New project: Fire sensing laser cut out system - and maybe more later.

[Graham Facer]

So I have 2 posts tonight. One is for an issue or 2 I'm having (though I may wait until tomorrow as I have some ideas after researching here...) but the other is a project that may eventually interest a lot of the folks here (and some may have tried it and have advice).

Anyhow I have been looking for an arduino micro controller project to do but one that wasn't useless (like blinking morse code in LED's) and eventually I realized I should be able to wire up one or many flame sensors in my laser cabinet and then if they sense flame for a certain length of time then they trip the laser power switch. So the gantry would continue but the laser would go off. Oh and an alarm would sound.

If I really get ambitious I might eventually try and rig it up to a relay controlled CO2 extinguisher for the ultimate in protection but that is several steps up in cost and complexity.

For now I have a $10 arduino uno rev. 3 knock off from ebay and a sample program that will sense the flame and start a count. If the flame disappears, the count resets, if not then the count eventually reaches a trigger and trips the relay/siren/whatever else I add.

So I'm still waiting on the flame sensor module and then I can play with it testing. The big questions are 1)if the cutting path will trigger it 2) if I can/should mount it with the laser head or under/over the table etc.

Anyhow should be fun to play with (for me at least) and hopefully reduce the damage of another fire (actually had a little one yesterday but no damage - just a little mess - need to go get a CO2 extinguisher.

I have been working on this for a bit but hoping the main sensor arrives in a few days for proper test.

Cheers, GF

[Graham Facer]

The micro controller is a SainSmart Uno R3 from ebay. It is powered by 5v which I hope to get from the USB inputs on the laser file input thingy but easy enough to figure out if that fails for some reason.

The sensor is one from DX (I think I got the 5 channel/sensor one but maybe 2 or maybe both - too lazy to look right now) and then also a higher value relay 20amp from DX too.

[Keith Colson]

Hi Graham

Great idea, I have been thinking about doing this myself for a while now. I just wanted something that would squawk so I could run and check the machine as I am never more than 50 steps away.

I was planning to stick about 4 or 5 thermistors just under glass lid . I chose thermistors for a few reasons. They are really simple to interface to a micro. They work really well when covered in dirt as things in the laser cutter get dirty. They are cheap and simple so you can use many at a very low cost. They won't false trigger i.e.most flames go out quickly. I am interested to see your progress.

Cheers
Keith

[Dan Hintz]

Projects like this come up every so often but never go anywhere... there are just too many problems to solve in such an uncontrolled environment. If you attach the sensors to the carriage, the head has likely moved on from where the fire is, so it does no good. If you use temp sensors, they likely won't trip until the fire is raging because the exhaust is pulling the air out of the cabinet before it can get hot enough and temp sensors have a long dwell time. Pyro sensors would need a wide view angle to see all of the table (even with multiple sensors), and how do you prevent false positives from the typical flare-up that self-extinguishes?

[matthew knott]

Wonder if monitoring if monitoring the temperature of the gasses flowing into the fume extractor would tell you anything in ? I would think you could use a TIC but as Dan points out, seeing the whole bed is near to impossible without multiple cameras and you would still end up with a system you cant really trust and you SHOULD be keeing an eye on it. Most fire detection systems are really to prevent loss of life or serious damage, a small fire in a laser will destroy it in seconds. Guess if you are determined to live it unattended it will be better than nothing but i would also have a normal smoke detector above the machine so hopefully you don't burn the neighborhood down!!!

[Scott Shepherd]

I've been down this path once before. I decided to do the same thing you mentioned, arduino with a fire sensor. In the end, I scrapped it all because a lot of fires happen under the work, not on top, and the visual fire sensors wouldn't do anything for that, since it's under the work. I stopped working on the idea because I found that not all flare ups were created equal, I couldn't detect the fires under the work, and some flames are different colors and it was my understanding that the sensors used color to determine the fire, and it appeared that it might not detect fire from certain products. It quickly became an overwhelming task to get right, and in the end, my thought was that I wasn't doing anything other than trying to give myself the ability to walk away from the laser when cutting and I didn't think that was a good idea.

Hopefully you can figure out the things that overwhelmed me and caused me to stop.

[Doug Griffith]

I went down that road as well and false positives stopped me in my tracks. I've since thought to create a more simple device that checks if my blower/air assist are running and sound an alarm if they aren't. My cheap little HF blower has died a couple times mid-project from brushes burning out and my paasche air compressor has overhearted a few times and stopped running. Both scenarios turn small little flare-ups into larger ones real quick.

