In industrial and laboratory systems that use autoclaves, the quality of superheated water vapor can be important for process control, efficiency and reliability. One relevant indicator is the amount of condensed water present in the steam: vapor is considered to be of higher quality when the mass fraction of condensed water droplets is smaller.

Within the project, the device has been designed for measuring the quality of superheated water vapor at the outlet of an autoclave. The device is based on a capacitive bridge powered by an audio-frequency source, where water vapor is introduced into one capacitor of the bridge. As the proportion of condensed water increases, the relative permittivity of the vapor also increases, disturbing the balance of the bridge and producing a measurable signal.

The signal obtained from the bridge is amplified using an instrumentation amplifier and prepared for further processing. The device was designed as a simple and robust solution: the laboratory prototype has been implemented by our team, while the functional prototype has been by the customer. Tests showed high sensitivity, with the device able to measure relative permittivity changes of 0.001.