Meggitt’s vibro-meter product line is standard and preferred by many of the world’s largest suppliers of gas turbines, covering sensors, protection systems, condition monitoring systems, software, and services. Our solutions address not only vibration, but also the combustion dynamics so vital for today’s low-emission designs that operate under metastable conditions. And our offerings address industrial, heavy-duty, and aero-derivative designs along with their driven equipment for truly plant-wide solutions. covering all types of machines.
Accelerometers with external electronics
Accelerometers with integral electronics
Moving-Coil Velocity Sensors
Dynamic Pressure Sensors
RTDs and Thermocouples
Magnetic Pickups (Variable Reluctance Sensors)
vibro-meter pioneered high-temperature measurements for gas turbines in the 1960s and over the ensuing six decades, we have never looked back. Today, we stand unrivaled in our know-how with sensors that serve as the industry’s benchmark for longevity and accuracy in even the most extreme environments. Nowhere is the environment more extreme than on gas turbines. Not only are extremely high temperatures involved for measurements like frame vibration, but billions pressure cycles must be endured for measurements like combustion dynamics. That’s why both industrial as well as aerospace customers turn to us for the most robust sensors available covering everything from pressure to vibration to speed with a comprehensive suite of offerings designed to monitor gas turbines and their driven equipment. In addition, our pioneering efforts in current-mode transmission mean that our solutions support longer field wiring distances while maintaining signal integrity and thus lower installation costs, better signal-to-noise ratios, and superior immunity to interference.
vibro-meter is the only supplier that provides an option for either current-mode or voltage-mode outputs on proximity measurements, allowing more flexibility and the ability to transmit signals over longer distances without interference.
These sensors are used on industrial rather than aero-derivative gas turbines because such turbines have journal (fluid-film) bearings and thus benefit from shaft-relative measurements. The same can be said of the driven equipment. These sensors measure shaft-relative radial vibration, shaft axial (thrust) position, speed, and phase. Proximity probes can also be used for overspeed measurements; because they are powered and use a bias voltage, they provide inherently superior self-check capabilities compared to passive speed sensors such as magnetic pickups.
vibro-meter is unrivalled in its accelerometer technology for extreme environments. Nowhere is this more important than on gas turbines.
When surface temperatures are above 350° C, or when ambient temperatures frequently exceed 100°C, our CA-series accelerometers represent not only the right choice but the world’s most robust and trusted technology for high-temperature accelerometer-based measurements. Our CA-series designs separate the sensing element from its conditioning electronics and thus allow the sensor to be placed in extremely hot environments (up to 700° C) while the signal conditioner (typically, our IPC 707) is mounted off the turbine where temperatures are more conducive to active electronics (85° C or less). High-temperature mineral insulated (MI) or soft-line cable is then used to connect the sensing element to its conditioning electronics. We have continually improved our designs with enhancements that minimize thermal transient effects and base strain sensitivity. Numerous leading manufacturers use our CA-series sensors on their heavy-duty gas turbine models including Siemens, Ansaldo, Mitsubishi, and others. The CA-series is also equally at home on aero-derivative gas turbines such as Siemens’ SGT-AXX series engines (including heritage Allison and Rolls-Royce models), Mitsubishi’s Pratt & Whitney engines, and GE’s LM-series engines.
vibro-meter is world-renowned for our accelerometer technology. For machinery vibration applications, very few can match the breadth of our portfolio or rival our quality. We are also the only supplier to offer the option for voltage-mode or current-mode transmission, providing superior immunity to noise and signal degradation over long wiring distances.
When surface temperatures will be below 350° C, our CE-series accelerometers with integral electronics can be used. A typical example of such an application is on the bearing caps of gas turbines with fluid-film bearings. Indeed, OEMs often mandate such measurements for machinery protection2Because these sensors are used for protection on GE heavy-duty gas turbines such as Frame 5, 6, 7, and 9 models, they are often installed redundantly with two sensors on each bearing cap. Other manufacturers, such as Solar®, typically use only one sensor per bearing cap and may or may not use proximity probes for protection.,3For example, a damped resonance occurs within the passband of the CV-213 at approximately 10 Hz. This results in a 90-degree phase lag at 1000 Hz as compared to 10 Hz and must be taken into account when using the signal for diagnostic purposes such as machinery balancing.. It is customary on such machines to integrate the native acceleration signal to velocity as many OEMs use velocity as the basis for their vibration severity limits. However, because these machines use fluid-film bearings, they are almost always also fitted with proximity probes that provide important, supplementary signals useful for both condition monitoring and protection purposes. In addition to use on gas turbine casings for velocity measurements, accelerometers with integral electronics are used for measuring gearbox vibrations on trains where a gearbox is used between the gas turbine and its driven machinery.
