What does the sodium tester measure in the context of steam quality?

The sodium tester is specifically designed to measure the electrical conductivity of water, which is a key indicator of water purity in steam systems. High levels of sodium in the boiler water can signify alkalinity and other impurities that might compromise the quality of steam generated. Since electrical conductivity increases with the concentration of ionic compounds, the sodium tester provides insight into water quality, ensuring that it is appropriate for steam generation. This is essential for maintaining steam quality, avoiding issues such as scale formation, and ensuring efficient operation of steam systems.

In this context, the other options are not relevant because pressure levels pertain to the force applied within the system, heat transfer efficiency relates to how effectively heat is being transferred, and temperature variations deal with differing temperatures within the steam system. None of these directly measure the specific purity of the water and its implications on steam quality like the sodium tester does.