I am using a K-type thermocouple with a MAX6675 to convert the thermocouple signal to a digital word, which is read by an 18X using modified code from Peter Anderson's site at http://www.phanderson.com/picaxe/max667x.html
When measuring the room temperature my numbers seem about right (around 20 degrees), however when the thermocouple probe is warm (I'm using a light globe for my tests) the measured temperature actually goes DOWN, all the way to zero as the probe heats up. As it cools back to room temp, the displayed temperature goes back UP to where it started.
Originally I had the temperatures displayed on an LCD but now I'm just trying to get the correct numbers through the programming cable on a terminal screen. Always test one thing at a time!
Code attached if from phanderson's site above. All that I have modified in this example is the pinouts from the 18X to the MAX6675, to leave pins 4 and 5 available to drive the LCD later.
The same thermocouple works just fine with my multimeter.
Would swapped polarity of the thermocouple at the MAX6675 cause this? I'm pretty sure I got it the right way around and I'm reluctant to try something that looks "wrong" here for fear of breaking my precious MAX6675!
When measuring the room temperature my numbers seem about right (around 20 degrees), however when the thermocouple probe is warm (I'm using a light globe for my tests) the measured temperature actually goes DOWN, all the way to zero as the probe heats up. As it cools back to room temp, the displayed temperature goes back UP to where it started.
Originally I had the temperatures displayed on an LCD but now I'm just trying to get the correct numbers through the programming cable on a terminal screen. Always test one thing at a time!
Code attached if from phanderson's site above. All that I have modified in this example is the pinouts from the 18X to the MAX6675, to leave pins 4 and 5 available to drive the LCD later.
The same thermocouple works just fine with my multimeter.
Would swapped polarity of the thermocouple at the MAX6675 cause this? I'm pretty sure I got it the right way around and I'm reluctant to try something that looks "wrong" here for fear of breaking my precious MAX6675!