GB2223380A

GB2223380A - Personnel location system

Info

Publication number: GB2223380A
Application number: GB8917031A
Authority: GB
Inventors: Roger William Leslie Hoyle
Original assignee: Shorrock Ltd
Current assignee: Shorrock Ltd
Priority date: 1988-07-27
Filing date: 1989-07-25
Publication date: 1990-04-04
Also published as: GB8817927D0; GB8917031D0

Abstract

A personnel location system comprises a plurality of locator units 12 disposed at predetermined locations and each providing a unique signal, an interrogator unit 30 e.g. carried by security personnel including a signal detector 48-52 linked via radio transmitter 46 to a central control unit 54 for transmitting the present location of the interrogator unit 30 in the form of a coded signal when the detector is stimulated by a signal from an individual locator unit 12. The coded signal may also include information relating to the particular locator unit 12. The signal received at the detector 48-52 may be produced in response to the proximity of coils in the interrogator, locator units, upon receipt of a polling signal from the interrogator unit or by scanning of a bar code on the locator 12 by an infra-red light emitted by the interrogator. In the embodiment shown, the signals received at a logic circuit 44 separately via a delay 42 and the circuits 50, 52 remain the same until the voltage induced in 14 by 32 is sufficiently large to turn on a data generator 22 whose output momentarily short-circuits the coil 14. <IMAGE>

Description

PERSONNEL LOCATION SYSTEM This invention relates to a personnel location system especially for locating security personnel during the physical inspection of a secured area by said security personnel.

Where an area is to be secured against intrusion or other unauthorised movement it is common to employ, in addition or as an alternative to passive intrusion detectors such as infra-red, ultrasonic or motion detectors, security personnel whose duties include the physical inspection of said secured area. Such physical inspections are commonly called 'watch tours' and it is usual to provide some means for keeping track of said personnel during the inspection. One known method of doing this, particularly applicable to routes substantially within a building or buildings, involves the use of a plurality of key operated switches disposed at pre-determined locations around the building or secured area. The security personnel each carry a key or keys adapted to operate said switches in sequence as each of the switches is passed during a particular inspection tour.Operation of a switch is signalled to a remotely located central control board. Thus the movement of security persons about the area can be monitored automatically or by an operator stationed at the control board. It is usual for the operation of such switches to be connected to a timing device such that each switch must be operated in a pre-set sequence and within a pre-determined time period from the operation of the previous switch in the sequence. If a switch is operated out of sequence, or the time between switch operations is longer than that allowed, an alarm is activated.

A further known method is to provide each security person with a radio transmitter which is then activated by its user at pre-determined time intervals with the user providing a radio receiver operator at a control location with an indication as to his or her present location. This system does overcome a problem inherent with the previous described key switch system which is caused by the presence of wire or cables connecting the key switches to each other and to the central control board. Where such wire or cables are installed in buildings they are easily tampered with, which factor is an important consideration when the secured area is, for example a prison or a similar detention establishment.

However it is possible that the fabric of the building could interfere with radio transmission rendering the signal garbled and impossible to understand. A further problem with this system, and also the key switch system, is their dependence on an action being performed by the security personnel involved. Human nature being what it is, it is quite easy for a security person to forget to perform the required action at the appropriate time leading to an alarm being generated unnecessarily.

It would be an advantage if a location system could be provided which would provide location information automatically without requiring any action by the security personnel.

A further method for tracking the location of security personnel which overcomes these problems is proposed by the applicant in a co-pending British Patent Application and comprises a loop aerial receiving signals from a low power radio transmitter carried by a security person. The time difference between the reception of the signal at each end of the loop aerial is used to determine the position of the transmitter in relation to the said loop aerial. Such a system is easily usable in an outdoor environment, for example, a perimeter fence guard patrol etc. In a building or similar enclosed structure such a system has certain inherent problems. Firstly the loop aerial must be disposed so as to conform to the path of the security personnel around the building.However, the aerial cannot be doubled back on itself at any point as this would lead to reception of a single signal at two different points on the aerial and hence an erroneous determined location. Furthermore the loop aerial itself would be vulnerable to tampering in much the same way as the wiring between key switch locations. Thus such a system cannot readily be used in a building environment where a guard patrol route would be tortuous and could also be on many different levels.