Robust, rugged, and reliable. Our moving-coil technology can be the right fit for selected gas turbines and driven equipment when surface temperatures will not exceed 204° C.
When temperatures will be below 204° C, our CV-series sensors can be used for measuring casing velocity. These sensors utilise a magnetic core within an encircling coil that move relative to one another and generates an output directly proportional to vibration velocity. They have the advantages of being self-powered and of providing a very strong output signal (typically 20 mV/mm/s) in native velocity units that require no integration and result in an excellent signal-to-noise ratio.
These advantages, however, come at the expense of a more limited usable frequency range (10 Hz – 1000 Hz), moving parts that wear out over time, restricted mounting angles (pure vertical ±100 degrees), and a phase response that is not linear within the passband3For example, a damped resonance occurs within the passband of the CV-213 at approximately 10 Hz. This results in a 90-degree phase lag at 1000 Hz as compared to 10 Hz and must be taken into account when using the signal for diagnostic purposes such as machinery balancing.. Regardless, some customers prefer this sensor type due to its simplicity, self-powered operation, and large native velocity output. Although we have numerous offerings in our CV-series, the model most suitable for use in elevated temperatures is the CV-213.
We pioneered the technology that moved the industry from periodic tuning to online combustion dynamics monitoring for today’s ultra-lean DLE combustors
These sensors are used to monitor pressure pulsations in gas turbine combustors and form part of a closed-loop control system that adjusts combustion under metastable (very lean) conditions to achieve extremely low emissions. They must endure very high temperatures (up to 650° C) and use integral, mineral insulated (MI) cable to exit the high-temperature environment before transitioning to soft-line cable for connection to the companion signal conditioner (IPC707).
Consistent with our culture and heritage of innovation, we are today developing a next-generation portfolio of dynamic pressure sensors that utilise optical technology, resulting in extended frequency response for even better combustion control. You can learn more here and here as well as register to receive periodic updates as this exciting technology nears commercial release.
These sensors are used for gas turbine bearing temperatures as well as other machinery-related temperatures such as generator winding temperatures, lube oil temperatures, and relevant process temperatures. vibro-meter monitoring systems are designed to be universally compatible with a very broad range of third-party RTDs and thermocouples including:
vibro-meter does not offer these sensors in its portfolio, but can assist you in procuring them.
vibro-meter monitoring systems such as the SpeedSys300 are designed to be universally compatible with a very broad range of third-party magnetic pickups, both active and passive types. These sensors are typically used for overspeed measurements on all types of gas turbines as well as spool-speed measurements on aero-derivatives and are often the default sensor type provided by the OEM.
Although magnetic pickups can be used for phase-reference measurements, proximity probes are generally advocated instead. Passive-type magnetic pickups are usually not designed to work at rotative speeds below 200 rpm. Although active-type magnetic pickups are available for such applications, a proximity probe or Hall-Effect sensor will usually be a better choice.
Hall-effect sensors are powered and offer advantages over passive magnetic pickups, including the ability for better diagnostic self-checks. They are often used for overspeed applications and our SpeedSys300 overspeed system is consequently designed to be universally compatible with a very broad range of third-party Hall-effect sensors.
Regardless, proximity probes are generally advocated as they have many of the advantages of Hall-effect sensors while being suitable for a broader range of applications (vibration, thrust position, speed indication, overspeed, and phase reference) and thus minimizing spare parts requirements.
vibro-meter is unique in the industry by offering both distributed and centralized platforms with very similar channel types between the two, allowing you to choose the platform that fits your field wiring and topology preferences rather than forcing you to choose between “full capability” and “limited capability” platforms. Each platform provides the flexibility of stand-alone condition monitoring, stand-alone machinery protection, or seamless integration of the two in a “zero footprint” fashion that requires no additional modules. And, each platform features integrated combustion dynamics monitoring meaning a single system can be used for both vibration and combustion dynamics. Lastly, consistent with industry best practices and standards, we offer a completely independent platform for overspeed protection of gas and steam turbines – our SpeedSys300.
