多极板阵列电容传感器肥料流量在线检测关键技术研究

Fertilizer flow online detection is the basis of precision fertilization, the biggest difficulty of which lies in the complexity of the field operating environment, complex fertilizer characteristics, and non-contact detection without destroying the fertilizer tubes. Since fertilizer transport tubes should be kept close and polish, this study will focus on the conversion mechanism from flow rate to electrical signal of fertilizer flowing through a tube, as while as parameters optimization method of plates' number, shape, dimensions, etc. Additional, the study will focus on optimization design method of capacitor arrays with optimal correlation between material flow and capacitance, and the design of multi-plate array non-invasive capacitive sensors. Further more, this study will encompass the development of high sensitivity amplitude and phase difference converter circuits, studying wavelet transformation and Kalman filtering based weak capacity signal extraction technology, designing anti-interference shielding devices and data acquisition systems, and through hardware and software filtering, the shielding of interference signals from mechanical vibration and engines. Further study will focus on measurement methods of fertilizer flowing speed in pipeline with electrical capacitance tomography, together with fertilizing machine speed, material moisture compensation and environmental temperature correction, the acquisition of material mass flow information, and the establishment relationship models between material flow and multi-sensor information. Finally, the study will explore the development of a material flow online detection system， by carrying out field tests, so as to provide a theoretical basis for a precision fertilizer feedback control system.

肥料流量在线检测是实施精准施肥前提,最大的难点在于复杂的田间作业环境、复杂的肥料特性及不能破坏排肥管的非接触式检测。项目针对精密施肥机的排肥管需要保持封闭通畅的特点，研究肥料流动过程中流量信号转换为可检测电信号的变送机理，研究极板对数、形状、尺寸等参数优化方法，研究肥料流量与电容值相关性最优的电容极板设计方法，设计非侵入式多极板阵列电容传感器。研制高灵敏度幅值和相位差转换电路，研究基于小波变换及卡尔曼滤波的微弱电容信号提取技术，设计抗干扰能力强的屏蔽装置及数据采集系统，通过硬件和软件滤波实现对机械震动、发动机射频等干扰信号的屏蔽。研究基于电容层析成像的管道内物料流动速度测量方法，结合农机行走速度、物料水分补偿和环境温度校正，实现物料质量流量的信息获取，建立物料流量与多传感器信息融合的关系模型。开发适用于施肥机肥料流量在线检测系统，并进行田间试验,为精准施肥反馈控制提供理论依据。

施肥量在线检测是实施精准施肥的前提，也是制约目前施肥机械精准化作业的难点。项目针对排肥管路需要保持封闭通畅特点，提出了基于电容法的非接触式肥料流量在线检测方法。通过仿真分析，揭示了电容传感极板数目与极板宽度对传感器测量输出性能的变化规律，提供了多极板电容结构的优化设计方法，设计了多极板电容传感结构；采用基于电容数字转换原理的信号调理方法，设计完成微电容信号调理电路，采用最小二乘滑动平均滤波算法对原始电容信号处理，实现了微弱电容信号的有效提取；研究了氮磷钾肥肥料质量与电容响应关系，获得了肥料质量流量与电容响应的线性模型，模型决定系数达到0.99，对模型进行了试验验证；完成了多极板肥料流量电容传感器的整机研制，开发了施肥量在线检测软件，构建基于CAN总线的施肥流量在线检测系统，解决了封闭管道内物料流量在线检测的技术难题。该系统能够快速、准确地获取精密施肥机的施肥流量，为实现高精度变量施肥反馈控制的奠定基础，对于提高田间施肥作业质量，节约肥料投入、减少土壤和地下水污染等，具有重要的经济效益和社会效益。