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FIRE SERVICE AND GENERAL FIRE SAFETY TOPICS => Technical Advice => Topic started by: Wiz on September 23, 2006, 01:11:26 PM
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Oh various sages of this forum please answer this anomaly that keeps me awake most nights at my current abode of the local Home For The Bewildered;!
BS5839 Part 1 2002 clearly states that where detectors are designed to be removed from their bases....removal of any detector(s) from the circuit should not affect the operation of any MCP......
I am probably wrong, but I seem to recall that sometime after that particular requirement was first added to a previous version of the BS, an amendment was subsequnently issued that required that such action should also not affect other automatic fire detectors as well as MCPs.
If my memory is correct, why has it changed back again?
And, whether my memory is good or bad, why are the continued operation of detectors in these circumstances not deemed to be as important as MCP's in the 2002 version?
(I appreciate that the shottky diode method will keep the integrity of the circuit complete anyway, but there could be other methods devised that met the recommendation, but disabled other detectors)
Thanks in advance for any input you can provide. Once solved, I have numerous other 'things that make my brain hurt' to ask you!
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New one on me.
Always been MCP.
You may be getting mixed up with Clause 12.2.2 h-removal of any mcp or detector should not affect the operation of any fire alarm device.
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New one on me.
Always been MCP.
You may be getting mixed up with Clause 12.2.2 h-removal of any mcp or detector should not affect the operation of any fire alarm device.
Well, as I said, my memory could be flawed.
Any thoughts why they don't think it is as important to keep detectors working?
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one reason maybe is humans are more effective than afd but need a ways of raising the alarm
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Oh wiz
What you gone and done that for? Now I will be kept awake wondering what a shottky diode is. And just as I have finally mastered the spelling of carbon tetrachloride in my fire safety recommendations.
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Oh wiz
What you gone and done that for? Now I will be kept awake wondering what a shottky diode is. And just as I have finally mastered the spelling of carbon tetrachloride in my fire safety recommendations.
Oh Kurnal,
Mr Shottky must know how to spell his own name and that's how he spelt it when he wrote to me recently seeking my thoughts on forward voltage drop. Or is this another trick of my memory and imagination? Kurnal, come join me in this Home For The Bewildered. The nice ladies looking after me might let you have some of my medicine to help you sleep, and all washed down with lashings of dihydrogen oxide!
But do you have any thoughts about the original question!
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one reason maybe is humans are more effective than afd but need a ways of raising the alarm
Graeme thanks for your input. I know what you mean and can see the absolute importance of keeping mcps functioning whilst that most effective automatic detection device, the human being, is around to detect a fire. But I'm still wondering why the cop didn't include afd in the recommendation (especially as they will continue functioning in the most common method of detector removal monitoring) ?
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mcp's are more likely to operate on less voltage from dropping when a detector is removed
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mcp's are more likely to operate on less voltage from dropping when a detector is removed
Yes Graeme, I think you are probably right with this answer. I had previously considerd the combined effect of the forward voltage drop of the monitoring diodes when removing detectors, during my nocturnal musings on the subject. But I discounted it because of the low FVD of Shottky diodes, and the wide operating voltage of most modern detectors.
However, I suppose the committee looked at it, and agreed it was more important that mcps continued working rather than afd, if also insisting on the latter, precluded the use of possible different removal monitoring circuits and/or detectors with a smaller voltage operating range.
I personally don't agree with the limited scope of the recommendation, because it seems that keeping all afds working on the removal of any other dectector(s) is easily possible these days and, surely, equally important as the mcps.
Thanks again for your well thought-out inputs. I will now sleep a bit easier, but I have other insomnia-inducing queries that I will put forward for your thoughts when I have recovered sufficiently from this one!
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I think you will find the shottkky diode contains coper which will still contract at a lower voltage,when the current is de creased the mcp will operate in some circumstances resulting in another false alarm.
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another little one,smoke detectors often go off when they detect steam.
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If you throw powder eg talc at a smoke alarm it will go off,a prank often done in care homes or Prisons....
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Oh wiz
What you gone and done that for? Now I will be kept awake wondering what a shottky diode is. And just as I have finally mastered the spelling of carbon tetrachloride in my fire safety recommendations.
Oh wise and helpful Kurnal, I know I previously gave a flippant reply to your posting on the basis that I found it, as I often do with the jokey parts of your replies, highly amusing. however it occurs to me that the reference to Shottky diodes may indeed have been a serious request for explanation.
