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Flame detection

Y

YD

Jan 1, 1970
0
That is actually a thermocouple. The 'tube' is miniature MICS cable.
DON'T even TRY to get an output from it. That WOULD be dangerous, like
BANG!, or wake up dead.

IIRC the gas fridge I used some 30 years ago it's actually a thermal
system. Bulb -> capillary -> diaphragm operated needle valve. System
filled with some suitable fluid. As the bulb heats up the fluid
expands, pushes on the diaphragm, diaphragm opens the valve. A push
button to keep the valve open until bulb heats up. Sometimes the bulb
may be omitted and the end of the capillary wound a turn or two around
the flame.

- YD.
 
Y

YD

Jan 1, 1970
0
No, they used to have yellow flames, those running from town gas. I
didn't take into account that this fridge runs from bottled gas; these
fridges have a BLUE flame, not a COLOURLESS one which some posters
thought. The visible light is easily detected with a phototransistor.

Those blue flames emit quite an amount of UV (hydrogen line). Don't
know if there are any cheap and easy-to-get sensors for that. I have a
sensor from the sixties I grabbed off a furnace controller. Gas-filled
bulb with two electrodes, runs at 150V, operates like a geiger tube.
Doesn't sense sunlight but makes quite a storm in the speaker if you
flick your bic close to it.

- YD.
 
D

Don Foreman

Jan 1, 1970
0
Electronics isn't really my field so this is an appeal for help for
something which is probably embarrassingly easy if you know what you are
doing.

I want to detect the presence or absence of a small gas flame (caravan
fridge) and light an led if the flame is there and turn it off if the
flame isn't there. A reasonably quick response time is needed.

Presumably a thermocouple (I think I have read the term "K type"
somewhere), a transistor an led and a resistor or two will be involved!
It would be nice if I could run it off 12v DC and it would be nice if
the current drain could be zero or at least tiny if the led is off.

Any thoughts welcome.

TIA

Peter

I used to work for Honeywell. The three methods usually employed for
flame proving are: thermocouple, flame rectification and UV
detection. Gas burners with no electric power available (e.g. water
heaters) use thermocouples to enable the main gas valve. Small
burners with electric spark ignition usually use flame rectification.
Larger industrial burners use UV detection.

Your remote "don't modify the burner" app suggests either a simple
fiber optic solution making the flame directly visible, or a UV
detector. Another poster suggested a suitable sensor from Hamamatsu.
If you can locate and obtain one of these, if you'd like to contact
me by email I'd be willing to help you design a circuit to use it.
 
D

Don Foreman

Jan 1, 1970
0
I know the problem, I toured much of Europe 30 years ago with a hired
campervan. The bloody fridge had the "flame viewing" window about 1
inch above the floor with a viewing angle of perhaps 15 degrees. The
only way to view it was with a mirror and the lights out.

There's a number of systems in place, I had a heatpump with gas
booster that used a TC sensor. It never failed in the 5 years I was
living there. Or they use a gas-filled capillary tube that shuts off
the gas with no flame.

More modern systems use an optical system, as other have suggested,
and it's possibly the easiest to home-build. The best detectors are
possibly the Hamamtsu ones. See:

http://jp.hamamatsu.com/products/node.do?dir=/division/etd/pd001/pd006&lang=en&ext=html

The datasheet may be seen at
http://www.hpk.co.jp/eng/products/ETD/pdf/R2868_TPT_1008E01.pdf

This sensor will need a low-current source of about 325 VDC. No
problem, a simple flyback converter from 12VDC would suffice.
 
P

Paul Hovnanian P.E.

Jan 1, 1970
0
Glen said:
From the instruction label inside my Dometic gas fridge:

IMPORTANT ... 2. Inspect the flame for colour, it should be blue
throughout - no yellow or other discoloration. ...

A yellow smokey flame is a very bad idea because the soot will foul
the heat exchanger. I expect you have seen a fridge with the burner
air holes blocked, or a fridge designed by someone completely
clueless; I have seen quite a few gas fridges and none were designed
to operate with a yellow flame.

