Film thickness measurement system using FPGA technology

The development of a technique for high spatial and temporal resolution film thickness measurement in oil-water flow is presented. A capacitance measurement system is used to measure thin water films near to the wall pipe. The system consists of seven parts: a signal generator, analog multiplexers, a planar sensor, auto-balancing bridges, logarithmic amplifiers, an analog-digital converter and a control unit. The measurement system is controlled by a NI FPGA RIO System. The FPGA has two state machines. The machines control the synchronization between the transmitter circuit board, the digitizer and a computer. FPGA technology has showed to be a flexible electronics, which let to change, easily, some important features as acquisition rate, number of channels and samples, among others. Experimental results of the technique indicated that the system can measure thickness between 400 μm and 2200 μm. Film thickness in oil-water flow was studied in a 12-m long vertical glass pipe, with 50.8 mm of internal diameter, using mineral oil (828 kg/m3 of density and 220 cP of viscosity) and tap water.