肥液pH值和电导率测量仪的设计与试验

Design and experiment on fertile solution pH value and electrical conductivity measuring instrument

为实现肥液pH/EC的快速在线检测,设计了一种pH/EC测量仪,主要由MSP430F2132单片机、pH/EC传感器、电源稳压模块、人机交互界面、pH信号调理电路、EC信号调理电路等组成.通过配制9种不同pH的溶液,在10~40℃范围内,测试了温度对pH值的影响,并与经验方程的计算值作对比,结果表明在适合农作物生长的土壤环境(pH值为6.5~7.5)中,由温度引起的测量误差可忽略.以1.0~19.5 ms/cm范围内的195种不同电导率值溶液为待测肥液,试验确定了采用8档电阻分档测量模式,其测量激励信号为幅值±3.5 V、频率4 kHz的方波信号,并进行了电导率的温度补偿.对测量仪进行了标定与验证试验,结果表明:pH值测量的最大绝对误差为0.04,EC值测量的绝对误差在±0.1 ms/cm内,能在农业工程上满足要求.

In order to realize rapid and on-site detection of fertile solution pH/EC,one instrument was designed,which was composed of MSP430F2132,pH/EC sensor,regulated power module,human-computer interface,pH/EC signal processing circuit,EC signal processing circuit,etc.Through preparing 9 different pH solutions between 10-40℃,one test for the effect of temperature on the pH value was made by comparing with the calculated value of empirical equation,and the result shows that in the soil environment(6.5-7.5 pH)which is suitable for crop growth,the measurement error by temperature can be neglected.195 different kinds of fertile solution were tested,whose EC value ranged from 1.0 to 19.5 ms/cm,and the test used 8 grades of resistance grading measurement mode,whose measuring excitation signal was square wave signal with amplitude±3.5 V and 4 kHz frequency,and temperature compensation of EC was made.The calibration and verification test of measuring instrument show that the maximum absolute measured value errors of pH and EC are 0.04 and within±0.1 ms/cm,which can meet the requirements of agricultural engineering.