If you don't think the OP should mess with the burner, how about a
thermistor an inch or so above the top of the stack, where it cannot
possibly interfere with flue gas flow? Or possibly a temperature
switch, if the flue gas temperature is always well above maximum
expected ambient?

My Dometic has a light pipe with a prism on the end for flame
observation, which works well and can be seen while standing up
although the door must be opened as it is located inside next to the
thermostat. The far end of the light pipe, which is basically a piece
of 1/4" or so acrylic rod, is well back from the flame so as not to
interfere with it.

The requirement to inspect the flame color for proper operation really
tips the balance in favor of a fiber optic approach. Although many of
the other systems will work to indicate the presence if a flame, in the
end, one still must peer through a poorly located inspection window.
 
R

Ross Herbert

Jan 1, 1970
0
Those blue flames emit quite an amount of UV (hydrogen line). Don't
know if there are any cheap and easy-to-get sensors for that. I have a
sensor from the sixties I grabbed off a furnace controller. Gas-filled
bulb with two electrodes, runs at 150V, operates like a geiger tube.
Doesn't sense sunlight but makes quite a storm in the speaker if you
flick your bic close to it.

- YD.


I am in agreement with Glen Walpert on the flame colour, or rather,
lack of colour. Since we are talking refrigeration for caravans, we
are talking bottled LPG, not town gas, and the correct flame colour
for LPG is blue with no yellow tip. I believe there is a high degree
of UV in this flame and it is possible that one of the InfraTec
sensors with a UV filter might do the job. Somehow, I think they might
be expensive.

http://www.infratec.de/en/sensorik/mainmenu/products.html
http://www.infratec.de/fileadmin/downloads/pdf/ir_filter_sensorik/IR_filters_and_windows.pdf
 
J

John Woodgate

Jan 1, 1970
0
dated Mon said:
I believe there is a high degree of UV in this flame and it is possible
that one of the InfraTec sensors with a UV filter might do the job.

But if you can SEE it, it must emit VISIBLE light. Why bother with UV?

For extra light, put a tiny piece of chalk in the flame. Limelight!
 
K

Ken Smith

Jan 1, 1970
0
Ross Herbert said:
for LPG is blue with no yellow tip. I believe there is a high degree
of UV in this flame and it is possible that one of the InfraTec
sensors with a UV filter might do the job. Somehow, I think they might
be expensive.

If it is U enough V, perhaps just looking for a leakage current from a bit
of zinc plated metal would be enough. Sunlight will discharge an
electrometer with a zinc plate attached.
 
K

Ken Smith

Jan 1, 1970
0
But if you can SEE it, it must emit VISIBLE light. Why bother with UV?

For extra light, put a tiny piece of chalk in the flame. Limelight!

If you are inserting something in the flame, insert two electrodes. Then
you can detect the flame and listen to the radio.
 
G

Glen Walpert

Jan 1, 1970
0
But if you can SEE it, it must emit VISIBLE light. Why bother with UV?

The problem with visible light is EMI from the sun leaking in through
the air inlet vent or the flue gas exit vent or cracks between fridge
and housing. This is normally much greater than the amount of light
emitted by the flame.

UV is the standard method of detecting flame presence in small oil
burners here, and the UV flame failure sensors are available fairly
cheaply but they are designed for larger flames (more UV). The tiny
flame of a fridge might not put out more UV than leaks in from
sunlight either.
For extra light, put a tiny piece of chalk in the flame. Limelight!

Good one. This is why I frequently enjoy your posts - your lame humor
is unsurpassed by any other regular poster. (DNA is in another humor
category entirely, not a direct competitor.)

I think omeone else suggested a temp switch attached to the flue pipe,
before I suggested one above it. Hard to beat a temp switch for
simplicity and no power use when open, if one can be found that closes
on temp rise a bit above max expected ambient and also opens upon
cooling to maximim ambient (small dead-band). Attaching to the
hottest part of the flue pipe should be trivial with a dab of epoxy
and/or or a bit of bailing wire.