[Graham Facer]

Ok great feedback. I can see the issues now. I try not to leave unattended but I'm a 2 man shop with a retail section so I am often pulled away. I usually try to check in at the start and then periodically. This is more a back up plan as if it just cuts the power to the laser - no harm no foul I'll just reset and restart.

I am leaning towards an under the table set up, false positives will, in theory, be done with a time setting. If the flame self extinguishes, the counter resets.

At any rate I'm treating this more as a hobby electronics project rather than a shop project so I'll carry on for now and post some feedback. Glad to hear others have tried, might save me some time in the end. Especially about the possible colour sensitivity of the sensors.

The tricky bit will be that I have the biggest issue with ABS (black) - both fires have been on that - and it also smokes like crazy when cutting. Anyhow, I might think about adding temp sensors to the underside of gantry as that is where the heat will damage the most. Anyhow, like I said, this is as much a project to learn the arduino as anything so I welcome the challenges - I'd thought it might be too easy but that has been dispelled!

Thanks, GF

[Matt McCoy]

Hey Graham: While I don't have anything to add to your cool sensor project, an angled mirror or small video camera helps to keep an eye on things from across the room.

[Scott Shepherd]

At any rate I'm treating this more as a hobby electronics project rather than a shop project so I'll carry on for now and post some feedback. G

That was the same thing I was doing :) It was educational to at least think about it and tinker with it some. One of my customers is heavy into electronics so I picked their brains about it and the possibilities. If it helps you in your situation then that's all the matters, plus you get to learn a lot from it all.

Just as a reference, Universal uses a temperature sensor inside the cabinet for their alarm system, so it's just monitoring the inside air temperature and setting the alarm from there.

[Dan Hintz]

I try not to leave unattended but I'm a 2 man shop with a retail section so I am often pulled away. I usually try to check in at the start and then periodically.

This is how everyone with a fire gets burned (no pun intended). They think "I'll just slip away for 30 seconds, what can happen in 30 seconds?" 20 seconds later their entire machine is engulfed in flames. No, that's not an exaggeration. Look at some of the threads here where people have stepped out of the room (some were in the same room but 10' away and not watching it)... entire shops have been destroyed.

Running jobs while dealing with customers is a sure way to eventually lose your entire shop. Don't say we didn't warn you.

[matthew knott]

Always thought something like this http://www.firetrace.co.uk/products/low-pressure-systems/ might save the day in a nasty situation. Yes its going to make a mess and yes the laser may never work again but at least it should put the fire out before it lights the whole building up.

[Graham Facer]

This is how everyone with a fire gets burned (no pun intended). They think "I'll just slip away for 30 seconds, what can happen in 30 seconds?" 20 seconds later their entire machine is engulfed in flames. No, that's not an exaggeration. Look at some of the threads here where people have stepped out of the room (some were in the same room but 10' away and not watching it)... entire shops have been destroyed.

Running jobs while dealing with customers is a sure way to eventually lose your entire shop. Don't say we didn't warn you.

True enough. But that's how it goes. I can't sit and watch a computer controlled machine all day and make a living and even if I was in the same room it could still happen and quite frankly I don't have the patience anyhow. I'm am not saying that to be argumentative, that's just my feeling on the matter (your approach is way better).

I'd rather lose a 10k machine then waste 10k of time a year babysitting it. As for the shop, well I've had a pretty good fire it in once and certainly never felt the shop was in danger (except maybe from the smell). I can see that changing if I was cutting wood but most of what I cut has a slow spread when on fire. We will never eliminate the risks of fire when cutting with a laser, not even standing over it, we can only work on minimizing the results.

Anyhow on the project, one suggestion my brother had was an temp sensor externally mounted for ambient and one at the intake for the vent and then track the difference. That might work too in conjunction, but the more I think about it, the more adding in a CO2 flood to the cabinet if I can get the false positive things down to a manageable level.

Cheers, Graham

[Dave Sheldrake]

307698

This started with a small fire in a laser that was unattended. It killed 3 (2 instantly and 1 died later) a 4th man now resides in a world of darkness having lost his sight and most of his facial skin.

I'm pretty laid back with the guys that work with me, they are friends as well as staff, if one of them left a machine unattended they would be unemployed the same day.

[Scott Shepherd]

I can see that changing if I was cutting wood but most of what I cut has a slow spread when on fire. We will never eliminate the risks of fire when cutting with a laser, not even standing over it, we can only work on minimizing the results.

Your website shows almost all of your products to be acrylic. If you are saying that that has a slow spread on fire, you might need to look for the post recently where thin acrylic was cut and caught fire. Acrylic is NASTY as far as fire. Been doing this about 8 years now and acrylic causes me GREAT concern. I'd leave wood long before leaving acrylic, and I cut a lot of acrylic.

