Measuring Hotend Temperature

[Fiero2M6]

I'm trying to print will PLA, and I'm having trouble measuring exactly what temperature my hotend is. How are you guys measuring it? I've thought of buying a thermocouple and using that, but it would be really nice to just use the thermistor already in the hotend. The SeeMeCNC website says that the thermistor has 4k Ohms of reistance at 200C. From my reading, the PLA should be at 185C. Does anyone have a temperature versus resistance graph for this thermistor? At a minimum, it would nice to know the thermistor's resistance at 185C.

[mhackney]

Over on the Yahoo SeeMeCNC group is a thread that has a spreadsheet with this info in it. It might be in the files area there too. I use a thermocouple and touch it right at the junction of the brass nozzle and steel hot end. Once you set for a particular temp, it is stable through power cycles so I don't measure every time.

cheers,
Michael

[mhackney]

Found the spreadsheet: Hot End Temp

[Fiero2M6]

Thanks for the info. On the graph in the spreadsheet, is the x-axis k Ohms of resistance of thermistor or is it the voltage of your thermocouple?

[mhackney]

You will need to ask the author. Search in the yahoo group.

[Fiero2M6]

Found it here: http://tech.groups.yahoo.com/group/SeeM ... r=1&tidx=1 The x-axis is the voltage at pin 12 of the comparator chip on the the thermostat. For PLA, it should be between 2.8 and 2.5 volts. He measured the hysteresis is about 12C. I'll probably try lowering that for better PLA printing.