GB2293472A

GB2293472A - Fire alarms

Info

Publication number: GB2293472A
Application number: GB9424775A
Authority: GB
Inventors: Trevor Charles Boxer; Fariz Khellaf
Original assignee: JSB Electrical PLC
Current assignee: JSB Electrical PLC
Priority date: 1994-08-25
Filing date: 1994-12-01
Publication date: 1996-03-27
Also published as: GB9417142D0; GB9424775D0

Abstract

An analogue addressable fire alarm system is provided with a control unit 2 and a plurality of auxiliary units 10, 12, 16 connected thereto in a signalling circuit 4. The control unit can apply to the signalling circuit an address to identify an auxiliary unit. The number of auxiliary units which can be connected to the signalling circuit is increased, as compared with a conventional system, by arranging for a plurality of auxiliary units to share the same address value, each of these units using one or more, but not all, data bits of a returned data value to return data to the control unit. <IMAGE>

Description

FIRE ALARMS The present invention relates to addressable fire alarms.

An addressable fire alarm system comprises a control unit and a plurality of auxiliary units including input devices (for example, manual call points and heat and smoke detectors) and warning devices which may be activated by the control unit to raise an alarm. The warning devices will typically include a plurality of sounders (such as bells, sirens, etc.) but may also include other devices such as strobe lights. An addressable fire alarm system may be an analogue addressable system, in which each auxiliary device may generate a digitised analogue signal or may be a simple addressable system in which each auxiliary device generates binary status data.

The input devices are connected to the control unit in a signalling circuit which is typically of loop configuration. A pair of signalling wires extending from the control unit, is connected to each device, and then, finally, returns to the control unit. Normally, the sounders are connected to the control unit through a separate radial or spur circuit. However, in many instances, it is desirable to connect the sounders to the signalling circuit instead in order to save the inconvenience and expense of providing a separate circuit for them.

The control unit communicates with auxiliary units on the signalling circuit by means of a communication protocol. Conventionally, each unit is allocated with a unique address and responds only to signals from the control unit addressed to it. The protocol then allows an addressed device to transmit data (which may be a digital representation of analogue data) back to the control unit. In the case of a sounder, the data transmitted back to the control unit typically represents the operative status of the device, and can be used to indicate that a fault has occurred.

A limitation of systems of this type arises because the protocol typically limits the length in bits of an address within the system. For example, the protocol may specify that an address comprises 7 bits. It is often the case that addresses comprising either all zeros or all ones are not used, in which case only 126 addresses are available for use. This may limit a system designer's choices when deciding whether sounders should be placed on the signalling or in their own circuit. If, during the design of a system, it becomes apparent that addresses will be in short supply, the designer may be forced to provide a separate sounder circuit in circumstances where this is not desirable.

It is an aim of the invention to provide a fire alarm system in which a plurality of auxiliary units such as sounders and input devices may be connected to a signalling circuit without the need to allocate a separate address to each unit, while retaining the ability for each unit to send a uniquely identifiable signal to the control unit in the event that its control circuitry should detect that a fault condition has occurred, or to indicate some other event.

According to a first aspect of the invention there is provided a fire alarm system comprising a control unit and a plurality of auxiliary units connected thereto in a signalling circuit, the control unit being operative in a cycle to apply an address to the signalling circuit and subsequently to receive from the signalling circuit a multi-bit data signal, a first group of the auxiliary units each having a unique address and each being operative on detection of its address in the signalling circuit to apply to the signalling circuit the multi-bit data signal, and a second group of the auxiliary units sharing a common address and each being operative, on detection of that common address on the signalling circuit, apply to the signalling circuit a respective one bit or a group of bits of the multi-bit data signal.

Thus, in a system of the present invention, there may be provided as many devices in the second group (which uses just one address) as the number of bits in the multi-bit are bits in the data signal permits without any loss in the ability of the devices to unambiguously indicate their status information to the control unit.

For example, a seven bit data signal allows seven one-bit devices, three two-bit and one one-bit device, and so forth, to be assigned to one address.

There may be further groups of auxiliary units of a nature similar to the second group, but having an address different therefrom. In this way, the number of units that may be connected to the system can be further increased. In systems where the multi-bit data signal comprises m bits, each unit in the second and further groups may be assigned a value n, where n is unique within the group, and each unit being assigned one or more bits within the data signal.

