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    • #24964
      dragon813gt
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      Decided to take this off the other form and move it here.

      The subject of infrared thermometers comes up quite often. I had two different types today so I decided to do some experimenting.
      First I warmed up the my pot which is PID controlled. The alloy used was 96/3/1 isotope lead. Here it is all warmed up and ready for measurement. The thermocouple is barely inserted in the lead. It’s in just enough to get a good reading. Since it’s not directly on the surface I’d expect there be some deviation in the readings. The thermocouple was tested like all my other temp sensors. It was inserted in a glass of water containing ice. It read 32 degrees just like it should.

      I first used my UEI 151 which I use all the time at work. I don’t use it for any precision work. I use it for quick measurements of ceiling diffusers or other items that I can’t easily reach. This one costs significantly more than the harbor freight one but it’s still affordable.

      You can see the emissivity settings in the first pic. None of them match molten lead. Molten lead is in the range of .35. In the second pic you can see that the further away the thermometer is from the object. The larger the area that it measures. It has to be pressed up against an object to get a good reading.
      First I just shot the molten lead. I shot it five times on each setting and averaged them out.
      .95 – 345 degrees
      .90 – 355 degrees
      .85 – 365 degrees
      Next up I floated a penny on top. Let it warm up and took the same five shot averages.
      .95 – 389 degrees
      .90 – 398 degrees
      .85 – 420 degrees

      I was using our FLIR camera at work today so I decided to bring it home for this test. It only reads up to 519 degrees so after my first tests I was thinking it would show results. This is not a tool I expect someone to go out and buy as it’s cost prohibitive.

      This has more emissivity settings. The glossy setting closely matches the lead but it comes with a warning.

      Just a general shot of the pot.

      Then I started taking the readings on the different settings. I didn’t take any averages because I could see this in real time. I did my best to take readings in the same spot. I didn’t bother with the penny test because of the readings from just shooting the lead.

      The results with the FLIR camera followed the same trend as the UEI. As the emissivity number was reduced, the temp readings increased. But the temp readings were still nowhere close to being correct. I’ve heard people say that they work and that it requires proper technique. My findings are that they don’t work. For the cost of the HF one you can purchase a proper casting thermometer that will work every time. It will also tell you the temperature of the lead that you’re pouring since the probe will be sitting down by the spout.

      I also know that the closer to the edges of the pot I measured the hotter the lead would be. I feel that this a moot point. I set the thermocouple that controls the PID in a few inches from the pot edge. So the IRs should have read the same.

      Since everyone like pictures here is one of my dog 🙂

    • #24976
      VANN
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      The pot is probably acting as a cavity radiator, I would assume that the outside edges are probably closer to the actual temp. Due to the reflective nature of most metals obtaining a correct temperature with most IR equipment is very hard, even when adjusting for the emissivity at best the temperature obtained would be a guess. The only way to get an accurate temperature reading is by the use of a thermal couple. When conducting my monthly and yearly IR inspections at work on bus bars and switch gears, I learned that electrical tape, spray paint, and cavity radiators are my friend.

      Try floating a 1/2 inch nut in the middle of the pot and aim for the center, this should give you a fairly good idea of the actual temperature.

    • #25064
      dragon813gt
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      I went over this in the thread on the other forum. Floating a penny or other object on top did not lead to an increase in accuracy. The point of this test was to prove that an IR thermometer is the wrong tool to use.

    • #25593
      Kevin S
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      Thank you! You saved me some money on an unreliable item.

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