Incorrect temperature reading

[DIY3D]

Hi,

When I measure the temperature of my nozzle with a infrared thermometer I'm reading +/- 54 Celsius at the brass or messing part, and about 30 C at the heated block.
This looks strange to me causeI have no problems with my prints and the thermometer is correct. Pointing to the HBP gives a temperature around 60 C
I'm using a KC-180B-1 Infrared thermometer.

Can somone explain what's wrong here?

Kind regards,
Marco

[ednisley]

Can somone explain what's wrong here?

You've hit two key limitations of IR thermometers...

1) The thermometer assumes the surface it's pointed at has an emissivity of 0.95, which is true for most organic substances. Metals have a very low emissivity, so their surface tends to read low; you're seeing ambient IR reflected from the metallic surface, not the surface's IR emission.

2) The measurement area is larger than the nozzle and hot end, so the sensor sees a lot of unheated background.

In general, an IR thermometer will work OK for large plastic objects as they build, poorly for the bare glass plate, and not at all for any shiny metallic surfaces.

[DIY3D]

Hi Ed,

Well, I can extrude some filament and focus the beam to the point where it comes out.

Thank you for the clear explanation.

Kind regards,
Marco

[ednisley]

focus the beam to the point where it comes out

The laser beam just marks the general region that you're sampling: the measurement isn't from that point source!

At least for my IR thermometer, the measurement area is 25 mm diameter at 125 mm from the aperture (an inch at 6 inches) and it doesn't get much smaller. The "thing to be measured" must fill that entire area to produce a valid measurement.

If you print a flat plastic plate, you can get a reasonable bed temperature measurement, because the filament won't remain at extrusion temperature for more than a few seconds after it comes out of the nozzle.

Within those limits, though, an IR thermometer works wonderfully well!

[jimc]

yes i totally agree with ed. the ir thermometers just arent for such tiny pinpoint items. you need a digital temp meter with a thermocouple that you can tape to the nozzle with kapton. it will need a small layer of insulation over it at well. the rubber coated fiberglass stuff that comes on the hotend from makergear will work fine.