Soil Moisture Measurement System for DPHP Sensor and In Situ Applications

This paper presents a prototype system for measurement of soil moisture with dual probe heat pulse (DPHP)sensors. DPHP sensor has two probes: heater probe and temperature sensor probe which is a T-type thermocouple. Probes are spaced 2 cm apart. The heater is operated for 120 seconds and the respective rise in the temperature is measured using T-type thermocouple. The system comprises instrumentation amplifier and micro controller AVR ATMEGA16 with inbuilt ADC, LCD display, and RF XBee PRO modules for transmitting the analog value from micro controller to the computer, which is far apart. Data processing of values is done in MATLAB. Developed system is tested on white clay soil for different known volumetric moisture content. Measurement results show that rise in the temperature measured by the developed system is inversely proportional to the increase in soil moisture content as in the literature. As two extreme points, output voltage of thermocouple changes by 85 mV for 2.2% soil moisture level while it changes around 49 mV for 80% soil moisture content.