Passive Probe: Mechanically-Modulated Field Sensing for Motion Tracking and Flow Estimation

Abstract

The internal mechanical motions of a dynamic system can serve as the basis for developing “free” sensors that probe operating state and potentially diagnostic health. Specifically, the interaction of a moving mechanical structure with an applied, nonintrusive field, e.g., an electric or magnetic field, can produce a signal that creates a sensor with little additional hardware. In this paper, bellows-and-diaphragm natural gas (BDNG) meters provide an illustrative example for three different approaches for transforming a metering mechanism and its consumption totalizer into a high quality flow meter. Detailed flow information provides a data-stream for nonintrusively monitoring the real-time operation of loads – in this example case, loads that consume natural gas such as burners, heaters, and engines. The flow information can also be used for fault detection and diagnostics, e.g., for finding leaks or correlating faulted operation with respect to the operation of electrical actuators or other flows of consumables like water. This paper examines three BDNG meters and presents a methodology for inexpensively adding digital flow-rate measurement capabilities to each meter. The methods developed here can in principle be applied to any dynamic machine for consumption estimation or fault detection. They can also be used with other nonintrusive field stimuli including light and sound. Mechanical retrofit techniques are described, and exemplary signal processing and estimation chains including compensation, flow rate estimation, and post processing are presented.