It is an object of the present invention, therefore, to provide a personnel location system which operates automatically, independent of action by the security personnel and which is usable within a building or enclosed environment.

With this object in view the present invention provides a personnel location system comprising a plurality of locator units and an interrogator unit, the plurality of locator units being disposed at predetermined locations about a secured area and each locator unit providing a unique signal and the interrogator unit including a signal detector linked to a radio transmitter such that the radio transmitter broadcasts a coded signal to a central control unit when the signal detector is stimulated by the reception of a signal from an individual locator unit which coded signal is indicative of the present location of the transmitter.

Preferably the interrogator unit also includes a resonant LC circuit supplied with modulated signal of short pulses from an oscillator, the LC circuit including an inductance coil which acts as the primary coil of a transformer, and each locator unit includes a secondary coil such that in the event of the interrogator unit being in close proximity to a locator unit a voltage is induced in the secondary coil, said voltage being used to power a data generator which controls a secondary coil shorting device thereby causing a variation in the primary coil's magnetic field which variation is detected by the signal detector as a binary code indicative of the locator unit's position.

Alternatively the signal provided by each locator unit is in the form of an infra-red reflective bar code readable by the signal detector which is in the form of scanner means reactive to reflected infra-red light, the reading of a bar code causing the broadcasting of the coded location signal.

Preferably the coded signal is in two parts, a first part being indicative of the particular interrogator unit broadcasting and a second part relating to the locator unit signal which has stimulated the coded signal broadcast and contains information on the location of the locator unit.

In a further embodiment the interrogator unit includes a low power transmitter broadcasting a polling signal and each locator unit includes an aerial for receiving said polling signal and battery powered radio transmitter operative to transmit the location signal indicative of the locator unit's location when a polling signal has been recieved, the location signal being received by the signal detector in the interrogator unit.

It will be understood that it is intended for the locator units to be disposed at various locations throughout a secured area and that a security person would carry the interrogator unit around with him or her. As the security person walks by a particular locator unit the interrogator unit would receive the location signal provided by the locator unit and broadcast the appropriate coded signal to the central control unit giving the current location of the interrogator unit based on its proximity to a specified locator unit. The locator units would be preferably placed at strategically important locations within the secured area such as doorways or corridor junctions etc.

The invention will be described further by way of example, with refererence to the accompanying drawing in which the single figure is a simplified block diagram illustrating a practical embodiment of the personnel location system of the present invention.

In the drawing the preferred practical embodiment is illustrated in a simplified form for clarity as comprising only one locator unit 12 and an interrogator unit 30. The locator unit 12 comprises a secondary coil 14 connected to a coil shorting circuit 16, a voltage monitor 18, a delay generator 20 and a data generator 22. In a complete personnel location system many such locator units 12 would usually be provided, each postioned at a pre-determined location within a secured area. Each locator unit 12 is self contained and in the preferred embodiment requires neither an internal or external dedicated power supply.

An interrogator unit 30 for the preferred embodiment includes a primary coil 32 supplied with a signal generated by an oscillator 34 and modulated with short pulses via a pulse modulator 36 and an amplifier 38. The pulsed signal from the oscillator 34 is counted down to a lower frequency and supplied to a pulse shaper 40. The pulse shaper 40 produces a modulating pulse for use as a reference signal and is supplied via a delay 42 to a logic circuit 44 which controls a radio transmitter 46.

When the interrogator unit 30 is not within range of a locator unit 12 an output from a ferrite cored detector coil 48 will consist of the modulated signal supplied to the adjacently located primary coil 32.

This output is amplified by amplifier 50, demodulated at detector 52 and then supplied to the logic circuit 44.

In the aforementioned absence of a locator unit this signal will match the reference signal and hence there will be no output from the logic circuit 44 to the radio transmitter 46.

