An affordable, open-source, microscale conductivity and temperature probe for density measurements in stratified flows

In stratified flows, conductivity (combined with temperature) is often used to measure density. The conductivity probes typically used can resolve very fine spatial scales, but can be fragile, expensive to replace, and sensitive to environmental noise. A complementary instrument, comprising a low-cost and robust probe, would prove valuable in a wide range of applications where resolving extremely small spatial scales is not needed. We propose using micro-USB connectors as the actual conductivity sensors; these have five gold-plated microelectrodes that can be readily exposed for two-wire or four-wire measurements. To take advantage of our choice of sensor, we design a custom electronic board for simultaneous acquisition from four sensors, with conductivity resolution of 0.1%, comparable to typical existing probes. We demonstrate our system through stratified flow experiments. The multi-channel capability can be used to approximately reconstruct density fields, whereas the customizable design enables measuring density near complex boundaries.