GB2133599A - Monitoring system for divers - Google Patents

Abstract

For monitoring a diver, an electroacoustic transducer fixed to the helmet or other equipment of the diver continuously transmits acoustical signals on a predetermined frequency to a monitoring station provided on an escort vessel. A clock generator in the helmet of the diver generates periodical test signals which have to be acknowledged by the diver by means of a response signal. If no response signal is generated the frequency of the transmission signals is increased and thereupon an alarm is generated in the monitoring station.

Description

SPECIFICATION Monitoring System for Divers The invention relates to a monitoring system for divers.

A safety system carried by a diver is known which generates periodic control signals and transfers these signals to the diver. The diver by means of an acknowledge push button can cancel these control signals.

Without such acknowledgement by the diver a rescue signal is generated. This rescue signal can be used for activating rescue equipment borne by the diver and additionally can be transmitted to a remote receiving station.

Based on this prior art it is the main object of the invention to remotely monitor the proper operation of a safety system carried by the diver. Such remote monitoring for instance can be performed from a fixed ground station or from aboard an escort vessel.

It is a further object of the invention to provide the possibility of acoustically locating the diver in a case of emergency.

Accordingly the present invention provides a monitoring system for divers, comprising: a diver unit including - clock means for generating a sequence of clock pulses, - means for providing the clock pulses to the diver as audio signals, - a response circuit controlled by the diver, - a time window circuit which generates an out put signal after each clock pulse unless inhibited by a signal from the response circuit occurring within a predetermined time, - transmitter means which generate a series of pulses at a predetermined carrier frequency and with a first or second PRF in dependence on the output signal from the time window circuit, and - an electroacoustic transducer fed by the trans mitter means; and a monitoring station, on a ship orthe like, including - an electroacoustic transducer for receiving pulses from the transducer of the diver unit, and - converter meansforindicating the nature ofthe received signals.

The monitoring station may include a monitoring system according to Claim 1, wherein the monitoring station includes a clock generator which feeds the monitoring station transducer with a series of clock signals at a clock carrier frequency, with the clock means of the diver unit being driven by the clock signals from the monitoring station received via the diver unit transducer.

Two embodiments of the invention will now be described, by way of example, with reference to the drawings, in which: Figure 1 is a block diagram of the first embodiment of the diver apparatus; Figure 2 is a block diagram of the associated monitoring station; Figure 3 is various pulse diagrams for explaining the function of this monitoring system; Figure 4 is a block diagram of a diver apparatus working in accordance with the transponder principle; and Figure 5 shows the block diagram ofthe associated monitoring station.

Introductory Summary A clock generator borne by the diver delivers at predetermined time intervals an acoustic test signal which the diver has to acknowledge by means of a response signal within a period of time determined by a time window circuit. If no acknowledgement is made, an alarm signal is initiated (as in the prior art arrangement). This alarm signal on the one hand is emitted by an electroacoustic transducer and therewith can be received by a monitoring station and be used for localizing the diver. On the other hand, by means ofthe alarm signal, rescue equipment such as a rescue vest or a rescue balloon can be operated.

Even during proper operation, that means that if the diver periodically acknowledges the test signal, the diver apparatus continuously transmits sound pulses on a frequency which is characteristic for the diver concerned. These transmitted pulses are received by the monitoring station and are used as acknowledgement for the proper operation of the diver apparatus. If the diver does not respond, the pulse repetition frequency of the transmitted sould pulses is essentially increased (for instance doubled) so that at the monitoring station on the one hand it can be determined that the signal transmission still operates properly and on the other hand an alarm signal is given. An essential feature of the system therefore is the continuous remote monitoring of the diver apparatus from the remote monitoring station.

Whereas in the first embodiment ofthe monitoring system the time sequence for generating the test signals is controlled by a clock generator within the diver apparatus, the second embodiment operates in accordance with the transponder principle. In this case a call signal is transmitted by the monitoring station to the diver and the diver is requested to acknowledge this by sending a response. In addition to the known transponder operation with check signal and response signal, the system here provides an automatic switching ofthe pulse repetition frequency ofthe signal transmitted by the diverto a higher pulse frequency if the diver does not generate a response signal. This increased pulse repetition frequency again indicates that on the one hand the diver apparatus operates properly and on the other hand an alarm case is present.Also in this case the signal transmitted by the diver in the case ofan alarm can be used for localizing the diver by means of a direction finding apparatus provided at the monitoring station.

