GB1582018A - Surveillance monitoring systems - Google Patents

Abstract

In continuous mode, the device operates with ultrasonic pulses (11) and only operates additionally with microwave radiation pulses (12) when the device section (1) operating with ultrasound emits a signal. The device component (2) with microwave radiation is only switched on (4) with delay after detection of the signal which indicates an event which, per se already exists. Radiation pulses of the two device components (1 and 2) are then used for carrying out a coincidence detection (15), preferably with speed comparison, which only then decides on an alarm signal (151). <IMAGE>

Description

(54) IMPROVEMENTS IN OR RELATING TO SURVEILLANCE MONITORING SYSTEMS (71) We, SIEMENS AKTIENGESELLSCHAFT, a German Company of Berlin and Munich, German Federal Republic, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following state ment:- The invention relates to surveillance monitoring systems of the type in which an ultrasonic sound transmitting device is used together with a microwave radio transmitter to produce respective echo-detection signals for comparison, which may produce an indication signal or trigger an alarm if the comparison satisfies predetermined conditions that signify an event of the type to be detected has occurred.

For intruder detection it is known to employ the Doppler radar principle, for example by the use of radio waves in the GHz range, and in one commercially available equipment very high-frequency, electromagnetic radiation is emitted, and any frequency shift in a received echo signal of a magnitude which indicates the presence of a moving person, e.g. a burglar, causes an alarm to be triggered.

Ultrasonic sound devices operating on the Doppler radar principle are also known, which operate with ultrasonic waves in the region of 40 kHz, for example. These also utilise any frequency shift of a received echo signal to trigger an alarm, when predetermined conditions are satisfied.

Our co-pending United Kingdom Patent Application No. 13517/77 (Specification No.

1,573,847) relates to an intruder detection system in which an ultrasonic wave transmitter and a radio wave transmitter are provided, each having an associated receiver operated in accordance with the Doppler principle, to emit an alarm signal when both Doppler components give coincidental characteristic response. Thus, this virtually completely safeguards the system against false alarms. In one embodiment described, a phase-locked loop is provided in one receiver circuit and the other contains an oscillator which is coupled to this PLL-circuit and tuned to the n-th frequency of the oscillator of the PLL-circuit, where n is the ratio of the respective wavelengths in air.There is also a product mixer whose output signal is fed via the regulating loop of the PLL- circuit back to the associated oscillator in order to tune the latter in frequency and phase to the frequency and phase of the input signal supplied to the product mixer. If a PLLcircuit of this kind is employed in the ultrasonic arm of the receiver, for example, and it is supplied with the Doppler-frequency signal demodulated by the ultrasonic Doppler detector, the oscillator of the PLL-circuit is constantly tuned to this Doppler-frequency.

This PLL-circuit is coupled to the aforementioned oscillator of the other receiver from which a mixed signal is then supplied to a product mixer in the radio receiver.

This product mixer also receives any demodulated Doppler-frequency-shifted echo signal arriving at its associated receiver. The oscillator of this other receiver thus differs in frequency by a specific proportion from the oscillator of the PLL- circuit of the other when the Doppler-frequency shift of the receiver signals is based on one and the same detected event, i.e. the presence of one and the same, moving person. In this event, this alarm device comprising these two receivers emits an alarm signal.

In a special embodiment, the described system is connected in such manner that in a special circumstance, an output of one single receiver can trigger an alarm signal. This allows a safeguard against deliberate interference, in which a burglar may employ his own transmitter in order to interfere with a receiver of the system. Normally, the receiver that will be subjected to such interference is the ultrasonic wave receiver, which can be saturated by a strong-amplitude signal from a burglar's transmitter device, and thus rendered incapable of functioning in order to receive any Doppler signal for analysis. The existence of an echo having an excessive amplitude automatically switches the system to trigger an alarm based solely on the analysis of the other receiver, as long as such interference persists.

A disadvantage of an intruder alarm which operates with microwave signals is that the range of such devices extends beyond that area that is to be monitored, for example, through windows and doors to the exterior.

