Temperature sensor NTC 100k
The G1 extruder has three NTC 100k thermistors — one per heating zone — that measure barrel temperature. The reading is handled directly by the main Octopus board, which feeds it to Klipper.
Specifications
Section titled “Specifications”| Parameter | Value |
|---|---|
| Type | NTC (Negative Temperature Coefficient) thermistor |
| Resistance at 25°C | 100 kΩ |
| Operating range | 0–300°C (Klipper firmware minimum is 0°C) |
| Read by | Octopus board (not the extruder_board) |
Klipper sensor_type | Barrel zones: NTC100K3950.up, .mid, .down in printer.cfg. The bed keeps EPCOS 100K B57560G104F — the name of the calibration curve from the earlier sensors; it is still an NTC 100k |
Location
Section titled “Location”One sensor per zone, screwed into the barrel next to its heater band:
| Zone | Position |
|---|---|
| Feeding Zone (T0) | Upper barrel section, near hopper |
| Melting Zone (T1) | Middle barrel section |
| Nozzle Zone (T2) | Lower barrel section, near nozzle |
The current sensor
Section titled “The current sensor”The sensor in use is an NTC 100k inside a small metal cartridge that screws into the barrel port, with its three calibration points set in Klipper.
If the part-cooling fan blows hard on the nozzle, the Nozzle Zone (T2) sensor can drop in temperature.
The calibration is per sensor, not per model. Each one is calibrated in
production and its three points are written into that machine’s printer.cfg.
A replacement is therefore not interchangeable on its own — the values come with
it.
How it works
Section titled “How it works”The thermistor’s resistance changes with temperature. The Octopus board reads this resistance and Klipper converts it to a temperature using a resistance/temperature table. Klipper then drives the heater (via the extruder_board relays) to hold the target.
The signal path runs: sensor at the extruder → JST at the extruder → ethernet cable (panel box → extruder breakout) → JST on the Octopus.
When it reads wrong
Section titled “When it reads wrong”A zone reading deeply negative — around -90 °C, usually flickering — or jumping by tens of degrees, is an open or intermittent connection, not a failed thermistor — the board sees infinite resistance and the curve maps that to the bottom of its scale. Finding the break is a troubleshooting job with its own page: Temperature sensor disconnected.
A zone that reads correctly but does not heat is the other side of the same barrel: the relay or the band, not the sensor — see Heater band.
Replacement
Section titled “Replacement”If a sensor truly needs replacing:
- Power off the machine and let the barrel cool completely
- Check the connections first (the JST at the extruder, the ethernet cable, the JST on the Octopus) — confirm the sensor is actually the fault before removing anything
- Do not force the sensor out of the barrel wall — you can strip the internal M3 thread. If you must remove it, do so gently, with no levering or prying
- Fit the replacement sensor into the same bore
- Reconnect the connector
- In the Klipper config, set the new sensor’s resistance/temperature curve using its 3 calibration values — do not run PID tuning
- Cold, all three zones should read within a few degrees of each other. A larger gap at room temperature is a wiring fault, not a sensor one
Related notes
Section titled “Related notes”- Temperature sensor disconnected — finding the break when a zone reads wrong
- Extruder board — heater relays (read of temperature is on the Octopus)
- Heater band
- Multi-Heating Zones
- Heater not reaching temperature