Non-Intrusive Monitoring, Developed by George

Non-intrusive monitoring, developed by George Hart, Ed Kern and Fred Schweppe in the 1980s at the Massachusetts Institute of Technology. It is commonly used in terms of non-intrusive load monitoring, a means of monitoring an electrical circuit which encompasses a particular number of appliances which are all able to turn on and off independent of one another. Instead of attaching a monitor to all of these appliances, non-intrusive monitoring uses electric meters to determine the different uses of power in a given home. Similarly, nonintrusive appliance load monitoring, engages via "a sophisticated analysis of the current and voltage waveforms of the total load, the NALM estimates the number and nature of the individual loads, their individual energy consumption, and other relevant statistics such as time-of-day variations" (Hart). Non-intrusive monitoring can be so ideal, because it can measure the voltage and current without having access to individual components or appliances of a house or other entity that's under assessment. In the example of a home, the final data can be extremely useful to public policy makers, energy auditors, consumers, appliance manufacturers, and can provide an accurate snapshot of energy consumed over time (Hart). This can highlight any deficiencies, irregularities, or issues within energy consumption.

Essentially, within non-intrusive load monitoring, these power meter readings offer a clear identification of the loads created by specific appliances, generating a realistic way to verify load sheds in homes and buildings (Bergman et al., 2011). Again, the clearest example of this is within home, during perhaps a two hour period. Between these two hours, the activity might demonstrate energy just from the heater and refrigerator: the refrigerator turns on and off three times, the heater -- twice those amounts (Hart). This process can easily illuminate the total energy used of these appliances and their individual expenditures: "By also considering measurements of the total reactive power or harmonic current, along with the real power shown, changes in the resulting vector function of time would reveal even more information about the particular appliances" (Hart).

The key thing to remember about non-intrusive monitoring is that one uses the information available from normal operation of an item, placing no extra requirement on the system (Thornton & Sanghera, 2011). This type of monitoring can be done with all types of energy, even the energy of sound -- this is where acoustic and vibration non-intrusive monitoring comes in. This type of monitoring can find or pinpoint acoustic signals or vibrations that are caused by the movement of material. "This movement causes impacts and frictional contact with a containing face, for example the inside of a pipe. The sensor is fastened to the outside of the structure, and its high frequency detection picks up these signals, which are often undetectable to the human ear" (pulsar-pm.com). This type of detection relies on tools which can be used in environments where there is a tremendous amount of machinery noise or the noise of procedures and developments because they work using advanced technology which allows them to find changes or disruptions in acoustic emissions from equipments or machinery as they're functions (pulsar-pm.com). This is again, one of the key aspects of non-intrusive monitoring: materials and processes are examined when they're engaged in their normal work and normal functioning. With the type of non-intrusive monitoring that harnesses vibrations and acoustics, a sensor helps to examine the acoustic discharges from machinery during work: these sensors are sensitive to the smallest changes in conditions. This type of monitoring is used in industrial scenarios like mills and plants, to work with automobiles and trucks to determine engine efficiency, or even in the field of medicine to determine the success of joint and limb replacements or therapies. The possibilities with this type of technologies are really boundless.

Different Types of Non-Intrusive Monitoring

Some of the different types of non-intrusive monitoring have already been alluded to. Non-intrusive appliance monitoring has already been described, and it benefits have already been touched on. This type of appliance monitoring gives energy auditors, homeowners, building-owners, manufacturers and other interested parties a clear picture of the combined energy that their appliances use as well as each separate one. It's a way of measuring energy output that gives one a more detailed picture of which electrical energies are contributing to the biggest or smallest consumption.

One of the major and most apparent disadvantages with this type of monitoring is that there are very real and immediate privacy concerns to the individual. These concerns come up most immediately when the energy of a house or other residential structure is being looked at. Fundamentally, the way that individuals or families use energy demonstrates patterns of behavior. Patterns of behavior are directly related to privacy rights: individuals have a right to keep things like what they're doing at home, when they're home, when they're showering or other embarrassing or even criminal activities private. The concern comes when individuals don't even know that their energy use is being monitored as well. It's definitely an issue of balance, as this type of monitoring provides valuable information to society at large, yet no one wants to sacrifice the rights or needs of the individual.

