A wireless multi-sensor system for soil moisture measurement

This paper presents a new multi-sensor system with wireless connectivity taking advantage of three different sensing techniques for automatic measurement of soil moisture in the field. The developed multi-sensor system deploys dual probe heat pulse (DPHP), capacitive and resistive based soil moisture sensors. Every sensor node is a fully operational system with instrumentation, controller, solar powered battery module and wireless data communication. This paper also compares the implemented sensors in terms of accuracy, power and cost. All implemented sensor nodes measure the soil moisture once per hour. The developed DPHP sensor measures the moisture with accuracy of ±3% with ON time of 3min and energy consumption of 30J per hour. The developed capacitive sensor exhibits accuracy of ±3% with negligible energy consumption as compared to the DPHP sensor. However the DPHP sensor is cost effective as compared to the capacitive sensor. The resistive sensor identifies the moisture content into four bands namely dry, low, medium and high. This sensor is the cheapest when compared to the other two sensors. Energy consumption of resistive sensor is 600mJ per hour, with measurement time of 15min. This multi-sensor system is tested with various soil samples and moisture levels including red soil.