Short Answer
A Type K EGT thermocouple does not have a resistance vs. temperature curve.
It does not output resistance like an RTD or thermistor.
Instead, it produces a small millivolt (mV) voltage signal that corresponds to temperature.
Why Doesn’t a Type K EGT Thermocouple Have a Resistance Value?
RTDs and thermistors are resistive devices. Their electrical resistance changes in a predictable way as temperature changes, which is why they can be described using resistance tables (ohms vs. temperature).
A Type K EGT thermocouple works differently. It is made from two dissimilar metals (Chromel and Alumel) joined at a sensing junction. When that junction is exposed to heat, it generates a voltage through the Seebeck effect.
- No excitation current is required
- No resistance measurement is used
- The output is a self-generated voltage signal
What Does a Type K EGT Thermocouple Output Instead?
A Type K EGT thermocouple produces a very small DC voltage, typically in the range of:
- ~0 mV at 32°F (0°C)
- ~41 mV at 1832°F (1000°C)
This voltage corresponds to the temperature difference between:
- The measurement (hot) junction
- The reference (cold) junction at the instrument
Because the signal is so small, it must be interpreted by a thermocouple-compatible device such as:
- A pyrometer gauge
- A temperature controller
- A data acquisition system
- A signal conditioner or signal amplifier
These devices apply cold junction compensation and convert the millivolt signal into a temperature reading.
Can I Measure Resistance to Check If My EGT Thermocouple Is Working?
You can measure resistance for basic continuity checks only, but not for temperature.
- A healthy thermocouple will typically show low resistance (a few ohms or less depending on length)
- An open circuit indicates a broken sensor or wiring issue
However:
- Resistance does not correlate to temperature
- Resistance measurements cannot be used to calibrate or verify accuracy
What Happens If I Connect a EGT Thermocouple to a Resistive Input?
If you connect a Type K EGT thermocouple to an input designed for an RTD or thermistor:
- The reading will be incorrect or meaningless
- The system may interpret the signal as noise or an open circuit
Always ensure your instrumentation is configured for Type K EGT thermocouple input.
How Should I Think About EGT Thermocouple Signals?
A simple way to remember the difference:
- RTDs / Thermistors → Resistance changes with temperature
- EGT Thermocouples → Voltage is generated by temperature
Bottom Line
A Type K EGT thermocouple does not have a resistance-to-temperature relationship.
It is a self-powered sensor that generates a millivolt signal, and it must be used with instrumentation designed to interpret that voltage.
A table of voltages for Type K EGT probes can be found HERE
Understanding this distinction helps ensure proper wiring, accurate measurements, and effective troubleshooting in any temperature sensing system.