Here's a puzzle for you

[MtnDon]

The roof on the CT is some sort of galvalume steel, greyish in color. I have an IR thermometer. Yesterday it was in the 60's outside. The sun shining on the white aluminum skin gave me a surface reading of 89 F. When I climbed a ladder and pointed the IR thermometer at the roof surface the reading jumped. Not up but down to 17 F. What!! So the roof surface has some coating (?) that absorbs IR ??? To my hand it was warm. So what is going on?

Roof will be given a white coat soon.

[OverTheTopCargoTrailer]

Oh GREAT MtnDon

When I climbed a ladder and pointed the IR thermometer at the roof surface the reading jumped. Not up but down to 17 F.

Your saying it was 60F outside & when on the roof it read 17F WOW

you are in the 3rd dimension of thermo dynamics,

but please come & apply that to my roof also

[rowerwet]

IR thermometers have a hard time reading off of metal. For a few years I heated my house in ME with a pellet boiler, when you really get into it a IR thermometer is a " must have" tool so you can see how the heat is being carried through the system and zones. I had to put masking tape on the metal fittings and on the PEX pipes to be able to get good accurate readings.

[MtnDon]

Oh. I have never run into that before and that includes reading cast iron wood stoves. But I guess the black coat helps. I'll have to try some other bare metals for the heck of it.

[MtnDon]

I heard back from a friend who is an instrumentation engineer for a large oil company. He spends most of his working time in the oil fields in the middle east. They do not use IR thermometers for this very reason. They use thermocouples and fiber optic temperature measurement.


As a note of interest, they use buckets of water for tool carriers; wrenches and the like.

[Socal Tom]

The text below is from the link below. I think it explains the issue.

http://www.thermoworks.com/blog/2012/03 ... ermometry/

Myths about infared thermometers
Not all surfaces are created equal. Depending on what you’re pointing your infrared gun at you’re likely to get variations in emitted infrared energy. This variation is called emissivity. Emissivity is a measure of a materials ability to emit infrared energy. It is measured on a scale from just about 0.00 to just below 1.00.
Generally, the closer a material’s emissivity rating is to 1.00, the more that material tends to absorb reflected or ambient infrared energy and emit only its own infrared radiation. Most organic materials, including the byproducts of plants and animals, have an emissivity rating of 0.95. These are ideal surfaces for accurate temperature readings.
Emissivity 3 Three common misconceptions about infrared thermometersSubstances with very low emissivity ratings, like highly-polished metals, tend to be very reflective of ambient infrared energy and less effective at emitting their own electromagnetic waves. If you were to point an infrared thermometer with fixed emissivity at the side of a stainless steel pot filled with boiling water, for example, you might get a reading closer to 100°F (38°C) than 212°F (100°C). That’s because the shiny metal is better at reflecting the ambient radiation of the room than it is at emitting its own infrared radiation.
What is fixed emissivity?
Fixed emissivity is a setting in some infrared thermometers (usually of 0.95 or 0.97) that attempts to simplify their operation while leaving them suitable for most material surfaces, including almost all foods. Other infrared thermometers come with adjustable emissivity settings, so you can more accurately prepare your thermometer for the type of surface being measured, particularly when measuring non-organic surfaces

[rowerwet]

I found the angle the IR gun was held at changed the temp by many degrees on copper, brass and stainless

[roadinspector]

The IR that I use has a specific cone to stay within for accuracy. The closer you are, the smaller the cone. When shooting at an angle or from a greater distance, the IR can pick up other surfaces which can give reading which will appear to be a bad reading.