Our “one card does it all” approach revolutionised the industry more than two decades ago and our 2nd generation of this popular platform provides new levels of value, power, cyber security, and flexibility.
The VM600Mk2 is our centralized monitoring platform in a conventional 19” EIA rack-mounted form factor. It provides integrated protection and condition monitoring capabilities for all gas turbine measurements, including combustor pulsations and combustion dynamics, and builds on the enormous success of our original VM600 platform by providing numerous second-generation improvements while maintaining backward compatibility with the substantial installed base of first-generation racks (nearly 250,000 protection and 100,000 condition monitoring channels).
Released in 2000, the original VM600 introduced the concept of “one module does it all” – a feature many others have since emulated but which was pioneered by vibro-meter.
Many OEMs have standardized on the VM600 for their gas turbine protection, condition monitoring, and combustion monitoring needs. You can learn more in our all-new whitepaper and by visiting the VM600Mk2 landing page.
Developed in conjunction with one of the world’s leading turbine OEMs, the VibroSmart architecture can reduce wiring costs without sacrificing functionality – employing our “one card does it all” philosophy pioneered in the VM600.
The VibroSmart System is our distributed monitoring platform in a 35mm DIN-rail mounted form factor. Developed in conjunction with a leading gas turbine manufacturer to reduce installation costs without sacrificing functionality, it provides integrated protection and condition monitoring capabilities for all gas turbine measurements, including combustor pulsations and combustion dynamics, and is ideal for new installations where wiring costs can be dramatically reduced by mounting the monitoring modules near the machine and using single or redundant network cables to bring necessary status and current values back to the control room.
The VibroSmart platform is being used successfully on numerous gas turbines including the GE LM2500, GE LM1600, Rolls-Royce RB-211, Rolls-Royce Avon, Allison 501-K, Siemens SGT-750 and Siemens SGT-A35 to provide integrated vibration and combustion monitoring.
Designed from the ground up for SIL-certified, stand-alone overspeed protection, this platform reflects innovative design features that set it apart in the industry while ensuring it can evolve with enhanced functionality while maintaining its SIL ratings.
The SpeedSys300 platform is an innovative overspeed protection solution design for stand-alone operation and independence from all other systems in accordance with API Standard 670 and industry best practices. It can be used in simplex, duplex, or triple-modular-redundant configurations for 1oo1, 1oo2, 2oo2, or 2oo3 voting and is certified for SIL 2 and SIL 3 applications. DIN-rail modules, as well as fully engineered rack-mount packages, are available.
Overspeed is a critical protection measurement on gas turbines and the SpeedSys300’s adaptability means it can be used economically – whether on the smallest aero-derivatives producing 5 MW, mid-size industrials producing 40 MW, or the largest heavy-duty units with outputs approaching 600 MW. This innovative, economical, and robust overspeed platform offers unparalleled protection integrity and is in the process of becoming the standard and preferred choice for several leading gas turbine OEMs.
Our condition monitoring software is designed to provide a seamless, unified environment for your machinery information regardless of what underlying hardware you may be using. Our configuration environments are designed for exceptional ease of use, allowing you to accomplish in minutes what formerly took hours, establishing an industry-leading benchmark for power, flexibility, and intuitiveness with a highly graphical approach. And, our expert system environment is designed to automate your machinery diagnostic and anomaly detection tasks while providing a highly intuitive dashboard of machinery status suitable for operators – not just machinery specialists.
Full-featured condition monitoring and configuration software that allows you to unify your underlying protection, condition monitoring, and other data sources into a single, powerful environment for maximizing machinery availability, reliability, profitability, and safety.
