What Is A Hot Junction?
TL;DR — Quick Summary
A hot junction is the measuring point of a temperature sensor—most commonly a thermocouple—where the positive and negative wires are welded together. It’s placed in the environment you want to measure, and works alongside a cold junction to determine temperature using the Seebeck effect.
What Is a Hot Junction?
A hot junction is the sensing point of a temperature sensor. In thermocouples, it’s where the two dissimilar metal wires are joined, typically by welding. At Peak Sensors, we use laser welding to create hot junctions without any additional medium, reducing the risk of contamination.
While the term is mainly used for thermocouples, it can also describe where a Pt100 resistance thermometer is connected to its leads—though in RTDs, the actual measuring element is the resistive element itself.
Hot Junction vs Cold Junction — Key Differences
| Feature | Hot Junction | Cold Junction |
|---|---|---|
| Definition | Point where the two thermocouple metals are joined and exposed to the measured temperature. | Reference point where thermocouple wires connect to the measuring instrument. |
| Purpose | Measures the actual process temperature. | Provides a known reference temperature for accurate readings. |
| Role in Measurement | Generates a thermoelectric voltage based on its temperature difference from the cold junction. | Its temperature must be known or compensated for to calculate the hot junction’s temperature. |
| Location | In the environment being measured (e.g., furnace, liquid, air). | At the sensor’s instrumentation end, often inside a terminal head or connector. |
How It Works in Thermocouples
- Temperature at Hot Junction — The metals at the junction experience the process temperature.
- Seebeck Effect — This temperature difference between hot and cold junctions generates a small voltage.
- Measurement — The voltage is measured and converted into a temperature reading, factoring in cold junction compensation.
Why Precision Welding Matters
High-quality welding, like laser welding, ensures:
- Minimal contamination risk.
- Strong mechanical bond.
- Consistent electrical properties for accurate measurement.
If you want to order a temperature sensor or you are unsure exactly what you need, get in touch and we can help you.