On 09/08/2012 22:46, Tim Streater wrote:
In article ,
Dave wrote:

Tim Streater explained :
In article ,
Dave wrote:

Looking to buy an infrared thermometer without breaking the bank
and also without knowing exactly what I'm looking at - for
instance, what is "emissivity" and does it need to be adjustable?

Was there some reason you were unable to look it up?

Yes. I'm thick. Rather than read lots of confusing big words, I just
wanted someone to say yes, these are good little gadgets or no,
they're a waste of money. Or for someone to say, that's not a bad one
but this one is better.

:-)

John's explained about emissivity (but I still think you could have got
that info yourself). While he's right that a variable emissivity device
will be useful in more situations, generally you can take emissivity to
be 0.95, fixed, which is what the cheaper devices do. This covers most
surfaces except shiny ones, so you'll get a decent result off a rad
painted black or white, but not a shiny chrome one.

Although black dry marker pen is reasonably effective and reversible as
a way to make the emissivity non-metalic. Though you can sometimes be
unlucky and find a surface that has pores and marks permanently with dry
marker.

Basically any shiny metal behaves to some extent as a reflector of IR
wavelengths. Most resin paints and common materials are black in the
thermal IR including glass windows.

Regards,
Martin Brown