This evening I ran a series of voltages through a Kanthal wound alumina tube in free air, yielding temperatures from 350 to 1100 C. The tube was instrumented with a Lumasense IR thermometer focused on the heater windings and a type K TC inserted into the alumina tube. The Kanthal wire was not covered with ceramic cement and presented a dark gray appearance. The Lumasense thermometer was operated in the 4-20 ma mode into a 250 ohm resistor, yielding a 1V (350 C) to 4V (1800 C) span. Emissivity was set at 100%, for now. Results showed a relatively poor match between the the TC temperature and the output voltage of the IR thermometer based on the span temperature limits. It was, however, possible to obtain an excellent match if the IR thermometer voltage readings were fit with a 1st order polynomial. See the attached figure for details. My recommendation for anyone using an IR thermometer is to calibrate it against a reliable standard such as a TC.
Jeff
