How can these vary as far as "angle of detection"? Can they be very directional and some parts be very broad (180 degrees even?) or does it all depend on the type of lens you might use?
I want to build a simple wireless heat detector for a stove and may not be able to point it "directly" at the stove. (I can get close though).
Thanks.
and some parts be very broad (180 degrees even?) or does it all depend on the type of lens you might use?
to point it "directly" at the stove. (I can get close though).
You will need to look at the datasheets for each individual part. Their angle of view can vary wildly depending on the materials and construction. Any 'optics' such as lense or sheilds will also have an effect. Remember, the wider the field of view, the less 'signal' from our stove you are going to received, so you want it wide enough to get your target, but not any wider!
Wonder if I can use one of these cheap PIR motion modules and adjust the sensitivity so it's NOT very sensitive?
I'm trying to detect heat from a wood stove about 3 feet away and using something that senses ambient room air temperature won't cut it -- need something that reacts the minute the stove is burning well -- thought maybe IR could do it?
And no, don't want to mount a thermal switch ON the stove.
sensitivity so it's NOT very sensitive?
something that senses ambient room air temperature won't cut it -- need something that reacts the minute the stove is burning well -- thought maybe IR could do it?
PIRs detect motion, not static heat.
Why not put a thermocouple or some such on the back of the stove, or on the flue? Or *inside* same?
Omega probably has something that will work, but it may not be cheap.
A thermocouple, or a transistor, in a small reflector could be made to work.
-- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
First, an IR sensor isn't going to react the minute the stove is burning well -- it's going to react the instant that the outside of the stove heats up, which is going to be considerably later than a minute after the fire inside the stove starts going strong.
Second, the temperature that an IR senses is totally dependent on the amount of "stove" that it sees. If the stove takes up 1/10 of the total included angle of what the sensor "sees", then you're going to measure an irradiation that's 10% stove and 90% room (and dogs, and people, and whatever else). Moreover, if the stove is not perfectly black (Google on "emissivity") then your signal from the stove will be further degraded because it'll reflect IR from the room to the exact extent that it's not emitting IR on its own. Most stoves _are_ black for just reason, because high emissivity means better heat radiation, but if you get an artsy ceramic stove that's all shiny pink then it will have low emissivity.
So to really carry out this task well you _do_ have to aim the sensor at the stove, and furthermore you need the sensor field of view to be small enough to include the stove and nothing but the stove. And you need an occluded view of the stove, and the stove's surface color will play a part in your measurement.
All in all, a thermal switch inside the stove is an easier answer in many, many ways, no matter how much it may fail to float your boat.
(I don't know if it's still kosher with the fire codes any more, but if single-wall stove pipes are still allowed you may get a quicker response by aiming at a single-wall pipe right as it comes out of the stove -- the flue temperature will be very reflective of the flame temperature)
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and some parts be very broad (180 degrees even?) or does it all depend on the type of lens you might use?
to point it "directly" at the stove. (I can get close though).
I'll assume a wood burning stove[1]: I built my own. I guess you could make it wireless, but you'll need some decent optics to insure that you're targeting the stove, not the room, which means indirect radiation isn't going to work. I presume that you're trying to keep the electronics from being overheated by the wood burning stove. You might try a length of fiber optic cable to couple the IR. These are overkill but might offer some hints:
[1] Note the magnetic bi-metallic temperature gauge on the flue pipe. That also acts as an alarm. When the stove temperature hits the Curie temperature of the magnet (above 500C), the magnet looses its grip on the stove pipe, and falls off onto the floor. I can usually hear it drop, thus reminding me to get off the computer and adjust the air intake before I burn the house down.-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
sensitivity so it's NOT very sensitive?
omething that senses ambient room air temperature won't cut it -- need some thing that reacts the minute the stove is burning well -- thought maybe IR could do it?
something like this?
comes in different versions with different field of view, from the comments it looks like it is the 10degree version
-Lasse
I saw that on sparkfun just this morning. Actually, don't need it to react "immediately" after a fire just when the stove starts radiating good heat from the surface (usually 1/2hr to an hour. And when it cools down, opens the circuit.
Want it wireless because I'm a neatnic -- don't want a wire dangling from my stove and have a nice 120v outlet on the floor right beneath it (hence, bud box and a sensor right there on the outlet).
