Optical Beam Detection ( Unwanted/False Activations )

[clio222]

Hi I`m looking for some advice with regards to unwanted/false activations from high level beam detection. Recently at my place of work we have had a few activations for no apparent reason. These activations have occurred over a long period of time 12months however they still cause major distruption to the business and require the attendance from the local Fire Service.

On following up the activations and trying to get to the root cause to prevent further activations the manufacturer has indicated that it is possible under certain environmental condtions caused by sunlight reflecting of adjacent external glazing that this is a possible cause .

It has been suggested that the adjacent windows in question are blanked/covered although I have have been informed that this would be a very costly process to carry this out due to the location of the window and the location of the building ( Airport )

My main question is this are we being fobbed off or is this possible and secondly how do we go about resolving the issue without to much expense.We have considered replacing the devices however going on the information by the manufactureres/installers this would not eliminate further activation under these " environmental conditions ".

Any advice gudiance would be greatly appreciated Thanks

[Phoenix]

You're not being 'fobbed off' with this cause.  It is a much talked about phenomenon for beam detectors and many people believe it to be a significant problem for these detectors.  I'm sure you'll get a definitive technical answer on here.

Looking at solutions, a possible alternative, not cheap but avoids covering the glazing, is a Vesda system - this may depend on air movements.

Possibly a more pragmatic, and cheaper, option would simply be to change the system to a two stage alarm that will give you an investigation time before the building is evacuated or the FRS is called.  If there is no fire, you can simply reset the system.

Stu



 

[Allen Higginson]

You're not being 'fobbed off' with this cause.  It is a much talked about phenomenon for beam detectors and many people believe it to be a significant problem for these detectors.  I'm sure you'll get a definitive technical answer on here.

Looking at solutions, a possible alternative, not cheap but avoids covering the glazing, is a Vesda system - this may depend on air movements.

Possibly a more pragmatic, and cheaper, option would simply be to change the system to a two stage alarm that will give you an investigation time before the building is evacuated or the FRS is called.  If there is no fire, you can simply reset the system.

Stu



 

It depends on the reason for the installation of the beams - if the beams were installed due to the height of the area protected then aspirating may not be suitable,as even at high sensitivity they dont go to the height of a beam.
If it is genuinely being caused by sunlight then you would have thought that this would have been taken into consideration at the design stage.I had heard of older types of beams being effected by sunlight but most nowadays have filters and tolerances built in - could it be due to dust being agitated by heat?

[clio222]

Thanks for the replies

At present we already have a 2 stage Fire Alarm system with a built in 10 min delay however due to the size of the building it is not always possible to investigate/silence & reset with the parameters. We also try to apply a policy of preventing activations even if we can silence and reset within the given timescales.

The building it`s self is kept in good order with a strict cleaning regime, this would limit the build up of dust. The devices are fairly new so I would have thought that they would have the filters that you speak about incorporated already but not sure.

However you have both answered my first question in that yes it is possible. hopefully there might be a quick fix. It has been suggested that we swap around the Transmitter and the Receiver would this have any bearing. sorry can`t remember what the activation was ie if it was the TX or the RX.

Once again any thoughts appreciated

[kurnal]

Presumably you have looked at adjustments you can make to the configuration of the system- percentage obscuration and duration of obscuration?

Older type systems were also very critical to building movements causing the beams TX/RX to go out of line- windy conditions and building expansion movements could be a factor?

I think Davo on this forum has had problems with vehicle strobe lights apparently causing activations.

[David Rooney]

However you have both answered my first question in that yes it is possible. hopefully there might be a quick fix. It has been suggested that we swap around the Transmitter and the Receiver would this have any bearing. sorry can`t remember what the activation was ie if it was the TX or the RX.

Once again any thoughts appreciated

Basically it's the Rx that does the working out and gives the signal to the fire system, so I wouldn't have thought that light reflected on to the Tx should make any difference. Therefore swapping the units over may make a difference.

If there is a chance this happens perhaps during extremes of temperature that may cause the building to move then the beams could be changed to the "self aligning" type, using a combined TxRx in one box and a parabolic reflector... or as suggested above you could probably program a delay - maybe 10 seconds - on the input unit to stop spurious alarms from brief "flashes" of light.

[GregC]

If you haven't got an isolator fitted either side of the beam it can cause problems when the panel carries out its checksum.

I am not sure if all panels work the same as far as this is concerned but on some panels its every 24 hours, the loop voltage is dropped and all the devices are looked for and when this happens occasionally the beam detector will energise in alarm unless an isolator is there to limit the current draw. ( it was a long time ago I found this out so some of the explanation might not be absolutely correct but it is important to have isolators each side of any beam detector, even says so in the apollo XP95 literature.)

