DISTRIBUTED CAPACITANCE MOTION SENSOR EMPLOYING ELECTRICAL SIGNATURE ANALYSIS

Capacitance sensors are among the most sensitive sensors employed for metrological and security applications. A variety of commercial systems exist that use capacitance sensors for security and safeguards applications. Among these are several systems that use distributed capacitance sensors in the form of cables that can be attached to items of interest. These are commonly applied as perimeter fence sensors, where the cables are attached to (typically) chain link fencing to detect signals that would be produced by cutting, climbing, or otherwise penetrating the perimeter fence. These products are extremely effective and serve their product markets well, reliably detecting intrusion events. However, the task of differentiating environmental noise from actual intrusion events is challenging. Moreover, it varies significantly with each application. The typical means for addressing this challenge is to use band pass filtering (usually only one or two selectable pass bands) as the primary means of signal analysis. Secondary analysis methods may include counting the number or duration of events that exceed a preset threshold to differentiate between situational noise and actual intrusion events. By employing more elaborate means of signal processing, the applications for distributed capacitance sensors may be significantly expanded. Electrical signature analysis (ESA) is a technology that has been applied to a wide variety of challenging measurement scenarios during the last two decades. It provides a means for extracting information from beneath what would conventionally be considered the \"noise floor\" of the applications to which it is applied. It combines elements of time domain analysis, frequency domain analysis, and pattern recognition to enable important diagnostic information to be extracted from signals as mundane as the current applied to an inductive motor. Through the use of ESA, specific signal characteristics have been exploited to identify incipient failures (bearings, gears, and pumps etc.), enabling preventive maintenance to forestall potential peril. We have combined the sensitivity of a distributed capacitance sensor with the specificity of ESA to greatly enhance the information that can be achieved through the use of these sensors. Data are presented from specific scenarios to illustrate these new capabilities.