Another type of non-invasive monitoring is the biological type. This is seen in thing like non-invasive blood glucose monitors for diabetics, sensors to detect drunk drivers and other tools which focus on biological functioning. For example, for glucose blood level monitoring, uses a sensor that sits closely against the skin: "a special camera, called a raman spectrometer, inside the sensor uses light to identify and analyze glucose molecules under the skin, via interstitial fluid. Each glucose molecule has a special "signature" the sensor identifies, and from there, analyzes and extrapolates a glucose value, which is transmitted via Bluetooth to a handheld device, like an iPhone or Android, or to a computer" (Allison, 2011). A ramen spectrometer is a type of device which also measures the vibrations in a system, demonstrating how this type of tool is a form of biological non-intrusive monitoring, and a vibrational one. The sheer advantage of this form of technology is that it has tremendously smart technology and human advantage: by having results download to a phone, the user's parents or even the paramedics can be called immediately if one's glucose is at a dangerous level. This demonstrates how sensors are making life for people with chronic illnesses safer and more livable. The beauty of the non-intrusive monitoring is apparent: the diabetic no longer has to prick their skin to monitor their levels of glucose, making their quality of life even higher.

The same is true for non-intrusive biological sensors which can monitor the level of intoxication of an individual driving a car. While this technology might still be developing, the possibilities are truly endless. According to Mothers Against Drunk Driving, one in three people will be involved in an alcohol related crash in their lifetime and almost every 90 seconds an individual is killed in a drunk-driving accident: "In 2011, 9,878 people died in drunk driving crashes - one every 53 minutes" (Madd.org, 2012). Biological sensors could have tremendous impact on eliminating or even greatly reducing the numbers of these accidents. Again, while these systems and sensors are still developing, they are designed to assess the "biological condition of a driver and issuing warnings during instances of drowsiness have recently been studied. Moreover, many researchers have reported that biological signals, such as brain waves, pulsation waves, and heart rate, are different between people who have and have not consumed alcohol. Currently, we are developing a noninvasive system to detect individuals driving under the influence of alcohol by measuring biological signals" (Murata et al., 2011). The advantages of such technology being a permanents feature in all automobiles is absolutely inspiring for human safety and for the good of society as whole. Of course, some people would argue that it reduces things like personal freedom: some people want the freedom to drive home tipsy, as the fact remains.

Already discussed were the possibilities of acoustic and vibrational forms of non-invasive monitoring which measure these forms of emissions from machines and entities in order to make assessments about their functioning. The possibilities for these types of instruments truly offer society and members of society a definitive advantage. An obvious advantage of this form of technology is the work and good that it can achieve for the environment. For example, passive, non-intrusive acoustic monitoring can observe the scallop valve movement of bivalve mollusks (Di Iorio et al., 2012). While this might not sound significant, bivalve mollusks are absolutely vital ecological and economic parts of coastal ecosystems: "The formation and size of growth increments delimited by striae are affected by environmental stressors. The mechanisms linking shell growth and striae deposition in relation to environmental variations are poorly understood but are likely associated with the animal's valve-movement behavior" (Di Iorio et all., 2012). Non-invasive acoustic monitoring can shed some light on this issue, illuminating confusions and mysteries about the development and stressors of sea life in a way that was unknown before. Similarly, this type of non-invasive acoustic and vibrational monitoring has been used by doctors to get a better assessment of in vivo hip conditions so that they can better comprehend things like total hip arthroplasty (Glaser et al., 2010).

Acoustic Signals

"Acoustic emissions are elastic waves generated by a rapid release of energy at a localized source. They are produced by events such as particle impact, gas evolution, boiling, phase transitions, precipitation. Some processes produce emissions that can be heard. A lot more emit either outside the audible frequency or at too low an intensity to be heard (McLenna, 1995, p.338). Using non-intrusive acoustic monitoring is definitely a way to monitor an entire structure continuously and effectively (Wu & Abe, 2003). Acoustic signal-based monitoring can assess individual entities and mechanisms or total structures, pinpointing abnormalities, failures or red flags which need attention (Wu & Abe, 2003). It provides experts with truly valuable information that allows for focused research and further evaluation, as well as improve the timing of repairs or rehabilitation, or help to tweak and adjust maintenance budgets (Wu & Abe, 2003). Managers, scientists, policy-makers and members of society should view this form of technology as a management tool and illuminator which can shed light on the needs of communities, individuals and structures, allowing one to better manage the integrity of these things which deeply matter.

