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| Design and experiment on fertile solution pH value and electrical conductivity measuring instrument |
| FENG Ruijue1, WANG Zhidong2*, LI Zhifeng1 |
| 1. School of Electrical Engineering, Guangzhou College of South China University of Technology, Guangzhou, Guangdong 510800, China; 2. Research Center of Smart Energy Technology, School of Electric Power, South China University of Technology, Guangzhou, Guangdong 510640, China |
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Abstract 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.
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Received: 18 September 2019
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