Fire/smoke alarms - advice please



The point is it only costs 3 to try an ionisation type, and it may prove ok. If it does, you can then get one that wires to the house.
NT
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On 16/10/2011 08:50, NT wrote:

Yes - good point. Of course, I'll never know if it really works unless the the kiln controller fails again and the shed burns down <g>... ..but it would prove that the cheapie detector isn't tripped by solder smoke / flux fumes etc!
Thanks Adrian
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Cheap ionisation detectors are very sensitive. All you need establish is that it doesnt false trigger. If it does, try an optical one for less sensitivity.
NT
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On 16/10/2011 20:01, NT wrote:

OK - thanks! Adrian
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On Sat, 15 Oct 2011 18:00:03 +0100, Adrian Brentnall

Well if you want the high tech solution get a computer and webcam, remove the webcam IR filter and run the free ISpy software which includes a flame sense motion detection option :-)
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Doesn't work though if your ignition source is an IR laser. I'm trying to emulate the Violet Fire system from Concorde, and I'm looking in the UV.
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On 15/10/2011 23:09, Peter Parry wrote:

May be a bit too 'hi tech' - more stuff to go wrong at the critical moment.....? Though I do have a spare webcam.....
Thinking about it - the most likely failure mode (if the kiln locked 'on') would be for the elements to burn out. I 'think' the fairly massive firebrick chamber would likely contain the heat, without getting hot enough to set fire to anything around it....
The Kiln Manual says
------------quote---- ERROR MESSAGES The following errors messages may appear in the display of your controller. Err 1 Error 1 occurs during a firing segment programmed to increase the temperature. When the kiln is maintaining the � requires that the kiln maintain a minimum rise of 12°F (4.8°C) per hour. This usually indicates that the elements or the relay have failed. The kiln will shut off. Err F Error F occurs during a firing segment programmed to decrease the temperature. When the kiln is maintaining the � requires that the kiln maintain a minimum fall of 12°F (4.8°C) per hour. This usually indicates that a relay has failed and needs to be replaced. The kiln will shut off. Err D Error D occurs during a firing segment programmed to increase the temperature. If the kiln temperature is 100°F (38°C) or greater above the set point for 15 seconds then the controller registers an error d situation. This usually indicates that a relay has failed and needs to be replaced. The kiln will shut off. FAIL This indicates that the thermocouple has failed and needs to be replaced. The kiln will shut off. tc-- This indicates that the thermocouple has been installed backwards. The thermocouple needs to be removed and reinstalled into the thermocouple block with the red wire inserted in the hole stamped “-”.
-------unquote---
So I'd imagine that Err1 might/should have caught this particular fault. Something was badly wrong with the temperature sensing. The thermocouple is good because I've swapped that to the other kiln, and it's working fine. Wiring to the thermocouple checks out OK. At process temperature (c. 760c) the temperature display was indicating 46c, at ambient it was showing 23c - so something wasn't right. The kiln was firing continually, waiting for the indicated temperature to reach 760c....
The fault's now changed, and the controller is showing 'Fail' - indicating that it can't 'see' the thermocouple.
It would be useful to have the extra capacity of the new (faulty) kiln, so today I shall swap the controllers between the kilns and see if that makes the fault one work. If it does then I shall return the duff controller for replacement under guarantee, and ask the manufacturer a few pointed questions about kiln safety systems!
Adrian
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On Sun, 16 Oct 2011 07:52:34 +0100, Adrian Brentnall

The safety system may well be the simplest and most reliable of all, the kiln will withstand the elements at full power indefinitely or until the heater element itself or some other component overheats in a predicted way and fails.
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For a Skutt Firebox it's an evens bet between element failure, or the element overheating the bricks and cracking them. They're an unusually powerful element for the size of kiln.
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Peter Parry wrote:

We had a dry powder or aff ( memory fade) extinguisher in the forwarder with a plastic hose running around the engine compartment. The idea was that the hose ruptured at the hottest point and the chemical emptied through the hole.
AJH
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Arduino, and learn to program it
(Or wait for me to finish mine)
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On 15/10/2011 19:54, Andy Dingley wrote:

<g> I've got a Pic-Axe development board somewhere about the place - seems there's a stand-alone chip (or maybe two) that translates from thermocouple-to-analog.....
Having got that far - there's a great temptation to turn it all into a controller <g>
Adrian
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Dead easy for kilns, as you don't care about cold junction compensation.
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On 15/10/2011 23:32, Andy Dingley wrote:

I think the chips I was seeing on Google (Max6675) do all of that for you....?
Adrian
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On Sat, 15 Oct 2011 15:22:38 +0100, Adrian Brentnall wrote:

Does seem a bit odd that something with a micro-controller doesn't have a watch dog.

