Lab Report 9.28.2008 "Thermocouple Circuit"

On September 28, 2008 the N.M.E design team met to resume the next phase of the project. Our primary objective was to build a circuit for the Omega Nickel Chromium K Type Thermocouple. To construct this circuit we bought necessary components from Radio Shack along with the LTC1050 Precision Zero-Drift Operational amplifier and LTC1025 Thermocouple Cold Junction Compensator (fig. 1).

We were able to build the circuit, but unfortunately not as desired. Apparently we were missing two essential components, a bread board and a (1) 100Ω (ohm) potentiometer. We tried to contact many of the surrounding electronics stores, but had little success. Our next option was to improvise and use basic electronic techniques to construct a partial potentiometer.

Fig. 1
Components

Our solution was to take (2) 100Ω (ohm) resistors, set them parallel to each other and obtain a 50 Ω (ohm) resistance. We also had (5) 150 Ω (ohm) resistors and followed the same procedure in order to obtain a 75 Ω (ohm) resistance. And finally we set a (1) 100K Ω (ohm), (1) 20K Ω (ohm), (1) 4K Ω (ohm) and a (1) 2.2K Ω (ohm) resistor in series to obtain a 127K Ω(ohm) resistance. After soldering all the components to the board we began testing (fig. 2). The resistance at expected intervals were correct as well as the reference and input voltages. Unfortunately the desired output from the thermocouple was not obtained. We will purchase the necessary components prior to the next meeting and will try to solve this problem.

Fig.2
Board Prototype

Jorge E. Fontanez
N.M.E. Design Team