土壤水分直读仪的试制

本水分仪是根据水土流失遥测预报科研项目的要求而制成的。为了遥测土壤水分,以含水土壤块作为电介质,测取土壤的水分——电容特性曲线。结果表明,土壤的电容量随土壤水分的增加而明显地增加,受其它因素的影响较少。仪器的传感器埋设于土壤中,它具有三个电极和间接的极间介质。相应地,它的测量电路采用具有三个输入端的变压器电桥,从而免除了电极边缘和外界干扰的影响。土壤水分的计量及其温差的补偿是在经验公式的基础上,通过模拟计算电路的运算,便可以在仪表上直接读出土壤含水量的百分值;也可以通过模——数转换而实现打印记录。

THE TRIAL-PRODUCE OF AN INSTRUMENT FOR MEASURING SOIL MOISTURE BY DIRECT READING

An instrument with direct reading meter for measuring soil moisture has been made to meet the needs of research in forecast of water loss and soil erosion by remote metering.In order to remotely detect soil moisture,soil blocks with different water contents were used as dielectric material to plot curves of soil moistune versus soil capacitance.The results showed that soil capacitance increases obviously with increase in soil water content and is little effected by other factors.Therefore soil water content can be determined by measuring its capacitance.Sensor of the instrument with three electrodes,between which indirect dielectric material is put,is buried in the soil.A transformer-ratio arm bridge with three terminals is adopted as its measuring circuit to eliminate the influence of electrode edges and exterior interference.Based on an empirical formula,soil moisture calculating as well as its temperature correction is worked out by means of an analogue computing circuit so that the percentage of water in soil can be directly read on the meter.The record can also be printed by an A-D converter.