Detailed Description In the embodiment of Figure 1 a transmitter frequency and clock generator 1 delivers on its output line 2 a transmission frequency fs which is characteristic for the concerned diver and is one of several possible transmission frequencies. This frequency for instance lies in the range 36 to 39kHz. On an output line 3 the generator 1 delivers a clock pulse sequence with a pulse period duration of for instance 0.1 s. This clock frequencey ft is suplied to an operation control circuit 4 which after receiving a clock pulse that means after a time interval of 1 s delivers a gating pulse on its output line 5.This gating pulse activates the pulse sequency control circuit 6 for a predetermined pulse duration of for instance 10, 20, 40 or 80 ms and permits the transmission frequency fs to be applied to the transmission stage 7, where it is amplified and then is supplied to the electroacoustical transducer 8 for being transmitted. These signals which indicate the proper operation of the diver apparatus can be received and indicated by the monitoring station which is provided on ground or aboard an escort vessel.

Furthermore clock generator 1 generates a system clock of for instance 30 s which via operation control circuit 4 initiates a test signal generator 9 so that this generator 9 at intervals of 30 s delivers an audible test signal of for instance 2 kHz and a duration of 1 s to a sound transducer 10 which is provided within the helmet of the diver. Simultaneously a set signal of clock generator 1 is supplied to time window circuit 11, by which this circuit is initiated for becoming responsive during a time interval of for instance 7s for receiving a response signal generated by the diver.

This response signal in known manner can be generated by means of a push button (dead man button).

It is more favourable to provide an acoustic generation of the response signal because in this case the diver keeps his hands free for the work which he has to perform. In the embodiment shown a throat-type microphone 12 is provided and feeds an amplifier rectifier 13. The electrical response signal generated in this manner is delivered to a comparator 14 where it is compared with a minimum level signal delivered by a level adjusting circuit 15. It is further determined whether or not the response signal is present for a minimum period of for instance 1 s. This prevents response signals from being erroneously derived from interference signals.If the signal supplied by rectifier 13 exceeds the minimum level signal, the comparator 14 delivers an output pulse to the response circuit 16 which in turn via output line 17 resets time window circuit 11 and therewith acknowledges the test signal generated by sound generator 10. This test procedure during normal operation is repeated in the rhythm of the system clock of for instance 30 s.

If the diver within the time interval determined by the time window circuit 11 does not generate a response signal, the time window circuit delivers an alarm signal on its two outputs 18 and 19. The signal on line 18 is forwarded to a pulse sequence control circuit 6 via operation control circuit 4 and switches the pulse frequency of the transmission signal fs to a higher frequency, for instance to double the pulse frequency. This frequency is emitted as a alarm signal by means of electroacoustic transducer 8. The monitoring station, in response to this increase of the pulse frequency, determines that this is a case of alarm. Simultaneously because of this continuously emitted increased pulse frequency the diver can be localized by means of a direction finding equipment.

On line 19the alarm signal is available for initiating a rescue apparatus such as a rescue vest, a balloon or something like that.

The system makes it possible to simultaneously monitor several divers if different transmission frequencies are allocated to them. If one of these divers encounters an emergency he can be located by means of a frequency selective direction finding apparatus without the monitoring of the other divers being interrupted. Forachieving a reliabledetermina- tion of the transmission frequency of the diver apparatus, the pulse length of the ultrasound pulses emitted by transducer 8 should not be shorterthan 15 ms. The power supply for the diver apparatus and corresponding test circuits for this apparatus are not shown in the drawing. If the acoustical or electrical interference level within the diver apparatus is known at the very beginning, the level adjusting circuit 15 can be omitted.

