SensorTalk: Extending the Life for Redundant Electrical Conductivity Sensor

Air and soil sensors are used in smart agriculture to autonomously collect the soil-related data. It is important that the measurements of the sensors are accurate. This article uses electrical conductivity (EC) as an example to show how to avoid the inaccuracy due to EC sensor aging. We consider a promising solution that packages I redundant EC sensors in one device (I > 1) called I-redundant EC sensor package. The redundant-sensor package outputs the measured data based on a voting process among I sensors, which makes soil measurement more accurate and reliable. Based on the I-redundant EC sensor package, this article invents the first out-of-the-laboratory automatic calibration procedure in the farm field. We also propose the SensorTalk mechanism to extend the life of the I-redundant EC sensor package through calibration. Most people have the illusion that the life of a redundant-sensor package is longer than a nonredundant sensor. This article proves that the life of a redundant-sensor package is shorter than its nonredundant counterpart. Then, we propose the self-calibration process of the redundant-sensor package to extend its operation life. For example, if the life of a sensor in the I-redundant package is six months with the aging-after-calibration factor gamma = 0.9, then SensorTalk may extend its life to 52.2 months for I = 9. We also shed some nontrivial insights. In many smart farming solutions, the sensors typically report the measured data with a frequency lower than one per 10 min Our study indicates that by increasing the sampling frequency up to one per 20 s, calibration for an EC value can be sped up by 19 times. Our study also suggests that an odd I number should be chosen. If we add one more sensor to make an even I number, the life of the redundant-sensor package is actually shortened.