An effective visible + IR sensor can be made with a pair of identical
thermistors glued to small bits of black metal sheet separated by an
insulator. A comparator can indicate when the one facing the flame
(from a reasonable distance so as not to block air flow) is hotter
than the one facing away from it. This will be largely insensitive to
solar EMI and variations in ambient temp.

Or just attach one of the thermistors to the stack and put the other
nearby. 2 thermistors, 2 bridge completion resistors (slightly
different for some offset), one cheap op-amp as comparator, one LED
with series resistor - almost as simple as the switch, but sucks a bit
of power when off. I think someone else suggested this one also, but
I am not paying much attention to this thread and don't recall who.

Of course none of these eliminate the need to regularly inspect the
appearance of the flame per the manufacturers instructions, especially
when re-lit after being off. It only takes one dead bug, bug nest or
dust ball to screw up combustion in these tiny burners, making the
flame turn yellow and sooty :).
 
T

Tim Williams

Jan 1, 1970
0
Ken Smith said:
If it is U enough V, perhaps just looking for a leakage current from a bit
of zinc plated metal would be enough. Sunlight will discharge an
electrometer with a zinc plate attached.

Charged which way? Quite a feat if the UV is kicking out positrons. ;-)

Checking a table I see zinc has a work function that isn't particularly
impressive;
http://hyperphysics.phy-astr.gsu.edu/hbase/tables/photoelec.html#c1
magnesium would be more suitable, at least as bare metal. However, zinc
oxide (present on the surface of zinc metal) is a known semiconductor (band
gap 3.2eV, which would respond to UV and blue).

Tim
 
K

Ken Smith

Jan 1, 1970
0
Charged which way? Quite a feat if the UV is kicking out positrons. ;-)

Yes, it would be markedly less sensitive if charged positive.
Checking a table I see zinc has a work function that isn't particularly
impressive;
http://hyperphysics.phy-astr.gsu.edu/hbase/tables/photoelec.html#c1
magnesium would be more suitable, at least as bare metal.

I don't think you can keep magnesium bare. I think it tries to turn into
Brucite when left on its own.
However, zinc
oxide (present on the surface of zinc metal) is a known semiconductor (band
gap 3.2eV, which would respond to UV and blue).

Basicly it applies its own sunblock. :>
 
R

Ross Herbert

Jan 1, 1970
0
But if you can SEE it, it must emit VISIBLE light. Why bother with UV?

Because LPG flame, according to the physicists, is in the UV range. It
may be visible under certain circumstances or if other impurities
exist. If it is pure LPG flame then I wouldn't want to gamble on it
being visible under all circumstances.
http://www.sbf1.sbfisica.org.br/pro... of Atoms/892.pdf#search="lpg flame spectrum"

LPG flame spectra was measured between 415 - 440nM which puts it in
the UV range so it is either totally or near invisible. In the gas
detection and flame detection industry (eg. LPG/LNG storage) General
Monitors FL3101 is a UV only flame detector but it is recommended for
LNG/LPG flame detection according to the spec sheet
http://www.generalmonitors.com/downloads/literature/flame/FL3100_FL3101_DATA.PDF
 
J

John Woodgate

Jan 1, 1970
0
dated Tue said:
Because LPG flame, according to the physicists, is in the UV range. It
may be visible under certain circumstances or if other impurities
exist. If it is pure LPG flame then I wouldn't want to gamble on it
being visible under all circumstances.

So the little window provided by the fridge makers so you can see the
flame is not only inconveniently-sited but fundamentally useless anyway.

I rather doubt it.
 
R

Ross Herbert

Jan 1, 1970
0
So the little window provided by the fridge makers so you can see the
flame is not only inconveniently-sited but fundamentally useless anyway.

I rather doubt it.

Yes, I agree with that logic. They do put the window there for a
reason. The major reason is that it is cheap, and provided that
everything is perfect, a healthy individual with 20/20 eyesight should
be able to see if there is a flame or not. A more sophisticated
electronic method would add considerable cost to the refrigerator and
it would seem that all manufacturers consider this is unwarranted.

