Fe-CuNi thermocouple (type J) is also named Fe- Constantan thermocouple. The positive leg made by pure lron, and the main chemical composition of negative leg Constantan (JN) is Cu: Ni≈ 55%: 45%. Although they are all called Constantan, JN does not give the same EMF output curve as EN and TN, it cannot be instead by other Constantan. The operating temperature range of type J thermocouple is-210~1200℃, but it is usually used in the temperature range 0-750℃due to embrittlement of Iron. TYPE AND MAIN CHEMICAL POMPOSITION(%) Type Chemical composition(%) NI Cu Mn Si Fe Fe JP / / / / 100 CuNi JN 45 55 / / / Standard IEC60584-1 Type EMF Versus Pt.67 (mV) 100℃ 200℃ 300℃ 400℃ 600℃ JP-JN 5.207-5.331 10.717-10.841 16.244-16.410 21.760-21.936 32.956-33.236 Physical property Type Density(g/c㎡) at 20℃ Melting point(℃) Tensile Strength (Soft annealed condition in 20℃) Elongation% (Soft annealed condition in 20℃) Resistivity at 20℃(μΩ·m) JP 7.8 1407 ≥240 ≥20 0.12 JN 8.9 1220 ≥390 ≥25 0.49