[Dave Sheldrake]

307699

Not mine but the owner is a member here and may well be able to tell you about acrylic fires.....

[Scott Shepherd]

I see you save laser fire photos too Dave ;)

[Keith Colson]

Dave, I think that one would have set off a fire sensor! Were they cutting with the paper on the top surface? I just don't get any flare ups at all unless I leave the kindling (top paper) on the acrylic.

[Graham Facer]

Well, I'm pretty sure we can design something to avoid these pictures. That's the goal.

Then I'll set something on fire to test it...

[Dave Sheldrake]

I see you save laser fire photos too Dave ;)

Got 50 or so of them Scotty :) all caused the same way :)


Dave, I think that one would have set off a fire sensor! Were they cutting with the paper on the top surface? I just don't get any flare ups at all unless I leave the kindling (top paper) on the acrylic.

It's the down-draft Keith, that accelerates a fire at incredible speed, a bit like a blacksmiths forge in some ways, much of the time it's detritus on the bed or in some cases under the bed. I've been out to some real horror stories over the years where a machine hasn't been cleaned for weeks :(

[Rodne Gold]

cheapest way , IMO , is to employ a minder and operator. Our operators would get summarily fired if they left a machine unattended, they all know that and its in their employment contract.
GCC has some sort of fire suppression system or warning system called Smartguard

[Gary Hair]

Your website shows almost all of your products to be acrylic. If you are saying that that has a slow spread on fire, you might need to look for the post recently where thin acrylic was cut and caught fire. Acrylic is NASTY as far as fire. Been doing this about 8 years now and acrylic causes me GREAT concern. I'd leave wood long before leaving acrylic, and I cut a lot of acrylic.

I agree, I've never had wood catch fire but I have had numerous times with acrylic. I'm always watching it so it never gets beyond a point where stopping the laser and merely blowing on it won't put it out, but as has been already said, that difference is seconds.

[Graham Facer]

OK I'm definitely raising my goal, a fully automated fire control system with escalating unattended response.

1) Cut laser/alarm
2) 15 sec delay and then fan shut off and full cabinet CO 2 purge followed by re-venting.

and maybe with push button settings for different materials.

Its quite frankly ridiculous that we'll spend tens of thousands for machines that need to be watched like a hawk less they self destruct. Its like having to watch a home furnace all day and night, lest it should burst into flame. I've been convinced that my attitude is hazardous, but I cannot hire a person to watch a machine that is not used full time and I wear enough hats as it is.

And please can we focus this thread on this problem/solution idea. I did not come looking for a burnt out machine thread, I came trying to avoid it.

Scott: Do you have some more details on what you tried (what sensors if you recall, where you had them - even your arduino sketch?).

[Rodne Gold]

Maybe this helps
http://laserprona.com/new/wp-content/uploads/2014/11/SmartGUARD-Fire-Alarm-Device_SI-SG-SGX.pdf

[Dan Hintz]

Its quite frankly ridiculous that we'll spend tens of thousands for machines that need to be watched like a hawk less they self destruct. Its like having to watch a home furnace all day and night, lest it should burst into flame. I've been convinced that my attitude is hazardous, but I cannot hire a person to watch a machine that is not used full time and I wear enough hats as it is.

And please can we focus this thread on this problem/solution idea. I did not come looking for a burnt out machine thread, I came trying to avoid it.

My daily driver cost $50k... but it doesn't drive itself. I could spend $1 million and it still wouldn't drive itself. Just because a machine is expensive doesn't mean responsibility for operation falls out of the window.

Several of us have given you a list of potential pitfalls in your solution, it's up to you to determine how to get around them. If you won't listen to those of us who have been there, done that, I don't see how much more help we can be. You're determined to make a fire prevention system that is likely doomed to not prevent fires, so I'll wash my hands of it now and just hope you don't get harmed in the process.

[Dan Hintz]

Maybe this helps
http://laserprona.com/new/wp-content/uploads/2014/11/SmartGUARD-Fire-Alarm-Device_SI-SG-SGX.pdf

Rodney, it's difficult to see, but it appears the sensor is the same type used for overhead sprinklers (alcohol-filled glass capsule)? I imagine if it's hot enough inside the cabinet to burst the capsule, the cabinet is already destroyed. The system may shut down the laser, but by then it's too late.

[Rodne Gold]

Dan , I have no idea of how it senses...
as you so rightly said , we as a community have given our input , so lets see what the OP can produce.
It might well work brilliantly and be $200... if so , I will take a dozen of em...

