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World Patents Pending  ©AirSense Technology Ltd. 1999

ISSUE 2.4

Page 30

T E C H N I C A L

.

M A N U A L

source.  In this case no reference system would be required to compensate for it.

The main factor in the determination of time in alarm or time in low sensitivity is the time

constant “T”.  This, as given above, is the volume of the room divided by the rate at

which outside air is added.  That is the time it would take a room to be filled with external

polluted air if none of the pollution was allowed to escape.  For this reason it is called

the filling time constant.  If the example worked through above, was concerned with

a room  of 500 cu.m. but all other data remained the same, then the filling time constant

(T) would be 12 minutes instead of 120 minutes.  The alarm level would be exceeded

for 42.7 minutes instead of 427 minutes.  The same would be true if the rate of fresh

air make up was 100% instead of 10% and the volume of the room stayed at 5,000

cu.m.  However, shortening the period in unwanted alarms by this amount is not a real

solution because 1 second in alarm constitutes as much of a problem as 42.7 minutes.

It has been shown that in a simple case the performance of a reference system can be

analysed by “rounding off a few corners”.  The main problem has been identified as the

filling time constant.

When considering a more complex system as in Fig. 5 the number of unknown variables

become so many and so large that the system is no longer amenable to analysis.

Содержание HSSD

Страница 1: ...Technical Manual Issue 2 4 Quality system cert no 404 Assessed to ISO 9001 afp 813...

Страница 2: ...22 Stratos detector referencing 32 Local and remote referencing 34 Terminal board jumper link connections 35 Apollo Series 90 Interface 35 Autronica BNX 3 36 Thorn AM521 37 Remote control software 38...

Страница 3: ...ng when no fire occurs The problem of unwanted alarms is a major one for instance frequent call outs to deal with non existent fires can lead to a tendency for alarms to be ignored Unwanted alarms fro...

Страница 4: ...is greater than a given amount it is assumed that this is due to a fire Unfortunately for general use the unwanted alarm conditions still occur even if not so readily as with the simple heat detector...

Страница 5: ...accurate laboratory measurements The different principles of Optical detection are described below Asimplifiedadaptationofthelaboratorymeterdescribedaboveimmediatelybecomes interesting as a smoke dete...

Страница 6: ...Scattering Detectors Most fires will generate light of one sort or another infrared light being the most prominent Extremely sensitive infrared cameras are available which could be used in an alarm sy...

Страница 7: ...systems etc It normally indicates the signals it is receiving from the detectors by means of lamps but the use of special PC programmes to display more comprehensive information is becoming more comm...

Страница 8: ...of these devices in an effort to reduce unwanted alarms Point detectors are usually set to give an alarm at a smoke density corresponding to between 2 and 4 obscuration per metre Although they are cap...

Страница 9: ...ction of smoke at a very much earlier stage in the development of a fire and as a consequence this may reduce damage levels considerably This saving of time more than offsets the delay due to the tran...

Страница 10: ...would detract from the appeal of the building Other important applications are found where their specific properties include museums art galleries warehouses telephoneexchanges penalestablishments du...

Страница 11: ...h in a different manner One uses a Xenon flash bulb as its light source whilst two take advantage of the very reliable semiconductor laser in this application Mean Time Between Failure can be in exces...

Страница 12: ...since either a very large particle or a very small particle will increase the count by one unit It is assumed that dust particles are larger than smoke particles and the particle counter can give a s...

Страница 13: ...ending into very short wavelengths well below the visible spectrum The intensity of scattered light at these wavelengths is high but is only of use when a light sensor is used which is sensitive to th...

Страница 14: ...ge this situation it is difficult to envisage that the effort required would be practical or cost effective when the alternative of a laser exists The semiconductor laser is at present the subject of...

Страница 15: ...he background levels will vary according to the time of day and the particular activities in the protected area The requirement then is to find what are the appropriate levels to set the pre alarm and...

Страница 16: ...ming a continual statistical analysis of the background pollution and continuously calculating the level at which a given probability of a signal occurring is acceptably low Such measurements and calc...

Страница 17: ...period or historical period that is represented by the histogram it also sets the time which the histogram requires to become truly representative of the distribution The method for doing this is an...

Страница 18: ...ferent levels of use These are usually day time and night time but for the sake of generality may be referred to as normal time and quiet time The problem of maintaining correct alarm trigger levels i...

Страница 19: ...tos provides a very adequate solution For reasons of power economy and reliability a low power air impeller is required to draw air down the sampling pipes This leads to the problem that the bore of t...

Страница 20: ...ings in the histogram give a warning that the filter is becoming fully loaded This progressive reduction in signal spread causes the detector to compensate thereby automatically maintain ing the sensi...

Страница 21: ...illuminated continuously for the whole duration of the delay time in order to be signalled unless the signal has risen very rapidly to beyond full scale If this is the case then the time delays may b...

Страница 22: ...ith the use of a reference detector and shows how special features of the STRATOS detector may be used in providing a solution When a room is to be protected with smoke detectors there are two prime c...

Страница 23: ...easurements must track one another to within 1 Another is that the signal from a detector does not carry on rising indefinitely it reaches a ceiling where in spite of increasing pollution the output s...

