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A05-0473-010  

Network Synchronisation

When Agile™ devices transmit data they require a lot of energy. 

Therefore, to maintain low battery power consumption, the devices 

are not in transmit/receive mode all the time; for much of the time 

they will be in a very low power (silent) mode. 
To communicate properly, the devices in the network must all 

transmit and receive at the same time. To do this, the communicating 

periods must be synchronised so that devices wake up together 

from their silent state to move data to and fro before going silent 

again. This synchronisation of the network is orchestrated by the 

gateway which maintains a constant ‘drum-beat’ throughout the 

mesh system.
In the Agile™ 200 Series RF Fire System, a complete cycle of 

transmit/receive windows takes approximately 5 seconds including 

the silent periods.

Figure 5: Synchronised Communication Sequence

5s approx.

~ s

½

~ s

½

~ s

½

Time

REQ 1

(->GW)

REQ 2

(->GW)

RESP

(GW->)

The Back-up Node

A mesh network that is operating normally is kept in sync by the 

Gateway. But if a gateway is removed from a system or is powered 

off, control of the network will be lost. All the devices will continually 

try to re-connect with the missing gateway and this will lead to high 

battery power consumption and significantly reduce the battery life, 

unless all the batteries are removed from the Agile™ RF devices.
To  prevent  this  situation  (for  example,  during  a  fire  system 

maintenance period), a special node has been created in the mesh 

that takes over the network synchronisation role should a gateway 

go ‘missing’. Hence, the network continues to operate, but in a 

low power (idle) state, minimising battery usage across the system 

while the gateway is off. Obviously, during this time, the Agile™ RF 

system will not be providing fire cover.
It can take up to 12 minutes for a backup node to assume control of 

the network, after the gateway has been switched off. It may take 

up to 10 minutes for the gateway to reclaim control of the network, 

when the gateway is re-powered on.

SITE SURVEY

What is a Site Survey?

Great care needs to be taken when assessing a site and choosing 

the right technology and design layout to use; wireless systems 

may not be suitable for every situation. Before committing to a 

design and physical implementation of a wireless fire system it is 

important to understand and ‘visualise’ the field strength of the RF 

network to ensure that vital areas of the building have adequate 

signal coverage. 
A site survey needs to be done to ensure that the RF fire system 

will work reliably after installation. 
A site survey involves the use of the AgileIQ™ Software Tools 

and Site Survey equipment to carry out RF energy scans and RF 

link  quality  checks.  The  RF  energy  scan  identifies  any  channel 

frequencies that are unsuitable and the link quality check ensures 

that RF communications between nodes is acceptable.

Why is it Necessary?

A site RF survey is a critical element in the process of designing 

and  installing  a  wireless  communications  network  in  an  office 

or building. The survey will determine the best placement of the 

sensors and manual call points to comply with the coverage and 

positional  requirements  of  the  fire  regulations  in  the  designated 

location.
In the UK, the Code of Practice for system design, installation, 

commissioning  and  maintenance  of  fire  detection  and  alarm 

systems (BS5839-1: 2002) specifically addresses the need to carry 

out an RF site survey. Section 27.2 states that installation of a 

radio-linked system should only take place after a comprehensive 

radio survey has been undertaken to ascertain the following:
● 

There are no other potentially interfering radio sources

●  There is adequate signal strength for communication
The  Code  also  requires  that  only  radio  survey  test  equipment 

approved  by  the  manufacturer  should  be  used  and  records  of 

signal readings should be kept for future reference

.

When doing a site survey, give adequate consideration to how 

the site will be used when the Agile™ RF system is working. For 

example, make sure that doors and windows are closed when 

signal strength measurements are being taken.
And when installing an Agile™ RF system, it is important to ensure 

that there have been no changes to the areas within a building, 

such as new internal walls or partitions, the introduction of tall 

metal enclosures or the introduction of other wireless systems 

since the original site survey was carried out. Any changes to the 

system design or the building may require an extra site survey to 

confirm the wireless fire system will still work reliably.