The possibilities for acoustic-signal-based monitoring are truly boundless as they are able to detect things that the human ear is completely incapable of doing. A shining example of the value and potential of this form of technology is with the monitoring of live chick embryos. At this time, the technology is semi-invasive, but in a few years this will surely change. The process demonstrates how acoustic signal monitoring can be used with success to observe and assess the development of chicks which grow into chickens and which have direct impact on feeding America and the expansion of the poultry industry as a whole (Liang et al., 2011). In the study, "Monitoring of live chick embryo based on acoustic and vibration signals with a new semi-invasive technology" (Liang et al., 2011) the researchers determine the healthiness and rate of development of a chick embryo by making a small hole with a pin at the top of an egg so that the heartbeat signal after amplification is tracked (Liang et al., 2011). A microphone is installed over the hole made, helping to distinguish the live embryo and making it distinct from a small and weak embryo (Liang et al., 2011). This type of data can help the researchers determine the whether the embryo is alive or not, something that is absolutely crucial for development of the poultry industries.

Yet another group of researchers decided to use acoustic monitoring for benefit in the animal kingdom. The study, "Target Classification and Localization in Habitat Monitoring" by Wang and colleagues seeks to determine if acoustic signal monitoring through the use of sensors can be used to recognize and locate animal calls (2003). This form of habitat monitoring has two objectives, "The first part is to determine whether observed animal calls are of the specified type using their spectrograms. Each type of animal call has its own characteristic spectrogram which is input to the system. The classification of an observed acoustic signal is determined by the maximum cross-correlation coefficient between its spectrogram and the specified characteristic spectrogram [3]. The second part is to locate the calling animal when its call is recognized" (Wang et al., 2003). Since the animal kingdom relies so heavily on the use of sounds as a form of communication and in their development and habitation, acoustic-based signal non-intrusive monitoring can be incredibly useful. As stated earlier, human beings have an extremely limited hearing ability, particularly when compared to the animal kingdom. In order to gain a better understanding about animal needs and behavior, acoustic-based monitoring can definitely help scientists shed some light on the multi-faceted range of processes.

For instance, the research study, "Acoustic Sensor Networks for Woodpecker Localization" by Wang and associates admits that sensors offer some of the most valid, effective and non-intrusive ways to study animals. Studying animal behavior truly relies heavily on things being non-intrusive because intrusive research disrupts natural behavior for obvious reasons. In this experiment the data gathered relied upon the vocalizations of woodpeckers, using four microphones arranged as a square (Wang et al., 2005). "All four audio channels within the same acoustic array are finely synchronized within a few micro seconds. We apply the approximate maximum likelihood (AML) method to synchronized audio channels of each acoustic array for estimating the direction-of-arrival (DOA) of woodpecker vocalizations" (Wang et al., 2005). Apparently, the work of Wang and colleagues feel that they uncovered the fundamental connection between microphone spacing of acoustic arrays and the solidity of woodpecker vocal tracks given the typical noise and interference that one will encounter when trying to record woodpeckers (2005). Experiments like these which depend so heavily on the work and interactions of acoustic signals monitored in a non-intrusive fashion, can truly illuminate a tremendous amount about animal research.

The biological areas of the sciences are not the only ones that can benefit from acoustic-signal monitoring -- though this arena is ideal for this form of monitoring as it forces scientists and researchers to find a means of detecting the sounds of energy and movement, things connected to all forms of life. For example, numerous fields of industry can benefit from these processes and technologies because so much of the correct functioning of their machine's mechanisms is connected to the acoustic signals given off. "Acoustic Emissions (AE) and surface vibration monitoring technologies, are promising non-intrusive approaches to online monitoring of industrial tumbling mill process and machine condition" (Meech et al., 2005). This allows technicians to receive valuable feedback as to whether or not their processes are running effectively or not or what certain malfunctions indicate and what needs to be changed. This data is so valuable as it can be received without taking apart equipment but via the most non-intrusive form of monitoring.

The potential benefits of acoustic-based monitoring truly are boundless. For instance, some companies use acoustic technology which examines and assesses the noise caused by sand grains on the pipe wall on the radius of a bend: "This noise can then be used to calculate sand production rates based on knowledge of background noise, flow rate and particle size. Acoustic sensors provide an immediate response to any changes in sand production by detecting acoustic signals emitted when a sand particle hits the pipe wall. Benefits include easy installation, the immediate detection of sand production, and low power consumption" (emersonprocess.com). This demonstrates how the technology can be used for the most ideal results possible, saving time and money.