The monitoring station shown in Figure 2 comprises two electroacoustic transducers which are a non-directional receiver transducer 21 and a directional receiver 22 consisting of two parts. The output signals oftransducer 21 are supplied to a preamplifier and filter 32. The amplified output signal of the nondirectional receiver 21 is by means of a switch 24 supplied to a frequency converter 25 which converts the received ultrasound pulse sequences into the audible range and supplies them via a sound fre quency amplifier 26 to a loudspeaker 27 or earphones 28. In order to locate a diver in an emergency, a sum/difference amplifier 29 is connected to the output of preamplifier 23 and derives from the output signals of the two parts of direction sensitive transducer 22 a sum signal and a difference signal.These two signals are fed to a phase selective rectifier 30 which controls an indicating device 31 which works like a tuning indicator. It may be a zero indicator or a light emitting diode indicator and it indicates whether or not the received signal is received with a maximum amplitude or in which direction the direction finding apparatus deviates from the direction between the monitoring station and the diver. Furthermore the sum signal from sum/differential amplifiervia switch 24, frequency converter 25 and sound amplifier 26 can be fed to loudspeaker 27 or earphones 28 respectively.

If the diver for any reason is prevented from responding within the interval of time as determined bythetime window circuit 11, he can cancel the alarm signal later on by generating a response signal. In this case the alarm signal on line 19 is terminated and via line 18 and operation control circuit 4 the pulse sequence control circuit 6 is switched to the lower transmission pulse frequency. This lower frequency indicates normal operation and therewith shows that on the one hand the monitoring system operates properly and on the other hand the diver is able to respond.

Figure 3 shows several signals. During normal operation the individual transmission pulses are spaced by 1 s and the transmission frequency allocated to the individual divers lies between 36 and 39 kHz. In accordance with the rhythm of the system clock of 30 s, a test signal of 1 s duration having an audible frequency of for instance 2 kHz is radiated via sound transmitter 10. If, within the time window of about 7 s which follows after the test signal, no response signal is received then the transmission pulse sequence is switched to a pulse distance of 0.1 s (that is to tenfold the original pulse frequency) therewith indicating a case of alarm.A delay circuit 20 may be inserted into the output line 19 of the time window circuit so that the alarm contact 20' is operated after a predetermined delay period, for instance after three monitoring cycies and then is supplied with a switch ing voltage.

Whereas in the embodiment according to Figures 1 and2 the system clock (that is, the rhythm of generating the test signals) is determined within the diver apparatus, Figures 4 and 5 show an embodiment in which this test or inquiry rhythm is determined at the monitoring station on board of an escort vessel or at the coast. This monitoring system operates in accordance with the so called transponder principle in which on a first frequency an inquiry signal is transmitted by the monitoring station and the diver has to respond to this inquiry signal by transmitting a response signal on a second frequency.If such response is not received, which means that the diver has not generated a response signal, the diver apparatus automatically switches to alarm operation and transmits an alarm signal within an increased pulse frequency which is received at the monitoring station and by means of an underwater direction finding system can be used for localizing the diver.

Corresponding parts of the circuitry have corresponding references. The diver apparatus shown in Figure 4 again is provided with an electroacoustic transducer8 which in this case is used for receiving as well as for transmitting operation. Connected to the transducer is a tuned receiver 113 which amplifies and rectifies the inquiry signals transmitted by the monitoring station in the form of a sound pulse of predetermined duration and with a predetermined ultrasonic carrier frequency fl. This sound pulse initializes a time window circuit 11 which determines a time interval within which the response signal has to be generated by the diver. Otherwise an alarm signal is transmitted.In order to inform the diver about the receipt of the inquiry signal, a sound generator 9 is connected to the receiver 113 and is activated by the received signal and delivers for predetermined period of time an audible test signal into the internal space of the diver helmet by means of a transducer 10 fastened to the helmet. The diver acknowledges receipt of the test signal acoustically by means of his throat type microphone 12 which via an amplifier and rectifier 13 delivers an electrical response signal to comparator 14. This comparator 14 compares the response signal with a minimum level signal provided by a level adjusting circuit 15, thereby suppressing acoustic and electrical interference. If the response signal exceeds the minimum level the comparator 14 delivers a pulse to the response circuit 16 which in turn via line 17 resets time window circuit 11.Furthermore response circuit 16 delivers at its output line 116 a signaltotransmitter control circuit 117 which during a time interval determined by means of timing circuit 118 activates transmission frequency generator 101 in such a manner that the transmission signal of predetermined carrier frequency f2 is transmitted with a low pulse sequence frequency fn.