[Bill George]

On commercial HVAC systems they have smoke detectors in the ductwork. Sometimes one before the fan and one after. These could be set to sound an alarm, say 20 seconds before the CO2 goes off. It shuts down the fan and the fire suppression is triggered. CO2 is cheap and I would rather have it trigger and dump than not.
On laser systems the smoke detectors would need to be adjustable to a higher or lower level as needed.

[Dan Hintz]

On commercial HVAC systems they have smoke detectors in the ductwork. Sometimes one before the fan and one after. These could be set to sound an alarm, say 20 seconds before the CO2 goes off. It shuts down the fan and the fire suppression is triggered. CO2 is cheap and I would rather have it trigger and dump than not.
On laser systems the smoke detectors would need to be adjustable to a higher or lower level as needed.

Anything that can catch fire will create smoke in the laser, so the moment you start processing material the alarm will trigger... and no, you can't set a lower limit to the amount of smoke as there will often be LESS smoke once something catches fire.

In other threads, we've already discussed the danger to human life of dumping CO2 (or other gases) into the bed to smother the fire, so I won't rehash that here. And if you wait 20 seconds from the time the alarm goes off to when the gas is flooded, your machine is likely already melted.

[Bill George]

As a commercial HVAC tech who worked in many large computer rooms I saw systems that worked. If its good enough for a multi million dollar data center it should work for a $20k laser. The room is vacated (before) and ventilated after the dump.

If using a CO2 extinguisher is hazardous then are dry powder ones safer? Choosing not to put out a fire because of the hazards of using an extinguisher would be a tough choice.

There are many ways to detect a fire, UV detectors, flame flickering and temperature sensing that does not rely on melting a link or capsule. I have an Omron controller setting on my workbench that with a RTV or thermocouple sensor can pick up a temperature change in a manner of seconds.

[Mike Lassiter]

It seems to me using a inert gas like nitrogen or co2 for the air assist would be the simplest and easiest thing to minimize flare-ups when cutting prone to catch fire materials. Perhaps it's not so simple, but I do know ULS has a computer controlled air assist dual system for my laser that allows using air, or inert gas. Perhaps that alone wouldn't be fool poof but with the possibility of fire on both sides of the material I can see where it would be hard to monitor the bottom side especially when the cutting table is likely filled will smoke while cutting. My laser has a battery powered thermal sensor in it. If the battery dies or gets weak the laser will not operate. I think the thermal sensor is mounted on the rear wall and will shut the laser down if it detects "excess" heat to prevent the laser from feeding the fire. However it seems to me by directing a stream of inert gas directly at the cut and using that to blow out the debris you are letting the laser cut the material but minimizing lingering flames by preventing or limiting the o2 needed to support the combustion.

What I get from Dan and Scotts comments is that if you make something that can detect "any" possible occurrences it is going to likely generate a lot of false alarms that will create more problems as far as productivity is concerned. My computer is 2 feet from the laser. I cannot go much farther away because ULS says to limit the USB cable to 6 feet max length. The port is about 1-1/2 feet from the right rear corner so by the time I come around the rear of the cabinet and to the front corner the 6 foot length is used up. So, I am always right there so to speak, and while I don't stand and watch every second the laser runs (depending on what is cutting) I am a one man show with our laser. We don't do near the volume that some of you do but I have over $60K invested in the laser and the small building we have it in. IMO the safeguards built into it hopefully would prevent a calamity but I think the first line of defense is me - the machine operator.

[Chuck Stone]

As a commercial HVAC tech who worked in many large computer rooms I saw systems that worked. If its good enough for a multi million dollar data center it should work for a $20k laser. The room is vacated (before) and ventilated after the dump.

Those systems cost more than a $20k laser, too.
And a total flooding system brings in a whole alphabet soup of government
agencies with their own regulations.. not something to be taken lightly.

And as you know, comparing suppression systems to extinguishers is similar to
comparing Big Three US laser engravers to the $459 Ebay imports ;-)

[Gary Hair]

I think the first line of defense is me - the machine operator.

You are a smart man Mike!

[Scott Shepherd]

Scott: Do you have some more details on what you tried (what sensors if you recall, where you had them - even your arduino sketch?).

I don't Graham. I have a customer that makes electronic things for a living. My vision was to create and sell an aftermarket kit that we could sell. I had a number of meetings with them (Electronic and software Engineers), and they did a lot of research on the sensors, etc. Every time we'd meet or talk about it, they'd talk to me about the parameters and at no point could I say anything was 100%, which meant it would be riddled with false positives and it wouldn't actually detect some really bad things (fire under material, which is far more dangerous than a flare up on top). The visual flame detectors were the direction we were going, but some times you get a flare up on many materials, when vectoring, that only lasts a second or two.