I think a fixed temperature alarm, mounted where it isn't going to get a blast of hot air when you open one of the kilns... They trigger when the "ambient temperature" gets into the high 50's C. I don't know how long the temperature has to be above the trigger point before they trigger. This sort of alarm is the type that building regs now require in some kitchens. An oven is a low temperature kiln so one assumes that these fixed temp alarms can cope with the blast of hot air from an oven at 250C being opened. OK 800C is considerably higher but do you open them when that hot?
--
Cheers
Dave.




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On 15/10/2011 22:03, Dave Liquorice wrote:

There may be some kind of inbuilt safety-circuit - there's something on the controller board that lives-up the 'safety relay' - but I don't know what the logic is behind it.. Not a watchdog in the 'uP's out to lunch - better stop everything' sense...

Sounds like a plan. It gets hot in there in the summer - but 'hot' as in 35c. Sometime open the kiln when it's live, but not for long, and only to have a quick peek at how it's going...
I guess it depends on what I'm trying to achieve.... whether I want to know that everything's operating correctly, or that the shed is in danger of catching fire imminently.... I think I'd prefer the first option, with a built-in 'power-kill' relay, if things seemed to be going out of spec.
Having said that, I shall install a new controller board and it'll never fail again, ever ...... <g>
Adrian
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On Sat, 15 Oct 2011 15:22:38 +0100, Adrian Brentnall

While I appreciate the desire for a fire alarm system, do you actually need one? The operating temperature of 700C, and by implication the maximum temperature attainable, isn't that high by pottery kiln standards (is yours an enamel kiln?). I have three pottery kilns, two electric ones in a spare room now used as a pottery workshop, and a gas-fired kiln in a wooden shed in the garden. All are capable of 1300C although seldom operated above 1260C. They are made of refractory brick and ceramic fibre, in a steel case. There is nothing there to burn.
The gas kiln is manually controlled, and is checked/regulated every thirty minutes over about an eight hour period. The shed is fully lined with fireproof fibre-board (similar to the old asbestos cement sheeting, but with another type of fibre reinforcement): walls, floor and ceiling. A doubly insulated flue passes up through the roof. The distance between the shed walls and the kiln is typically two feet all round. Despite the outside of the kiln being much too hot to touch when going full blast, the fibre-board shed lining adjacent to it only gets warm.
The two electric kilns in the bedroom-that-was are rated at 7kW and 3kW respectively. They are located in one corner of the room. The walls in that corner are lined with plasterboard on battens, up to a height of about four feet, such that there is a 2 inch gap between the board and the wall. The board is also covered with aluminium foil (the widest Baco cooking foil that I could get, stuck on with evostick. Be wary of modern 'aluminised' plasterboard, the stuff with a moisture barrier; it's covered with aluminised plastic film which is probably not very heat-resistant). To protect the wooden floor, the kilns stand on a sheet of the fibre-board resting on a wooden pallet to provide an air gap. The kilns are probably no more that 12 inches away from the aluminium-coated plasterboard at the nearest point. Firing the kilns is done overnight (Economy-7), using an automatic programmable controller. As with the gas kiln, even though the outsides of the electric kilns get far too hot to touch, the aluminised plasterboard only gets warm.
The only precaution I take when firing any of the kilns is to make sure there are no combustible materials close to the kilns before starting. In your case, I would make sure that the shed walls in the immediate vicinity of your kiln, and the floor it stands on, are protected from radiant heat in much the same way as I have done mine, and I see no problems. After all, the outside of the kiln doesn't get _that_ hot, and the amount of heat it radiates isn't going to do any harm if the shed walls and floor are reasonably well protected.
If you're thinking of a thermal fuse, then one idea might be a thick piece of ordinary 'silver' wire (92.5%Ag, 7.5% Cu), m.p. 920C, in a thermocouple-type ceramic holder, wired in series with the elements. Kiln overheats; silver wire melts; kiln cools. Not too difficult to make up. A friendly jeweller should have that sort of wire.
--

Chris

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