscillating circuit 22 is tuned to the frequency f A 2 of the other emitter, that is to say that the impedance reaches in this case its maximum value The oscillating-parallel circuit 22 has the function of separating from one another the two frequencies f Al and f A The same separating unit still contains the other circuit elements, in particular the oscillating-parallel circuit 24 and the oscillating-series circuit 25, which are connected in parallel with the series connected connection which consists of the oscillating-parallel circuit 22 and the

  oscillating circuit-series 23, in which case the oscillating circuit

  series 25 has agreed on the frequency f A 2 * The parallel oscillating circuit 24 connected in series has the function of preventing the signals corresponding to the high level of frequency f Al to continue to be transmitted, that is to say

  that we are assured of a transmission with the spacing

  By appropriate sizing, it can be obtained in all cases that one of the oscillating circuits does not influence in any way and to a great extent the agreement of the other circuit. The windings of the oscillating-parallel circuits 23 and 25 A dual function On the one hand they constitute the primary windings of the transformer arranged to separate the high voltage parts and the low voltage parts and on the other hand they establish, with the aid of the secondary windings arranged on the primary windings, the passive impedances of the transmitters

8, 14 and receivers 9, 13.

  Another function of the separating units 7 and 12 is that they prevent, on the one hand,

  50 Hz frequency can reach the output of the transmitter.

  and at the input of the receiver and they also prevent the passage of high voltage signals existing in the line, through the separating unit, in the low voltage circuits, so that they fill

  simultaneously a protection function against electro-

  execution. An admittance measuring circuit 20, indicating that the horn 21 is ready for operation, is connected to the transmitter control unit 15. The principle of the admittance measurement has been highlighted in FIG. 4 represents the

  block diagram of the admittance measuring circuit 20.

  Thus the principle of the admittance measurement is evidenced by the circuit arrangement of FIG. 3 In the bridge circuit, the signal UI is proportional to the current of the horn 21 while the signal Uu pst is proportional to the voltage horn 21 The bridge circuit also contains

  a potentometer with which the bridge is balanced.

  When Uu U then U / Uu = K = Y, where Y denotes the admittance of the horn In this case, the output voltage of the bridge t U = O. When the variation of the value XU has reached a value of certain predetermined value, the desired variation of the admittance and this variation of admittance occur

generates the locking signal.

  FIG. 4 represents the operating mode and a block diagram of the admittance measuring circuit. The admittance measuring circuit 20 contains an acoustic frequency generator whose input is connected to the output of the control unit. 15 and which is one of the inputs of the admittance measuring circuit 20 Under the action of the unit

  transmitter control unit 15, the acoustic frequency generator

  that 30 starts working so that the horn 21 is

  switched on via a current transformer.

  It is checked as follows if the electrical circuit of the horn 21 is not open: The acoustic frequency transformer 31 applies a signal proportional to the voltage of the horn 21 to the rectifier 34, which produces the signal Uu for the bridge Le U signal, proportional to the current of the horn 21 is generated in another rectifier 33, which is associated with a current transformer 32 The output signal of the bridge circuit 35 is proportional to the admittance of the horn and it excites the comparator The essential feature of the function is that, when the signal reaches the comparison threshold, the output stage 37 is energized so that at the output of the admittance measuring circuit 20 there is a signal The acoustic frequency generator 31 actuates the power supply unit 38 which supplies electric power to the comparator 36 and the output stage 37. the two comparison thresholds of the square-wave comparator have two admittance values which can be adjusted as desired within the admittance range of the horn 21. In the device according to the invention, it corresponds to the nominal admittance of 1 / 10 Mh O two values

limits, namely 1/30 and 1/3 Mho.

  In classical horns providing a pre-signal,

  only a short circuit or a complete cut is detected.

  With the aid of the device according to the invention, it is possible

  It is possible to detect both faults and shunt faults already in the installation period. This advantage is of extreme importance in underground operations because the sound signals the start of the machine.

  warn people in the vicinity of the machine.

  The admittance measuring circuit 20 used for the control and control of the horn 21 transmits the remote control command both during a localized start and during an accidental and automatic start In the control circuit, on the side switches 4, 5, it is

  possible that a defect will occur although the probability

  be the least, and therefore it is unacceptable that in all cases the horn produces a signal which warns the people working in the vicinity of the machine. The same signal is however also appropriate.

  so that the timer relay can continue

  to operate and is only stopped by using the remote control acting on the switch 5 placed on the supply side The order is established using the pushbuttons and it is programmed using the relays With blades connected in series To avoid unintentional starting, electrical circuits

  relays are locked to each other.

