Archive for May 13th, 2013

Makergear M2: Thermistor vs. Thermocouple

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:

First Heat - M2 thermistor - Fluke with thermocouple

First Heat – M2 thermistor – Fluke with thermocouple

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…

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