When the interrogator unit 30 is brought into range of a locator unit 12 a voltage will be induced in the secondary coil 14 of the locator by the primary coil 32 of the interrogator. Once the voltage monitor 18 detects an acceptable supply voltage level, its inhibit signal is removed permitting the data generator 22 to commence operation. A synchronising signal is derived from a pulsed signal in the secondary coil 14 and is delayed by delay generator 20. The synchronising signal is then used as a clock signal for the data generator 22 whose output is supplied to the coil shorting circuit 16 which is operative to momentarily short-circuit the secondary coil 14. This causes a variation in the primary coil's 32 magnetic field and a change in the voltage induced in the detector coil 48 which is supplied to the logic circuit 44.The voltage variations can thus be interpreted by the logic circuit 44 as a unique binary code transmission indicative of the location of the locator unit 12.

In response to the binary code transmission the logic circuit 44 generates an output containing two parts, a first part being unique to the interrogator unit 30 and a second part being an identification of the locator unit 12 which has caused the output. This output is broadcast by the radio transmitter 46 as a coded signal which is received by the aerial receiver 54 at the central control unit. The coded signal is decoded and supplied to a display terminal 56 or other suitable monitoring apparatus where it is displayed as the present location of that particular interrogator unit 30. Thus it is possible to track the passage of a particular interrogator unit 30 past a number of locator units 12 placed about the secured area.

It is to be understood that the foregoing is illustrative and not restrictive of the scope of the invention and variations may be made thereto. For example the locator unit may alternatively comprise an aerial receiver, coupled to a signal detector and a low power radio transmitter such that receipt of a polling signal by the aerial will cause the transmission of a pre-determined location signal. In this embodiment the locator unit would preferably be provided with an internal, self-contained power source, for example a battery and the interrogator would comprise a low power radio transmitter broadcasting a polling signal and a signal receiver to receive the location signal provided by the locator unit. The reception of the location signal from the locator unit would cause the logic circuit to generate an output to its radio transmitter as described previously. In a further alternative embodiment the locator unit would be in the form of a card having infra-red reflective patches which would be seen as a bar code when illuminated by an infra-red light source. The interrogator for reading such a locator unit would include as an infra-red scanner which would illuminate the bar code and detect the reflected portions thereof as a location signal. The receipt of the location signal causes the transmission of the code signal to the central control unit as previously. Other variations may also be possible.

Claims

1. A personnel location system comprising a plurality of locator units and an interrogator unit, the plurality of locator units being disposed at predetermined locations about a secured area and each locator unit providing a unique signal and the interrogator unit including a signal detector linked to a radio transmitter such that the radio transmitter broadcasts a coded signal to a central control unit when the signal detector is stimulated by the reception of a signal from an individual locator unit, which coded signal is indicative of the present location of the transmitter.

2. A personnel location system as claimed in claim 1 in which the signal detector is linked to the radio transmistter by logic circuitry.

3. A personnel location system as claimed in claim 1 or claim 2 in which the unique signal provided by the locator unit is indicative of the location of a particular unit.

4. A personnel location system as claimed in claims 1, 2 or 3 in which the interrogator unit includes a resonant LC circuit supplied with modulated signal of short pulses from an oscillator, the LC circuit including an inductance coil which acts as the primary coil of a transformer, and each locator unit includes a secondary coil such that in the event of the interrogator unit being in close proximity to a locator unit a voltage is induced in the secondary coil, said voltage being used to power a data generator which controls a secondary coil shorting device thereby causing a variation in the primary coil's magnetic field which variation is detected by the signal detector as a binary code indicative of the locator unit's position.

5. A personnel location system as claimed in claims 1, 2 or 3 in which the signal provided by each locator unit is in the form of an infra-red reflective bar code readable by the signal detector which is in the form of scanner means reactive to reflected infra-red light, the reading of a bar code causing the broadcasting of the coded location signal.

6. A personnel location system as claimed in any preceding claim in which the coded signal is in two parts, a first part being indicative of the particular interrogator unit broadcasting and a second part relating to the locator unit signal which has stimulated the coded signal broadcast and contains information on the location of the locator unit.

7. A personnel location system as claimed in claims 1, 2 or 3 in which the interrogator unit includes a low power transmitter broadcasting a polling signal and each locator unit includes an aerial for receiving said polling signal and battery powered radio transmitter operative to transmit the location signal indicative of the locator unit's location when a polling signal has been received, the location signal being received by the signal detector in the interrogator unit.

8. A personnel location system substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.