This invention relates to alarm systems. In particular, but not exclusively, it relates to the allocation of addresses to addressable devices on alarm systems and to the expansion of those alarm systems.

Alarm systems generally comprise one or more control units (otherwise known as alarm panels) connected by wires or wirelessly to a plurality of sensors of various types and alarm indication and control devices such as sounders, lights, remote signalling devices, keypads and so on. Signals and control information may be transferred between the various devices and the control unit by a bus which is a shared medium used to transfer information between the devices. This will usually be a wired connection but alternatively can be a wireless system. In order to be able to identify which particular peripheral device is intended to be accessed, or to pass a signal, each device must be given its own unique identification or address. Each uniquely identifiable connection point for a detector is termed a 'zone input' or 'zone' ; additionally output devices are also connected to the bus via 'outputs' .

It is common practice to connect alarm zones to a bus system so that groups of alarm zones (perhaps 8 or more zones) may be connected to remote bus expanders to reduce the amount of wiring used in an installation. These expanders are generally manually allocated and addressed by means of local removable links or rotary switches by the installer at the time of installation. It is important that the installer does not allocate the same address to two or more expanders as this can give rise to fault conditions which may be difficult to trace.

There are several disadvantages with this approach. Firstly, it is customary that when a bus is expander is put on the system, a block of zones (such as 8) is then reserved within the control panel. This can be inconvenient and inefficient since the installation geography may be such that only a proportion of the zones allocated to each expander is actually used. For example, whilst one expander may use 8 zones (ie be attached to 8 devices) another expander may actually use only 2 zones even though 8 zones have been allocated to it. This can limit the number of zones available for use elsewhere in the system since the total number of zones is limited by the control panel design.

Furthermore, zone expanders are frequently installed in positions within a building where access is difficult, such as above false ceilings or elsewhere. Additionally, as time passes, additional expanders may be added by other installers and the topology of the system may become fragmented and difficult to understand by those unfamiliar with its history. For example, an installer investigating a fault on a zone labelled 73 may know that zone 73 is connected to expander 9 but it may not be immediately apparent where expander 9 is physically located. Up to now, the knowledge as to which zones have been allocated often exists only in the form of paper documentation which can easily be lost. There is also a risk that a new expander may be allocated to an address that is already in use. Thus a considerable amount of time can be wasted in discovering the configuration of a system when viewing an existing installation.

In many installations it is common for expanders to be hidden from view, typically in ceilings voids, service ducts or other areas. This means that if the installation documentation is poor, or perhaps is lost or destroyed, then the devices may be difficult to physically locate for future maintenance and support.

The present invention arose in an attempt to provide an improved system.

According to the present invention in a first aspect there is provided an alarm system comprising a control panel, a signalling bus and at least one expander connected to the signalling bus, wherein the control panel is provided with means such that as the, or each, expander is connected to the bus it is automatically allocated an expander address.

The bus may be wired or wireless. Preferably, the address allocated to the expander is retained by both the control panel and the expander itself.

According to the present invention in a further aspect, there is provided a method of installing devices on an alarm system having a control panel and a signal bus, the method comprising connecting one or more expanders to the bus, each expander being adapted to mount one or more zone devices, wherein as each expander is connected to the bus an address is allocated to said expander by entering a special 'addressing' mode on the control panel.

Preferably, the address allocated to the expander is retained by both the control panel and the expander.

According to the present invention in a further aspect, there is provided an alarm system comprising a control panel and a plurality of expanders connected to the control panel, one or more of the expanders being provided with audible indication means, wherein the system is provided with a method of discovering the physical location of any of said devices by using said indication means, comprising means for the control panel to issue a particular signal to one or more of said expanders, said expander being operable to actuate the indication mean in response to said signal to thereby indicate the position of the device to an observer.

The control panel is preferably arranged to issue a signal to a particular device upon a specific instruction given by an operator.

The invention further provides an expander provided with an audible indication device.

According to the present invention in a further aspect, there is provided a method of identifying the physical location of a device in an alarm system having a control unit, comprising causing the control unit to issue a particular signal to said device, causing an audible indication device at said device to actuate in response to said signal. By providing audible indication means (such as a sounder) an expander can be easily located even when out of sight. According to the present invention in a further aspect, there is provided an alarm system comprising a control panel, a bus, at least one expander and at least one alarm zone associated with each expander, wherein the control panel is adapted to be able to allocate up to a predetermined number of alarm zones and to allocate zones only as they are required by each expander.