[David Rooney]

If you haven't got an isolator fitted either side of the beam it can cause problems when the panel carries out its checksum.

I am not sure if all panels work the same as far as this is concerned but on some panels its every 24 hours, the loop voltage is dropped and all the devices are looked for and when this happens occasionally the beam detector will energise in alarm unless an isolator is there to limit the current draw. ( it was a long time ago I found this out so some of the explanation might not be absolutely correct but it is important to have isolators each side of any beam detector, even says so in the apollo XP95 literature.)

Greg I can understand isolators either side from the single cable fault/maximum zone area point of view but I've never heard of this 24 hour checksum business ...

I know some panels do a 24 hour calibration of devices... is this what you mean or have I totally lost it ??   

[Colin Newman]

I recall back in the days of the Gent 3400 beam detectors the issue of sunlight on the receiver was "fixed" by attaching a "snout" to the receiver aperture.  This shielded the receiver from interfering sunlight although it does make the beam detector more sensitive to building movement.

[GregC]

If you haven't got an isolator fitted either side of the beam it can cause problems when the panel carries out its checksum.

I am not sure if all panels work the same as far as this is concerned but on some panels its every 24 hours, the loop voltage is dropped and all the devices are looked for and when this happens occasionally the beam detector will energise in alarm unless an isolator is there to limit the current draw. ( it was a long time ago I found this out so some of the explanation might not be absolutely correct but it is important to have isolators each side of any beam detector, even says so in the apollo XP95 literature.)

Greg I can understand isolators either side from the single cable fault/maximum zone area point of view but I've never heard of this 24 hour checksum business ...

I know some panels do a 24 hour calibration of devices... is this what you mean or have I totally lost it ??   

Couldnt think of a proper term so used checksum as a descriptive  but yes thats what I meant

[Wiz]

If you haven't got an isolator fitted either side of the beam it can cause problems when the panel carries out its checksum.

I am not sure if all panels work the same as far as this is concerned but on some panels its every 24 hours, the loop voltage is dropped and all the devices are looked for and when this happens occasionally the beam detector will energise in alarm unless an isolator is there to limit the current draw. ( it was a long time ago I found this out so some of the explanation might not be absolutely correct but it is important to have isolators each side of any beam detector, even says so in the apollo XP95 literature.)

Greg I can understand isolators either side from the single cable fault/maximum zone area point of view but I've never heard of this 24 hour checksum business ...

I know some panels do a 24 hour calibration of devices... is this what you mean or have I totally lost it ??   

Couldnt think of a proper term so used checksum as a descriptive  but yes thats what I meant

Greg, the older style Apollo beam detectors used quite a bit of current, particularly on start up and also in alarm. This was also why you could only install a maximum of about 7 of these  (with no other devices on the loop) to any loop anyway.

The simple fact is that short-circuit isolators will operate if the current drawn by the devices reaches a critical level. i.e the isolator thinks there might be a short-circuit by the amount of current drawn. If those devices are high-current devices such as beam detectors then it doesn't take many to draw too much current.

To further complicate matters the current drawn by devices is not always constant. If the highest current drawn by each device co-incided at any time then this might be enough to trip the short-circuit isolator. Therefore you might have a system that all seems to be o.k. but you don't realise that the current being drawn is on the edge of operating a short-circuit isolator. All of a sudden an extra couple of mA's is drawn i.e (one device goes into alarm) and that is enough to also operate the isolator!

Apollo eventually advised that a short-circuit isolator be installed either side of their older style beam detectors.

The current Apollo beam detector (been around now for about 8 years) has short-circuit isolators built-in so further short-circuit isolators are no longer required.

[GregC]

fk me 8 years have gone that quick 

It only seems like yesterday that our problem surfaced and was fixed.

[spanner]

In the past I have had a few problems with beams causing false alarms or faults, here are some of the causes I have found.

Beam alignment
Build up of dust on either the TX/RX or TX & reflector
Cobwebs on either the TX/RX or TX & reflector
Reflector mounted on a light colour walls
RF signals near either the TX/RX or signal analyzer unit
Excess movement in building structure

What type of beams are they? Do you know the make and model?

[Davo]

Prof

Still getting false alarms from vehicle strobes in spite of reducing the  number of beams


davo

[Wiz]

Prof

Still getting false alarms from vehicle strobes in spite of reducing the  number of beams


davo

davo,

No previous posts in this thread seem to have any mention of vehicles or strobes. In fact you don't seem to have previously posted on this thread at all!

I'm confused. Is your post in code?

Is it just a secret message between you guarding the banter bar door and that barsteward Prof. K?