If so, and I apologise if I am telling you something you do understand, I will try to give an explanation of the main role in using a Shottky diode in automatic detector removal monitoring because it may help others in the forum and also explain the previous posts of Graeme Millar and myself.
A system of monitoring the removal of detectors from their bases often uses the method of inserting a semiconductor known as a diode in the base of the detector. This diode only has effect when the detector is removed, because whilst the detector is still inserted in the base, it's own internal circuitry short-circuits the diode and keeps the zone wiring circuit connected to devices further along the circuit. When removing the detector from it's base, the diode is no longer short-circuited but it now, itself, provides the continuation of the circuit for the electrical current powering the system to reach devices further along the line.
However many diode types, whilst allowing current to flow through, also cause a drop in voltage. This is known as Forward Voltage Drop and can be as much as around 2V with some diode types. So, as you can imagine, the cumulative effect of unplugging a number of detectors could easily mean that the nominal operating voltage of, say, 24V dc could be far far less by the time it reaches equipment further down the line. It could eventually become so low that it is insufficient to allow that equipment to operate.
The Shottky (sometimes spelt Schottky) type of diode has a low Forward Voltage Drop, typically around only 0.3V, and therefore using this type of diode in the detector bases allows far far more of them to be in circuit, as detectors are removed from bases, before the overall circuit voltage reduces to an unusable level.
I apologise if the above is only 'teaching people to suck eggs'. I'm only trying to help!
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another little one,smoke detectors often go off when they detect steam.
never!!!!
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I think you will find the shottkky diode contains coper which will still contract at a lower voltage,when the current is de creased the mcp will operate in some circumstances resulting in another false alarm.
Lucky, I've never heard anything like this before and I'd love to hear a more precise explanation of the circumstances. Trying to think the scenario through of a typical fire alarm zone circuit, I can only imagine an increase in current from the 'normal' operating situation causing a fire condition. I can't think of any situation where a Shottky diode wired in series with the zone circuit would cause this.
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another little one,smoke detectors often go off when they detect steam.
I take it that my musings are too in-depth for this forum!!!!! Where are you when I need you Kurnal?
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Wiz
How kind you are to imply faith in my jabberings. I have been holding back on this one for two reasons- the first is that I dont know the answer and secondly hoping that someone else would know and then I could agree with them, pretend I had been very busy and look very clever indeed.
I thought the hirsute man of Northern England may had had a stab at it as well.
I dont have any knowlege of the change to BS that you refer to.
But heres a stab at a possible explanation. As alarm systems have developed over the years I guess that, as GM infers above, the operation of MCPs would be seen as sacrosanct. After all if someone operates one of those then you do have a fire for real and it matters big time. Whereas at first the use of detection was seen as potentially unreliable at first and was a bonus used in conjunction with the traditional passive methods of fire safety.
I also remember an early system in a hospital that used to be prone to unwanted signals (thrips and the like) and after the second call of the evening we firefighters had a policy (in our ignorance) of just unplugging the detector head involved. So thats all right then! Yes I shudder to think of the consequences now.
But now things have changed and AFD is now used in the basic fire strategy for a building and often in lieu of other methods of fire protection. So it becomes absolutely vital that if it is part of a fire strategy must be bulletproof. And as it happens the technology has advanced at the same time to ensure that first by by the use of diodes, then active EOLs and now intelligent systems the resilience of the system has also improved in parallel. Almost by co-incidence.
But you are right- It does seem surprising that the BS does not appear to have kept pace.
Sorry not to be of any more use on this one. But I don't pretend to be a techie. And your question has at least prompted me to read around the subject again. Have to go now- I can hear the nurse coming.
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Kurnal, thanks for input. It seems my belief that the inclusion of afd in the recommendation as an earlier ammendment and dropped for 2002 was another figment of my delerious imagination. Graeme almost certainly hit the nail on the head about why mcps are considered more important and I agree with you that it makes no sense that the latest standard couldn't incoporate something that seems so obvious.
Lucky had me going for a while. But I'm now guessing that he strayed into the wrong place by mistake and had to say something to cover his embaressment before leaving. I think he might even be a fellow resident in this Home For The Bewildered. I'm now keeping my eye on a couple fellow residents because they always seem to be a bit 'lucky' with portion size when the tiramasu is dealt out at lunchtime!
