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Optical fiber liquid level sensor for hydroponics

Grant number: 14/22541-6
Support Opportunities:Research Grants - Innovative Research in Small Business - PIPE
Duration: July 01, 2015 - August 31, 2016
Field of knowledge:Interdisciplinary Subjects
Principal Investigator:Claudio Oliveira Egalon
Grantee:Claudio Oliveira Egalon
Host Company:C O Egalon Consultoria - ME
City: São José dos Campos
Associated grant(s):16/16583-3 - Side illuminated optical fiber sensors for hydroponics, AP.PIPE
Associated scholarship(s):15/16200-4 - Liquid level optical fiber sensor for hydroponics, BP.PIPE


Currently, most hydroponic reservoirs levels are controlled by a mechanical system. These systems use a buoy that floats above the liquid surface: when the liquid reaches a certain level, the buoy actuates a mechanical switch that either allows or stop the flow of water into the reservoir. Although inexpensive, this system has a series of problems: 1. the plant roots may cause the float to become stuck in its guide resulting in reservoir overfill and water spillage. 2. These floats cannot be easily interfaced to a digital system preventing the recording of the amount of water, against time, in the reservoir and3. They are not sensitive enough to determine water consumption by the plant which can be used to determine plant health. The objective of this project is to develop an inexpensive optical fiber sensor, with a high spatial resolution, to determine liquid level in hydroponic containers. This sensor can be used at both the macroscopic and microscopic levels. At the macroscopic level, on the order of a few millimeters, the sensor will be used to ensure the container has a proper liquid level. This will prevent water spillage and the increase in the concentration of nutrient salts which can be become toxic above a certain level. At the microscopic level, on the order of a few microns, the fiber will be used as an optical potometer to determine plant water usage: an indicator of plant stress. Using our unique side illumination optical fiber sensor technology, we will manufacture a very sensitive liquid level sensor. This sensor consists of a tapered optical fiber, mounted over a support with a linear array of LEDs to side illuminate the fiber at different sections along its length. Upon side illumination, a fraction of this light is coupled into the fiber core: the amount of signal being a function of the refractive index surrounding the fiber core. We conducted preliminary experiments and determined that the signal of a submerged sensing point is less than half of that exposed to air. In this project, a three sensing point device will be tested in a regular water container. Afterwards, the sensor will be used in an actual hydroponics system during plant growth. Later on, a more advanced version of this device, with 30 sensing points, will also be built and tested. The anticipated result is a low cost optical fiber sensor that is rugged, easy to use, can make liquid level measurements and determine the amount of water used by the plant. This device will find applications in hydroponics crop production, in fertigation, in the automotive industry and in the beverage, the oil and gas and food industries. (AU)

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