This disadvantage does not exist in corresponding devices using ultrasonic radiation, although such ultrasonic devices can occasionally give a false alarm when the transmitted ultrasonic radiation is considerably influenced by turbulence of the atmosphere or a movement such as that of curtains caused by air turbulence.

A considerable improvement in respect of safely avoiding a false alarm without adversely affecting the monitoring sensitivity is achieved by the intruder alarm described in our aforementioned United Kingdom Patent Application, which operates upon a coincidence of ultrasonic and radio wave Doppler echoes. This alarm system is fundamentally entirely satisfactory, but has the disadvantage common to all Doppler alarm devices opering with microwaves, namely, that operation consumes a relatively large amount of electricity, which can be of considerable significance when, as is extermely desirable for monitoring purposes, the entire alarm installation and thus also the alarm device itself are to be fed from a battery, for additional safety.

One object of the present invention is to provide a system which reduces the powerconsumption disadvantage referred to above.

The invention consists in a surveillance monitoring system in which an ultrasonic sound transmitter/receiver and a micro-wave transmitterlreceiver are provided, each receiver being designed to operate on the Doppler principle, and both said transmitter! receivers being connected to a common power supply, said system further comprising analysis means to produce an output signal if respective echo signals are simultaneously received indicating the occurrence of an event to be monitored, when operating, and the connection of the microwave transmitter output stage to the common power supply being effected via a switching circuit that is controlled by the output of said ultrasonic receiver so as to be operative only when an ultrasonic echo signal is received, and for a length of time which is sufficient for analysis of the micro-wave signal.

The invention will now be described with reference to the drawing, which illustrates the block schematic circuit diagram of one exemplary embodiment.

An ultrasonic transmitter/receiver 1 is connected to a current supply source 3. A micro-wave transmitter/receiver 2 is connected to the current supply source 3, via a controllable switching circuit indicated by a switch 4. Respective transmitting elements 11 and 12 are fed by the units 1 and 2. Any echo signal output signal appearing at the output 111 of the receiver portion of the unit 1 is fed as a control signal to the switch 4, and closes this switch to set the microwave unit 2 into full operation. When the unit 2 is in operation, and a Doppler signal, based on an event which produced the ultrasonic echo mentioned above, appears at output 121 of the unit 2, there is then produced an output signal based on event coincidence.

In the embodiment represented in the Figure, a special feature has also been taken into account, namely that only the current supply to the most power-consuming part of the unit 2, i.e. the transmitter section, is interrupted by the switch 4, and connected to the current supply source 3 by the closure of this switch. The transmitting section 21 fundamentally comprises a Gunn diode. It will normally be extermely expedient for the other circuit section of the unit 2, in particular its input amplifier stages, to be constantly connected to their power supply source in order to avoid transient disturbances of the type that result at start-up, and this can be accepted since these amplifier stages consume only an insignificant amount of electrical power.

As described in our above-mentioned United Kingdom Patent Application, the two outputs 111 and 121 are preferably compared, and in this embodiment are connected to a frequency comparator circuit 15 having two inputs, as is described in detail in the earlier application. With this arrangement, an output 151 of this circuit provides a signal only when in addition to the event coincidence, there is also a speed coincidence, thus giving an increased safeguard against any false alarm.

Further protection can be obtained by the inclusion of band-pass filters to eliminate echo-signals whose Doppler frequency is such that the event producing that echo is not of a type considered to be of interest.

The invention is based on the recognition that for area monitoring, for an intruder alarm such as described in our abovementioned United Kingdom Patent Application, or for other monitoring applications utilising coincidence of an ultrasonic echo and micro-wave-echo, it is possible to maintain reliability of the system without maintaining the radio section in operation at all times, provided that the ultrasonic unit is kept in operation, i.e. during the entire monitoring period, so that the micro-wave unit can be operated only when the ultrasonic unit emits an output signal.This output signal indicates that an event is occurring in the area to be monitored, which could consist of the entry of an intruder in the case of an intruder alarm system, or of some other event, such as the passage of a product on a conveyor belt in a production unit, or of an object or person in cases where the passage or counting of people or things is to be effected as the events to be monitored. The output of the ultrasonic unit could be produced by turbulence, and a false output signal is prevented by bringing the microwave unit into operation to give a check on the signal to determine whether an event to be indicated has occurred or merely a false signal initiated by some phenomenum. The length of time for which the micro-wave unit is switched on can be contrived to be relatively short, namely as short as is sufficient to carry out this check.

