Equipment for measuring hot end temperature?
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@zapta The problem with your analogy with other measuring devices is that they mostly have the sensor encapsulated within the device whereas for fdm printing, we use a remote sensor. Whatever is being measured has to be converted to an electrical signal of some sort. With electronic scales for example, the device which responds to changes in force or pressure is usually a load cell (or several connected using a Wheatstone bridge). So it's reasonably easy to calibrate the device as a whole by checking it against known standard weights. On our printers, the sensor is nothing more than a device which changes resistance with temperature. So we actually measure resistance then do a mathematical conversion to get temperature. We can calibrate the whole against a known standard but if we change the sensor then we have to recalibrate. The same would apply to our electronic scales if we changed the load cells. In fact, load cells are notoriously prone to drifting and scales are usually "tared" before use.
Ultimately most electronic measuring devices can drift over time. So the only way to be sure of accurate readings is to calibrate the device (including its sensor) against a known, traceable standard, then take a measurement, then re-check the calibration. This is in fact what we used to do when I was involved in measuring vehicle exhaust emissions.
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@zapta A class A RTD is probably the most reliable, affordable temperature measurement device you can use to cover a moderately wide range with no special calibration. A thermocouple of appropriate type can be used without any calibration, and fairly good accuracy, over a very wide range, but the resolution isn't so good. If you want to go first-class, an SPRT (standard platinum resistance thermometer) is ideal, but costs. These are RTDs manufactured to extremely precise specification (loosely wound, special platinum wire, so thermal stresses don't change it, etc.).
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@deckingman, my goal is to first calibrate the sensor itself, when calibrate the sensor itself, removed from the printer. It's funny that you mention load cells because I also play with load cell and having no problem calibrating them with known weights. A known temperature is much difficult to achieve. I am still waiting for the thermowell to calibrate at 100c with water (I tried nylon bags and it leaked and deionized water but they still conduct electricity). I also saw that people calibrate with molten reference tin at ~230 but haven't tried it yet.
@mendenmh, you are right and this is the best class A RTD I could find in my price range (it's a hobby project). https://atlas-scientific.com/probes/pt-1000-temperature-probe/ . I calibrate the resistance measurement with 0.01% resistors I got from ebay and will use short two wires RTD wiring.
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@zapta Make sure when you do the boiling water 100C point, that you look up the local barometric pressure, and then use a conversion table to get the correct boiling point. It varies quite bit, especially if you are at altitude. This is why an old explorers trick in the mountains was to keep a thermometer, and put it in boiling water to measure the altitude.
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Thanks @mendenmh. I am close to sea level but will make sure to check the barometric pressure. I also saw all kind of other rules of thumb (e.g. immersion depth) and realize that I will just scratch the surface with my limited knowledge and means.
E.g.
http://www.isotechna.com/v/vspfiles/pdf_articles/Temperature Calibration-Depths of Immersion.pdf
