Semi-Automated Setup for the Manufacture of Dual-Probe Heat Pulse (DPHP) Soil-Moisture Sensor

Abstract

In the dual-probe heat pulse (DPHP) sensor we have developed, a voltage pulse is applied to the heat probe across a powder-coated ultra-thin nichrome wire that is wound on a thin copper rod encased in a steel tube. The rise in temperature measured by an adjacent thermocouple probe is used to estimate the volumetric soil-moisture content because heat capacity of the soil is largely influenced by the moisture in the soil. The focus of this paper is on semi-automated manufacture of the DPHP sensor. In the current method of prototyping of the sensor, manual winding of the powder-coated nichrome wire in a double helix around the copper rod is tedious and the nichrome wire is prone to breakage or loss of insulating powder coat. Furthermore, soldering of the nichrome wire along with the connecting wires on the solder pad is time-consuming. The semi-automated double-helical winder mechanism developed in this work makes use of two stepper motors, while the solder setup is foot-pedal-controlled and has the soldering iron attached with two motorized solder wire feeders.