A sensor comprised of an electronic circuit and a hybrid single and dual heat pulse probe was constructed and tested along with a novel signal processing procedure to determine changes in the effective dual-probe spacing radius over the time of measurement. The circuit utilized a proportional–integral–derivative (PID) controller to control heat inputs into the soil medium in lieu of a variable resistor. The system was designed for onboard signal processing and implemented USB, RS-232, and SDI-12 interfaces for machine-to-machine (M2M) exchange of data, thereby enabling heat inputs to be adjusted to soil conditions and data availability shortly after the time of experiment. Signal processing was introduced to provide a simplified single-probe model to determine thermal conductivity instead of reliance on late-time logarithmic curve fitting. Homomorphic and derivative filters were used with a dual-probe model to detect changes in the effective probe spacing radius over the time of experiment to compensate for physical changes in radius as well as model and experimental error. Theoretical constraints were developed for an efficient inverse of the exponential integral on an embedded system. Application of the signal processing to experiments on sand and peat improved the estimates of soil water content and bulk density compared to methods of curve fitting nominally used for heat pulse probe experiments. Applications of the technology may be especially useful for soil and environmental conditions under which effective changes in probe spacing radius need to be detected and compensated for over the time of experiment.

中文翻译：

---

用于自动检测有效热脉冲探头间距半径的信号处理，作为自校准热脉冲探头的基础

构造并测试了一种由电子电路和混合单双热脉冲探头组成的传感器，以及一种新颖的信号处理程序来确定有效双探针间距半径随测量时间的变化。该电路利用比例积分微分（PID）控制器来控制热量输入土壤介质中，以代替可变电阻器。该系统专为机载信号处理而设计，并实现了USB，RS-232和SDI-12接口，用于机对机（M2M）数据交换，从而使热量输入能够在土壤处理后不久就适应土壤条件和数据可用性。实验时间。引入信号处理以提供简化的单探针模型来确定热导率，而不是依赖于后期对数曲线拟合。同态和导数滤波器与双探针模型一起使用，以检测有效探针间距半径随实验时间的变化，以补偿半径以及模型和实验误差的物理变化。为在嵌入式系统上有效地对指数积分求逆而开发了理论约束。与名义上用于热脉冲探针实验的曲线拟合方法相比，将信号处理应用于沙土和泥炭的实验可改善对土壤水分和堆积密度的估计。