The situation sounded like it would just send false positive after false positive, and you'd be running back to the laser to check that.

In the end, we all agreed that it wasn't something we wanted to invest any more time or money into.

[Bill George]

Scott A simple time delay adjustable would take care of the flare ups on starting a cut. And nothing said you couldn't have more than one method. I will trust your judgment, but it seems like something that worked could really speed up production.

[Scott Shepherd]

That was the problem Bill, some flare ups are okay. A flare up in the Y axis when cutting Rowmark might last 3 seconds, and I might have paper mask on it so it's okay. A 3 second flare up un unmasked acrylic might lead to a terrible fire. A flare up on wood, I might ignore to some degree, but again, on acrylic, not so much.

People a lot smarter than me were on the project and after I told them the conditions, they said we were chasing a moving target, which it is. There is nothing that works or could be filtered out that easily, and like I said, if you're getting buzzers going off for false positives (there's no way for the system to know if a fire is okay to leave or set an alarm because there's no way to know the difference in looking at it, since all fires start the same), then you're going to be constantly running back to the laser anyway. If every time I get 10 feet from it, it goes off and I have to walk back to it (or run), then I might as well just sit there and be around it when it's cutting.

If I had the OP's situation, I'd do like I used to do, and how someone else has mentioned, I'd put a webcam on it, I'd open that webcam stream on a computer where I talk to customers, and I'd just casually scan the monitor while talking to customers. You could have that running in 20 minutes and it works great.

(I didn't do it and go to another room, I watched it in the corner of my monitor while I did other computer tasks).

[Graham Facer]

My daily driver cost $50k... but it doesn't drive itself. I could spend $1 million and it still wouldn't drive itself. Just because a machine is expensive doesn't mean responsibility for operation falls out of the window.

Several of us have given you a list of potential pitfalls in your solution, it's up to you to determine how to get around them. If you won't listen to those of us who have been there, done that, I don't see how much more help we can be. You're determined to make a fire prevention system that is likely doomed to not prevent fires, so I'll wash my hands of it now and just hope you don't get harmed in the process.

Hi Dan,

Well I hope you don't feel as if I've not listened. But its not a fire prevention system I am looking for - we seem all agreed that is impossible but can be limited by the operator/setup - this is a damage mitigation system.

Fire prevention would be to create a system that prevents combustion, the design of this will be to prevent continued combustion.

[Bill George]

I think some good ideas have been presented. Scott the webcams might be a good option. If the object was to save the machine it might not be feasible, but to prevent the building from burning to the ground might be.

[Graham Facer]

Thanks Rodne... hard to see how that GCC system mounts and what sensor they use (though Dan sounds like he might be right) but thanks for the link.

[Matt McCoy]

Graham: What about a wireless remote that can activate the system by cutting the power and/or activating fire suppression from across the room? I would imagine a sensor/alarm setup used in conjunction with the video monitoring I suggested, would allow the operator to keep an eye/ear on the laser and quickly determine if the trigger is valid or a false-positive.

1) Hear the alarm
2) Check the monitor
3) Decide to let the machine continue or hit the switch.

[Graham Facer]

Hi Matt,

A remote kill switch would be relatively easy though the wireless communication issues would need to solved, but once it got the command the shutting off of the laser part should be easy.

For now I'll call that plan B. A camera/alarm/cutoff would help but might be too far on the unattended side for me though I'd be happy to work on that at the same time if others are interested. I have a wireless IP cam handy so it would not be that big of a deal (in theory).

Anyhow, until I get the sensors I don't have a lot more to add but I'd still be interested to get details on Scott's attempt. I ordered up a bunch more sensors on DX last night and a 1/4" air solinoid so now I wait for parts and maybe work on the program a bit.

Graham

[Matt McCoy]

RF might be an option. I could even envision using this system to monitor in another part of the building.

[Dan Hintz]

As a commercial HVAC tech who worked in many large computer rooms I saw systems that worked. If its good enough for a multi million dollar data center it should work for a $20k laser. The room is vacated (before) and ventilated after the dump.

If using a CO2 extinguisher is hazardous then are dry powder ones safer? Choosing not to put out a fire because of the hazards of using an extinguisher would be a tough choice.

There are many ways to detect a fire, UV detectors, flame flickering and temperature sensing that does not rely on melting a link or capsule. I have an Omron controller setting on my workbench that with a RTV or thermocouple sensor can pick up a temperature change in a manner of seconds.

Bill, have you bothered to read the thread from the beginning? We've already discussed these points before. Sensors for house fires are different than those needed here. A system designed for a server room is significantly different than that for a small laser system (not to mention orders of magnitude more expensive).