VibroSight is a suite of powerful applications used for not just condition monitoring but also communications, data import/export, and configuration of our monitoring hardware platforms. When using VibroSight for condition monitoring, all of the plot types required for deep analysis of gas turbines and their driven equipment are available, including advanced combustion monitoring features, under steady-state and transient operating conditions. For an extensive overview, visit the VibroSight landing page. For a deep dive into each of the nine constituent applications that comprise the VibroSight suite, visit the VibroSight catalogue pages.
Configure and test your SpeedSys300 overspeed hardware in an intuitive, convenient, and powerful environment.
Our SpeedSys300 software is used for the configuration and maintenance of our SpeedSys300 overspeed systems. It is a stand-alone software package that, like our VibroSight suite of tools, is designed for highly intuitive ease-of-use. Configuration can be performed offline and then downloaded to the modules. The software can also be used in online mode to retrieve diagnostic information from modules, to generate reports on device configuration and statuses, to view detailed event logs and speed trends, and to fully exercise alarm and other functionality during proof testing.
Machinery Protection System Verification Services
Sensor Calibration Services
Condition and Combustion Monitoring System Upgrade Services
Project Engineering, Management and Planning Services
Factory Acceptance Testing (FAT) and Integrated Factory Acceptance Testing (IFAT) Services
Machinery Diagnostic Services
Advisory and Consultancy Services
Long Term Service Agreements (LTSAs)
vibro-meter provides comprehensive services that extend beyond just our gas turbine monitoring and protection instrumentation to encompass your broader needs such as machinery diagnostics, training, system integration, product rental, and project management. Some of our customers have a high degree of self-sufficiency and need little more than occasional technical support, while others prefer to outsource the installation, maintenance, and even operation of their systems.
Wherever you fall within this spectrum of needs, we have both standard and tailored service offerings to fit. In addition to the short descriptions below, you can read more in our Services Brochure.
These services verify the operation of your already installed protection system, whether VM600, VM600Mk2, or VibroSmart. Although our monitoring systems do not require calibration, periodic functional testing to verify that the system working within published specifications is recommended at 2-year intervals. These services cover the monitoring system, its connected sensors, and its communications with associated automation platforms such as the plant’s distributed control system. Although a machine or plant outage is not necessary to perform these services, they are often scheduled during an outage when the machine is open, allowing easier access to embedded sensors and thus more extensive verification as well as the opportunity to replace or repair any sensors that are damaged or performing outside of published specifications.
These services verify that your sensors are performing within published specifications and calibrate them where required. Sensors can be returned to the factory for calibration or can be calibrated in the field. Factory as well as field calibration services are performed using equipment calibrated to NIST-traceable references.
These services are similar to System Verification Services, but are performed at time of initial system deployment and include the installation activities – not just the verification activities. These services also include training so that operators and others will be proficient in using the newly installed systems.
These services address the migration of hardware and software from older vibro-meter condition monitoring environments to our latest VibroSight software. Where the VM600 platform is used with CMC16 modules, the hardware is upgraded to our latest XMx16 modules. Servers are upgraded, mimic diagrams are updated, and integration with other automation platforms such as plant distributed control systems is updated so that functionality is maintained or enhanced under the new environment.
These services provide a comprehensive turnkey solution for upgrades, new installations, migrations, retrofits, and system expansions by delivering all design and project management activities in addition to execution activities. They are integrated and harmonized with your overall planning to ensure that critical tasks are not impaired and schedules do not conflict.
These services allow robust functional testing of new systems before they leave the factory, and typically occur once the systems are mounted in cabinets and pre-wired to terminations, ready to accept field wiring at site. Signals are simulated during FATs to ensure point-to-point wiring is correctly installed and labeled, alarms and signal processing are configured and working properly, relays are configured and wired properly, and digital communications such as Modbus or Profibus are mapped and working properly. When condition monitoring is included with the machinery protection, this functionality is tested as well. This testing can also be carried out at locations other than vibro-meter premises when full integration with other systems, such as the plant DCS, must be exercised and verified.
Field engineers with machinery expertise are available to collect data from your machinery using portable data acquisition equipment or your installed condition monitoring systems. The collected data is reviewed and diagnostic reports are produced regarding machinery health such as the likely malfunction, its severity, and recommended corrected actions along with any corresponding urgency.