Страница 24: ...urs instantaneously Although this will not be realised in any practical case it will be closely approached An area is taken which either has filtered air fed into it from outside or has air being extr...

Страница 25: ...me towards X and in theory never actually reach it This effect is illustrated in Figs 3 4 Plant Room A A Filter Air Inlet 0 Pollution at Inlet as seen by reference detector Transport delay through duc...

Страница 26: ...ted in Fig 1 may have an effect in reducing the amount of pollution in the incoming air Its efficiency is shown as E in Figs 3 4 If it is 100 efficient then E 1 and there is no apparent need for refer...

Страница 27: ...Density 0 CALCULATED POLLUTION ADDED Time Density required for alarm Smoke Density D 1 E It is a common error made by many people that the time scale for pollution increasing in a room is different fr...

Страница 28: ...building via an air filter which is 30 efficient at removing pollution and travels 25 metres down an air duct 2m2 area to the room A reference detector is placed after the air filter to provide refere...

Страница 29: ...ficant compared to them and they illustrate very clearly a very large problem It can be argued that a step change in the external pollution will never occur and represents the worst case This is true...

Страница 30: ...m but all other data remained the same then the filling time constant T would be 12 minutes instead of 120 minutes The alarm level would be exceeded for 42 7 minutes instead of 427 minutes The same w...

Страница 31: ...Outlet Inlet Outlet Inlet Outlet Inlet Outlet Inlet Plant Room The ability to vary the air conditioning in one of the rooms can effect the flow into all the rooms Air ducts will become long with the...

Страница 32: ...t is to modify the reference signal such that modified sig representing signal representing signal representing pollution entering the area pollution leaving the area pollution added from within the a...

Страница 33: ...error adjustments around the setting of the Reference back off time delay mins in function 8 will achieve good results Very good matching can be obtained under most normal conditions and will be a ver...

Страница 34: ...L A V E D E T E C T O R TM Master 1 Local y Remote n Slave loop Reference Slave H I G H S E N S I T I V I T Y S M O K E D E T E C T O R TM ISOLATE TEST RESET S M O K E D E N S I T Y AUX FIRE PRE ALAR...

Страница 35: ...minal board to configure the line connections for different interface boards These links need to be connected to bring the line connections from the interface board out to the back box Given below are...

Страница 36: ...chnology Ltd 1999 ISSUE 2 4 Page 36 T E C H N I C A L M A N U A L Autronica BNX 3 Master 3 Slaves Master 2 Slaves Master 1 Slave Single Master Line in ve Line 1 Line out ve Line connections Line 2 Lin...

Страница 37: ...Technology Ltd 1999 ISSUE 2 4 Page 37 T E C H N I C A L M A N U A L Thorn AM521 Master 3 Slaves Master 2 Slaves Master 1 Slave Single Master Line in ve Line 1 Line in ve Line connections Line 2 Line o...

Страница 38: ...nd date The time and date must be set correctly for the event log and chart recorder log The time is set in 24 hour format HH MM and the date set in DD MM YY Typing an invalid time or date causes an e...

Страница 39: ...enu is not possible if the flow is currently being set up During flow set up the aspirator is cycled through it s different speeds and a note is taken of the flow readings The flow limits are set eith...

Страница 40: ...This screen graphically displays the operation of the ClassiFire function The detector to display can be selected by pressing F1 F4 4 Chart recorder log Stratos has the facility of storing a chart rec...

Страница 41: ...error rate Interference on the slave loop can cause corruption of the data passed between a master and it s slaves This is compensated for by the Stratos master but too much interference could indicat...

Страница 42: ...te Alarm level Slave 2 byte Detector level Slave 2 byte Alarm level Master byte Detector level Master byte Alarm level Slave 2 byte Detector level Slave 2 byte The format of the chart recorder data as...

Страница 43: ...r see following list for types byte number of detectors or 0x00 byte 0xff word 0x01 word 0xff word Fast histogram data 32 words obscuration 100 or 0x00 word detector number or 0x00 byte period DAY NIG...

Страница 44: ...ow Fault LED flag 0 off 1 high 2 low 254 flash n bytes Head fault LED flag 0 off 1 on 254 flash n bytes Isolated LED flag 0 off 1 on 254 flash n bytes Separator LED flag 0 off 1 on 254 flash n bytes B...

Страница 45: ...mum string length is 30 characters Exceeding these limits will result in strings being lost or ignored In addition the time between the first character and the terminating CR must be less than 33 mS S...

Страница 46: ...a multiple detector system all detectors have their readings stored The maximum duration is divided by the number of detectors n Changing the sample rate will clear the data in the chart log NB Setti...

Страница 47: ...he extremely high air flow characteristics of the Stratos Aspirator PipeCAD is incompatible with other aspirating smoke detection system types The pipe design software for the Stratos system requires...

Страница 48: ...64 Gebouw C3 2741 EZ Waddinxveen Nederland Telephone 31 1825 635696 Facsimile 31 1825 635691 e mail conrad airsense nl AirSense Oy Ukonkellonkatu 19 Karhula 48800 Finland Tel 358 9 400 652131 Fax 358...

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