ChromelKonstantan

ChromelKonstantan refers to the thermocouple pair formed by Chromel (a nickel–chromium alloy) and Constantan (a copper–nickel alloy), used in Type E thermocouples for temperature measurement. The combination is chosen for its relatively high Seebeck coefficient and stable performance in various atmospheres.

Composition and naming: Chromel typically comprises about 80% nickel and 20% chromium, with small additions to improve oxidation resistance. Constantan is about 55% copper and 45% nickel, with trace amounts of manganese, iron, and other elements to stabilize resistivity and corrosion resistance. The spelling Konstantan is an alternative regional variant of Constantan.

Thermoelectric properties: In Type E thermocouples, Chromel serves as the positive leg and Constantan as the negative leg. The Seebeck coefficient for this pair is relatively high, typically around 68 microvolts per degree Celsius over a broad range, providing good sensitivity. The emf versus temperature is nonlinear and requires calibration for accurate measurements. The typical operating range is approximately -200 to 900 °C, with reliable performance in oxidizing and inert environments.

Applications and considerations: Chromel–Constantan thermocouples are widely used in industrial and laboratory temperature sensing where higher sensitivity is advantageous. They offer good stability at moderate to high temperatures but can experience drift and oxidation-related degradation at very high temperatures. They are generally not suited for cryogenic applications. The combination complements other thermocouple types (such as Type K and Type J) by offering higher output for similar temperature ranges.