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How do I know what emissivity factor to use for IR thermometer?

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mzzj:

--- Quote from: amspire on September 12, 2019, 12:29:47 pm ---When testing temperature, I often just put some thin paper tape, plastic tape or most acrylic paints on the object I want to measure. Maybe not pure white paint. This way, you get the 0.95 emissivity, regardless of the object's surface.

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This is also my first suggestion if possible in any conceivable way.
Sometimes doesn't work for obvious reasons like red hot steel strip traveling at 100km/h past the measurement point.

Fraser:
I bought an Exergen D501 RS (remote sensor) IR thermometer a few years back. A very nice piece of kit and very accurate in my experience :) I will be honest and say it’s ability to operate without the need for an emissivity setting did make me wonder about its viability, but it does seem to work very well in my use.

https://www.wolfautomation.com/media/pdf/irscanner/exergen/dseries/exergen-microscanner-dseries-brochure.pdf

Fraser

mzzj:

--- Quote from: Fraser on September 12, 2019, 12:42:11 pm ---I bought an Exergen D501 RS (remote sensor) IR thermometer a few years back. A very nice piece of kit and very accurate in my experience :) I will be honest and say it’s ability to operate without the need fir an emissivity setting did make me wonder about its viability, but it does seem to work very well in my use.


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Idea seems similar to Gold cup pyrometers(ir thermometers)
https://www.ametek-land.com/products/industry-application-specific/gold-cup-reference-pyrometer-for-reformer-tubes

Conrad Hoffman:
I put some black acrylic paint on most things I need to measure. Otherwise, I use a thermocouple and set the IR to read equal to that. I never trust the thing to be better than a few degrees. Generally works well enough for anything I do.

741:
The "Gold Cup" page says "A hemispherical reflector produces a measurement area which is emissivity independent – ideal for tubes of unknown emissivity. The reflector edge prevents reflected radiation entering the area"

Is the idea that the only IR 'flux' seen is that which is 'directly in front of' the detector. (The IR sensor sitting in a 'radio telescope' arrrangement)? If so, that seems easy to implement, though perhaps expensive to produce the hemisphere. I'm unsure how visible smoothness relates to IR optics. There will be some reflection from the sensor itself, but that can be calibrated out I guess.

Can a cheap 'IR gun' be usefully enhanced with something similar and home-made? A problem is the IR sensor would need to look back into the reflector.

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