EP0676733A1

EP0676733A1 - Detection system and method of operating same

Info

Publication number: EP0676733A1
Application number: EP95302274A
Authority: EP
Inventors: Thomas Lovell; Thomas Vlasits; Peter Gale; Peter David Minns; Edward Korolkiewicz; David Llewellyn Lewis
Original assignee: Harrison Brothers (Steeplejacks) Ltd
Current assignee: Harrison Brothers (Steeplejacks) Ltd
Priority date: 1994-04-09
Filing date: 1995-04-05
Publication date: 1995-10-11
Also published as: GB2288263A; GB9407098D0; GB9507126D0

Abstract

In an improved detection system of the type wherein detectors (13 to 18) are linked to a central monitoring unit (11, 12) by radio, each detector includes a radio receiver (22) as well as a transmitter (23) and also includes a timer (24) to control the timing of the operation of the receiver and transmitter. The monitoring unit is able to transmit to each detector a synchronisation signal to coordinate the operation of the timers. Signals from the detectors are transmitted to the monitoring unit in predetermined sequence, with the result that overlapping of signals, and the confusion which may otherwise arise, are avoided.

Description

The present invention is concerned with detection systems comprising a multiplicity of detectors. The invention includes a method of operating such a detection system. The system and method are particularly suitable for detecting fires but may be used, suitably adapted, for detecting other eventualities, such as intrusions or other events threatening the security of a location.
Detectors which operate to give warning of the existence of conditions signifying a fire for example are widely used, either singly or as a group of detectors spread around the site protected by them. Single detectors may give a direct audible signal but such a signal may be of little value on an extensive site and may pass unheard. It is therefore usual for the warning signals from a group of detectors to be received at a central control unit, at which it is possible to respond quickly to any signal received.
Conventionally, such signals to a central location are passed by a direct line. The installation of a number of lines for this purpose may prove to be a relatively expensive exercise and in addition may be inconvenient or undesirable in some situations, for example where architecturally sensitive buildings or structures of historical significance are involved. In such situations at least, it is preferred to pass signals from detectors to a central control by radio.
A very limited number of radio-linked detection systems are available and in such systems, signals may be generated at a detector in two ways. Either the signal is a direct response to the occurrence of an incident, for example the onset of fire conditions or the presence of a fault in the detector, or the signal is produced as a matter of routine at a pre-determined interval, for example to verify that the detector is functioning correctly. It may be a statutory requirement or a strong recommendation that such latter verification signals be transmitted, say, every half-hour or every few minutes.
Where there are a significant number of detectors monitored by radio from a central control unit, signals from two or more detectors may be transmitted at overlapping times, although the intention is that the signals should not overlap. The difficulty is that the timing of the individual transmissions becomes increasingly critical as the number of detectors and/or the planned frequency of verification increases, with the result that the accuracy of the individual timers controlling the individual detectors becomes a more important factor. Timers of adequate accuracy over a prolonged period are not readily available; the timing achievable by available timers which are otherwise suitable for the purpose tends to drift over a period.
If such signals overlap, then the messages conveyed by the signals may become confused or may be lost or the signals may be interpreted wrongly.
It is therefore an object of the present invention to provide a fire detection system, and a method of operating such a system, by which the disadvantages of available such systems using multiple detectors are reduced or eliminated.
The detection system according to the present invention comprises a number of detectors for fire or other eventualities, each detector including a radio receiver, a radio transmitter and a timer adapted to determine the timing of the operation of said receiver and of said transmitter, and a monitoring unit adapted to transmit to each detector a synchronisation signal whereby the operations of said timers are co-ordinated and to receive signals from said detectors in predetermined sequence.
The method according to the invention of operating a detection system comprising a number of detectors each including a radio receiver, a radio transmitter and a timer, comprises transmitting to said detectors synchronisation signals to co-ordinate the operations of said timers and receiving and monitoring, in predetermined sequence, signals from said detectors.
Thus, by means of the detection system and method according to the present invention, each detector may send its required signal, for example an "OK" signal verifying that the detector is functioning properly, only in its own, unique time-slot, at the time set by its timer, which is synchronised by the signals from the monitoring unit. In this way, only one verification signal or the like is transmitted at a time and overlap of such routine signals is completely avoided. The transmission of "emergency" signals, for example a fire warning, is performed in the same way, that is, in time-slots reserved for alarm signals, so interference between such signals is thereby avoided. Preferably, upon receipt of any transmitted information from a detector, the monitoring unit transmits to the detector an acknowledgement of receipt of the information, in a time-slot reserved for such acknowledgements.
The operation of a receiver at the site of each detector requires a source of power to enable the detector to receive and transmit signals. While that power may be provided from the mains electrical supply, it is convenient, and simplifies installation of the detectors, for them to be powered by batteries, which may advantageously be of a "long-life" type. It is not necessary for the receiver to operate continuously, ready to receive synchronisation signals from the monitoring unit; such continuous operation would require an unduly high consumption of power and would, in the case of a battery, greatly limit its operating life. The provision of a timer at each detector allows the receiver to be switched on just before it is due to receive a signal and to be switched off after the signal has been received, and for the transmitter to be operated only at the time when it is due to transmit a message. In one preferred form of the invention, a signal transmitted from the monitoring unit at predetermined intervals includes a check signal whereby the local timer is brought into alignment with the required timing sequence if it has departed from it.
The invention will now be further described, by way of example only, with reference to the accompanying drawings, which illustrate one preferred embodiment of the detection system according to the present invention and wherein:-

Fig. 1 illustrates a simplified version of the system, comprising just two control panels and associated detectors;
Fig. 2 is a schematic representation of a single detector; and
Fig. 3 illustrates a typical sequence of time-slots allocated for the transmission of specific forms of signal.

