Non-intrusive stress measurement (system), or NSMS, is a method for determining dynamic blade stresses in rotating turbomachinery. NSMS is also known by the names "blade tip timing" (BTT), [1] "arrival time analysis" (ATA), "blade vibration monitoring" (BVM), Beruehrungslose Schaufel Schwingungsmessung (BSSM), and "blade health monitoring" (BHM). NSMS uses externally mounted sensors to determine the passing times of turbomachinery blades. The passing times after conversion to deflections, can be used to measure each blade's vibratory response characteristics such as amplitude/stress, phase, frequency and damping. Since every blade is measured, stage effects such as flutter, blade mistuning, and nodal diameter can also be characterized. [2] The measurement method has been used successfully in all stages of the gas turbine engine (fan, compressor, and turbine) and on other turbo-machinery equipment ranging from turbochargers to rocket pumps. The ability to apply the technology to a given situation is dependent upon a sensor type that can meet the environmental requirements. [3]
A set of sensors is used to measure the arrival times of rotating blades. These arrival times, in comparison to a baseline, are used to determine blade deflections. The blade deflections over a number of revolutions and/or across a number of sensors can be used to determine vibratory characteristics. This information, in conjunction with a finite element model (FEM), can then be used to determine the dynamic stresses in a rotating part. [2]
Any sensor or probe that can provide a precise indication of a blade's passing can be used in NSMS. Commonly optical probes using fiber optics are used to obtain a high level of spatial resolution. A light source, typically a laser, and fiber optics are used to direct a constant beam of light into the path of a rotating blade. As a blade passes the probe, light is reflected and captured by fiber optic and routed to a photo detector for conversion to an electrical signal. Field type sensors such as Eddy Current, Capacitive, and Microwave sensors are useful in harsh environments and for long duration testing.
NSMS technology was patented as early as 1949, [4] with many improvements patented since that date. Some recent US practitioners believe that NSMS was first developed in 1980, by major aircraft engine OEMs (and the US Air Force). [5] It may be envisioned as a replacement technology to rotating strain gauges, however it is currently used as an essential complement to strain gauges. The technology is widely used for turbo-machinery development and high cycle fatigue (HCF) troubleshooting. Due to the direct blade observation, external mounting and inherent serviceability of the sensors, NSMS has been used since at least 2006 as a long-term health monitoring method. [6] More recently, multiple practitioners are becoming active in this application of the technology. [7]
A viscometer is an instrument used to measure the viscosity of a fluid. For liquids with viscosities which vary with flow conditions, an instrument called a rheometer is used. Thus, a rheometer can be considered as a special type of viscometer. Viscometers can measure only constant viscosity, that is, viscosity that does not change with flow conditions.
Photonics is a branch of optics that involves the application of generation, detection, and manipulation of light in form of photons through emission, transmission, modulation, signal processing, switching, amplification, and sensing. Photonics is closely related to quantum electronics, where quantum electronics deals with the theoretical part of it while photonics deal with its engineering applications. Though covering all light's technical applications over the whole spectrum, most photonic applications are in the range of visible and near-infrared light. The term photonics developed as an outgrowth of the first practical semiconductor light emitters invented in the early 1960s and optical fibers developed in the 1970s.
Flow measurement is the quantification of bulk fluid movement. Flow can be measured using devices called flowmeters in various ways. The common types of flowmeters with industrial applications are listed below:
A strain gauge is a device used to measure strain on an object. Invented by Edward E. Simmons and Arthur C. Ruge in 1938, the most common type of strain gauge consists of an insulating flexible backing which supports a metallic foil pattern. The gauge is attached to the object by a suitable adhesive, such as cyanoacrylate. As the object is deformed, the foil is deformed, causing its electrical resistance to change. This resistance change, usually measured using a Wheatstone bridge, is related to the strain by the quantity known as the gauge factor.
A rheometer is a laboratory device used to measure the way in which a viscous fluid flows in response to applied forces. It is used for those fluids which cannot be defined by a single value of viscosity and therefore require more parameters to be set and measured than is the case for a viscometer. It measures the rheology of the fluid.
Phosphor thermometry is an optical method for surface temperature measurement. The method exploits luminescence emitted by phosphor material. Phosphors are fine white or pastel-colored inorganic powders which may be stimulated by any of a variety of means to luminesce, i.e. emit light. Certain characteristics of the emitted light change with temperature, including brightness, color, and afterglow duration. The latter is most commonly used for temperature measurement.
A fiber Bragg grating (FBG) is a type of distributed Bragg reflector constructed in a short segment of optical fiber that reflects particular wavelengths of light and transmits all others. This is achieved by creating a periodic variation in the refractive index of the fiber core, which generates a wavelength-specific dielectric mirror. Hence a fiber Bragg grating can be used as an inline optical filter to block certain wavelengths, can be used for sensing applications, or it can be used as wavelength-specific reflector.
Structural health monitoring (SHM) involves the observation and analysis of a system over time using periodically sampled response measurements to monitor changes to the material and geometric properties of engineering structures such as bridges and buildings.
