Analysis of a Soil-Moisture Sensor for Potential Failure Modes and Mass Manufacturing

Abstract

We present techniques for mass manufacturing of a soil-moisture sensor that includes a heat probe and a temperature probe. The requirement of mass manufacturing necessitated a few changes in design of the heat probe. We also present an improved design using the standard method of reliability analysis. Potential failure modes were identified for the sensor, and the modifications to the design were made accordingly. The approach to design was aimed at improving the accuracy and repeatability of the sensor as well as making it suitable for mass manufacturing. Automating the process of manufacturing the sensor as a mechatronic system is outlined. By doing so, we aim to bring down the cost of the sensor considerably, thus enabling the use of sensors in large quantities for deployment in a field. IntroductionSoil-moisture sensors are beneficial for controlled irrigation practices in agriculture. Since the moisture level might vary from point to point in a field, enough sensors need to be deployed over the entire field. Hence, the sensor must be made affordable, reliable, and accurate. This can be achieved through automated mass-manufacturing processes while ensuring reliability. In our earlier work [1, 2], we developed, prototyped, analyzed, and tested a soil-moisture sensor. It takes, on an average, 10 h to make one sensor manually. It is a laborious process and manual method affects the consistency of sensor performance. In this paper, we undertake translational research aspects to make the sensor suitable for producing in large numbers with consistent performance for extensive field studies.The sensor under consideration is called a dual-probe heat-pulse (DPHP) sensor (Fig. 1). It consists of two probes: a heater and a thermocouple. The heater comprises a nichrome wire (50 µm diameter) wound around a relatively thick copper wire