RTD Temperature Sensors in Coffee
An RTD, or resistance temperature detector, is a temperature sensor that measures temperature from a predictable change in electrical resistance. RTDs are valued for stability, repeatability, and accuracy and are used in industrial systems, coffee roasters, and some espresso equipment.
How an RTD works
The sensing element is made from a metal whose resistance changes with temperature. Platinum is common because its resistance-temperature relationship is stable and well characterized. A familiar example is a Pt100, which has a nominal resistance of 100 ohms at 0°C.
RTD vs. thermistor
Both devices infer temperature from resistance, but their behavior differs. An NTC thermistor typically changes resistance much more dramatically over a smaller temperature range, while an RTD generally offers a more linear and stable response over a broad range. The electronics must be designed for the specific sensor type.
Where coffee equipment uses RTDs
- Roaster bean- or environmental-temperature measurement
- Boiler or brew-system temperature control
- Data logging and process monitoring
- Applications where repeatability matters more than ultra-fast response
Probe response still matters
The sensing element is only part of the measurement system. Probe diameter, sheath material, immersion depth, location, airflow, thermal contact, and electronics all affect what the display shows. A highly accurate RTD in a poorly chosen location can still produce a measurement that does not represent the coffee or water condition you care about.
When replacing a sensor, do not substitute an RTD, thermistor, or thermocouple simply because it fits physically. The controller expects a specific electrical characteristic.
For coffee-roasting equipment, browse coffee roasters. For additional equipment terminology, visit the Coffee, Espresso & Brewing Equipment Glossary.