Sentence:  Three <WSD>thermocouples</WSD> were placed at different locations in the aluminum disk surrounding the anode holder to determine its temperature . 
Meaning of the word marked with <WSD> tags:  a kind of thermometer consisting of two wires of different metals that are joined at both ends; one junction is at the temperature to be measured and the other is held at a fixed lower temperature; the current generated in the circuit is proportional to the temperature difference