Heat Press Temperature Accuracy

owleyes said:

Hi,

I just got a used Geo Knight DK20s heat press. I have a digital laser thermometer that I'm using to check the accuracy of the display readout. Although I'm getting some variations with the angle that I hold the gun/device, for the most part it's reading about 30 degrees higher than the display. I'm not sure how to determine which one is right. Do I need to get a second tester to break the tie? Is it expected that there should be such a difference? All I did was transport it 3 hours from it's previous location.

Thanks,
Steve

Click to expand...

If the platen is teflon coated and black it is OK.

If the platen is not black it will not properely read accurate without calibration, this is due to a physics phenom called "blackbody radiation".

http://support.fluke.com/hart-sales/Download/Asset/4100366_6203_ENG_A_W.PDF

But a IR thermometer is still usual IF you also have an accurate contact thermometer.

The contact thermometer requires "soaking" meaning it must be kept on the surface till it is fully heated at the contact area, this is a bit tedious and slow if you wish to measure the entire platen. Whereas a IR thermometer (laser as a pointer) gives an instantaneous measurement and is easy to test an entire platen all over, especially for dead spots.

Pick a spot in the center of the platen with the contact thermometer, note it's reading, then probe the same spot with the IR thermometer, the difference of the 2 is your "offset". Just add the offset back to the IR measurements from other places in the platen and that you should be good.

If you know the "emissivity" of the base metal then some IR's let you input that and it will adjust the reading accordingly. Only the more expensive ones offer that feature. Or you can manually offset the reading using the contact thermometer as the "baseline"

Emissivity table ...

http://www.scigiene.com/pdfs/428_InfraredThermometerEmissivitytablesrev.pdf

Generally speaking a black surface give an Emissivity of 1.0

A little more explanation on this may be found here.

https://www.thermoworks.com/infrared_tips_what_is_emissivity

I use both an IR and contact thermometer.