  The relay producing the switch-on signal and its holding current circuit are arranged in such a way that, for proper operation, the following conditions are fulfilled: 1 The rest condition of the "DANGER" push-button and the "DANGER" relay must correspond an active condition of reception of carrier frequency, that is to say that the transmitter placed on the supply side must be

in the condition "EMISSION".

  2 In the case where the input conductor is faultless, that is to say when the driver is neither cut nor shorted. 3 When both of the above conditions are met,

  the relay is activated when the push-button "ENCLENCHEMENT" is pressed or it passes through the

  diary of its auxiliary contact, in a condition of maintenance; the carrier frequency transmitter on the machine side is engaged; the transmitter control unit is also engaged, it determines the code of the engagement order, it controls the ability to operate the horn 21, it initiates the engagement process, that is, mean that the carrier frequency signals modulated with the established code continue to be

  transmitted cyclically with synchronous modulation.

  The receiver 9 of the carrier frequency signals contains a coincidence acoustic protection circuit, the block diagram of which has been shown in FIG. 5.

  transmit the received frequencies f Al or f A 2, of the oscilla-

  receiver 38, which is connected to the input of a difference-setting circuit, in which case a signal representing the differential frequency appears at the output of the difference-setting circuit 40 and is then applied to the comparator The frequency comparator 42 compares the attenuated signal in the divider 41 of the receive oscillator 38 with the frequency of the differential frequency signal and, when the frequency deviation falls within the range between the set limit values, it appears at the output the reception frequency

  whereas, however, when the signal provided by the

  out of the set range, it appears at exit one

lock signal.

  With this circuit arrangement, it is ensured to exclude the possibility of a reception considered as erroneous with a high probability in affected circuits.

by parasites.

  FIG. 6 diagrammatically shows a processing circuit 45 which is incorporated in the carrier frequency receivers 9, 13. This processing circuit 45 is an integrated sampling circuit for determining the duration of the signal, which circuit can to be used advantageously especially during transmissions with a large

  noise level because it enables the identification of

  the received demodulated signal and considerably reduce the distortion of the received signal.

  so that, when receiving signals of a definite duration,

  the signal must remain within a predetermined time range for the detection to be

  If the signal goes out of the predetermined time range

  mined, it is considered a noise and no longer intervenes.

  The operating mode of the processing circuit is as follows: The already demodulated signal is applied to a circuit of

  delay 46, which is a monostable multivibrator

  With a re-triggering operation in which the time constant is approximately one order of magnitude shorter than the minimum duration of a signal The function of the multivibrator is to eliminate short-term disturbances. The output signal of the delay circuit 46 excites on the one hand a gate circuit 47 and on the other hand a divider 48

  gate circuit 47 then lets pass the signal of the oscillation.

  receiver 43 to divider 48, when there is a signal at the output of delay circuit 46 Divider 48 divides the signals of gate circuit 47 into correspondence at a determined constant-and these signals appear in parallel outputs La output of the circuit 48 is connected to the counting unit 49 which consists of three counters and which counts until

  that a signal appears at the output of the delay circuit.

  46 when the signal ceases, a signal appears or not at an output of the counting unit 49 in connection with the processing performed In the next phase, the counting unit 49 returns to zero and also the gate circuit 47 is when it appears at the exit of the circuit of

  delaying 46 a new signal, the process is repeated.

  The counting unit 49 could also be formed of a single counter and in this case it would appear only one

output signal.

  The protection of external drivers of the

  tif is provided by the internal oscillators and by the electronic detection circuits The structure and function of the detection circuits agree with those of the admittance measuring circuit 20 because, in all cases, the disturbing variations of the admittance of the circuit in

  question are detected and indicated.

  The detection circuits are each associated with a conductor and they independently control each other the conductors so as to provide in case of faults, immediately the lock command, the actuation signal and the indication This measure is necessary as between the carrier frequency transceivers and the maneuvering installation of conductors with a length of at least 3 meters as connecting elements and

  damage can lead to insufficient function.