An optical fiber, or optical fibre, is a flexible glass or plastic fiber that can transmit light from one end to the other. Such fibers find wide usage in fiber-optic communications, where they permit transmission over longer distances and at higher bandwidths than electrical cables. Fibers are used instead of metal wires because signals travel along them with less loss and are immune to electromagnetic interference. Fibers are also used for illumination and imaging, and are often wrapped in bundles so they may be used to carry light into, or images out of confined spaces, as in the case of a fiberscope. Specially designed fibers are also used for a variety of other applications, such as fiber optic sensors and fiber lasers.
Luna Innovations is an American developer and manufacturer of fiber-optics- and terahertz-based technology products for the aerospace, automotive, communications, defense, energy, infrastructure, security, and silicon photonics industries. It is headquartered in Roanoke, Virginia. Luna's products are used to test, measure, analyze, monitor, protect and improve products and processes to enhance the safety, security, and connectivity of people.
An autocollimator is an optical instrument for non-contact measurement of angles. They are typically used to align components and measure deflections in optical or mechanical systems. An autocollimator works by projecting an image onto a target mirror and measuring the deflection of the returned image against a scale, either visually or by means of an electronic detector. A visual autocollimator can measure angles as small as 1 arcsecond, while an electronic autocollimator can have up to 100 times more resolution.
A balancing machine is a measuring tool used for balancing rotating machine parts such as rotors for electric motors, fans, turbines, disc brakes, disc drives, propellers and pumps. The machine usually consists of two rigid pedestals, with suspension and bearings on top supporting a mounting platform. The unit under test is bolted to the platform and is rotated either with a belt-, air-, or end-drive. As the part is rotated, the vibration in the suspension is detected with sensors and that information is used to determine the amount of unbalance in the part. Along with phase information, the machine can determine how much and where to add or remove weights to balance the part.
Bently Nevada is an asset protection and condition monitoring hardware, software and service company for industrial plant-wide operations. Its products are used to monitor the mechanical condition of rotating equipment in a wide variety of industries including oil and gas production, hydroelectric, wind, hydrocarbon processing, electric power generation, pulp and paper, mining, water and wastewater treatment. The company was founded in 1961 by Don Bently. Bently Nevada is headquartered in Minden, Nevada, about one hour south of Reno. Don Bently was the first to manufacture a commercially successful eddy-current proximity probe which measured vibration in high-speed turbomachinery by allowing the direct observation of the rotating shaft. The company also performed research in the field of rotordynamics, furthering knowledge of machinery malfunctions such as shaft cracks and fluid-induced instabilities. Its research also helped refine the equations used to describe vibratory behavior in rotordynamic systems.
Electro-optical sensors are electronic detectors that convert light, or a change in light, into an electronic signal. These sensors are able to detect electromagnetic radiation from the infrared up to the ultraviolet wavelengths. They are used in many industrial and consumer applications, for example:
Capacitance sensors use capacitance to measure the dielectric permittivity of a surrounding medium. The configuration is like the neutron probe where an access tube made of PVC is installed in the soil; probes can also be modular (comb-like) and connected to a logger. The sensing head consists of an oscillator circuit, the frequency is determined by an annular electrode, fringe-effect capacitor, and the dielectric constant of the soil. Each capacitor sensor consists of two metal rings mounted on the circuit board at some distance from the top of the access tube. These rings are a pair of electrodes, which form the plates of the capacitor with the soil acting as the dielectric in between. The plates are connected to an oscillator, consisting of an inductor and a capacitor. The oscillating electrical field is generated between the two rings and extends into the soil medium through the wall of the access tube. The capacitor and the oscillator form a circuit, and changes in dielectric constant of surrounding media are detected by changes in the operating frequency. The capacitance sensors are designed to oscillate in excess of 100 MHz inside the access tube in free air. The output of the sensor is the frequency response of the soil’s capacitance due to its soil moisture level.
Photothermal spectroscopy is a group of high sensitivity spectroscopy techniques used to measure optical absorption and thermal characteristics of a sample. The basis of photothermal spectroscopy is the change in thermal state of the sample resulting from the absorption of radiation. Light absorbed and not lost by emission results in heating. The heat raises temperature thereby influencing the thermodynamic properties of the sample or of a suitable material adjacent to it. Measurement of the temperature, pressure, or density changes that occur due to optical absorption are ultimately the basis for the photothermal spectroscopic measurements.
A fiber-optic sensor is a sensor that uses optical fiber either as the sensing element, or as a means of relaying signals from a remote sensor to the electronics that process the signals. Fibers have many uses in remote sensing. Depending on the application, fiber may be used because of its small size, or because no electrical power is needed at the remote location, or because many sensors can be multiplexed along the length of a fiber by using light wavelength shift for each sensor, or by sensing the time delay as light passes along the fiber through each sensor. Time delay can be determined using a device such as an optical time-domain reflectometer and wavelength shift can be calculated using an instrument implementing optical frequency domain reflectometry.
Oxsensis Ltd. is a British-based engineering business specialising in energy and aerospace equipment.
PhoSFOS is a research and technology development project co-funded by the European Commission.
Optofluidics is a research and technology area that combines the advantages of fluidics and optics. Applications of the technology include displays, biosensors, lab-on-chip devices, lenses, and molecular imaging tools and energy.