Electrical signature analysis (ESA), a versatile and powerful, yet truly non-intrusive, technology pioneered at Oak Ridge National Laboratory (ORNL) can be readily integrated into most electro-mechanical equipment to greatly enhance condition diagnostics and prognostics capabilities. ESA provides diagnostic and prognostic information comparable to conventional vibration analysis but requires only access to electrical lines carrying input or output power rather than to the equipment itself. Thus, either onboard or remote analysis is possible—even continuous monitoring if desired. ESA has already been tested on and successfully applied to a wide variety of systems, including military, industrial, and consumer equipment.

Load and speed variations in electro-mechanical systems generally produce correlated variations in current and voltage. ESA analyzes these small perturbations and matches them to their source. The resulting time and frequency signatures reflect loads, stresses, and wear throughout the system and allow an extensive range of mechanical diagnostic information to be obtained from a single sensor attached to an electrical line.

Few available technologies can be so seamlessly integrated into existing maintenance programs. With the addition of a few sensors, ESA diagnostics can pinpoint electrical and mechanical problems and target maintenance on an as-needed basis, thereby increasing equipment reliability and maintenance efficiency and minimizing unexpected downtime.

Technical Basis

ESA provides a breakthrough in the ability to detect and quantify mechanical defects and degradations in electro-mechanical equipment and unwanted changes in process conditions. ESA is truly non-intrusive and does not interfere with the operation of the equipment being monitored.

As a result of continued R&D by ORNL, ESA has matured as a diagnostic/prognostic technology. ORNL has developed several signal processing and signature analysis methods to capitalize on the intrinsic abilities of conventional electric motors and generators to act as transducers.

Time-dependent load and speed variations occurring throughout an electro-mechanical system will generally induce small variations in the motor’s and/or generator’s electrical response. These variations are observed as a change in current (for a motor) or a change in voltage (for a generator.) ORNL researchers have pioneered the development and application of signal conditioning techniques for extracting these small electrical perturbations and relating them to their source and have thus opened a new field for diagnostic innovations.

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Motor Operated Valve
(showing areas monitored by MCSA)

Motor-Operated Valves

Motor-operated valves are used in large numbers throughout many industries. In the mid-1980s, ORNL, with funding from the U.S. Nuclear Regulatory Commission, evaluated methods for monitoring aging and service wear of nuclear power plant motor-operated valves (MOVs). In addition to evaluating standard condition monitoring methods employing equipment-mounted sensors, ORNL researchers focused their efforts at developing diagnostic techniques that used the motor’s running current, since it could be acquired remotely and non-intrusively. These new techniques provided a breakthrough in detecting load and speed variations generated anywhere within the MOV and converting them into revealing “signatures” that could be used to detect component degradation and precursors to MOV failures.

ORNL named this new monitoring technology Motor Current Signature Analysis (MCSA), a term that is widely shown by ORNL to provide the sensitivity necessary to detect a large variety of MOV problems including gear wear and binding, degraded lubrication, over-tightened stem packing, valve seating problems, bent valve stem, improperly set switches, etc. The successful application of MSCA as a monitoring technology for MOVs provided a foundation on which additional tools were developed by ORNL for monitoring and analyzing electrical current, voltage, and power signals. These developments are applicable to both motor and generator systems and now comprise a powerful technology suite called Electrical Signature Analysis (ESA).

Motor current time waveform and frequency spectrum for a motor-operation valve (MOV) showing electrical signature
features that reflect the condition of the MOV at many areas where degradation can be detected

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ORNL Patented Technology

ESA is now recognized as a viable diagnostic technology by a large number of companies. Forty-seven U.S. patents now reference the first ORNL patent, which was issued in October 1990. ORNL has a total of fifteen patents on ESA. For more information on ESA technologies that are now available, please visit our technology transfer site.

Cumulative Number of U.S. Patents Referencing The First Oak Ridge ESA Patent

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