It would also be hidden pretty much from movement of people in the room.
they detect rapid temperature changes. probably unsuitable.
maybe a black thermistor and a headlight reflector to focus the heat?
hoe long does it take the stove ti get hot after it's burning well enough?
can you put a sensor on (or in) the flue?
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Harbor freight, $20 infra red thermometer. laser pointed.
Fresnel lens, quite accurate. Best 'thermometer' value in my entire collection. I have more accurate contact type transducers, but this one does the job, and I carried it in my pocket for a coupe years too. Still works fine.
maybe I'll get one and take the guts out. never owned one of those and wond er how "directional" an IR sensor can be? I mean, I understand the laser be ing able to point but an IR detector? I suppose you just make sure there ar e no other IR sources close to it (how close?)
Sure, if you point it toward a ceiling vent with nothing nearby but?
how "directional" an IR sensor can be? I mean, I understand the laser being able to point but an IR detector? I suppose you just make sure there are no other IR sources close to it (how close?)
You can put a heat sensor at the focus of a parabolic or spherical reflector and get a very directional thermal IR detector. Copper is an ideal reflector, but a small stainless bowl would work well. A good sensor is a TO92 transistor: run a little current through the BE junction and measure the voltage drop against a similar transistor that's not exposed to the IR. The circuit could be very simple, just a comparator if all you want is on/off.
When I was a kid, I put a transistor at the focus of a flashlight reflector and sensed the heat of my hand from several feet away.
The ultimate system would use a germanium lens (envision kilobucks) and some exotic detector.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
Well yes, but he probably meant the sensor in the PIR motion detector. They use a thin film type sensor. The sensor is also microphonic.
how "directional" an IR sensor can be? I mean, I understand the laser being able to point but an IR detector? I suppose you just make sure there are no other IR sources close to it (how close?)
There are a zillion cheap wired or wireless motion-activated devices. Pick one that has the output you want. Remove the fresnel lens. Stick it behind a small computer fan to act as a shutter. May have to cut some of the blades off. Run the fan as slow as practical. Stick a pipe on the front end to restrict the field of view. Point it at the stove. Depending on the filtering in the device, the fan speed may make a simple sensitivity adjustment. Or maybe adjust the size of the hole in the end of the pipe.
and
what a great idea -- that's what I'll do -- fun project to play with, will have to come up with a cool reflector. small metal funnel maybe?
and
to come up with a cool reflector. small metal funnel maybe?
Flashlight reflector would be better... a funnel usually has straight sides. ...Jim Thompson
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I love to cook with wine. Sometimes I even put it in the food.
and
to come up with a cool reflector. small metal funnel maybe?
I used a metal flashlight reflector, which has the right curved shape. I don't think a funnel would focus as well, but may be good enough. Or, as I suggested, a small spherical metal bowl. There must be some other hemispherical metal thing at Home Depot that accidentally works. It should be shiny bare metal inside, no paint or plastic, to be a good reflector at thermal wavelengths. Or line a plastic thing, half of a small ball maybe, with aluminum or copper foil. We're not talking precision optics here. You could use visible light to tweak the focussing.
I'm thinking two TO92 transistors used as diodes, with a small current, 100 uA maybe, through each. One sees the focussed IR and the other just nearby ambient temperature. The voltage difference should change some millivolts, maybe 10s of millivolts, when the reflector points at the hot stove. It would be fun to try. A DVM on its "diode" range might be all you need to experiment with one transistor in a reflector, get an idea how feasible it is.
Hmmm, the transistors could be a diffamp. Why waste that gain?
A mechanical IR chopper would be great, but that involves moving parts.
Fun! Let me know if any of that works.
-- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
how "directional" an IR sensor can be? I mean, I understand the laser being able to point but an IR detector? I suppose you just make sure there are no other IR sources close to it (how close?)
and
a aand
The cheap way:
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wonder how "directional" an IR sensor can be? I mean, I understand the laser being able to point but an IR detector? I suppose you just make sure there are no other IR sources close to it (how close?)
and
a aand
Yeah, that's a nice reflector.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
just bought a couple. been getting a lot of stuff from china and that's another post I've been meaning to do.
how in the world they provide some of those complete modules at such a cost is beyond me. (and using parts from TI, etc). many of these I've computed parts cost alone (even in qty) -- and it's impossible there would be a profit. ?
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