Are IR thermometers accurate?

[lazybloke]

Anyone know anything about the accuracy of IR themometers?
I've got cheapo PK51A from I-Pook. Forecasts say a min of -6 tonight but I'm reading -12.7 on my car trailer.
The car tyres are -12.1C and the drive paviours are "only" -11 C.


I'd write off the thermometer as inaccurate junk, but it gives perfectly steady and plausible temperatures for the freezers and the fridge. What gives?

 

[slowmotion]

The accuracy depends on what the sensor software assumes the surface emissivity of the object being measured might be. If it gets the emissivity wrong, you get a crap temperature reading.

It's been a while since I did IR thermography, BTW. Back in those days we had to fill up the camera with liquid nitrogen.

 

[classic33]

Try it on a white surface, then a black. Average the two readings.

 

[slowmotion]

Try it on a nice polished piece of stainless steel. That might be interesting compared to a brick wall.

 

[lazybloke]

Try it on a nice polished piece of stainless steel. That might be interesting compared to a brick wall.

Yep, noticed that with the kettle.

Just been outside again and am getting inconsistent results. I reckon the battery needs changing. I feel the same.

 

[slowmotion]

[QUOTE 5165837, member: 9609"]why don't you use a standard thermometer outside then compare it to that ?[/QUOTE]
Good idea. Set up samples of different materials outside and point the gizmo at them once they are all sitting at the same ambient temperature. Polished metal, brick, timber, plastic...whatever. Then do the same thing in a really hot room.

The surface emissivity varies with the material, and it also varies with the temperature of the sample. If the gizmo gets the SE wrong, you will get a duff measurement from it.

 

[lazybloke]

@User9609 Am not normally fixated on temperature, so don't have any other way to measure. Except a jam one and a medical one - neither go anywhere near minus figures).

IT turns out the temp really did fall to -9, according to the official reports., so maybe the IR thing isn't so bad after all.

Edited to add: could have used my Garmin. doh!