How Do K-Type and J-Type Thermocouples Differ in Hot Runner Applications?

K-type and J-type thermocouples are the two most widely used configurations in hot runner systems. Type K (Nickel-Chromium/Nickel-Alumel) offers a wide temperature range from -200°C up to 1370°C and strong stability, making it the standard choice for premium systems. Type J (Iron-Constantan) has a temperature range up to 800°C and is widely used in general applications. For above 480°C, K-type thermocouples are recommended, while J-type is prohibited. J-type is only suitable for medium and low-temperature enclosed heating environments. High-temperature open industrial heating scenarios choose K-type thermocouples. J-type compensating wires are red/white in color (Fe-CuNi), while K-type uses different color coding. J-type positive electrode is iron (magnetic), negative electrode is copper-nickel alloy (non-magnetic); K-type positive electrode is nickel-chromium alloy (non-magnetic), negative electrode is aluminum-nickel alloy (magnetic). J-type and K-type thermocouples must never be mixed-wiring color codes must be carefully identified. High-end applications such as medical devices, optical parts, and precision connectors usually rely on imported brands with K-type thermocouples for ultra-stable temperature control. Husky's supporting special high-precision K-type thermocouples can realize real-time temperature monitoring within ±0.3°C. Germany's Günther and EWIKON's standard supporting thermocouples adopt grounded K-type measuring junctions for ultra-high temperature molding scenarios of engineering plastics such as PEEK and PA66+GF. General industrial parts can achieve reliable performance with mid-range J-type thermocouples while reducing procurement costs. When selecting between K-type and J-type, consider the molding accuracy requirements, plastic material characteristics, cavity quantity, and working environment. The thermocouple type must match the temperature controller settings. Exceeding the temperature limit of J-type thermocouples is strictly prohibited.