A simple probe made from two kinds of wire (i.e. platinum, rhodium) welded together. This probe is wired to a sensitive electronic meter that displays a reading of the voltage it generates when heated.
However the world of high temperature measurement and thermocouples is a complex one. There are many kinds of thermocouples. Some generate a nice smooth voltage increase that bears a direct relationship to temperature increase, others require complex software to make the translation. Wire manufacturers produce detailed charts that show the mV output at each temperature, some technicians weld together their own thermocouples with confidence the output will match the charts. There are different manufacturing processes, calibration techniques, response to different atmospheres, abilities to measure different temperature ranges, different types decay in their accuracy in different ways, variations in frequency of need for recalibration, etc.
Maintaining accurate pyrometers can be expensive and typical inexpensive type K devices used in potters kilns are not accurate at higher temperatures (most potters won't pay for the platinum/ 10% platinum-rhodium (type S) thermocouples and control systems that really should be used, and the more expensive plated switches and contacts). However the type K are more resistant to oxidation than types E, J, and T at temperatures over 500C.
Non-contact infrared temperature measurement guns are now available on Amazon and within price-reach of anyone. Some advertise ability to read up to 1800C. Of course, the quality needs to be assessed. For example, if they claim +/-2% accuracy on readings for 320 ~ 2120F, does that mean they can be out by 42F at 2120? That is more than a cone! Search terms like "digital pyrometer", "IR pyrometer", "infrared pyrometer".
Devices that melt and bend in a ceramic kiln at specific temperatures when subjected to specific up ramps. Today, cones are used to calibrate controllers.
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