Troubleshooting a furnace temperature controller problem -- part 2
One of the benefits of teaching Instrumentation at a technical college is that other programs around campus use real instrumentation, thus providing students with real troubleshooting opportunities. Here, the Machine Technology program had a problem with a heat-treat furnace, where one temperature controller read a vastly different temperature than the other controller. Students documented their troubleshooting of this problem in a few short video clips.
In this very short video clip, students took two successive voltage measurements of thermocouple signals to see whether the thermocouples were outputting different amounts of voltage or not. If the two signals were different, it would mean the cause of the different temperature displays was due to a bad thermocouple. However, the two thermocouples turned out to produce the same voltage, which meant the thermocouples were both good and the problem was within one of the controllers. The students also compared these millivoltage signals against a thermocouple table to see if the temperatures were realistic, and they were.
This is a great example of a useful diagnostic test, showing us where the problem was located, and where it was not located.