Strange behaviour of IR temperature meter

[ruffrecords]

I have one of those IR temperature meters that I use for seeing how hot heat sinks and the like get. It works great when pointed at most tings. However, today I was measuring the temperature of a silver coloured metal shield which forms the top of a tube mixer. After a couple of hours it is quite warm to the touch yet the IR meter thinks it is only around 20 degrees Centigrade. I pinched the regular thermometer from the garden and place it on top of the mixer. It now reads 35 degrees but the IR meter still thinks it is 22 degrees. I have checked on a black surface (the top of the external power supply) and although that does not feel warm the IR reads it as 28 degrees so I think it is working. I am going to place a strip of black electrical tape on the top of the mixer shield and see what reading I get.

Cheers

ian

 

[Khron]

It's not strange, it's expected.

https://www.fluke.com/en/learn/blog...od accuracy,glossy paint can affect accuracy.

 

[Voyager10]

This Wikipedia article: Emissivity - Wikipedia covers it quite well.

 

[ccaudle]

This Wikipedia article: Emissivity - Wikipedia covers it quite well.

Thanks for the link, I was not familiar with the term "emissivity" before, makes sense after reading that article.
The visible and IR photo of the Leslie cube was kind of eye opening, it had not occurred to me before that the accuracy difference between painted and bare metal would be that large.

 

[Philbo King]

I always used a small piece of masking tape on the item being measured to avoid reading IR reflections.

 

[ruffrecords]

Thanks for all the relies/

So if I understand this correctly, an IR temperature meter measures the IR radiation from an object and uses some assumed emissivity to convert that into a temperature.

Cheers

Ian