Our machinery diagnostic services can also be used to generate customized algorithms within your installed VibroSight Rulebox software, allowing it to perform automated diagnostics by embedding the same analytical processes and domain expertise utilized by our own engineers.
For machinery with no (or insufficient) condition monitoring instrumentation, we provide rentals that can be used on a short-term or extended-term basis. For customers without embedded vibration and machinery diagnostic expertise, the data collected by rental instruments can also be used in conjunction with our Machinery Diagnostic Services. This data can often be transmitted electronically to avoid the cost of site travel by our field diagnostic engineers.
These services are designed to address a wide range of a la carte or bundled activities such as generating project specifications, site surveys to assess machinery and corresponding recommended monitoring, ongoing predictive maintenance services, recurring audits of machinery condition at specified intervals and after major events, and many others that can be custom-tailored to your unique needs.
An LTSA is a bundle of tailored services provided on an ongoing basis rather than a la carte, on-demand basis. LTSAs can cover the entire system, or only selected parts thereof, such as the condition monitoring portion of the system but not the sensors or protection hardware. The composition and duration of the LTSA is formulated based on your needs as we understand that one-size-fits-all solutions are rarely able to address the specific needs and economics of each installation and each customer.
Training can be delivered virtually via video conferencing or in-person at our facilities, your facilities, or other facilities such as hotels or conference centers. Training is delivered by certified professionals and is assembled based on your specific needs to cover sensors, monitors, software, vibration diagnostics, measurement fundamentals, system maintenance, system operation, and other specialized topics pertaining to machinery monitoring and protection such as cybersecurity and gas turbine combustion monitoring. We maintain dozens of standard training modules that can be mixed, matched, and customized to meet your needs, and modules to address new topics can be developed as required.
All of the vibration measurements customarily made on gas turbines and their driven equipment for both protection and condition monitoring are available in our monitoring system platforms. In addition, our platforms provide dynamic pressure measurements used for combustion dynamics and combustor pulsations. Vibro-meter also provides the measurement chains (sensors, signal conditioners, and cables) along with numerous accessories for a complete installation. In the few instances where we do not provide sensors (such as temperature), we can provide guidance to assist you in sourcing them yourself or we can source and install them for you as part of turnkey installation and project management capabilities.
* Although Meggitt vibro-meter® does not provide temperature, pressure or valve position sensors, our protection and condition monitoring systems can integrate these readings.
† These sensors can also be used in conjunction with shaft relative vibration sensors to obtain absolute measurements if orientated to coincide with shaft relative measurement planes.
This measurement is made by means of a proximity probe, usually affixed to the bearing housing and observing the vibratory motion of the shaft within its bearing clearance. The probe can return both AC and DC signal components, corresponding to dynamic motion (vibration) toward and away from the probe, as well as the average position (DC component of signal). The average position shows the location within the bearing clearance where the shaft rides on its film of lubricating oil. It is about this point that dynamic motion occurs.
Although this can be a single-channel measurement with a probe mounted in only a single vibration plane, it is more common – particularly on critical machinery – to mount a second probe in an orthogonal axis so that position and vibration in both an X- and Y-plane can be observed, ensuring that any motion within the bearing clearance is detected.
These measurements are routinely used for both protection and condition monitoring. The amplitude of the signal corresponds to the amount of vibration and can be related to bearing clearances. It is made in units of displacement, either micrometers or mils.
This is the axial movement of the shaft at the thrust bearing, relative to the thrust bearing housing. It may be made at the end of the shaft or at the thrust collar. A similar measurement is called rotor position and is when the axial position is made relative to the machine casing rather than the thrust bearing.
Like shaft-relative vibration measurements, shaft axial position is made via a proximity probe. Unlike shaft-relative vibration, it is generally the DC component of the signal (position) that is of interest rather than axial vibration (AC component of signal). Axial thrust movement in excess 2mm (80 mils) is rare and a probe with a 2mm range is usually sufficient. However, due to mounting constraints, the sensor must sometimes be installed further away from the shaft. In such cases, larger diameter probes are available with longer measurement ranges.
