Special limits of error thermocouples are made with a higher grade of wire, which increases their accuracy. They are more expensive than the more common standard limits of error thermocouples which use standard “thermocouple grade” wire.
“We are often asked, what is the difference between special limits of error, standard limits of error, and extension grade thermocouple wire? Today’s discussion will review base metal thermocouple tolerances for special, standard, and extension grade wire. First, we will look at the difference between a thermocouple wire producer and the different types of thermocouple wire users. Then, we will look at emf (electromotive force) data for single-leg thermoelements and how to determine temperature deviation. Finally, we will touch on how thermocouple wire is manufactured at the wire producer.”
Article by Ed Valykeo, Thermocouple Specialist at Pelican Wire, Naples, FL.
Source: Heat Treat Today