Moron. The hot plate gets a lot hotter without a pot or pan of food to dissipate the heat. If it only went to 212 F it wouldn't get the food hot for hours, or days. All it would do is warm it up enough to let it spoil faster.
-- You can\'t have a sense of humor, if you have no sense!
More important, what temperature destroys the sensor?
-- You can\'t have a sense of humor, if you have no sense!
Fuckhead. I said "doesn't get much above".
Now piss off, idiot. *plonk*
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spamme0 wrote in news:h62gi6$e5j$ snipped-for-privacy@news.eternal-september.org:
That would make IR thermometers USELESS for the average person,who is unlikely to know the emissivity of what various targets they are measuring.
-- Jim Yanik jyanik at kua.net
Besides that, if the surface is a hot plate, it is going to have a high emissivity, and all the suggestions were about high emissivity sources.
I have one of those IR thermometers. Marked on its body is a statement of assuming emissivity is .95. Printed in the instructions is a statement that in general, nonmetallic surfaces tend to have emissivity close to .95, and that metals tend to significantly lower emissivity.
To add to the list of materials that these thermometers will not read accurately: Thin films of at least some plastics, such as dry cleaner bags and thinner food storage bags. The wavelengths used by these thermometers have some ability to pass through such plastic films, especially if the plastic material is polyethylene.
- Don Klipstein ( snipped-for-privacy@misty.com)
On Fri, 14 Aug 2009 02:46:19 -0700, Michael A. Terrell wrote (in article ):
These are *non-contact* sensors. How can pointing it at an IR source from a distance damage it?
It is going to depend on the sensor.
Eyeballs are non-contact sensors, try staring at the sun.
-- Jim Pennino Remove .spam.sux to reply.
I'm a little confused here - would lower emissivity actually lower the measured temp, or just take longer to get an accurate reading?
Emissivity is the _rate_ at which the object releases heat, right?
Thanks, Rich
Your eyeballs have lenses, which focus the light/radiation onto a very small spot on the retina - haven't you ever lit a piece of paper (or ants!) on fire using a magnifying glass?
Do IR pyrometers have that kind of focus?
Thanks, Rich
Like I said, it depends.
Most instruments have a lens system.
-- Jim Pennino Remove .spam.sux to reply.
Think about it. Its easier than you think.
-- You can\'t have a sense of humor, if you have no sense!
On Wed, 12 Aug 2009 17:11:02 -0700, life imitates life wrote (in article ):
You win the booby prize ("You may now choose your booby."). The display says "OL" when the stovetop coil exceeds 500f.
So the limitation is in firmware. Damn!
Thanks for all who contributed.
The resistor bolometer has limits to what IR it can be exposed to.
Did you even read the instructions?
There IS "contact". It is just that some of you are too stupid to get the fact that light also has the potential to move matter.
It is a hard to miss fact for some of us. For some of you, however, setting your alarm clock poses difficulties.
Yes, LIGHT IMPINGES on the sensor, idiot.
Emissivity is a measure of how well a surface radiates the heat it carries. That is why a polished surface usually has a much lower emissivity than its matte finished surface of the same media.
There are more angles of incidence within the medium to release IR from on the matte (rough) surface.
The smooth surface reflects the IR back down into the medium.
There are no all metal skillet handles that are not polished.
So, the lower the emissivity, the less an instrument can "see" radiating, despite the actual temperature of the medium. So we have developed a scale, and can adjust the gain of the instrument to compensate for mediums with surfaces that are not radiating as well as others at the same temp.
A round post looks like a straight fuzzy line to the instrument because there is only a small line that is perpendicular to the instrument's field of view where a lot of radiation is coming back toward the instrument.
Pure optics. Take the field of view. Say you are looking at a 6 inch spot.
That spot is focused down to what is typically a 2 mm resistor bolometer sense element. It usually sits a couple mm down in the "transistor can" under a germanium window or other such IR window media.
That 2mm spot has the entire "image" cast upon it. It is exactly like when you put a pinhole in a box and look at the sun on the back wall of the box. That image of the sun is a perfect casting of the actual image.
Same with IR. Instead of a CCD of whatever size like with video, the resistor bolometer is only 2 mm square.
Just do not point your IR meter toward the sun. It will fry the sense element.
Actually, the best instruments go straight from the primary mirror to the sense element.
IR video has a lens system, and cheap IR has a fresnel , but most radiate directly onto the sensor.
Most are set up like a reflector telescope.
Lens systems cut energy, raising the noise floor.
Better not tell anyone here. It will ruin their claims that I am never correct. Won't be the first time.
If you want to know who to filter, just filter all of the idiots that mouth off at this post.
a
I noticed you snipped all the links showing IR pyrometers with lenses.
-- Jim Pennino Remove .spam.sux to reply.
a
I notice that you snipped where I mentioned that lenses ATTENUATE the signal!
I did make an entire line of high temp devices that used a Pyrex lens. They get placed in a cooled jacket, and get put right on a glass gob line looking at blazing hot molten glass gobs.
A single parabolic mirror yields the absolute best image on the sense element. The ultimate mirror is gold. All first surface, of course.
Usually, a thin film is over the tube as a dust shield.
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