Question

Why ungrounded thermocouple have a higher response than exposed thermocouple

Answer 1

Grounded, ungrounded and exposed. With a grounded tip the thermocouple is in contact with the sheath wall. A grounded junction provides a fast response time but it is most susceptible to electrical ground loops. In ungrounded junctions, thethermocouple is separated from the sheath wall by a layer of insulation