Aside from immediate financial savings, acoustic-based non-invasive monitoring can also assist with the maintenance of certain forms of infrastructure and support. For instance, the study, "On the opportunity to use non-intrusive acoustic emission recordings for monitoring uniform corrosion of carbon steel and austenitic stainless steel in acid and neutral solutions" attempts to shed light on the issue of the uniform corrosion of steels (Jaubert et al., 2005). The researchers acknowledge how this corrosion is very widespread and is the cause of the destruction of a range of industrial parts which are responsible for a large amount of economic and environments failures (Jaubert, et al., 2005). While it's true that classic corrosion formula can predict and shed light upon the average rate of corrosion for certain materials, the reality is that these formulas cannot give one an instantaneous value of corrosion in real-time. However, using acoustic signaling in connection with the release of energy within an item that's creating a transient elastic wave propagation, corrosion information can be obtained in a quantitative fashion (Jaubert et al., 2005).

Essentially the researchers found that, " it appears clearly that acoustic emission measurements are in good correlation with aggressiveness of the corrosive media, and a semi-quantitative correlation is obtained between AE activity and corrosion rate for austenitic stainless steel. Whereas initial surface conditions greatly influence the acoustic activity, AE monitoring appears to be a rewarding technique for detecting corrosion rate evolutions during process modifications" (Jaubert et al., 2005). The results of these findings are extremely influential for the world at large. Essentially, there's a more effective way for determining the real rate that something is corroding: this means that there can be greater preventative measures and more precise maintenance measures for public safety and public efficiency, as many of these industrial materials are used as support for bridges, highways, trains, locks, gears and other items. It's the responsibility of public leaders to make sure that they are strong and stable when in use, and acoustic-based non-intrusive monitoring is a viable option to receive this information -- as none of these structures have to be destroyed or invaded to gather this info.

Assisting with maintenance in industrial machines truly is one of the overwhelming benefits that acoustic-based non-intrusive monitoring is capable of. "Acoustic emission, as a technique, is well established for monitoring the condition of rotating machinery, detecting cavitation in pumps, detecting defects in boilers during pressure testing, detecting gas leaking through relief valves, etc." (McLenna, 1995, p. 338). For those who work outside of fields which require the reliance on intensive industrial machinery, it can be difficult to comprehend or imagine just how massive and intricate these forms of machines are. These are structures which have intensely complex parts that are all inter-connected and work together in an interlocked system of pumps, pulleys, hydraulics -- all enveloped and solidified by steel supports, nuts and bolts. To the average person, these structures look incredibly intimidating, and if something goes wrong, or might about to be going wrong with any of them, not only is it important to know right away, but it is simply far too impractical to attempt to take apart any of these structures in order to figure out what's going on and will waste entirely too much time, costing thousands and thousands of lost revenue in certain cases.

Another ideal use for acoustic-based non-invasive monitoring is with fluid bed processes. These types of processes turn out to be great candidates for this type of work because the primary form of transportation for this mechanism is the upward movement of low density areas or gas bubbles (McLenna, 1995). "An acoustic emission transducer will detect an increase in signal as a bubble passes due to the surge of accompanying particles. The regular flow of bubbles appears as series of rhythmic pulses in the average intensity of the acoustic emission signal (McLenna, 1995, p.339). Generally, this form of monitoring is so ideal for these types of processes because they can reveal so many details about what exactly is going on, offering up truly promising possibilities for diagnosis in a range of fields.

However, some of the real benefits of acoustic-based non-intrusive monitoring occurs in the work of diesel engines. Diesel engines are the power supply for a wide variety of machines as these engines work by generating the crucial drive power to conquer the resistance loads as a result of burning fuel and converting it to the energy content of the inlet mixture in order to power mechanical movements (Elamin et al.,). Because the diesel engine is so powerful and has so much potential, there is a danger of it becoming degraded by incipient faults, which can also cause substantial economical losses to the user (Elamin et al., 2010). Acoustic monitoring is one of the many methods of scrutinizing these engines to ensure they're working as effectively as possible.