Preferably, the multi-bit data signal is transmitted in the ring circuit by voltage or current pulse position modulation in which each bit of the data signal is represented by the presence or absence of a voltage or current pulse, as the case may be, occurring at a predetermined time after an initiating event. In systems of this type, provided that no two units have the same address and the same n, no two units will attempt to apply a data signal to the signalling circuit simultaneously.

Most commonly, the auxiliary devices of the second and further groups will comprise sounders which generate a one-bit signal being indicative of the sounders readiness or otherwise to operate. Alternatively, the auxiliary devices may include detectors which typically generate a two-bit signal, one bit being set to indicate that the detector is present and fault-free, and the other being set to indicate that a fire has been detected.

In some fire alarm systems, it is desirable that the control unit is able to selectively activate some, but not all auxiliary devices in the system. For example, in certain circumstances it may be desirable to activate only sounders close to where a fire has been detected or to activate sounders sequentially. In systems according to the present invention, groups of auxiliary devices to be actuated simultaneously may be allocated to the second or a further group. Where any one auxiliary device must be activated independently of the others, it must be in the first group of devices and so have a unique address.

Preferably, the control unit is further operative to generate a control signal to which the auxiliary units are responsive, there being a first value of the control signal to which, for example, sounders react by generating an alarm, and a second value of the control signal to which sounders react by generating status information, as described above.

From a second of its aspects, the present invention provides a method of operating a fire alarm system comprising a control unit and a plurality of auxiliary units, each auxiliary unit having an identifying address and at least two of the auxiliary units having an identical address value x wherein each of said at least two auxiliary units has an identifying number n, the number n being different for each unit with address x, the control unit and auxiliary units being interconnected for the passage of signals therebetween; the system being operated in signalling cycles during which the control unit generates a signal comprising an address component followed by a data component comprising a plurality of data bits, the said at least two auxiliary units each being operative, on receipt of a signal containing address value x, to set a data bit or a group of data bits of the signal to a value indicative of its status.

Where each auxiliary unit generates a one-bit data signal it preferably sets the nth data bit of the multibit data signal.

Preferably, the signal further comprises a control value, the action of each auxiliary unit being modified in dependence upon the control value.

In operation of systems where the units are interconnected by means of electrical conductors, the signals may comprise voltage and/or current pulses. In embodiments such as this, the method may be implemented by application by the control unit of a series of voltage pulses, these pulses being modulated by the control unit to generate the address, and being unmodulated to provide a clock signal by means of which each auxiliary unit may time its generation of data bits. The data bits may conveniently be constituted by the presence or absence of a current pulse occurring between sequential voltage pulses.

From a third of its aspects, the invention provides an auxiliary unit, for example, a sounder, for use in the first and second aspects of the invention.

An embodiment of the invention will now be described in detail, by way of example, with reference to the accompanying drawings in which: Figure 1 is a schematic diagram of a conventional addressable fire alarm system; Figure 2 is a schematic diagram of a fire alarm system embodying the invention; Figure 3 is a diagram illustrating the data received by a control unit of the system from sounders connected to the system; Figure 4 shows the data transmitted between the main unit and the sounders during an operation cycle; and Figures 5 and 6 correspond to Figures 3 and 4 where data is received from conventional sensors.

With reference first to Figure 1, a fire alarm system comprises a control unit 2 to which is connected a loop circuit, indicated at 4 and being a signalling circuit, a radial sounder circuit indicated at 6, and a multiplicity of other connections of largely conventional arrangement.

The sounder circuit 6 and the sounders connected to it may suitably be placed in most parts of a building to which radial wiring be conveniently be provided.

In the loop circuit 4, multiple auxiliary devices are connected, arranged in four zones A, B, C, D. An isolator unit 14 is connected in the loop circuits between adjacent zones A..D such that, in the event of a failure in the loop circuit 4, only one zone is affected.

In each zone A..D there is provided an analogue detector 10 which generates a multi-bit data signal indicative of the condition (e.g. temperature) which it is operative to detect. Additionally, manual call points 16 are provided in two of the zones.

The fire alarm system of Figure 2, which embodies the invention, has many components 2,4,10,14,16 in common with the system of Figure 1. However, the radial sounder circuit is omitted, the sounders (being auxiliary units) being provided instead on the loop circuit 4, one per zone A..D, as indicated at 12.

