Posted 31 Dec 2022 Hi All, I have a 1746-NT8 and am using a type K thermocouple. The module is configured properly and the cjc's on on the terminal block. All channel lights flash until a thermocouple is no longer seen as an open. When inputting -328 degrees farenheight the light goes solid green for that channel and the input table reads -29,453 and when you go to +2498 degrees farenheight it flashes Green for that channel which seems like over temp. When I back it off to 2488 it goes solid green again and the input table reads 32,757. Is this normal, or should you be able to go the whole range from -328 to +2498 degrees farenheight and the status light should stay solid? The manual says type k thermocouple should go from -428 to 2498 farenheight, bit when you google type k thermocouple range it says the range is -328 to 2300 degrees farenheight. Thank you Share this post Link to post Share on other sites
Posted 2 Jan 2023 (edited) I've never used a 1746-NT8, but my reading of the 1746-NT8 manual says that it should theoretically cover the range -454°F through 2498°F. The blinking green channel LED indicates an over range input at the mV generated by whatever you're using to simulate 2498°F. The fact that when you back the simulator off to 2488°F indicates to me a calibration issue: whatever the simulator is putting out the module interprets as the top of the A/D range: 32,757 counts at what thinks is should be 2488°F. The top of the A/D range, 32,757 counts should be interpreted as 2498°F, not 2488°F. I think you need to calibrate the input so that the module indicates 2498°F when the simulator provides the mV at 32,757 counts. As to the practicality of using Type K's above 2300°F (or below -30°C), or other upper levels, there's lots of bar stool opinions by long term users. The 2498°F top value for Type K comes from the NIST tables (1370°C). Many, many vendors have a lower limit on their Type K's based on reality experiences. Honeywell's HC-900 thermal PAC ranges a Type K only up to 2192°F (1200°C). Type K's can exhibit a fairly short 'valid' life at the high end of NIST table. The problem is that the thermocouple can drift, which happens much more rapidly at high temperatures, and if the element does not break open, the T/C card still 'sees' a mV signal, but since the thermocouple has drifted the temperature calculated for the mV signal is false. There is no way to compensate for drift. You don't know how much or in what direction the drift is, because the T/C still appears valid because it's not an open circuit (it's not a thermocouple break condition). Edited 2 Jan 2023 by DanW proof reading Share this post Link to post Share on other sites
Posted 3 Jan 2023 How accurate is your simulator? Are you sure? Share this post Link to post Share on other sites
