IMPLEMENTING A THERMOCOUPLE COLD JUNCTION COMPENSATION IN THE CLASSROOM

A. Fernández Cobeño, P. Fernández Sánchez

Universidad del Pais Vasco (UPV/EHU) (SPAIN)
In the Industrial Electronics and Automation Engineering graduate degree courses students have to learn how to correctly select and use different types of electronic sensors. Temperature is an extremely important real-world variable and there are multiple types of commercially available electronic sensors devoted to measure this variable. Moving a step further, we can say that thermocouples are one of the most widely used temperature-measurement devices in industrial applications thanks to their ease of use, overall cost and, above all, wide temperature range. The technological applications of thermocouples usually involve the so called CJC (Cold Junction Compensation), which includes the definition and function of a reference (cold) junction, making to some degree, the teaching/learning process not particularly straightforward. Therefore, the teaching process might greatly improve if some kind of real CJC experience could be implemented in the classroom prior to the development of the laboratory sessions.

In the aim to give a better understanding of the thermocouple CJC, the authors, as a first step, designed a low-cost temperature-measuring electronic circuit based on a thermocouple thus involving a CJC. Secondly, the aforementioned circuit's electronic simulation, via PSpice software, was successfully achieved thanks to the macromodelization of the temperature sensors. Doing so, this simulation can be used in the classroom as a virtual laboratory. In order to give access to the simulation via the Internet, the authors used the Moodle platform to share the simulation archives with the students. Finally, the authors implemented a portable prototype of the previously designed and simulated electronic circuit. So, it is possible to show on the classroom’s whiteboard in real time how the temperature measurement is achieved thanks to the use of the Hewlett Packard HP34970A data acquisition device and its adequate programming through the software HP Benchlink Data Logger. This way the classroom becomes a virtual/real laboratory as well. The authors think that the degree of interdisciplinarity achieved in the classroom following the “circuit design-simulation software-real prototype-commercial data acquisition system” procedure shown with this set-up can be used to the students’ own advantage for a better learning process of the thermocouple’s CJC. Besides that, introducing this standard operating procedure, usually a normal working practice in the professional life, is of great interest for the students’ know-how when looking for solutions for new technological applications in the field of electronic engineering.