Impact of thermocouple measurement errors on heat rate estimation in capacitor discharge welding

Abstract

Accurate temperature measurement is critical for modeling and controlling highly transient processes such as capacitor discharge welding (CDW), where conventional sensors may introduce significant errors. This work investigates how different thermocouple measurement strategies affect the accuracy of heat rate estimation in such conditions. Two experimental setups were analyzed: one using 30 AWG thermocouples with 90 ms sampling, and another using 40 AWG thermocouples with 4 ms sampling. A refined three-dimensional transient thermal model was developed, explicitly including sensor bead geometry and Joule heating effects in the thermocouple wires. The unknown heat rate at the weld bead was estimated using the nonlinear Function Specification Method. Comparative results demonstrated that improved sensor selection and higher sampling rates reduced residual errors and enhanced solution stability in the inverse heat transfer problem. The findings highlight the critical influence of measurement design and thermal model detail on the reliability of inverse solutions for highly transient thermal conditions such as CDW. Additionally, the inclusion of the thermocouple bead geometry in the model was presented as an effective alternative to minimize errors commonly associated with contact-based temperature measurements.