The illustrated detection system is based upon just two monitoring units in the form of control panels 11, 12 but may readily include several control panels, depending essentially upon the total number of detectors in the system. In the illustrated system, three detectors 13, 14, 15 are associated with control panel 11 and three detectors 16, 17, 18 are similarly controlled by control panel 12. An alarm sounder 19 is associated with control panel 11 and two further alarm sounders 20, 21 are associated with control panel 12. The arrows in Fig. 1 represent radio links and as shown, signals can be sent and received in both directions between each of the control panels and its associated detectors and sounders, and also between the control panels.
Each of the detectors 13 to 18 includes within it four components, as represented schematically in Fig. 2. Those components are a radio signal receiver 22, a transmitter 23, a timer unit 24 and a battery 25 which provides the electrical power for the other three components. The receiver 22 is designed to receive radio signals transmitted by the control panel with which it is associated, while the transmitter 23 is designed to send radio signals to the control panel, either at a predetermined interval to report the status of the detector or, in a time-slot reserved for that purpose, to indicate an "alarm" condition (for example fire or an intruder) detected by a sensor (not shown) in the detector.
The transmission of signals of all types between the various illustrated units is governed to follow a strict sequence of time slots controlled by the control units in cooperation with the timer units 24. That is, in the system overall, each type of signal, for example status-reporting signals, alarm signals and signals confirming the receipt of transmitted information, is consigned a specific short time slot or several time slots within which it may be transmitted. Each timer unit 24 controls the timing of those time-slots in sequence and the synchronising of the operation of the timer units 24 is controlled by the regular transmission of a common time reference signal (called in this example the "broadcast" signal) by the control units 11, 12 to their associated detectors or, preferably, by a master panel (not shown).
A typical sequence of time slots is illustrated in Fig. 3, which is a plot of signal slots against time, in the direction of the arrow. Time slots bearing the letter 'B' are the slots reserved for the transmission of the synchronising "broadcast" signal. Time slots 'C' are for signals between control panels. The time slots identified by the letter 'S' are dedicated to signals from the detectors reporting their status at predetermined intervals, for example that the individual detector is operating satisfactorily or requires attention. Finally, time slots 'A' are reserved for alarm signals. Power from the battery 25 to the receiver 22, to enable it to receive the "broadcast" signal or an acknowledgement of a signal previously transmitted, is provided only in those time slots in which the receiver is required to operate.
As will be apparent from the foregoing description, the detection system and method according to the present invention make it possible for a multiplicity of detectors to be monitored by radio from a central control position without the potential for conflict of signals which is a feature of presently available such systems. The detectors may all be associated with the same monitoring unit or several such units may be provided, each synchronised by a central unit and each associated with several of the detectors, thereby achieving overall synchronisation of all of the detectors. As a further advantageous possibility, adjacent detection systems in nearby locations may be so controlled that potential conflict of signals from the adjacent systems is also avoided.

Claims

A detection system which comprises a number of detectors for fire or other eventualities, each detector (13-18) including a radio transmitter (23), and a monitoring unit (11, 12) to receive radio signals from said transmitters, characterised in that each detector also includes a radio receiver (22) and a timer (24) to control the timing of the operation of said receiver and of said transmitter, and further characterised in that said monitoring unit is adapted to transmit to each detector a synchronisation signal whereby the operations of said timers are coordinated and to receive signals from said detectors in predetermined sequence.
A detection system according to Claim 1, characterised in that each detector includes a source of electrical power.
A detection system according to Claim 2, characterised in that said source of electrical power is a battery (25).
A detection system according to any of the preceding claims, characterised in that it further comprises at least one alarm sounder (19-21).
A detection system according to any of the preceding claims, characterised in that it comprises at least two monitoring units (11, 12), each associated with several said detectors (13-15, 16-18), and also a central unit adapted to synchronise the operation of the monitoring units and detectors.
A method of operating a detection system which comprises a number of detectors, each of which includes a radio receiver, a radio transmitter and a timer, characterised in that said method comprises transmsitting to the detectors synchronisation signals to coordinate the operations of the timers and receiving and monitoring, in predetermined sequence, signals from the detectors.
A method according to Claim 6, characterised in that the signals of different types are alloted different time-slots in a repeated sequence of time-slots.
A method according to either of Claims 6 and 7, characterised by the step of acknowledging the receipt of signals from the detectors.
A method according to any of Claims 6 to 8, characterised in that electrical power is provided for each receiver and transmitter only at times when said receiver or transmitter is required to receive or transmit a signal.