You can use this Type J thermocouple from RS PRO to measure changes in temperature. It has a five-second response time to give you a fast reading.
The thermocouple's probe is made from 316-grade stainless steel, so it's protected from rust and corrosion, providing a long working life. The material also has excellent heat resistance, allowing the unit to measure temperatures of up to +700°C.
This thermocouple has a measuring point formed from a positive iron conductor and a negative constantan (copper–nickel) one. These dissimilar alloys meet in a junction and create voltage when the temperature changes. This makes for highly accurate measurement. The product has an aluminium terminal head with an Ingress Protection (IP) rating of IP67, indicating that it's both dust-tight and waterproof. This means you can use it in harsh industrial settings or outdoors.

• Maximum sensed temperature of +700°C
• Probe diameter of 6 mm
• Probe length of 400 mm
• 316L stainless steel probe material
• Response time of 5 s
• Meets RoHS (Restriction of Hazardous Substances) standards
• Connection head termination type
• Type J thermocouple