Preferably, each expander is allocated only sufficient zones, of the total number of zones, that equal the number of devices, or groups of devices, attached to each expander desired to be attached. Thus, even though an expander may have the capacity to connect up to 10 zones or devices, if only 4 devices are connected to that expander than only 4 of the total number of zones are allocated. In general terms, if an expander has n possible zones but only x detected (or groups of detectors where 2 or more detectors are connected to a single zone) are connected to the expander than only x zones are allocated to that expander at the control panel. If further detectors are connected to the expander then further zones may be added to that expander as appropriate.

The invention further provides a method as described above.

Thus, with this feature the remaining zones remain unallocated and do not consume system capacity. With prior art systems in which each expander is automatically allocated in zones, regardless of whether it requires the use of n zones, then zone capacity is used up much more quickly (or much faster) and is wasted.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

Figure 1 shows an alarm system with control panel and expanders;

Figure 2 shows a simplified system; and

Figure 3 shows an alternative simplified system. According to Figure 1, part of an alarm system is shown very schematically. This includes a control panel 1 (otherwise known as an 'alarm panel') and this may be of many different types and/or capacities. Connected to this, over a bus 2, are a number of expanders El, E2, E3, E4, E5, E6 and so on. In practice, of course, there may be more than this and this might only show part of a system. Note that some of these devices, such as El and E2 are simple expanders whilst others are different types of devices. For example, E3 is a keypad incorporating, for convenience of installation, provision for two local zones. Such keypads may be placed in selected locations within a building or other environment and used to allow location operation by a local operator remote of the main panel 1. E4 is a radio expander which is connected to the (wired) bus 2 but serves to connect a plurality of devices via wireless connection. E5 is a further keypad providing two local zones. As shown by asterisks, some of the zones are unused. In this specification, an expander encompasses all the above and more; any device that can consolidate a plurality of zones.

Note that while only one bus is shown in the figure, in some embodiments there may be more than one and two are shown, for example, in Figure 3. Three or more may alternatively be provided.

Each of these expanders is connected to a number of other devices, which devices may be sensors or indication devices, for example. The sensors may be passive infrared (PIR) detectors, microwave detectors, combination detectors, proximity sensors, various types of fire or smoke alarms or any other type of sensor depending upon the nature of the alarm system. Indicators may be sounders, bells or other audible devices, lights, or other visual devices, or many other types of devices.

Although not shown in the figure, some of these devices may be connected directly to bus 2 whilst others are connected through expanders. Expanders in themselves are well-known.

The bus may typically be a wired bus used for monitoring and sending signals to the various devices, whether through the expanders or directly, or alternatively it may be a wireless transmission system using any other number of wireless transmission protocols, the scope of which is outside the scope of this specification.

The control panel includes means for allocating an address to each device. There will usually be a maximum number of addresses, dependent upon the capacity of the system. This may be, for example, 128, 256 or any other number. Each of the devices can therefore be accorded an address and the panel can then communicate directly with that device by sending a message to that address and/or receive signals from the device and, by determining the address of that device, know which device it is and therefore what the situation is. For example, a particular device may be actuated by an intruder.

When an expander is connected to the bus, such as expander El, it is allocated an address by the alarm panel in response to an instruction from the installer via the panel user interface. In preferred embodiments both the panel and the expander then retain the address details..

In embodiments, the control panel 1 is used to assign an address to each expander. After an expander is added on to the system, then the control panel is arranged to look for address requests from bus devices. In one example, an installer triggers the actual device (expander) to be addressed to send a request to the panel. The panel then notes this and replies with the new address. On completion of this exchange, the expander (or other device) stores the newly allocated address for use in future communication and the panel adds the address to a list of recognised devices, thus preventing the address from being reissued. In normal operation the control panel will not respond to devices which have not been assigned to an address. Other address allocation schemes may be used. The address allocation is done after an expander is connected to the bus.

Note that in previous systems the installing engineer had to physically set the position of switches or other selection mechanisms at each peripheral device.

As is shown in Figure 1, each expander device supplies a number of zones. Thus, expander El is associated with 10 zones (zone numbers 11 to 20). Expander E2 also has 10 zones (21 to 30). Radio Expander E3, 1 to 30 zones (31 to 60) and so on. On each of these zones, a different device (or group of devices) can be connected. Thus, each expander serves to expand the capabilities of the system.