  On the machine side, the power supply necessary for starting the device is provided by the accumulator 19 which is provided with the regulator 18 because, for

  the power supply of the carrier frequency transceivers

  otherwise no other food is available

  While the motors 1 and 2 are in a stopping condition When the motors 1 and 2 are switched on, the control unit 17 charges the accumulator 19, this load being controlled by the regulator 18. is associated with a relay controlling the alternating current

  and which stops the horn after the engagement of the engines.

Claims (3)

  A method for providing a carrier-frequency remote control in duplex operation, characterized in that, by the use of appropriate separating elements, it is possible to ensure accurate signal transmission also in the case of highly variable network loads and without involving wave suppressors   with stop action and hybrid systems with carrier frequency.   Method according to Claim 1, characterized in that the signals to be transmitted are monitored and identified   on the receiving side and in that only the signals   in this way are transmitted to the receiver.   3 A carrier-frequency remote control device with duplex operation, in particular for milling and loading machines with a milling cylinder in   mines, the device comprising engines and interrupters   characterized in that the first switch (4) is connected to a second switch (5) arranged as a main circuit breaker, which also establishes the connection with the power supply network (3) and further with motors (1, 2); in that both ends of the cable   connecting the motors (1, 2) and the first interrup-   (4) are each connected to a separating unit (12, 7); in that the common point of the motors (1, 2) and the network cable is connected to the input of a control unit (17) of which   the first exit is connected via a regular   tor (18) and an accumulator (19) at the first input of a transmitter (14); in that the second input of the aforementioned transmitter (14) is connected via an emitter control unit (15) to the input of the first divider unit (12) while the output of the transmitter (14) is   connected via a receiver (13) and a receiver   digital drive (16) at the second input of the control unit (17) and that the second output is connected via the second input of the transmitter control unit (15) to a horn (21). ); in that the output of the second separating unit (7) connected to a high-current cable is connected via another receiver (9) and a digital receiver (11) to the first input of the control unit (6) while the input of the separating unit (7) is connected to the output of a transmitter (8); in that the first input of the aforementioned transmitter is connected directly, and the second input via another transmitter control unit (10), to the first input of the control unit (6) , the second input of this control unit (6) being connected to the network via the cable of   connection and the second switch (5) arranged as a disjunction principal.   Device according to claim 3, characterized in that the common point of the horn (21) and the transmitter control unit (15) is connected to the inlet of an admittance measuring apparatus (20). ) and in that the first output of the admittance measuring apparatus (20) is connected to the first input of the transmitter control unit (15)   while the second output is connected to the horn (21).   Device according to one of claims 3 or 4,   characterized in that the separating units (7, 12) are constituted by two series circuits connected in parallel,   the series circuits each consisting of an oscillating circuit   parallel (22, 24, 26, 28) and an oscillating-series circuit (23, 25, 27, 29) and the series-circuit windings   (23, 25, 27, 29) being each provided with a secondary winding   adapter and a secondary insulation winding.   Device according to any one of the claims   3 to 5, characterized in that the admittance measuring apparatus (20) comprises an acoustic frequency generator (30) whose output is connected via a transformer   (31) with a rectifier (34) and with the power supply unit   the output of the rectifier (34) is connected to one of the inputs of a bridge circuit (35) whose another input is connected via another rectifier (33) and a current transformer (32) to one of the outputs of the admittance measuring apparatus (20) while the other output of the admittance measuring apparatus (20) is connected via an output stage (37) and a comparator   at the output of the bridge circuit (35).   7 Device according to any one of the claims   3 to 6, characterized in that the carrier frequency receivers (9, 13) each contain a coincidence acoustic protection circuit (44), which consists of a circuit (39) arranged for transmission of the received signal or else of a differential frequency setting circuit (40) which is connected to the output of the aforementioned circuit, one of   inputs of the different frequency setting circuit   wherein (40) is connected to a receiver oscillator (43) while the output of the frequency setting circuit   differential (40) is connected to one of the inputs of the comparator   frequency converter (42) whose other input is connected via a divider (41) to the oscillator receiver (43).   8 Device according to any one of the claims   3-7, characterized in that the receivers (9, 13) contain   each processing circuit (45), said processing circuits being connected to the coincidence acoustic protection circuits (44); in that the processing circuit (45) contains a delay circuit (46) whose input is connected to the input of the processing circuit (45) while its output is connected to one of the inputs of a circuit gate (47) and a counting unit (49), the other input of the gate circuit (47) being connected, via the output of the receiver oscillator (43), to the other input of the counting unit (49), the output of the counting unit   forming the output of the processing circuit (45).