Later Edit;
Now I'm sure about my suspicions of Lucky! I've just read his previous posts elsewhere in this forum and one contains the words 'staff are making it difficult to carry out the roll' . I tried to get out yesterday with a bit of steak and onion pie in my pocket and Matron was very angry. And I would imagine that the roll must have been very big if he had to carry it! He should have asked for my help!
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Sorry I didn't join in the post over the weekend, busy driving a mini digger in the garden!
I do not remember the ammendments calling for detection to work when you remove a head, but in practice most conventional detectors will be capable of generating an alarm in the event of removal of a single detector. You could calculate for each zone the theoretical probability if you had the panel terminal voltage, the alarm current threashold, the individual cable resistance head to head, diode and EOL spec, and head alarm current. Using kirchoffs you could then calculate a number of scenarios where the detection would/ would not work. Easier to say the callpoints should work and leave it at that, otherwise you would have to rethink conventional panel technology.
Has lucky been recaptured? Good post!
PS please dont go around unplugging heads because one day my friends you will unplug a Vigilon head and then the world as we all know it will come to an end. ( before anybody asks, you have to go into the software and stop the loop BEFORE you touch it or it will probably CRASH!!)
Dave
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The world has already ended. It ended when I took over the building with the vigilon panel and started trying to make sense of the menu and configuration. Thats when I was admitted to the home. And they wont let me out till I have mastered the manual. Everytime it breaks I try to hit it with the big hammer but it still doesnt work so I end up having to pay someone else £350 per day to hit it with their big hammer, they hit it just like I did but they seem to make it work.
Try disabling a device on a loop and then trying to find which one it was to re-enable it later. Every vigilon panel should come with a memo board built in!
If you are suffering from kirchoffs and sneezes a sharing a hot toddy with matron can work wonders.
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A drop in current would indicate a fault,so the system may activate.
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Oh here is my night time medication,until tomorrow,zzzzzzzzzzzzzz
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A drop in current would indicate a fault,so the system may activate.
You've lost me there??
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The world has already ended. It ended when I took over the building with the vigilon panel and started trying to make sense of the menu and configuration. Thats when I was admitted to the home. And they wont let me out till I have mastered the manual. Everytime it breaks I try to hit it with the big hammer but it still doesnt work so I end up having to pay someone else £350 per day to hit it with their big hammer, they hit it just like I did but they seem to make it work.
Try disabling a device on a loop and then trying to find which one it was to re-enable it later. Every vigilon panel should come with a memo board built in!
If you are suffering from kirchoffs and sneezes a sharing a hot toddy with matron can work wonders.
Does the printer not work ob your Vigi's??Now,if you want a panel that is really good for isolation mystery try the Menvier (defender 4000?) - if you are not sure if your isolation worked and you do it twice (or moe) it logs that as two (or more) isolations.Add this to the ones you have already done it can become a pain.
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All the log tells me is that devices were disabled/ enabled in loop x. And it only counts 1 per loop irrespective of how many I disable. It often gives me fault messages that arent in the book. Still the hammer finish looks attractive in some lights.
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A drop in current would indicate a fault,so the system may activate.
Welcome back Lucky! Now that I have established that you really are a fellow resident of The Home For The Bewildered, I also now appreciate that there are different levels of bewilderment and you have obviously stumbled into this room by mistake.
But watch out, Matron is on the prowl looking for whoever keeps nicking the leftover food. I've told her that she should suspect the Hairy Monster From The North, who is a recently arrived fellow resident and has a very bad case of oral expectorations (according to long-time resident, The Kurnal) but she strongly suspects YOU since the incident with the roll. It has also been reported to her that you have started imagining seeing dinosaurs and I overheard 'them' talking about increasing your medication. Be careful about upsetting 'them'. Long time resident and agitator, CT, tried it a few months ago and no-one has heard from him since!
Finally, If you are considering a 'fault' as an 'activation' then you would be right.
I am now also considering the possibility that your posts are actually in code. I look forward to your next message.
Got to go now. See you at the 'movement to music' class tomorrow.
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Wiz you have missed the point. I have a theory.
Lucky IS the leftover food. You cant resist to pick at him then he gives you indigestion and keeps repeating on you.
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Wiz you have missed the point. I have a theory.
Lucky IS the leftover food. You cant resist to pick at him then he gives you indigestion and keeps repeating on you.
