Campbell Scientific's FW04, FW1, and FW3 thermocouples measure atmospheric temperature gradients or fluctuations with research-grade accuracy. The models vary acording to their diameter (smallest to largest in terms of listed order). The FW05, having the smallest diameter, experiences the least amount of solar loading but is the most gragile. For all of these thermocouples, solar loading is small enough that a radiation shield is not required.
The wires are comprised of a chromelwire and a constantan wire joined at a measurement junction. A voltage potential is generated when the measurement end of the thermocouple is at a different temperature than the "reference end" of the thermocouple. The magnitude of the voltage potential is related to the temperaturedifference. Therefore, temperature can be determined by measuring the differences in potential created at the junction of the two wires. A reference temperature measurement is required.