With the stock thermistor and my added thermocouple epoxied to the M2’s nozzle, I stepped the temperature upward, let it settle, and recorded the temperature from the Pronterface status display and my Fluke thermocouple meter:
Because the firmware servos the temperature through the stock thermistor, that line is dead straight at the exact setpoint values: the reference never disagrees with itself. The thermocouple, however, reads low by about 12%: according to it, the nozzle runs much cooler than the thermistor value.
Huh?
Several explanations come to mind:
- The firmware is using a lookup table that doesn’t match the thermistor
- The Fluke thermocouple meter reports the wrong value
- The thermocouple junction is defective
- Despite the epoxy blob, the two sensors aren’t at the same temperature
- Something else is kaflooie
This obviously calls for more data…
