IR thermometers - water temp?

[Simon C.]

Following on from the recent IR thermometer thread where everyone seems to have one...

I understand they won't work on some surfaces, eg shiny ones. Will they measure water temp, eg bath water? Any comments on accuracy? Less concerned with absolute accuracy than consistency - if it repeatedly over or under reads then that can be compensated for.

TIA.

[phoenixbbs]

I've used mine to read water temps with what seemed like a good consistency :-}

[Mr Benn]

IR thermometers operate on radiated heat and the reading they display depends on the emissivity of the surface. They won't accurately record water temperature - you need a contact probe.

You can measure temp of shiny surfaces but you need to first paint the surface with a matt finish to increase the emissivity.

[David WE Roberts]

This probably answers the question I was about to start a thread to ask.

Which was 'how do you callibrate your IR thermometer?".

Having bought one I have been using it but wondering how accurate it is.

Is seems to agree with one digital clock thermometer, possibly agree with another 'weather station' indoor thermometer but disagree with the 'weather station' outdoor thermometer.

Working outside this afternoon I noticed that a bucket of water had a thin film of ice over most of the surface. Now allgedly this should stay at 0C until all the water had turned to ice IIRC (something about the latent heat of thingummy keeping the water warm when water turned to ice). However the IR thermometer read the surface temperature as -1C.

I thought I might be able to calibrate using water as it froze and as it boiled - but now I am not so sure.

Accuracy is, IIRC, +-2.5C anyway so -1C falls within this range. It is consistent, however, for the same target so if I could calibrate it reliably I would then know what the 'fiddle factor' was.

I have two of those 'weather station' thingies from different manufacturers (one bought fromTchibo the other from Aldi/Lidl) and in both cases I left the inside unit and the outside temperature sender side by side for a while and they never agreed on the temperature. Go figure.

Whatever, it is bleeding cold outside at the moment. Heat loss from the walls and windows doesn't seem too bad, though. There was 2-3C difference in the temperature between block paving that had been in sun and shade. Paving in the shade was showing as -2C.

Cheers

Dave R

[JohnW]

Glad to see that, like a lot of us, you are spending your time walking round measuring the temperature of everything. The dog is getting pretty sick of having its ears lifted to see how it is getting on. Oven door is 38 BTW, oh and the consumer unit is 24. Perhaps there should be a contest for the most odd temperature in that it is nowhere near what you thought it might be.

John

[Mike Lane]

David WE Roberts wrote on Jan 26, 2010:

I have often tried to calibrate thermometer probes at home using home-made equipment cobbled together in the kitchen. I remember many years ago trying to do this with a homebuilt semiconductor temperature probe. I found after much experimenting that the only way to achieve a reliable 0C 'triple point' measurement was to fill a vessel with a mixture of crushed ice and water, leave it in the fridge for several hours, and take the measurement after stirring the mixture vigorously.

It doesn't surprise me at all that a spot measurement of the surface of an ice sheet is below 0C. Even a millimetre of ice between the ice-water interface and the measurement will make a difference.

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "David WE Roberts" saying something like:

Same here and the inside thermometers were always a degree apart. No matter, I'm not running a sinetiffic spearmint, or nuffin.