Just out of interest what is the range of these things, I have a cheapo £7 I bought on ebay which I have used around the house and it appears pretty accurate. The current temp for here is 0C so I get within +- half % I then point it up to the sky and I get -40C , that must be a good few thousand feet up. Visually on buildings I can see it around 400 feet away but am I getting a fix on heavens door.
Well if you can find something very infra red absorbent that will also show a very cold temp assuming its not radiating the heat back your way. Are you particularly interested in measuring the temp of space then? Brian
In article , ss writes
The laser pointer on these devices give a bit of a false impression of the measurement field of view. My one here claims a 12:1 field of view meaning at 12m it is measuring a field of about 1m across. At 400ft you will be measuring 33ft across.
Pointing upward you will likely be measuring the temperature of airborne moisture or other contaminants but on a clear night in the countryside you may be seeing higher. If you really are measuring the heavens then I expect you will be hitting the lower measurement temperature of the instrument which will probably be in the -30 - 50degC range that you experienced.
Remember these things work by detecting the long wave IR being emitted by a body and as you get lower in temperature, the LW IR emitted by the inside of the body of the instrument will hopelessly distort the results. A bit like having a camera with a torch turned on the sensor. If you want better results then you will need to cool the sensor and spend lots of money.
I would hope you have turned the laser off before waving it around. The plod will be very unhappy if they see you trying to dazzle planes, etc. Unhappy enough for you to get your doors kicked in and for you to be carted off before any questions are asked.
No, its just indicating the lowest temperature it can manage. It ought to be *much* lower!
The laser has nothing to do with the temperature sensing capability - its just showing you where you are pointing it. The size of the reference patch its looking at will grow with distance. Mine sees a patch of about 1" diameter at a distance of 8" from target. It then rises by 1" diameter for every additional 8" separation from target.
It's showing the cloud temperature (it can see faint clouds you will struggle to see by eye). If there is absolutely no cloud cover, mine can't get a reading from the sky, which is not surprising as the temperature is -270C, and it needs a much larger detector to detect the blackbody wavelengths around 6cm corresponding to -270C, e.g.
One thing I've never been sure about is what these devices report when there's a wide variation of temperatures visible in the field of view.
Sometimes you are a complete prick den,
Pretty sure mine shows "out of range" for any target including enough sky.
As you say its looking at the wrong place in the spectrum to really see the CBR itself!
I presume its a type of "average metering" much like an optical detector...
Empty space fits that description.
He seems to be measuring the sky temperature. The temperature of outer space itself should register as -270 deg C or so according to the CMB radiation temperature of circa 3 deg K.
The problem is that the water vapour in the atmosphere will reflect IR radiation from the ground back to the IR thermometer, hence the -40 deg C reading.
Appropo of this, I took an opportunity, a few nights back when we had a very clear sky, to 'measure' the sky temperature with my "elcometer
214" IR thermometer. This time, I managed to get it to under-range (Lo error) unlike previous atempts a few months back when I was only seeing -27 or so deg C (the night sky wasn't quite clear enough back then for my purpose).By pointing away from vertical I was able to see readings of -38, then -39 and finally -40 deg before tilting at a slightly higher angle of elevation provoked another "Lo error" indication. When I checked the specs on the meter, I was surprised to see the low limit being quoted as -35 deg C. Perhaps the subsequent 5 degrees aren't regarded as being sufficiently accurate enough to be included?
Anyhow, all I could say for sure was that the sky reading was lower than -40 deg (C or F) +/- the meter's calibration error.
Exactly so! :-)
I dont need more accurate results, It was just something I happened to do for no reason and was surprised at the result and that got me thinking what the heck am I measuring. I went out last night and did the same with low cloud coverage and the temp was -27 which was less than the previous night with a clear sky -40. To be honest it is just one of those things that caught my attention and I was curious to the reasons why. I had a look at the thermometer and it states -50C ~ 380C, never even knew that was on it until you guys explained what was happening.
around.
Key phrase "trying to dazzle planes". The authorities take a very dim view of deliberately aiming a laser at an aircraft. "Endangering an Aircraft", ooo no, they've made a new crimnal offence:
Out in your back garden and no aircraft obvious is not likely to get your door broken down though.
It's important to keep in mind that the laser spot is merely a visual guide to indicate the centre of the capture area. The D:S ratio for mine is a broad 8:1 meaning a spot diameter of ten feet for a distance of 80 feet with a red spot of laser light of maybe 1/4 inch diameter dead centre (idieally).
Not all IR meters have such control over the laser. Mine (an elcometer214 model) doesn't and the OP's being a cheaper unit is even less likely to allow the laser to be disabled other than by sticking a piece of black vinyl adhesive tape over the laser aperture.
Appropo of your warning, I did land up pointing the laser beam into the sky in the general vicinity of our local copper chopper. It was purely coincidental since I was poking my arm out of the window to get a quick reading rather than stand outside in the cold.
When I realised where in the sky the copper chopper was, it occurred to me that they may have experienced a brief flash or two of red laser light from my random sweeping of the sky for a lowest temperature reading, after which, I took more care in pointing the laser to avoid the copper chopper. It was only after I'd abandoned getting a really low reading that I wondered about the possibility of our front door getting kicked in by the cops.
Knowing how paranoid the cops are in regard to laser shine on their helicopters, I can imagine them over-reacting to the harmless brief random flashes from someone simply trying to get a sky temperature reading with a cheap IR thermometer. :-( I guess I managed to completely miss the copper chopper since there was no further untoward cop activiy to suggest such a paranoid reaction.
The next time I want to get an initial reading via a window to see whether it'll be worth the trouble of standing outside and freeze my bollicks off, I'll tape over the laser to take my readings by stealth should I ever hear any sound of copper chopper activity again.
Especially during the say and with the power of laser typically equipped on a thermometer.
s/say/day/ ?
Not so sure about the power aspect of a laser in yer typical IR thermometer. From what I've seen on'telly the problem is that the laser scatters when it hit's the plexiglass screens and you become engulfed in very bright flare. Even a low powered laser is pretty damn bright when you look straight down the beam.
The colimation of the average laser diode/optics probably isn't that good so at a thousand feet the "spot" may well be several inches across. If there isn't too much snow and it's not too cold/windy later I might venture out with my class 111b green laser pointer and a ruler.
Does anyone else remember seeing the Echo I and Echo II satellites mentioned in the Holmdel Horn Antenna article?
The times that they were visible in the UK were published in the Daily Telegraph in the weather column.
Yes, sorry - day.
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