Low-cost fluid flow sensor to enable electronic control of fractional distillation columns

Abstract

A sensor is described that measures fluid flow up to 20 ml/minute, and down to 0.001 ml/minute. The measurement involves counting drips as they fall through a pair of optical beams. The beams are formed using a pair of ordinary optical proximity sensors arranged to face each other so that each photo- receiver sees the other sensor’s emitter. The beams operate at two different frequencies so as to prevent reflected signals interfering. Only two sensors, an 8-pin microcontroller, and four resistors are required for the sensing. Calibration for a specific fluid is straightforward. An ethanol-water mixture produces 16 drips/ml, significantly different from the default pharmaceutical value of 12 drips/ml.