[Jerome Stanek]

In the server rooms I worked in the sensors were linked together and it took 2 or more the set off the Halon fire suppression system

[Bill George]

Graham, CO2 cylinder pressure is as I recall around 900 PSI. You can get small R size tanks which are 20 CF filled at any welding supply house. The companies like Pepsi or other local fountain distributers can also sell and fill the larger tanks.

Does your sensor monitor exhaust fan intake temperature? Seems like if you had a fire the temperature would rise quickly, not gradual. Perhaps a comparison between ambient air and exhaust air temperature or just exhaust air temperature.

Check here, we ordered a lot from these folks> http://www.kele.com/temperature-sensors-and-transmitters.aspx

RADIANT ENERGY FIRE DETECTORS Retail > http://www.koetterfire.com/fire-detection-systems/

and of course Honeywell makes them, http://www.honeywellanalytics.com/en/products/Fire-Sentry-SS4-Flame-Detector

[Graham Facer]

Graham, CO2 cylinder pressure is as I recall around 900 PSI. You can get small R size tanks which are 20 CF filled at any welding supply house. The companies like Pepsi or other local fountain distributers can also sell and fill the larger tanks.

I know, I make my own seltzer (first with a DIY setup and now with a hacked sodastream). I get them filled at the fire extinguisher place for $20. I have a 10# that I can test with though ideally if a paintball sized bottle would work they are cheap to refill. My guess is a 5-10# is needed. I think paintball ones are less.

Anyhow, checking the mail - no sensors today.

[Graham Facer]

Hi Matt,


Anyhow, until I get the sensors I don't have a lot more to add but I'd still be interested to get details on Scott's attempt. I ordered up a bunch more sensors on DX last night and a 1/4" air solinoid so now I wait for parts and maybe work on the program a bit.

Graham

Sorry Scott - I had it in non linear view of the thread - I see the details now.

[Bill George]

Graham I added to my post info on RADIANT ENERGY FIRE DETECTORS which need to be considered.
And after detecting a fire by any means you would automatically shut off the fan (and machine) and discharge the CO2 inside the laser. So all you need to do is fill the machine plus a little extra so 10 or 20 cf should be enough. Then of course you need to ventilate the room and bring in fresh air.

[Graham Facer]

Graham I added to my post info on RADIANT ENERGY FIRE DETECTORS which need to be considered.
And after detecting a fire by any means you would automatically shut off the fan (and machine) and discharge the CO2 inside the laser. So all you need to do is fill the machine plus a little extra so 10 or 20 cf should be enough. Then of course you need to ventilate the room and bring in fresh air.

Yikes - am I right in seeing those are $2k and up each? If so, I might stick to the cheap route. If there was an in-between sensor in the $100 range I could try that but I think I'll still see how far I can get on the $5-10 sensors first. But great information if I want to beef it up.

Thanks!

[Bill George]

Yikes - am I right in seeing those are $2k and up each? If so, I might stick to the cheap route. If there was an in-between sensor in the $100 range I could try that but I think I'll still see how far I can get on the $5-10 sensors first. But great information if I want to beef it up.
Thanks!

I will check with my commercial Honeywell supplier here in town tomorrow. But they are under new ownership and I don't know the owners anymore.... so discounts are more than likely gone. I am sure Johnson Controls also has more or less the same thing. But when your talking $30,000 for a new laser machine and lots more for a new building, what's a few dollars :rolleyes:

Amazing the amount and different types of flame detectors out there available.> http://www.globalspec.com/industrial-directory/flame_detector

[Scott Shepherd]

I can't find any reference to the sensors we were looking at. I thought they were on Mouser or DigiKey, but my searches for them hasn't turned any up and I've looked through old emails with the guys and I can't find where they emailed me any links to it. I do know they weren't cheap. The things were like $150 each and they detected fire, but not like fire on a pilot light, they visually saw the flame no matter where it was, not like a pilot light where it's just detecting a flame in a certain spot.

[Graham Facer]

OK well, The project is started - and I'll be honest I'm not as optimistic tonight. I got my first 2 sensors in on Friday and started messing with them. Well you get what you pay for!

That said, I'm not prepared to completely write them off yet but they do have me baffled a bit.

Long story short is that they are very sensitive to incandescent lights. So in my test lab/kids playroom where the lighting is pretty high (and all incandescent), they trip all the time. Not only that but they supposedly have LED's on the tiny boards that tell you when they trip and they are supposed to have adjustable potentiometers that would vary the trigger. What they really have is a potentiometer that varys when the LED trips up but does nothing to the actual analog output - which only has a value but never trips per say. As for the digital output, it basically always sees something to register as high or is defective (as it was still showing that when clasped in my hand.