Recent scholarship and research continues to display the wealth of possibilities for acoustic monitoring and diesel engines in the arenas of maintenance and diagnosis. Fog and colleagues engaged in an experimental investigation in the finding exhaust valve burn-through on a 4-cylinder, 500mm bore, 2 stroke marine diesel engine that has a yield of around 10,000 BHP (Mba et al., 2006). The researchers monitored three distinct types of valve, from normal to those with a large leak and the vibration and structure-born stress waves were observed and recorded (Mba et al., 2006). Ultimately the findings demonstrated that acoustic emissions were comprised of more emissions for demonstrating the valve and injector related mechanical events at the time of the combustion process as opposed to time-series monitored from other sensors (Mba et al., 2006). This is indeed significant for all engineers who work on the performance aspects of Diesel engines as these types of acoustic emissions offer more clues as to the details and issues that could be connected to working with these engines at any given time. Recalling the work of Friis-Hausen and associates, the discovery of two distinct failure modes in marine diesel engines: exhaust valve leaks and defective injection (Mba et al., 2006). The exhaust valve is responsible for sealing the combustion chamber from surroundings while compression is occurring -- an act which essentially guarantees maximum pressure in the cylinder while the combustion event was occurring and assures maximum engine performance (Mba et al. 2006). Mba and associates point out that in this study, there was found to be a successful classifier, which could make the distinction between the leak sizes in the exhaust valve on the basis of the r.m.s acoustic emission signals alone. This discovery was indeed significant for a multitude of reasons particularly, that it gave clarity to the repair process, taking out so much of the guesswork of maintenance of this complex process. Using acoustic emissions signals essentially allowed for quicker differentiation between the causes of problem when trouble-shooting, saving time and eliminating speculation.

The benefit of the use of acoustic based-signals via non-intrusive monitoring can also be used for the detection of misfire. The work of El-Ghamry and colleagues demonstrated the value of acoustic-based signal in discovering the strength of air fuel mixtures in a 30.56 litre Perkins 4-stroke, 8-cylinder turbocharged gas engine (Mba et al., 2006). Though findings by this same team of researchers also demonstrated that acoustic emissions could also act as indirect measurements of cylinder pressure (Mba et al., 2006). "The AE r.m.s was correlated to the pressure in the time and frequency domain… El-Ghamry noted the advantage of employing the cepstral analysis for the model, stating that it used the frequency content of the AE r.m.s signal rather than the energy content, which gave the advantage over signals with low energy content" (Mba et al., 2006). These results are indeed significant, as depending on the frequency of the acoustic signal means that researchers can still get a clear reading regardless of what the given energy content is.

In the research article, "A study of the tribological behaviour of piston ring/cylinder liner interaction in diesel engines using acoustic emission" by Douglas and colleagues examines the application of non-intrusive acoustic emission measurements in the task of providing information in connection to the rapport between piston rings and cylinder liners in a collection of diesel engines (2006). The researchers determine that this form of monitoring is indeed effective and can provide a new form of exploration in to this truly crucial dynamic and process of engine operation (Douglas et al., 2006). "AE generated during normal engine operation is known to consist of contributions from a number of different sources such as injector and valve activity. A recent ?nding has been the identi-cation of AE signals associated with the ring/liner interface which presents the opportunity for in-service monitoring" (Douglas et al., 2006). This paper explores and analyzes the range of potential acoustic emission dynamics: asperity contact, lubricant flow and others (Douglas et al., 2006). The superiority of this research is that it shows how acoustic-based non-intrusive monitoring is absolutely a promising method for the scrutiny of the tribological dynamics of the piston ring/cylinder liner interface (Douglas et al., 2006). The importance of this research is not to be underestimated as it's able to achieve feats which ordinarily would be impossible or nearly impossible. Such findings demonstrate the sheer feats of success that acoustic-based non-intrusive monitoring can accomplish, that other forms are simply not capable of. Furthermore, this method is not just successful at illuminating pertinent data, but its inherent non-intrusiveness means that the delicate balance of the engine's performance is not affected (Douglas et al., 2006).

This is indeed crucial as negatives impacts or effects that could compromise the reliability of the engine or the overall performance of the engine would be largely counter-productive. Furthermore, the remarkability and ease in which acoustic-based non-intrusive monitoring can be used in these cases indicate that it can also be a successful ally "for the in situ appraisal of component condition, wear rates and lubricant performance and could signi-cantly aid condition-based monitoring strategies" (Douglas et al., 2006). In a word, the success of the usage of acoustic-based monitoring in this case demonstrates the potential for it to be further improved and to further evolve so that it can function at an even higher level of advancement for even more challenging tasks and opportunities.