How to Plan a Site Survey

The RF energy and link quality tests are important as they ensure 

the  RF  fire  system  will  work  reliably  in  the  building  where  it  is 

installed. 
It is preferable to preplan how the tests will be carried out during 

the site survey visit. Use a plan-view of the building to identify the 

likely positions of devices with respect to customer requests, local 

regulations  and  fire  systems  requirements.  Identify  each  device 

location with a device type and unique code. Consider how the RF 

mesh network will provide coverage across the site, being mindful 

of the potential attenuation that walls and other objects can cause. 
Site layout drawings can be marked up manually to show the 

planned positions of devices, or an electronic copy of the site layout 

drawings can be loaded into the Agile IQ™ Software Application to 

assist with a site survey. Using the Agile IQ™ design feature, it is 

possible to draft a layout diagram of the Agile™ RF devices, create 

Summary of Contents for AGILE

Page 1: ... Series RF devices can transmit and receive they are transceivers When two devices communicate directly with one another they have set up a link the devices at each end of a link are known as nodes A set of devices or nodes communicating together is called a network There can be a wide range of network topologies as shown in the examples following VLF LF MF HF VHF UHF SHF EHF IR Visible light 10kH...

Page 2: ...bout 100m Some common building materials are listed in Table 1 together with typical energy loss figures which can be expected A normal double brick wall for example can reduce a signal s strength by up to a third or more All these factors will contribute to the occurrence in a building of areas of varying signal strengths and reception characteristics Figure 1 Relationship Between Distance and RF...

Page 3: ... and hence each RF link has bi directional communication As every RF device is a transceiver the network can be organized to minimize the use of repeaters This is achieved by allowing each device to receive and re transmit information from its neighbours on to the master device the gateway The Concept of Mesh Hierarchy When there is a direct path between nodes say from device 1 to device 2 the two...

Page 4: ...scans and RF link quality checks The RF energy scan identifies any channel frequencies that are unsuitable and the link quality check ensures that RF communications between nodes is acceptable Why is it Necessary A site RF survey is a critical element in the process of designing and installing a wireless communications network in an office or building The survey will determine the best placement o...

Page 5: ...e a facility diagram or floor plan drawing that depicts the location of walls walkways etc 2 Visual inspection Walk through the facility to verify the accuracy of the facility diagram Add any potential barriers that may affect the propagation of RF signals such as metal racks and partitions items that are not shown on the floor plan 3 Device positions Determine the preliminary location of devices ...

Page 6: ...structions Therefore a system design should take into account obstructions and the level of signal attenuation caused by Wall type and thickness Structural supporting beams Tall metal cabinets such as those that are from floor to ceiling and IT equipment in tall metal enclosures A system design should also consider the site operating conditions like Strong local interferences such as from certain ...

Page 7: ...e system Some possible changes that may help to find a suitable network include Move the gateway to provide wider connectivity with the Agile RF devices Re arrange the Agile RF devices to minimise link lengths Allow longer links or repeaters to be used Add a repeater or another Agile RF device to a marginal or poor link Consider if the wall attenuation is set too high and can be reduced How to Res...

Page 8: ...ic obstructions exist such as near lifts and escalators Do ensure that gateways are accessible for maintenance Do ensure where possible the RF devices are positioned in a line of sight A simple way to check is just to look from a device and see if the other devices are in view Figure 8 Example of Using the Line of Sight Technique In this arrangement the sounder strobe could have been located on th...

Page 9: ...e simulated with a test magnet on an Agile detector see device installation instructions for details and a fault can be created in a system by removing a device from its base Tamper Fault Don ts Don t locate RF devices behind obstructions that can weaken RF signal and cause poor link quality Don t locate Agile RF devices back to back where there is little or no attenuation as 1m separation is requ...

Page 10: ...10 A05 0473 010 SYSTEM SENSOR EUROPE Pittway Tecnologica S r l Via Caboto 19 3 34147 TRIESTE Italy www systemsensoreurope com ...

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