I agree that even a blue flame is visible - provided that you can get
your head into the right position - something which often is not
possible to achieve in a caravan - and your eyesight is good enough to
allow recognition that it may be alight.

For domestic use, such as in refrigerators, LPG is Propane which
should burn with a blue flame, as shown in the blurb for this
jewellers LPG gas torch http://www.apecs.com.au/guild/lpgas.htm
If incomplete combustion takes place, or soot is present, then there
will be a yellow colour to the flame and it will be highly visible. It
may be that manufacturers of gas refrigerators have worked out that
after settling in the flame will start to become "sooty" and therefore
visible.

Bivar, and probably many others, make flexible lightpipes which might
do the job if the OP is feeling in an experimental mood.
http://www.bivar.com/pdf/flexible.pdf
 
J

John Woodgate

Jan 1, 1970
0
dated Tue said:
It may be that manufacturers of gas refrigerators have worked out that
after settling in the flame will start to become "sooty" and therefore
visible.

My understanding is that only a small amount of heat is required and a
'with air' (Bunsen) flame is too hot as well. So the flame is more like
a candle flame. Certainly, the flame in the fridge in my friend's
caravan was quite visible if you didn't try in bright daylight with
nothing to create a shadow,
 
S

Smaug Ichorfang

Jan 1, 1970
0
I don't remember where I saw it, possibly in a piece of equipment burning
hydrogen (invisible flame). A simple loop of nichome (or platinum or
niconel, or whatever) in the flame. Heat of the flame causes the wire to
glow brightly. No glow, no flame. Very simple, cheap, easy to implement.
 
R

Rich Grise

Jan 1, 1970
0
My understanding is that only a small amount of heat is required and a
'with air' (Bunsen) flame is too hot as well. So the flame is more like
a candle flame. Certainly, the flame in the fridge in my friend's
caravan was quite visible if you didn't try in bright daylight with
nothing to create a shadow,

But a propane flame will have _some_ UV, it's just not _all_ UV,
which a hydrogen flame almost is. a hydrogen flame is almost impossible
to see, which is why they use the UV sensors. The UV from propane
is just a lucky co-winky-dink. :)

Cheers!
Rich
 
D

Don Klipstein

Jan 1, 1970
0
Because LPG flame, according to the physicists, is in the UV range. It
may be visible under certain circumstances or if other impurities
exist. If it is pure LPG flame then I wouldn't want to gamble on it
being visible under all circumstances.
http://www.sbf1.sbfisica.org.br/procs/2006/pdfs optics/
Spectroscopy%20and%20Confinement%20of%20Atoms/
892.pdf#search=%22lpg%20flame%20spectrum%22

Not Available
LPG flame spectra was measured between 415 - 440nM which puts it in
the UV range so it is either totally or near invisible.

415-440 nm is visible - from middle or bluish violet to violetish blue.

Meanwhile, I have tried making fluorescent objects fluoresce from a
torch using propane (which LPG largely is), with a blue flame with various
fuel/air ratios ranging from carburizing flame to oxidizing flame. The
results appeared to show at least as much visible light as UV, although
there was some significant UV.
In the gas detection and flame detection industry (eg. LPG/LNG storage)
General Monitors FL3101 is a UV only flame detector but it is recommended
for LNG/LPG flame detection according to the spec sheet
http://www.generalmonitors.com/downloads/literature/flame/
FL3100_FL3101_DATA.PDF

I took a look:

The UV sensitivity is for wavelengths 185-260 nm.

I don't think flames could make much of those wavelengths because of
temperatures only around 2000 Kelvin, but apparently they have to make
something there or else nobody would make a detector on that basis. My
guess is that a detector of these wavelengths would be good for detecting
flames because most other light sources don't produce/deliver such
wavelengths.
Although I would suspect such a detector to detect bigtime electric
arcs, germicidal lamps, and broken HID lamps.

- Don Klipstein ([email protected])
 
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