If however the diver within the time interval determined by time window circuit 11 does not generate a response signal, then the output pulse of time window circuit 11 is delivered to transmitter control circuit 117 via line 18. This circuit 117 then via line 119 controls the transmitter generator 101 in such a manner that it generates a transmission pulse sequence with increased (for instance doubled) frequency fh.

This increased transmitter frequency is transmitted to the monitoring station via transmission stage 7 and transducer 8. During the transmission receiver 113 is inhibited via line 120. The transmission of the alarm signal with increased pulse frequency is not interrupted but used for localizing the diver. Also in this case several divers can be monitored simultaneously by the same monitoring station by allocating different carrier frequencies to the individual divers.

The structure of the monitoring station as shown in Figure 5 shows a receiver 23 tuned or tunable to the transmission frequency f2 ofthe individual diver, followed by a frequency converter 25, low frequency amplifier 26 and loudspeaker 27 or earphone 28. In addition to these components the monitoring station comprises an additional transmission channel consisting of timing circuit 21, transmission frequency generator 122 and transmission amplifier 123. Timing circuit 121 generates a pulse of predetermined duration which activates transmission generator 122 to transmit an inquiry pulse on the transmission fre quench fur which is different from receiving frequency f2. This inquiry pulse is forwarded via transmission amplifier 123 to the electroacoustic transducer 21.

During the transmission of the transmission pulse, receiver 23 is inhibited via line 124. That portion ofthe transmission station used for direction finding of the diver is not shown in Figure 5. It may have the same configuration as shown in Figure 2 but any other underwater direction finding equipment can be used for these purposes.

The electroacoustic transducer 8 furthermore can be used for voice transmission between the diver and the monitoring station. For this purpose a switch has to be provided which during voice transmission has to be operated by the diver and connects microphone 12 via amplifier 13 and a frequency converter to the transmission stage 7 and simultaneously inhibits the monitoring circuit and in the case ofthe embodiment of Figure 4 also inhibits receiver 113. When releasing this voice transmission button the monitoring system is switched back to monitoring operation so that the monitoring system cannot be intentionally switched off by the diver. Circuits for such kind of voice transmission are known from the technique of underwater telephone connections. The electroacoustic transducer 18 can for instrance be fixed to the helmet of the diver or to another part of the diver equipment for instance to the oxygen apparatus or respirator.

Claims (10)

1. A monitoring system for divers, comprising: - a diver unit including - clock means for generating a sequence of clock pulses, - means for providing the clock pulses to the diver as audio signals, - a response circuit controlled by the diver, - a time window circuit which generates an output signal after each clock pulse unless inhibited by a signal from the response circuit occurring within a predetermined time, - transmitter means which generates a series of pulses at a predetermined carrier frequency and with a first or second PRF in dependence on the output signal from the time window circuit, and - an electroacoustic transducer fed by the transmitter means; and a monitoring station, on a ship orthe like, including - an electroacoustic transducer for receiving pulses from the transducer of the diver unit, and - converter means for indicating the nature ofthe received signals.

2. A monitoring system according to Claim 1, wherein the monitoring station includes a clock generator which feeds the monitoring station transducer with a series of clock signals at a clock carrier frequency, and the clock means of the diver unit is driven by the clock signals from the monitoring station received via the diver unit transducer.

3. Monitoring system according to either previous Claim, wherein the monitoring station includes alarm apparatus activated when receiving transmission signals with second pulse frequency.

4. Monitoring system according to any previous Claim, wherein the diver unit includes an alarm contact which is activated by the time window circuit if no response signal is generated.

5. Monitoring system according to Claim 4, including a time delay circuit switched between the time window circuit and the activating circuit for the alarm contact.

6. Monitoring system according to any previous Claim, wherein the response circuit comprises as generator a sound receiver, preferably a body sound or throat type microphone.

7. Monitoring system according to any previous Claim, wherein the diver apparatus additionally comprises a receiverwhich can be connected between the electroacoustic transducer and the sound generator.

8. Monitoring system according to any previous Claim, wherein for distinguishing the transmission signals of different divers, the transmission frequency, the pulse frequency and/or the pulse rate of the transmission signals can be changed.

9. Monitoring system according to any previous Claim, wherein the electroacoustictransducer is fixed to a diver helmet.

10. Monitoring system according to any one of Claims 1 to 8, wherein the electroacoustic transducer is fastened to the diver equipment, for instance to the respirator system of the diver.