Side illuminated optical fiber sensors for hydroponics

• Grant number: 16/16583-3
• Support Opportunities: Research Grants - Innovative Research in Small Business - PIPE
• Duration: July 01, 2017 - December 31, 2019
• 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 research grant: 14/22541-6 - Optical fiber liquid level sensor for hydroponics, AP.PIPE
• Associated scholarship(s): 17/16624-4 - Side illuminated optical fiber sensors for hydroponics, BP.PIPE

Abstract

Nutrient concentration and liquid level information are important monitoring parameters in hydroponic systems. Whereas nutrient concentration has a direct effect on the yield and quality of plants, liquid level measurement is required to ensure nutrient water is available. Yet, growers do not instrument most hydroponic systems: either because available technology is inconvenient and expensive or because readily available and inexpensive instrumentation provides only a fraction of the required information. Typically, nutrient water is prepared with concentrations thought to be appropriate. However, several irrigation cycles, the nutrient concentration decreases due to plant absorption, and the recycled water changes to unknown levels. At this point, the water is discarded leading to nutrient waste, nutrient pollution and widespread environmental contamination of aquatic, ground and drinking water. This cause blue baby syndrome in infants and harmful algae blooms (HAB) that produce highly potent toxins that affect aquatic life. Although inexpensive instrumentation is readily available, such as pH, Electric Conductivity (EC) and Total Dissolved Solids (TDS) meters, only overall ion concentration can be determined from these devices. For this reason, they cannot provide the concentration of specific ions. The situation is similar to liquid level measurements. Typically, liquid level is controlled by overflow pipes and float and solenoid valves without any sensing technology whatsoever. However, when monitoring technology is used, such as pressure gauges, the resulting measurement can be done only in a single place with a spatial resolution of 10 cm. Although acceptable to storage tanks, this resolution and single point sensing capabilities are unacceptable for liquid films, typically 1 to 2 cm thick, that flow along the channels of NFT's (Nutrient Film Technique) liquid culture systems. Clearly, there is a needed for better and inexpensive instrumentation to monitor liquid levels and nutrient concentration. The objective of this project is to provide a complete monitoring system for hydroponics. During our Phase I we demonstrated a reliable optical fiber liquid level sensor with a 1 cm spatial resolution: in this Phase II we will build a device with 2 mm spatial resolution or better. In previous grants, we also developed a unique optical fiber colorimeter that can determine the concentration of different nutrients: nitrate, potassium, iron and others. Both devices use our patented side illuminated optical fiber technology that has a special fiber mounted over a support with a linear array of LEDs. The LEDs side illuminate different sections of the fiber producing multiple sensing points and a signal at the fiber end face. Whereas the signal of our liquid level sensor depends on the refractive index of the medium surrounding the fiber, the colorimeter's signal is affected by the color of the liquid sample. We anticipate a low cost, roughly R$1,000, system that can monitor liquid level and nutrient concentration within the required range of the industry. With this system, we will provide a full monitoring solution for the hydroponics community. (AU)