Development of an electronic drag-force flow meter by using load cell

Author(s)

Antonio Pires de Camargo

• Document type: Master's Dissertation
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2010-01-29

Examining board members

Tarlei Arriel Botrel; Edson Eiji Matsura; Olivio José Soccol

• Advisor: Tarlei Arriel Botrel

Abstract

New available equipments and technologies in the market are each time more important for the agricultural section development and modernization. The electronics and automation area have great value on this evolution, speeding up activities as well as decreasing costs, mainly those costs regarding with necessary labor to execute routine tasks. On irrigation there is a common objective of choosing techniques that optimize crops water use, increasing efficiency and reducing losses of water distribution and application processes. The flow metering in an irrigation system is indispensable stuff when an efficient water management is desired. There are many tools, devices and methods of flow metering each one with its respective features. Considering a technology innovation principle this work had the purpose to develop an electronic flow meter easy to use and low cost, using electronic devices. Nevertheless this research had the following objectives: a) An electronic flow meter development by using load cell; b) Hydraulics tests in order to determine a math equation that matches the instantly flow inside a pipeline; and c) Flow meter assess determining performance parameters. The research was done at Hydraulics Laboratory, Rural Engineering Department (Laboratório de Hidráulica - Departamento de Engenharia Rural), ESALQ/USP on Piracicaba-SP-Brazil. The developed equipment is based on drag force that a body experiences when immersed in a fluid stream. The flow meter developed has some screen options allowing user tasks definition like: metering, calibration, and make some internal configurations. In the metering task the flow value is updated on intervals close to 7 seconds being possible to select or change units showing flow results. The calibration task was developed to avoid or release the specialized labor need, equipments, computers or any sophisticated and complex method. In this task, it was implemented Least Square Method in order to calculate coefficients of a fitting equation. This equation was used to estimate flow from digital signals acquired from the electronic circuit. The configuration interface allows the visualization and change the fitting equation used by the system. It also allows the data transmission for computers by serial port (RS-232 protocol). The proposed flow meter is able to work from 7 to 28 m³.h-1 with uncertainty of ±1.4 m³.h-1 (± 2.7%). The coefficient of local head loss (K) was close to 0.55 for Reynolds number values higher than 105. In this work, the greatest drag force expected acting on the flat circular body and cylindrical object is about 1.87 N, resulting in a force on load cell up to 3 N. (AU)