glass-bead thermistor

Does anybody know what other thermistors would work for the extruder head. i have had a hard time finding the glass bead type here in the USA in less then 1000 ea.

hi bruce,

i looked up thermistors on mouser, and i found a couple hits. here is the search page i got: [www.mouser.com]*

i cant give an authoritative answer, but i will alert the core guys and i'm sure one of them can say for sure.

from adrian:

Yup - that one should do. The design is pretty tolerant: any small
bead-type thermistor with a room-temp resistance between 10K and 100K
should be ok; Simon's written a capacitor calculator on the wiki
(http://reprap.org/bin/view/Main/ExtruderIO) that tells you what
capacitor value (C3) to use in the circuit for any reasonable
thermistor.

Best wishes

Adrian

Within reason, the specific resistance and beta values aren't too important.

The more difficult thing to find is a thermistor that is rated to go up to a decent temperature without breaking down or having its leads fall off. You probably also want one with some kind of thermal conductor to transfer the heat to the sensor efficiently. For example, some thermistors have a metal tab that you can attach to the heating element. Without that, it's probably better for measuring temperature in immersion (air, liquid, etc).

For my takeoff on the Mk 2 I've dispensed with the thermistor altogether and control temperature by keeping track of how much current I'm running through the heater coil in the firmware via a software PWM routine. Running at a full 2 amps and no filament feed the extruder barrel stagnates at about 205-210 degrees C at a room temperature of 20 degrees. For the plastics I'm extruding that doesn't cause any trouble and there's precious little dribbling like you get with CAPA because, I suspect, of their higher viscosity.