On the plus side, they do register changes in light/IR and I just did test them with a compact fluorescent vs an incandescent lamp and it basically does not see the fluorescent.

I think I will test them out in the cabinet this week to see if the relatively dim light (and fluorescent at that) of the cabinet helps (though then I'd have to also program them to only look for flame when the door is closed - but easy bridge if any of the rest works - could likely tap into the existing lid sensors).

I think the board versions of the flame sensors might have been a waste of money but at least they are easy to wire up. The biggest challenge is that the field of vision for the sensors is very limited. Even with the fan shaped, 5 sensor, version it sort of needs to be dead on, on the right plane.


If anyone knows of some other flame sensors that might work, let me know.

I'll post again once I see how (badly) they work in the cabinet.

Oh and just for kicks, one sensor is high value when sensing and the other is the reverse!

Graham

[Graham Facer]

Bill would something like this be suitable do you think? SharpEye 20/20 UV/IR (http://www.ebay.com/itm/Sharp-Eye-UV-IR-FLAME-DETECTOR-20-20-LB-VOLT-18-32-VDC/151245059037?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%2 6asc%3D20131003132420%26meid%3Df984995f95804d5a8e7 b620735033204%26pid%3D100005%26rk%3D5%26rkt%3D6%26 sd%3D321407084969&rt=nc)

[Keith Colson]

On Ebay "10 pcs NTC Thermistor Temperature Sensor" 10 of them for $2.80. Sorry I am still trying to talk you into thermistors haha. No reaction to light!

I am very interested to know if there is a reason they won't work with the right thresholding software. I have contemplated building one with an array of thermistors. The price is right for testing.

Cheers
Keith

[Graham Facer]

Keith - I might just add them to the list of things one the way to try. At that price, its worth playing with isn't it.

Graham

[Bill George]

I really don't know why a fast reacting temperature sensor set at say 165 Deg F mounted inside the exhaust air intake with a lock out circuit would not work? Yes a flame detector would work, but I think the "real" ones are pretty expensive. I really have not had time to research.

[Scott Shepherd]

Sounds like you got flame sensors. Flame sensors won't work (as you are figuring out). They are designed to tell whether or not a pilot light is lit to know whether or not to shut the gas off or allow it to come on type situations. They aren't designed to catch a flare up across the table, they are made to stick into a fixed place where flame is either present or it's not.

Measuring average temperature in the cabinet isn't going to work either. It simply doesn't work that way. I did a lot of testing a while back on air flow through the cabinet and the airflow varies throughout the cabinet a substantial amount, and the placement of your cutting in those different areas would give quite different results. If you have great air flow and a fire in the center of the cabinet, you might be getting the same reading as you'd get on the edge without a fire. It's just not that simple. If it was, we'd all have temperature sensors or $3.00 XYZ sensors on our machines doing this. I don't think you are going to get this done low tech (basic sensors). Going high tech and getting sensors that can see the flame across the table is the only option I know of and those aren't cheap.

[Dave Sheldrake]

Sounds like you got flame sensors. Flame sensors won't work (as you are figuring out). They are designed to tell whether or not a pilot light is lit to know whether or not to shut the gas off or allow it to come on type situations. They aren't designed to catch a flare up across the table, they are made to stick into a fixed place where flame is either present or it's not.

Measuring average temperature in the cabinet isn't going to work either. It simply doesn't work that way. I did a lot of testing a while back on air flow through the cabinet and the airflow varies throughout the cabinet a substantial amount, and the placement of your cutting in those different areas would give quite different results. If you have great air flow and a fire in the center of the cabinet, you might be getting the same reading as you'd get on the edge without a fire. It's just not that simple. If it was, we'd all have temperature sensors or $3.00 XYZ sensors on our machines doing this. I don't think you are going to get this done low tech (basic sensors). Going high tech and getting sensors that can see the flame across the table is the only option I know of and those aren't cheap.

Scotty's pretty much bang on, my Mitsu LPE 160F extraction system has fire suppression provided by CO2 gas, start thinking around the same sort of money as a high spec Speedy 300 and you won't be far off as a start point. It relies on FLIR technology to "see" a flame and it's core temperature then decides how long it will allow that hot spot to remain before purge.

If it could be done at reasonable cost then China would be on that train many years ago as would the big Western names.

[Bill George]

FYI we were using UV flame detectors 40 - 50 years ago, to sense flame in large industrial boilers. When the boilers had a flame out for some reason you did not want to have that 2 and 3 inch gas main dumping gas into a hot chamber. The UV detection ignored the light from the red/white hot refractory walls.
The technology today on flame detection is light (pun intended) years ahead of those days.

