Maplin IR Thermometer.

[Clint Sharp]

Quick heads up, Maplin have an infrared non contact thermometer on sale for 19.99, reduced from 35. ISTR some people were wanting them for balancing CH systems and other DIY stuff?

[Harry Bloomfield]

Clint Sharp laid this down on his screen :

If it is the orange and grey plastic cased unit, they have been that price for a good six months. I bought one to replace a more substantial (and expensive) one after I dropped it and the display shattered. The new one is good and accurate, but the display is not so large. It compared well against a £100 Fluke unit, as in correct to the last digit.

[Fergus McMenemie]

SNAP. I droped mine as well and it just would not work afterward. Now while it was a great toy and I guess I will pick up another one I was always confused by the way it utterly failed to properly report the temperature when upto bare copper pipe.

It seemed good when pointed at most other things, it was just copper it failed on!!

Any ideas?

[Harry Bloomfield]

I have the same problem. I have not tried it, but what about wrapping some black tape around the pipe?

Odd how they work on some surfaces, but not others. They seem to half work on a stream of water, or even better water run over a stainless surface. I would not be without mine, certainly beats climbing to check a/c output and pipe temperatures.

It wasn't the orange one I broke BTW, but it more expensive predecessor.

[Roger Mills]

The reading you get does depend on the reflectivity of the surface.

For consistency, I've fixed little squares of black tape near the inlet and outlet of each radiator, and on every pipe whose temperature I want to measure.

[Andrew Gabriel]

They are normally calibrated for surfaces with an emissivity of about 0.95 and that's not far off what most surfaces are. Polished copper (as in a piece of new pipe) has an emissivity of about 0.04 -- that means that the infrared emitted by it is simply far too dim for the thermometer to be able to see anything.

Copper sheet is used as thermal wrap for telecommunications and other space satelites because it's so good at shielding against both absorbing and emitting infrared. Most polished bare metals will behave similarly, but most of them don't last more than that a few hours before they've tarnished enough not to be bare metal anymore (even if the tarnished coating may not be obvious to you). Copper takes much longer.

As others have said, a bit of sticky tape or dab of paint will do. I sometimes point the thermometer at the radiator boss where the inlet/outlet pipes connect - the enamel coating works fine.

[Adrian C]

Anyway of modding this as a poor man's thermal imager? Say, some control mechanism to make the unit step over specified small incremental distances, and then do a lovely false colour plot from data read?

(Nope, not the radio controlled helicopter again...)

[Andrew Gabriel]

Probably much easier to take a cheap B/W security camera, most of which operate down into the infrared anyway and often even have a filter to prevent them seeing in the infrared. Take out any such filter, and replace it with a filter to block the visible light.

[Mr Benn]

It needs a surface with a high emissivity apparently after speaking to someone from Fluke. The surface doesn't have to be black, but needs to have a matt or slightly rough finish. These thermometers give false readings on other surfaces. It was suggested to me that painting a surface with tippex would be good enough to get an accurate reading.

[Bruce]

Will human skin do?

[Andrew Gabriel]

Yes. Almost anything except polished metal surfaces will do. Avoid pointing the laser in someone's eye though! (Suggest turning the laser off if you can - it's not very useful.)

[Andy Dingley]

Why not just buy one?

[Harry Bloomfield]

Andrew Gabriel submitted this idea :

I find the laser spot very useful - with it you can 'hit' a spot from way across a room or an high ceiling to get the temperature of a distant object. They make them very much easier to aim.

[Andrew Gabriel]

It's misleading - it doesn't measure the temperature of the spot. It sees a cone, most of them with a 1:8 ratio, so it measures a circle of diameter about 1/8th of the distance between the gun and the target. I don't know what their behaviour is when there are many different temperatures visible withing the viewing cone.

[Andy Dingley]

Generally they over-read the mean temperature, owing to the Stefan- Boltzmann law. Especially so when there's a small hotspot in a largely cooler field, it gets a disproportionate weighting.

[Harry Bloomfield]

Andrew Gabriel submitted this idea :

My own use of one leads me to a conclusion that they indicate a biased average, of the temperature of the cone. Biased some way towards the temperature of the hotter object they see.

It is fairly easy to check the accuracy of the spot, by pointing the unit at a warm radiator and seeing how far off the radiator you have to aim to get a background temperature.

[Andy Champ]

I thought they used gold! Beats out thinner (= lighter) and the cost of the material is nothing to the cost of getting it up there...

Andy

[Mike]

They do.

[Dave Liquorice]

That'll be near infrared though won't it? The thermal image cameras the the fire service use to locate hot spots or people in smoke filled buildings or the police use for spotting hot tyres/engines or hiding people at night use far infrared.

I have a cheap B&W camera that suffers CCD overload if you point a IR remote at it and can almost see by the light from a few IR LEDs. It shows the glowing embers of a fire quite well that my eyes can't see. But these are all quite bright sources it's no good for pointing out the window at night to spot prowlers. Or pointing at the house to see where the heat is being lost.

[Andy Dingley]

Metal foil wraps are used to _heat_ equipment, as it has a high absorptance / emittance ratio where it absorbs solar radiation in the visible but has low emittance in the infra red (spacecraft are colder than the Sun, thus emit at longer wavelengths). Titanium is used, as it makes a useful foil material, but both gold and copper are used too as outer foils. White paint is used in the opposite sense, for cooling, as it has a low absorptance / emittance ratio (emits more IR than solar gain). This is the coating that has the most trouble with aging under the harsh UV and vacuum environment.

Plastic (Kapton, Mylar, Teflon) multi-layer foils with a vacuum- sputtered metal (gold, aluminium, silver) coating on them are for insulation and thermal stability, not for passive thermal control through solar radiation.