During the time in which the microwave unit is also in operation, a coincidence checking operation can be performed. In the remainder of the time, no coincidence operation takes place, but there is adequate monitoring of the relevant area with economical use of the power supply. It should be mentioned that the microwave transmitter requires approximately ten times as much power as the ultrasonic unit.

A special, further advantage which is achieved is that the liability to produce false response signals or alarms is actually reduced, since even with full Doppler coincidence checking false alarms can be based on random coincidences, namely when different objects having approximately the same relative speed are recorded simultaneously, one by each unit, e.g. when an operating micro-wave unit records a person moving outside the area to be monitored, and the ultrasonic unit records a turbulence which has occurred within the area to be monitored.

By only rendering the microwave unit operative upon receipt of an echo by the ultrasonic unit the system will not in fact record those random coincidences which occur individually and for short lengths of time, because the micro-wave unit is not set into operation until a finite period following its connection to the supply source by the ultrasonic unit output signal, and carries out the check of the event after some delay. This delay can be deliberately increased. An indication or alarm signal is only emitted when the event has been established by the micro-wave unit and is still detected by the ultrasonic unit.

By combining the principle of actuating the micro-wave unit only when a signal has been emitted from the ultrasonic unit in a system constructed as described in our above mentioned United Kingdom Patent Application a monitoring process comprising both event coincidence and speed coincidence can be achieved, and the system can be such that it is caused to respond only to those frequency shifts in the two components which are based on identical relative speeds.

However, the system can be advantageously employed solely with event coincidence.

This event coincidence is based on the measure that the micro-wave unit is switched on only by the ultrasonic unit, and this switch-on occurs only when the ultrasonic unit has established an event which could in itself consist of a true signal or a false signal.

The check carried out with the micro-wave unit then establishes whether this is a genuine event, e.g. an intrusion into the monitored area, or whether the other unit has simply produced a random false signal. The mere fact that a signal is produced by the microwave unit when it is rendered operative is itself equivalent to the effect provided by a coincidence circuit, which latter circuit can therefore be dispensed with, if so desired.

The above references to intruder alarms for the detection of unauthorised entry to an area by a burglar or other undesired person is only one sphere of use of the system, although of great importance. The system can also be used in a pure counting process, to check the passage of persons or things through a given area.

WHAT WE CLAIM IS: 1. A surveillance monitoring system in which an ultrasonic sound transmitter/ receiver and a micro-wave transmitter/ receiver are provided, each receiver being designed to operate on the Doppler principle, and both said transmitter/receivers being connected to a common power supply, said system further comprising analysis means to produce an output signal if respective echo signals are simultaneously received indicating the occurrence of an event to be monitored, when operating, and the connection of the microwave transmitter output stage to the common power supply being effected via a switching circuit that is controlled by the output of said ultrasonic receiver so as to be operative only when an ultrasonic echo signal is received, and for a length of time which is sufficient for analysis of the micro-wave signal.

2. A system as claimed in Claim 1, in which said switching circuit is connected into the current supply line of the entire microwave transmitter.

