IR Pyrometer / Thermometer

[made2hack]

Hello all,

I don't know anything about how IR thermometers work so excuse my ignorance.

But, why is a thermometer that can read say up to 1250 deg C maybe 3-4 times the price of one that can only read up to 400 deg C? I mean aside the obvious that it can read higher temp, what makes it able to read a higher temp? What chip / lens (don't know if this is correct) allows this to happen?

When dealing with thermocouples, I know that a K-type will do 1350 and afterwards it will physically melt. To go higher, say S type, you need Platinum / Ruthenium alloy.

But a non touch thermal IR, what goes into a higher spec?

ON a side note, is this One-Hung-Lo really able to do 2200 deg C?

[ebclr]

Low temperature Ir thermometer have another IR spectrum than High temperature ones, Low temperature normally use a of the shelf sensor base on thermopile

On the other hand high temperature uses Silicon or germanium sensors ( like a photodiode ) , Please note that temperature standards for calibration is much more expensive on the high temperature than the low temperature ones.

Price difference is due to quantity and also a more robust construction, more expensive calibration on high temperature, for every 1000 pcs of low temperature only one high temperature is sold.

[ebclr]

The thermometer you post isn't a high temperature one , is low temperature, forget this is a crap .....

 Ir thermoneter that costs less than 200 USD have a 90% chance to fail on high temperature


A real high temperature is like this

http://www.metalworkingworldmagazine.com/handheld-infrared-thermometer-raynger-3i-plus-for-high-temperature-applications/

[Kleinstein]

The low temperature (e.g. < 300 C) IR thermometers use real IR sensors, like thermopile ones. This is actually quite hard, but gets often cheap due to large quantities.

For the higher temperatures (e.g.. > 300 C) one can use cheaper Si based detectors, but as a downside materials are more different in this wavelength region. So to get a good reading, they usually add all kind of extras, like measuring with different wavelengths or testing reflection to. Together with lower quantities this makes the higher temperature ones often more expensive. If the Chinese want to they could sell you some for 500 C- 5000 C for $5 if it's the right quantity.

[made2hack]

Yeah, that Raytek model, sexy. But the price.....

I'm gonna use a thermocouple for now.

Any thoughts on the Uni-T models?

[ebclr]

What is your application ?

[made2hack]

I will be building  an electrical kiln at one point, and would like to double check or simply read the molten metals without necessarily sticking in a thermocouple.

[ebclr]

Bad news for you, Ir thermometers are based on IR emission, and not all material emits Ir on the same way, The capacity to emit more or less IR of a material is called emissivity, ( this is quite complex and changes with temperature and format ), Unfortunately for you, liquid metals are the worst case scenario for IR thermother to operate, and very few models can do this on a reliable manner , and all cost some k's dont expect to do this with cheap products will not work even with the very expensive ones isn't a easy task.  If you don't have a very big budget stay with discartable thermocuples. All low cost pyrometer for this aplication will be a waste of time and money

[made2hack]

Yeah, I see. The Raytek is way out of my price range.

DO you know anything of old school optical pyrometers? Do they suffer the same problem with emissivity? Or no since they use some kind of optical properties?

[Kleinstein]

Old school pyrometers suffer the same problems. In some cases the old comparing ones (e.g. those with an filament heated until it gets visible) might be a little better - similar to good newer ones that use 2 wavelengths.

It depends on the materials: very clean metal surfaces are rather good IR reflectors. So it gets really hard to impossible to measure from IR emission. A more oxidized surface is not that bad, especially at higher temperature / shorter wavelength.

[ebclr]

Have one kind of pyrometer that don't suffer from emissivity is called ratio pyrometer ( include two color and two wavelengths kinds ), but unfortunately again they suffer for another issue that is called color emission ratio imbalance, in theory ratio pyrometer cancel emissivity making a divide operation between two measures on 2 different wavelengths, this works only when the object being measured is a "perfect grey body"means they have same emissivity for all frequencies ( read temperature )  on all measured range for the two sensors but in real world few maybe none alloy material when liquid do this grey body behaviour making again the measurement very hard or near impossible due to ration imbalance.

If anybody know any IR technology that measures melted alloys on a reliable way, tell-me I still support the idea that is impossible to do that with IR on a reliable way.