The Big Three Thermistors, Thermocouples, and PT100 RTDs

As a Product Manager at RobotDigg, I am often asked: "Which sensor should I use for my hotend?" Whether you are building a standard Voron, a high-temp industrial extruder, or a custom automation rig, choosing the right temperature sensor is the difference between a perfect first layer and a melted mess.
Here is the professional breakdown of the "Big Three": Thermistors, Thermocouples, and PT100 RTDs.

1. Thermistors: The Everyday Workhorse
The most common sensor in the 3D printing world is the NTC (Negative Temperature Coefficient) Thermistor. At RobotDigg, our standard is the 100K Ω NTC 3950.
How it works: Its electrical resistance decreases as the temperature rises.
Best for: Standard printing (PLA, ABS, PETG) where temperatures stay below 280°C.
Pros:
Cost-Effective: Extremely inexpensive.
Plug-and-Play: Most 3D printer mainboards (like BIGTREETECH or MKS) have built-in support for thermistors without needing extra modules.
Cons: * Limited Range: The glass bead or epoxy can degrade if pushed past 300°C.
Non-Linearity: Accuracy drops at the extreme ends of its range.

2. Thermocouples: The High-Temp Specialist
If you are printing PEEK, PEI (Ultem), or working with metal smelting, you need a Type-K Thermocouple.
How it works: It uses two dissimilar metals joined at one end. When the junction is heated, it produces a tiny voltage (the Seebeck effect).
Best for: High-temperature industrial applications reaching up to 1000°C+.
Pros:
Extreme Durability: Can handle heat that would vaporize other sensors.
Fast Response: The tiny junction reacts to temperature shifts almost instantly.
Cons:
Requires an Amplifier: You cannot plug this directly into a standard thermistor port; you need a MAX6675 or MAX31855 breakout board.
Sensitive to Noise: The millivolt signals can be distorted by interference from nearby motor cables.

3. PT100 (RTD): The Precision Master
The PT100 is a Resistance Temperature Detector (RTD). "PT" stands for Platinum, and "100" means it has a resistance of 100 Ω at 0°C.
How it works: As the platinum element heats up, its resistance increases in a highly linear and predictable way.
Best for: High-precision engineering and "Prosumer" 3D printers (up to 500°C).
Pros:
Accuracy: Far more precise than a thermistor or thermocouple.
Stability: Does not "drift" over time, ensuring your 250°C today is the same as 250°C next year.
Cons:
Cost: Platinum isn't cheap!
Complexity: Requires a MAX31865 amplifier. For the best accuracy, a 4-wire setup is used to cancel out the resistance of the lead wires.

PM's Final Recommendation
The Hobbyist: Stick with a high-quality NTC 100K Thermistor. It’s easy to replace and more than enough for 90% of desktop printing.
The High-Temp Maker: If you're building an enclosure for Nylon or Polycarbonate, upgrade to a PT100. The accuracy ensures your layers bond perfectly every time.
The Industrialist: For ovens, kilns, or specialized volcanic hotends, the Thermocouple is your only choice for raw heat endurance.