3. A system as claimed in Claim 1 or Claim 2, in which the two receiver outputs are fed to a frequency comparator which produces a signal only if the respective echo signals have respective Doppler frequencies with a predetermined relationship indicating that the echo signals are produced by an event having equal speed for each monitoring wave.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. period, so that the micro-wave unit can be operated only when the ultrasonic unit emits an output signal. This output signal indicates that an event is occurring in the area to be monitored, which could consist of the entry of an intruder in the case of an intruder alarm system, or of some other event, such as the passage of a product on a conveyor belt in a production unit, or of an object or person in cases where the passage or counting of people or things is to be effected as the events to be monitored. The output of the ultrasonic unit could be produced by turbulence, and a false output signal is prevented by bringing the microwave unit into operation to give a check on the signal to determine whether an event to be indicated has occurred or merely a false signal initiated by some phenomenum.The length of time for which the micro-wave unit is switched on can be contrived to be relatively short, namely as short as is sufficient to carry out this check. During the time in which the microwave unit is also in operation, a coincidence checking operation can be performed. In the remainder of the time, no coincidence operation takes place, but there is adequate monitoring of the relevant area with economical use of the power supply. It should be mentioned that the microwave transmitter requires approximately ten times as much power as the ultrasonic unit. A special, further advantage which is achieved is that the liability to produce false response signals or alarms is actually reduced, since even with full Doppler coincidence checking false alarms can be based on random coincidences, namely when different objects having approximately the same relative speed are recorded simultaneously, one by each unit, e.g. when an operating micro-wave unit records a person moving outside the area to be monitored, and the ultrasonic unit records a turbulence which has occurred within the area to be monitored. By only rendering the microwave unit operative upon receipt of an echo by the ultrasonic unit the system will not in fact record those random coincidences which occur individually and for short lengths of time, because the micro-wave unit is not set into operation until a finite period following its connection to the supply source by the ultrasonic unit output signal, and carries out the check of the event after some delay. This delay can be deliberately increased. An indication or alarm signal is only emitted when the event has been established by the micro-wave unit and is still detected by the ultrasonic unit. By combining the principle of actuating the micro-wave unit only when a signal has been emitted from the ultrasonic unit in a system constructed as described in our above mentioned United Kingdom Patent Application a monitoring process comprising both event coincidence and speed coincidence can be achieved, and the system can be such that it is caused to respond only to those frequency shifts in the two components which are based on identical relative speeds. However, the system can be advantageously employed solely with event coincidence. This event coincidence is based on the measure that the micro-wave unit is switched on only by the ultrasonic unit, and this switch-on occurs only when the ultrasonic unit has established an event which could in itself consist of a true signal or a false signal. The check carried out with the micro-wave unit then establishes whether this is a genuine event, e.g. an intrusion into the monitored area, or whether the other unit has simply produced a random false signal. The mere fact that a signal is produced by the microwave unit when it is rendered operative is itself equivalent to the effect provided by a coincidence circuit, which latter circuit can therefore be dispensed with, if so desired. The above references to intruder alarms for the detection of unauthorised entry to an area by a burglar or other undesired person is only one sphere of use of the system, although of great importance. The system can also be used in a pure counting process, to check the passage of persons or things through a given area. WHAT WE CLAIM IS:

1. A surveillance monitoring system in which an ultrasonic sound transmitter/ receiver and a micro-wave transmitter/ receiver are provided, each receiver being designed to operate on the Doppler principle, and both said transmitter/receivers being connected to a common power supply, said system further comprising analysis means to produce an output signal if respective echo signals are simultaneously received indicating the occurrence of an event to be monitored, when operating, and the connection of the microwave transmitter output stage to the common power supply being effected via a switching circuit that is controlled by the output of said ultrasonic receiver so as to be operative only when an ultrasonic echo signal is received, and for a length of time which is sufficient for analysis of the micro-wave signal.

2. A system as claimed in Claim 1, in which said switching circuit is connected into the current supply line of the entire microwave transmitter.

3. A system as claimed in Claim 1 or Claim 2, in which the two receiver outputs are fed to a frequency comparator which produces a signal only if the respective echo signals have respective Doppler frequencies with a predetermined relationship indicating that the echo signals are produced by an event having equal speed for each monitoring wave.

4. A surveillance monitoring system sub

stantially as described with reference to the drawing.

5. An intruder alarm employing a system as claimed in any preceding Claim.