Which materials are required for Type J thermocouples?

• A. Iron and Constantan
• B. Copper and Nickel
• C. Chromel and Alumel
• D. Platinum and Rhodium

Answer: (A)

Type J thermocouples rely on the thermoelectric effect between two dissimilar metals to generate a voltage that changes with temperature. For Type J, the metal pair is iron and Constantan. Iron serves as the positive leg and Constantan as the negative leg, producing a reliable voltage-versus-temperature characteristic over a moderate temperature range. This specific pairing is chosen for its balance of cost, availability, and performance at typical industrial temperatures. Other material pairs belong to different thermocouple types (for example, Chromel and Alumel form Type K, and platinum with rhodium pairs are used for Types S/R), so they don’t match Type J.