Oxidization, Contamination, and Automation for High Temperature Verification of Thermocouples

Abstract

During the process of verifying K type thermocouples at high temperatures, the sheath turns gray or breaks down and flakes off. This creates a risk of contaminants and damage to product in a vacuum braze furnace. The cost of recertifying the thermocouples and cleaning of the furnace block when a thermocouple sheath breaks down is high. After working through this process for many years, I came up with a new furnace setup that reduces the potential for contamination of product. This paper will explain the process, verification station set up, tools and materials used to reduce oxidization of the sheath material. We have updated from an inconel isotheral block furnace to an alumina isotheral block furnace. This eliminates the contamination to the reference PRT being it also has an alumina sheath. The why is when an alumina sheath is contaminated with inconel the OEM will not calibrate the PRT because of possible contamination to the silver fixed point cell. The automation improvement has reduced cost in labor and down time.