The control unit 2 communicates with the auxiliary units 10,12,16 by signals applied to the loop circuit 4 in accordance with a predetermined protocol, the signals comprising electrical pulses within the loop circuit 4 which represent a stream of binary digits (bits). In accordance with the protocol, each of the auxiliary units 10,12,16 is preset with an address value. The address value is a numerical value capable of representation by seven bits, this offering a total of 126 unique addresses since address values of all zero or all one value bits are not normally used.

The protocol defines the form of a signal which the control unit 2 may initiate on the ring circuit 4. The portion of the signal in which data is generated by the control unit 2 comprises a 7 bit address, as described above, followed by a 3 bit command code. The addressed auxiliary unit then responds by generating data comprising a 1 bit priority interrupt flag, a 7 bit "analogue" value, a 2 bit signal data value and a 7 bit address value.

In a typical conventional system, each of the auxiliary units 10, 12, 16 has a unique address. During operation, for each auxiliary unit 10, 12, 16 in turn, the control unit 2 initiates a signal containing the address of a control unit and places this on the loop circuit 4. The auxiliary unit 10 responds by placing a binary encoded detection value in the analogue bits of the signal together with its own address (the latter being in order that the control unit 2 may verify that the corrected auxiliary unit has been activated) this information being transmitted back to the control unit 2.

Thus, in a conventional system, the sounders 12 would each have a unique address. If the controller intended to instruct a sounder 12 to raise an alarm, it would generate a signal comprising the address of that sounder, together with a value in the command bits corresponding to an instruction for the sounder to raise an alarm. If the control unit 2 were simply performing a routine check on the sounder 12, it would generate a signal comprising the address of the sounder together with a command instructing the sounder 12 to report on its status, whereupon the sounder would respond by placing status information in a predetermined part of the signal for transmission back to the control unit.

In the present embodiment, the analogue detectors 10 and call points 16 constitute a first group of auxiliary units, while the sounders 12 constitute a second group of auxiliary units and each sounder 12 has the same address value. Each sounder is also allocated an identifying number between 1 and 7. In the system, there may be further groups of sounders each having a common address.

However, within each group, the identifying numbers allocated to the sounders must be unique.

In order to activate a group of sounders 12 to generate an alarm signal, the control unit 2 behaves substantially as described above, generating a signal comprising the address of the groups of sounders 12 plus a command indicative that the sounders 12 are to activate. However, rather than just one sounder being activated, all sounders 12 of the selected group are activated. In order to perform a routine check on the status of the sounders 12, the control unit 2 generates a signal, again substantially as described above.

However, in responding to this signal, each of the addressed sounders 12 sets one of the analogue bits within the signal to indicate its current status. The bit set by a given sounder is determined by that sounders identifying number. That is to say, sounder with identifying number 1 sets the first bit of the analogue field, and so forth.

With reference to Figure 3, there is shown diagrammatically the analogue field of a signal generated by a system comprising, a group of 7 sounders sharing a common address. The first analogue signal, shown at 20, indicates that all sounders are operative. The second signal, shown at 22, indicates that sounder 4 is defective.

In Figure 4, there is shown a complete signal in which a group of 7 sounders with an address value of 109 is interrogated, and reports that the fourth sounder (allocated to bit 3) is defective.

Further auxiliary units may be added to the system such as conventional addressable detectors. Unlike analogue detectors, a conventional addressable detector of a two-state device which generates a binary signal indicative of the detection or otherwise of e.g. a fire.

Additionally, a conventional addressable detector generates a binary condition signal to indicate its presence and correct operation. Thus, a conventional addressable detector needs use only two bits to communicate its status fully.

In the present embodiment, a further group of auxiliary units comprises three conventional addressable detectors, each with address 110. When these are addressed, the first detector places its status information in bits 1 and 2 of the multi-bit data signal, the second in bits 2 and 4 and the third in bits 5 and 6.

Bit 7 may be used by a one-bit device, e.g. a sounder, or may simply be left unused.

With reference to Figure 5, there is shown a data field generated by three conventional addressable sensors and a sounder each having a common address. The first signal, shown at 30, represents a normal situation, where each sensor sets a first bit to 1 to indicate that it is present and operational, and sets a second bit to 0 to indicate that no fire (or other event) has been detected.

As above, the sounder sets its bit to 1 to indicate proper operation. The second signal 32 represents an abnormal situation in which the first sensor has detected a fire (both bits set to 7) and the third sensor is faulty or missing (both bits 0). The second sensor and the sounder respond normally.

