What is the temperature range a Type J thermocouple can sense?

• A. -190°C to +800°C
• B. -200°C to +700°C
• C. -100°C to +900°C
• D. 0°C to +1000°C

Answer: (A)

Type J thermocouples, made from iron and constantan, are rated to sense a broad span of temperatures where the metal pair remains stable and the millivolt output remains reliable. The commonly cited usable range is roughly -190°C to +800°C. This window lets you measure negative temperatures where iron still produces a measurable emf and stay within temperatures high enough that the materials don’t degrade or drift too much, which would spoil accuracy.

Other ranges either exclude negative temperatures or push beyond the safe upper limit for Type J, which would lead to inaccuracy or damage. So the -190°C to +800°C range best matches the practical operating window for this type of thermocouple.