Many thrust bearings are designed to have a total range of 1–0–1 mm where the thrust collar can move in the normal or counter direction against the normally active or inactive thrust bearing pads. Excessive movement corresponds to damage of the thrust bearing and an axial rub between rotating and stationary parts such as blades contacting vanes on a gas turbine. As such, this measurement is extremely important for machinery protection, and also has diagnostic value for condition monitoring purposes.
While not as useful as the DC component of the signal which signifies the average axial position, the AC component of the signal (axial vibration) has diagnostic value and can be indicative of problems with the turbine’s compression section or the driven machine when it is a centrifugal or axial compressor or blower. Axial vibration in such instances is often indicative of surge or incipient surge. Because the shaft axial (thrust) position measurement is so important, it is usually made by means of two (or even three) redundant probes that compare their readings and use logical AND voting.
The measurement can also be done by means of a single probe but will have not voting. The thrust bearings on gas turbines are generally large enough to easily accommodate two probes – either to observe the thrust collar directly or to observe the end of the shaft near the thrust bearing.
To ensure radial and axial (thrust) bearings are not too heavily loaded, or starved of necessary lubrication, it is customary to embed an RTD or thermocouple into the bearing pad(s) carrying the shaft load or on the outer race for rolling element bearings. When excessive temperatures are observed, the machine must be shut down because bearing failure may be imminent, resulting in damage far beyond an easily replaceable component.
Often, sudden catastrophic changes in a machine will result in instantaneous changes in shaft position or vibration, and the thermal inertia of the bearing materials will cause temperature to rise more slowly than vibration levels, but still relatively fast.
For this reason, it is not advisable to vote temperature and vibration using AND logic. By the time both measurements indicate a problem, it may be too late to trip the machine and prevent damage.
Each independent shaft in a machine is usually fitted with a once-per-turn mark, such as a key or keyway at a coupling, allowing a proximity probe to observe the passing of this mark with each shaft revolution. This provides a precise reference in time against which all other measurements along the shaft can be synchronized. For example, a Y probe on a bearing may observe the shaft’s maximum positive excursion at 23 degrees of rotation after the phase reference mark, while the corresponding X probe might give a maximum positive excursion at 128 degrees of rotation.
This information is extremely valuable for diagnostics and allows not only simultaneous sampling of all sensors along a shaft, but also to sample at precise increments of shaft rotation (so-called “synchronous” sampling), where the vibration is sampled at some multiple of shaft rotative speed – such as 64 times per revolution or 128 times per shaft revolution.
Fundamentally, a phase reference measurement is a timing measurement, but it is usually expressed in degrees of shaft rotation after the timing mark occurs. This mark can also be used for basic speed indication, but cannot update fast enough for overspeed measurements. For this reason, a toothed wheel is usually used. For example, a shaft rotating at 3000 rpm cannot update its speed reading faster than one full shaft rotation (20 ms) when only a once-per-turn mark is provided.
In contrast, the same machine with a 50-tooth wheel will generate a pulse 50 times per shaft revolution, or every 4 ms. Because an overspeed system on a gas turbine must often respond in 30 ms or less, a surface that generates a pulse every 4 ms (allowing three or more successive speed measurements to be acquired before a shutdown decision is made) is far superior to one generating a pulse every 20 ms (allowing only one speed measurement before a shutdown decision is made).
As noted above, a phase reference measurement is made using a proximity probe observing a once-per-turn shaft discontinuity such as a key or keyway. However, this will rarely update at a rate suitable for accurate speed indication, much less overspeed protection.
As such, a multi-tooth surface will be used – often a gearwheel made specifically for speed measurement purposes. While such a surface is recommended for greater accuracy in speed indication purposes, it is absolutely essential for overspeed protection measurements for the reasons discussed in the phase reference section.
Also, overspeed should never be measured by a single (non-redundant) sensor. Instead, there are usually three redundant sensors observing the same multi-tooth surface and then monitored in a 2-out-of-3 voting arrangement that represents an optimal balance of missed trips versus false (spurious) trips.
1-out-of-2 arrangements are also used (sometimes on gas turbines), but are less common on gas turbines where 2-out-of-3 is routinely used instead as part of a SIL 3 protection loop. On aeroderivative gas turbines, there are normally 2 (and sometimes 3) separate spools that are aerodynamically rather than mechanically coupled, thus necessitating separate speed measurements for each spool.