Kurnal, there are many that say you are a 'tough nut to crack'. But once again your Wiz-dom is spot on! I'll be moving to a new part of The Home shortly, hopefully Lucky won't be able to climb the stairs and find me, so I'll have nothing to nibble on and will then be free of my stomach pains (actually, they are mostly brought on by belly-laughs!)
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Everytime it breaks I try to hit it with the big hammer but it still doesnt work so I end up having to pay someone else £350 per day to hit it with their big hammer, they hit it just like I did but they seem to make it work.
Breakdown of £350 invoice:
Hitting with big hammer - £ 10.00
Knowing where to hit - £340.00
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Therefore the conclusion reached for my original questions are:
1) It has never been a recommendation of BS5839 Part 1 that automatic fire detectors need to continue working
when other afd are removed
2) No one knows why they shouldn't be included, since it is technically possible to do so.
I am now moving rooms within The Home. I'll be a bit busy whilst moving my bag of shottky diodes and book explaining Kirchoffs First Law (what goes in must come out).
However you are all invited to a house-warming drink in my new room later this week where I will take the opportunity to ask you all searching questions about beam detection.
Don't tell Lucky of my plans.
RSVP
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Luckyis the food
he talks mince
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However you are all invited to a house-warming drink in my new room later this week where I will take the opportunity to ask you all searching questions about beam detection.
RSVP
brilliant. can i bring my Mechanno set?
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brilliant. can i bring my Mechanno set?
That will be great. Try not to let the bits rattle in the box as you walk the corridor.-Lucky has super-sensitive hearing.
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wiil do and i will bring along a flask of warm lemon tea
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And I will bring my ammeter and diode tester so that when we unplug the detector to smoke something dodgy we can be sure that mr Kirchoff will go next door and down the corridor and will still alert the matron when she burns the toast.
Is your bag of tea still attached to your leg Greame?
And if we are lucky you may share some with us.
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I'm concerned. All our plans may be shot. I've just overhead the doctor say most of the residents in here are ******* bonkers and Matron saying she's going to break out the restraints. I might try to escape tonight. Lucky wants to go with me. I don't think he's up to it - he's still imagining he can see dinosaurs.
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I wouldn't want to give Kurnal nightmares, but we have over 200 buildings mostly with Vigilon systems!
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Thats good news. 200 on your side of the Irish Sea means they aren't on my side. If you want to borrow my hammer I will gladly post it to you.
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Long time resident and agitator, CT, tried it a few months ago and no-one has heard from him since!
CT did escape along with DaveB shortly after I won my scholarship to the home. I think they may have not liked me blaming them for causing the end of civilisation as we know it. Matron says I am paranoid - but who wouldn't be when people are plotting my downfall all the time?
I think CT is held in another institution now due to his inability to stop his pen quivering over blank pieces of paper and writing new rules for us all to fall out about. Theres a new one coming out soon on green boxes. Still it all brings payday I guess. And its better than him doing elvis impressions.
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The hammer would almost certainly be more use than the manual!
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I think CT is held in another institution now due to his inability to stop his pen quivering over blank pieces of paper and writing new rules for us all to fall out about. Theres a new one coming out soon on green boxes. Still it all brings payday I guess. And its better than him doing elvis impressions.
So it's..
One for the money, two for the..... any offers?
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Long time resident and agitator, CT, tried it a few months ago and no-one has heard from him since!
CT did escape along with DaveB shortly after I won my scholarship to the home. I think they may have not liked me blaming them for causing the end of civilisation as we know it. Matron says I am paranoid - but who wouldn't be when people are plotting my downfall all the time?
I think CT is held in another institution now due to his inability to stop his pen quivering over blank pieces of paper and writing new rules for us all to fall out about. Theres a new one coming out soon on green boxes. Still it all brings payday I guess. And its better than him doing elvis impressions.
Have you noticed that the person in question (or is it an impersonator ( Elvis?)) has returned?
It's always good to have a past resident back with us in The Home For The Slightly Bewildered. But is he o.k.? So far, he is just shuffling around a room humming Happy Birthday at the moment. Do you think THEY may have got to him?
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Never had any problem with mcps. But the nightmare still is waking up with the room on fire because your alarm hasnt doe a proper job.
Fit 4 Europe! (http://www.fitforeurope.com/italy/lake-como-lago-di-como/)