So, an RTD is a current device and a thermocouple is a voltage device. The thermocouple is two dissimilar metals, welded together at a tip to create a voltage, a millivoltage. So an RTD is a resist of metal that changes resistance on increase or decrease in temperature.
When deciding between an RTD and a thermocouple ruggedness is one consideration, and a thermocouple would be a little bit more rugged than an RTD, has wider temperature range. RTD is not as quick to react as a thermocouple, but it is more accurate. RTD is also more reliable.
Lastly, in deciding between a thermocouple and an RTD, cost would be a consideration. Thermocouple is about a third the cost of an RTD.
Transcript from video at: https://www.youtube.com/watch?v=g0H_kyVJXxc&feature=youtu.be