[Graham Facer]

Ok I've done my first in cabinet testing. I took the single sensor model and pointed it straight down the channel in the knife table and then set some acrylic alight and then started calibrating. After I while I moved on to a laser test.

Then good news is that it basically does not see the laser itself while cutting acrylic. I then worked on creating a flare up condition - luckily my table was pretty cruddy so it wasn't too hard - and dialed it in some more. I've uploaded a video to youtube here (http://youtu.be/XTO0rXumkMI). The test is a little more sensitive than I would like for a shut down but it would be OK for a 2 stage system (alarm - then shut down). Careful - the alarm is loud if you have the sound up.

Anyhow, the downside is of course that on a 1200x900 table like I have I might need to wire up and monitor 50 of them and at a few bucks each it still adds up. But its a start and much better than I thought after last night.

Anyhow - time for paying work now.

Graham

[Bill George]

Graham I did finally get a hold of some people with prices on the Honeywell Fire Sentry FS24X and the price is nearly $2K or so. I'm sure it could be had for a little less if you got a hold of the right people. Its still out of the hobby laser or sideline business laser acceptable price range. By the time you got the rest of the system up and running it would be double that.

[Graham Facer]

Just an update. You may have seen my other thread about issues with my old tube and then with my new tube. Needless to say this project is on hold until I am am capable of starting a fire with the laser again. And likely when its winter again.

Summer just doesn't lend itself to projects like this. But on the plus side, I finally got my batch of 25 flame sensors to rig up and do a large test and my valve solenoid - though I got 24v not 12v - but that might work with the control power supply for now. The valve would control the CO2 flood in the cabinet.

[Kev Williams]

I didn't thoroughly read thru this thread (don't have time!), but here's my 2 cents...

I've had a few fires...

One, I had a nitrile glove hanging down into the cabinet from the side, which ended up in the X-path of the beam when the gantry got down far enough...

I've also had a few transfer tape fires. Always from a piece of loose tape, never from well-stuck tape. Usually the blower extinguishes the flame. Sometimes the blower creates a really fast smolder...

...But the common denominators in my fires have been the same:

1--While shutting off the laser would prevent further fires, it will do nothing to stop the existing fire--
2--Shutting off the blower would probably do more harm than good--
3--Whenever ANYTHING is on fire, ash and burning debris gets sucked up by the blower...

Ergo--

1- shut off the laser AND add a VERY LOUD ALARM--
2- Do NOT shut down the blower-
3- If some sort of flame detector is to be installed, wouldn't it make sense to install it within the blower hose rather than the laser cabinet?

[Scott Shepherd]

I didn't thoroughly read thru this thread (don't have time!), but here's my 2 cents...

...But the common denominators in my fires have been the same:

1--While shutting off the laser would prevent further fires, it will do nothing to stop the existing fire--
2--Shutting off the blower would probably do more harm than good--
3--Whenever ANYTHING is on fire, ash and burning debris gets sucked up by the blower...

Ergo--

1- shut off the laser AND add a VERY LOUD ALARM--
2- Do NOT shut down the blower-
3- If some sort of flame detector is to be installed, wouldn't it make sense to install it within the blower hose rather than the laser cabinet?

That was my experience with a fire as well. #2 especially. It was the blower pulling the flames sideways that helped keep it from being a tall flame that burned up lots of stuff.

[Jeff C Johnson]

I know I'm 6 years late coming to this thread, and I briefly scanned the past posts, but I'm wondering if the easiest solution would be to have a thin cable that is in the gantry that when it burns, it breaks the connection. No guarantee that it would happen in the right place, but most fires that I've seen start around the head which is attached to the gantry. Then just break the door panel switch connection to turn off the lasing and dump a bunch of CO2 in there (not extinqhuisher, but a large body of CO2 in a 4 inch PVC like a potato gun. And of course an audible alarm. No substitute for watching the unit of course.

[Graham Facer]

I know I'm 6 years late coming to this thread, and I briefly scanned the past posts, but I'm wondering if the easiest solution would be to have a thin cable that is in the gantry that when it burns, it breaks the connection. No guarantee that it would happen in the right place, but most fires that I've seen start around the head which is attached to the gantry. Then just break the door panel switch connection to turn off the lasing and dump a bunch of CO2 in there (not extinqhuisher, but a large body of CO2 in a 4 inch PVC like a potato gun. And of course an audible alarm. No substitute for watching the unit of course.

Well I abandoned this project. I've found recently my almost fires have been junk on the knife blade edges that catches fire with prolonged exposure to a cutting flare up. Then it drips on to waste underneath.

So yeah decided supervision is the main part.

Graham