Vibration-Based Non-Intrusive Monitoring

As one scholar on vibration-based monitoring explained it, the phrase "running smoothly" is very much a testament to the fact that human beings have long monitored the status of their machines based around the vibrations these machines produce or do not produce (Williams & Drake, 1994). "Vibrations signals carry information about exciting forces and the structural through which they propagate to vibration transducers" (Williams & Drake, 1994). The fact of the matter is that quite simply, a healthy machine produces vibrations of a particular "color," whereas if there is something dysfunctional about the component of a machine, this vibration degrades and it immediately becomes apparent that something is terribly wrong with the entire functioning of the machine. Vibration monitoring can thus be incredibly useful when it comes to diesel engines, to assist in monitoring the entire integrity of the machine. The benefits of vibration monitoring are readily apparent and immediate which explains why they've been used for so long. There's a range of equipment which supports this function and it is relatively inexpensive for use on diesel engines; using this equipment doesn't take a lot of time to gain mastery of its use and the non-intrusiveness of the vibrational transducers is yet another benefit (William & Drake, 1994). When it comes to diagnosing diesel engines, non-intrusive monitoring is really the only option: in order to make an appropriate and correct diagnosis one needs to be able to determine what is problematic when the engine is actually functioning. Non-intrusive, vibration-based monitors are able to do this in a manner which is reliable and gives quick results.

Using vibrational-based non-intrusive monitoring for diesel engines can be an absolute lifesaver when it comes to maintenance and treatment of these engines. "Early fault detection and diagnosis for medium-speed diesel engines is important to ensure reliable operation throughout the course of their service. This work presents an investigation of the diesel engine combustion related fault detection capability of crankshaft torsional vibration. The encoder signal, often used for shaft speed measurement, has been used to construct the instantaneous angular speed (IAS) waveform, which actually represents the signature of the torsional vibration" (Charles et al., 2009). Charles and colleagues aptly acknowledge that previous studies have demonstrated that the IAS signals and the Fourier transform (FFT) analysis can be successful in assessing engines that contain fewer than eight cylinders; however, whether or not this is relevant to medium speed engines is still under debate as a result of the high number of cylinder and the massive moment of inertia (Charles et al., 2009). Charles and colleagues thus explain in their paper how the effectiveness and reasonable level of success of the general FFT-approach has come under scrutiny by bolstering the signal processing in order to better assess the IAS signal which has been tried on an engine of the 16-cylinder size (2009). They also acknowledge a newer method of presentation which has roots founded in the polar coordinate system of the IAS signal, thus bettering features of distinction on the faults when juxtaposed to the FFT-based tactics of the IAS signal (Charles et al., 2009). For the bulk of the research, the authors discuss two experimental studies which address these issues using engines of 16 cylinders and of 20 cylinders and the findings of the polar presentation technique in juxtaposition with the FFT-based mode (Charles et al., 2009). What the researchers are able to accomplish very aptly is that their findings truly demonstrate how adaptable and how important vibration-based non-intrusive monitoring is. The particular mechanism that these researchers were studying, capability of crankshaft torsional vibration, is something that needs to be studied while the engine is running in order to determine the possible issues with its functioning. Such vibrational diagnosis and monitoring can adapt to various engine sizes and can still assist in illuminating various maintenance or service issues.

Study after study speaks to the effectiveness of using vibration signals as a means of truly successful non-intrusive monitoring of diesel engines. The proper creation of diesel engines and their correct functioning is completely reliant on injection parameters, such as injection number and the timing of injections, the fuel quantity and the average pressure of such injections (Carlucci et al., 2006). In fact, Carlucci and colleagues attempt to use vibration-based non-intrusive monitoring as a means of determining the proper dynamics of these injection parameters in the research study, "Analysis of the relation between injection parameter variation and block vibration of an internal combustion diesel engine" (2006). Carlucci and associates acknowledge that it is widely known just how influential the impact of injection parameters have on the entire vibration of the engine block; the authors of the study attempt to further determine the potential of using engine block vibrations as a tool for diagnosing "the combustion modifications induced by these parameters. So, the possibility of following the combustion modifications by means of two accelerometers positioned at two different zones of the engine block has been analyzed, defining a characteristic 'signature' for each parameter" (Carlucci et al., 2006). It was found that the vibration signals really were impacted by forces like the injection pressure and injected quantities (Carlucci et al., 2006). This was determined through the use of Fourier and time-frequency analysis to define the amount of connection between in-cylinder pressure and the signals given off by the vibrations (Carlucci et al., 2006). While the specifics of this type of research were incredibly illuminating as to yet another diagnostic tool that can be used with specific dynamics and movements within a diesel engine, it also shows yet again the reliability and versatility of vibration-based non-intrusive monitoring. The evidence demonstrated by Carlucci and associates continually speaks to how vibration-based monitoring can be used with ease for a wide variety of the various small and large functions within diesel engines.