High resolution simultaneous dual liquid level measurement system with CMOS camera and FPGA hardware processor

摘要

In this paper a new high precision automatic measurement system for liquid level measurement in membrane distillation application is presented. Membrane distillation (MD) is a relatively new process that is being investigated worldwide. It has some advantages in relation to other separation processes such as conventional distillation and reverse osmosis (RO), which are: high quality of distillate, low operating temperatures, low operating pressure, low power consumption allowing the use of alternative energy sources such as solar and geothermal energy. For MD process it is necessary a very high precision system to measure the solution level in the reservoirs, able to detect changes smaller than 0.05 mm. This is due to the small fluxes through the membrane, and therefore it is necessary to detect the small changes produced in the liquid levels in the reservoirs. Until now such measurement has been made manually, by means of a cathetometer, but it resulted very uncomfortable. In order to overcome this issue, a high resolution and accuracy system (0.013 ± 0.008 mm), that makes automatic measurements of both reservoirs, cold and hot, is proposed. This system is based on a laser beam, assisted with a high resolution 3 Mpixels CMOS camera and a computer vision processor implemented in a FPGA, with a measurement rate up to 12 times per second.