Embodiments of the invention provide a method by which the allocation of zones to expanders is optimised so that zones are not left unused. The zone capacity on each expander is allocated only as it is required. Thus, although expander 1 has the capacity for 10 zones (zone numbers 11 to 20) if in fact only four of these zones are used (connectable or connected) to devices (detectors or other devices not shown in the figures for clarity) then only four of the zones are allocated addresses at the control panel. It should be remembered that the maximum number of available zones is limited and thus by allocating addresses only to zones which are actually used then the usage of these addresses is optimised.

Unused zones can be manually re-allocated if desired to make more efficient use of installed expanders, eg zone 009 could be manually reallocated to 1 <01 <05 or 1 <04 <05 on expander E4 could be remapped to zone 010.

The situation arises because although a panel may be expanded with, say, 4 expanders of 10 zones each, the layout of the specific installation (geography, layout of the building, etc) might in some instances be more conveniently achieved with a larger number of expanders but each only partially loaded. In embodiments of the invention, a mapping between the physical number of zone inputs and the total panel zone capacity is broken. As described, the control panel has an internal pool of zones available, of a maximum number, and these can be mapped to any physical input. In the example set out above, a forty zone panel can then accept a larger number of partially loaded expanders (which serves to ease wiring load) without the expense of buying a larger capacity panel. Each zone can still be identified within the system by a numbering system, as is shown in the figure. In this figure, each zone (such as zone numbers 11 to 20) is mapped to an input which is identified by a description comprising several elements. Firstly, the number of the bus to which the expander device is connected. Then, a device number - indicating to which expander on the bus the detector is connected, and finally a zone input - indicating which zone input within the expander the detector is using. Note that this method is not limited to zone inputs (ie detector inputs) but can also be applied to outputs (sounders, other indicators) as well. In one embodiment, inputs and outputs are

differentiated in the control panel displays by the form of the separators of the three elements of the address description; for example, an input might be described as 1<01<01 and an output as 1>01>01. As well as dedicated expanders other bus peripherals, such as the keypads E3 and E5, can also provide extra zone inputs and outputs in addition to their primary functions.

Referring again to Figure 1, expander 1 is a dedicated zone input expander and provides 10 inputs. These are identified as bus number 1, device number 01 and zone input number 01 to 10. Expander 2 is similar but with device number 02, hence the zone numbers are 1<02<01 to 1<02<10. Device E3 is a keypad, addressed as device number 03 and which can provide two zone inputs 01 and 02, thus leading to zone numbers 1<03<01 and 1<03<02.

As described, there can be more than one bus. Figure 3 shows a system in which a panel 1 is connected to two buses 2a and 2b, each of which has two expanders E21, E22, E23 and E24. Figure 2 shows schematically a panel 1, connected via a bus 2, to a number of devices 10, 11, 12, 13. These may be expanders or may be detectors or other devices connected directly to the bus, or a combination of these. In many installations it is common for expanders with no user interface to be hidden from view, typically in ceilings voids, service ducts or other areas. This means that if the installation documentation is poor, or perhaps is lost or destroyed, then the devices may be difficult to locate for future maintenance and support. In embodiments of the invention the devices, typically expanders, can be provided with means for activating an audible device. This is shown schematically at 10a, for example, and may be a sounder, bell, or other audible device or may alternatively or additionally be a light or other visual indicator. It is most preferably, and advantageously, an audible device, so that if the device is out of sight (eg in a ceiling void) it can be heard. The control panel 1 can be provided with a function, preferably actuated by a installer, which, when actuated, causes the control panel to send a request over bus 2 to a particular addressable expander, such as expander 10, causing it to activate its notification device 10a. Thus, if an installer wishes to know the specific location of an expander within a building he can give a specific request to the panel to send a special signal to expander 10a which then sets off its, audible sounder. The installer can then follow this sound and locate the device. Alternatively, the sounder on all, or a selection of expanders, can be actuated.

Expanders in any alarm system may be provided as audible and/or visual identification means, not just those which are addressable as described.

Sounders, or other audible indication means and their construction also well known in themselves. They need not necessarily be of the type used as alarm alerts, sounds, and can be relatively low power devices, although the invention is not limited to these. PIN protection may be required before this special signal can be sent in order to make sure that only authorised persons can do this action in order to prevent the system layout being mapped malevolently.

PIN protection may be also used when setting initial addresses