These speeds are used as part of the protection system for filtering casing vibration to the associated spool speed. Speed and overspeed sensors can include magnetic pickups (i.e., variable reluctance sensors), Hall-effect sensors, and conventional eddy-current proximity probes as used for vibration and position measurements.
Aero-derivative gas turbines use rolling element bearings and mounting accelerometers at or near the bearings is impractical. Consequently, the accelerometers are mounted on the engine frame (often part of the support structure). However, such mounting locations are too far from the bearings to extract detailed bearing information (it is not only small in amplitude, but often swamped by other higher-amplitude signals such as blade passage).
The ability to monitor discrete bearing-related components is thus very limited and is instead primarily focused on identifying filtered vibration present at the various shaft (spool) speeds, indicative of gross problems such as loss-of-blading or catastrophic bearing failure that manifests at spool rotative speed.
In contrast, industrial and heavy-duty gas turbines use fluid-film bearings and proximity probes can almost always be fitted to the bearings. Many OEMs, however, mandate bearing cap seismic velocity measurements for protection, and proximity probes only for condition monitoring. Because the preferred engineering units are velocity rather than acceleration, signal integration (acceleration to velocity) must be used if the sensor does not provide a native velocity signal. Also, because these sensors are fitted to the bearing cap where temperatures are considerably cooler than elsewhere on the turbine, our CE-series models with integrated electronics can sometimes be used, or our CV-213 velocity sensor. In contrast, measurements on the frame rather than on bearing caps usually represent considerably higher temperatures (up to 700° C) at the mounting locations and must use our CA-series sensors with external conditioning electronics.
A few gas turbine designs exist where the machine is highly compliant and it is useful to have both shaft-relative and bearing absolute measurements combined so that motion of the shaft relative to free space can be ascertained. The vector summation of the two signals (shaft-relative and bearing absolute) is made within the monitoring system and is thus a two-channel measurement. Shaft-relative vibration is made via a conventional proximity probe, as was discussed above in the section for those measurements. Bearing absolute vibration is made by means of a seismic sensor such as a moving-coil velocity pickup or a piezoelectric accelerometer.
Velocity sensors are generally preferred, however, because they require only a single stage of integration (conversion from velocity to displacement) to the permit vectorial combination with the displacement measurement from a shaft-relative proximity probe. The shaft absolute measurement requires both the bearing absolute and shaft-relative measurement to be made in the same measurement plane. For example, if a shaft-relative probe is mounted at 45° right of vertical, the corresponding bearing cap sensor must be mounted in the same orientation – 45° right of vertical.
In addition to measurements at bearing locations, it is common practice to monitor the absolute vibration of the turbine casing – often near the combustion section. The primary reason for this is not to detect bearing, blading, or other rotor dynamic problems but combustion problems. During combustion, flame instability may trigger pressure pulsations (see dynamic pressure section below), resulting in casing vibration. Monitoring the casing to detect combustion issues is thus important for two reasons:
When monitoring casing vibration, it is imperative that the sensors are installed directly on the turbine casing, below the turbine insulation. However, this means they are subject to extremely high temperatures (up to 700°C) and therefore require our CA-series sensors. The CA series decouples the sensor from the signal conditioner and thus keeps the signal conditioning electronics from being exposed to the extreme temperature at the sensor mounting location.
A dynamic pressure sensor is fitted to each combustor on most modern gas turbines to measure pressure pulsations and combustion dynamics. This is because the turbines burn fuel as lean as possible to reduce emissions to environmentally acceptable levels, but in so doing create metastable flame conditions and corresponding pressure pulsations that will damage and even destroy combustors if left unchecked.
The characteristic frequencies associated with these metastable conditions vary according to manufacturer and combustor. By tuning the monitoring system to these characteristic frequencies, the damaging pulsations can be detected and the fuel/air mixture adjusted to an operating point where the combustor will not be damaged.
The dynamic pressure sensors are thus used as part of a closed-loop control system that keeps combustion from persisting in a state that will damage the combustors. Highly sophisticated filtering and detection is used, as provided by the monitoring system. The dynamic pressure sensors are mounted in extreme environments where temperatures of up to 650° C and billions of pressure cycles must be endured.
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