Chet from Omega answers which thermocouple you should be using. Grounded vs Ungrounded. A thermocouple is a sensor for measuring temperature. This sensor consists of two dissimilar metal wires, joined at one end, and connected to a thermocouple thermometer or other thermocouple-capable device at the other end. When properly configured, thermocouples can provide temperature measurements over a wide range of temperatures.
Thermocouples are known for their versatility as temperature sensors therefore commonly used on a wide range of applications - from an industrial usage thermocouple to a regular thermocouple found on utilities and regular appliances. Due to their wide range of models and technical specifications, it is extremely important to understand its basic structure, how it works, its ranges as to better determine what is the right type and material of thermocouple for your application.