Figure 9 shows the sound signal 32 as a complete signal in which the sensors and sounder share address 110 (decimal).

Claims

CLAIMS:

1. A fire alarm system comprising a control unit and a plurality of auxiliary units connected thereto in a signalling circuit, the control unit being operative in a cycle to apply an address to the signalling circuit and subsequently to receive from the signalling circuit a multi-bit data signal, a first group of the auxiliary units each having a unique address and each being operative on detection of its address in the signalling circuit to apply to the signalling circuit the multi-bit data signal, and a second group of the auxiliary units sharing a common address and each being operative, on detection of that common address on the signalling circuit, to apply to the signalling circuit a respective one bit or a group of bits of the multi-bit data signal.

2. A system according to claim 1, comprising further groups of auxiliary units of a nature similar to the second group, but having an address different therefrom.

3. A system according to claim 1 or claim 2, in which the multi-bit data signal is transmitted in the ring circuit by voltage or current pulse position modulation in which each bit of the data signal is represented by the presence or absence of a voltage or current pulse, as the case may be, occurring at a predetermined time after an initiating event.

4. A system according to any preceding claim in which the auxiliary devices of the second and further groups comprise sounders which generate a one-bit signal being indicative of the sounders readiness or otherwise to operate.

5. A system according to any preceding claim in which the auxiliary devices may include detectors which typically generate a two-bit signal, one bit being set to indicate that the detector is present and fault-free, and the other being set to indicate that a fire has been detected.

6. A system according to any preceding claim, in which the multi-bit data signal comprises m bits, each unit in the second and further groups may be assigned a value n, where n is unique within the group, and each unit being assigned one or more bits within the data signal.

7. A system according to any preceding claim, in which groups of auxiliary devices to be actuated simultaneously are allocated to the second or a further group, and any one auxiliary device must be activated independently of the others, it is in the first group of devices and so have a unique address.

8. A system according to any preceding claim in which, the control unit is further operative to generate a control signal to which the auxiliary units are responsive, there being a first value of the control signal to which, for example, sounders react by generating an alarm, and a second value of the control signal to which sounders react by generating status information.

9. A method of operating a fire alarm system comprising a control unit and a plurality of auxiliary units, each auxiliary unit having an identifying address and at least two of the auxiliary units having an identical address value x wherein each of said at least two auxiliary units has an identifying number n, the number n being different for each unit with address x, the control unit and auxiliary units being interconnected for the passage of signals therebetween; the system being operated in signalling cycles during which the control unit generates a signal comprising an address component followed by a data component comprising a plurality of data bits, the said at least two auxiliary units each being operative, on receipt of a signal containing address value x, to set a data bit or a group of data bits of the signal to a value indicative of its status.

10. A method according to claim 9, in which each auxiliary unit which generates a one-bit data signal it preferably sets the nth data bit of the multi-bit data signal.

11. A method according to claim 9 or claim 10, in which the signal further comprises a control value, the action of each auxiliary unit being modified in dependence upon the control value.

12. A method of operation of a system where the units are interconnected by means of electrical conductors according to any one of claims 9 to 11, in which the signals comprise voltage and/or current pulses.

13. A method according by application by the control unit of a series of voltage pulses, these pulses being modulated by the control unit to generate the address, and being unmodulated to provide a clock signal by means of which each auxiliary unit may time its generation of data bits.

14. The data bits may conveniently be constituted by the presence or absence of a current pulse occurring between sequential voltage pulses.

15. A fire alarm system substantially as described with reference to Figures 2 to 6 of the accompanying drawings.

Amendments to the claims have been filed as follows a signal comprising an address component followed by a data component comprising a plurality of data bits, the said at least two auxiliary units each being operative, on receipt of a signal containing address value x, to set a data bit or a group of data bits of the signal to a value indicative of its status.

12. A method of according to any one of claims 9 to 11 operation of a system according to any one of claims 1 to 8 where the units are interconnected by means of electrical conductors in which the signals comprise voltage and/or current pulses.

13. A method according to claim 12 in which the signals are carried by application by the control unit of a series of voltage pulses, these pulses being modulated by the control unit to generate the address, and being unmodulated to provide a clock signal by means of which each auxiliary unit may time its generation of data bits.

14. A method according to claim 13 in which the data bits are constituted by the presence or absence of a current pulse occurring between sequential voltage pulses.