 Hello, this is the last class on this course on machinery of all diagnosis and signal processing the 40th lecture. Before I get into the case studies few examples of applications of machinery condition monitoring in real life, I would like to just quickly go over the brief overview of the course and the syllabus content. Basically, we had this course in few modules, but the main principle was to work on the machinery condition monitoring and then few of the modules we talked about was maintenance principles, then about the instrumentation issues and because of this fact that for machinery fault diagnosis throughout the world, few very important practices are followed mostly 70 percent of the cases being vibration based analysis followed by about wear and debris analysis which form about the remaining 20 percent. The last 10 percent could be the motor current signature analysis and the few of the NDT techniques. So, if I was to see what we have studied in this course, the most important aspect was the vibration based monitoring and vibration based monitoring is particularly helpful for finding out faults in rotating machines because all the rotating machines can be represented by a mass springed as part systems and by and the excitations could be because of defects in the rotating systems like unbalance, misalignment, looseness, crack and so on. And then we get a response based on this response, we try to find out the fault. So, in fact, one of the very first case study would be the case of vibration monitoring and then we have few other techniques like MCSA that is the motor current signature analysis and wear, debris analysis and of course, the NDT techniques. In the past lectures, whenever I had discussed about some of the issues I had tried to bring in few real life examples into the classroom. So, if you look into the lectures of the previous classes, you will see some of the examples which could be treated as case studies. So, in this class on case studies I will be specifically on to about 4 case studies and that would be the most general being the motor care box vibration measurements because of the fact that any plant in the industry is actually driven by a motor which could be directly driving a gear box, a blower, a fan, a compressor, any other crushing unit etcetera. So, this configuration becomes very important you can say as a template for all industries. And there are ISO standards available which let us know regarding the acceptable vibration levels before a machine can be considered to be defective because of excessive vibrations. So, this is followed and this is given depends on the machine power. I will refer you to this ISO standard and for those of you who are practicing engineers in the industry a good idea would be to a good place of reference would be this ISO standard because it clearly states the machine power and then what is the acceptable vibration levels. So, in this first case study I will tell you about what is the acceptable level and how in a particular plant we did measure such a vibration level and were worried that some of the things were not wrong. So, the first level in any condition based health monitoring system is to have an overall idea of the vibration level and of course, once the vibration levels are higher than an acceptable limit we have to find out the fault or what we have to do then is the fault diagnosis. So, fault diagnosis is triggered or the fault diagnosis exercise is triggered if the vibration levels are not acceptable not acceptable vibration levels and this is as per the ISO standard. So, once we have such an non acceptable vibration level we will do the fault diagnosis and in this series of 40 lectures we have told you some of the techniques and which are just told right in the beginning of this lecture and of course, I will this is beyond the scope of this lecture people do anyway the fault prognosis through mathematical models to find out what is in the RUL remaining useful life I had talked about one application of the cutting tool life remaining cutting tool life in a machining operation in one of my early lectures remaining useful life of the machinery and that is what is what we are looking for I know that is a fault, but my doing all this exercise is to know whether my machine is going to survive it or machine is going to last how long or machine needs immediate replacement. So, this kind of decisions will be only made once I have a fault prognosis, but of course, this is not in the per view of this course may be in a second level course on machinery fault diagnosis we can look into this issues and then we will now go to the specific examples of motor gear works for measurements. Another few case study would be the bearing seat damage in VFD drive electric motors which had briefly told while you are talking about motor current signature analysis and a new area which is coming up is in condition monitoring is the wireless data acquisition. So, you know you would have seen when we have a machine where all this transducers are mounted cables have to be drawn to the data acquisition unit and then of course, the competitive base systems does the analysis on the acquired data from such transducers, but many a times it becomes cumbersome it becomes inconvenience to have lot of cables coming from different sensors in the plant. So, people are exploring into wireless data acquisition like, but earlier I would have mentioned to you how the bandwidth limitation limits us as to what kind of data rates we can acquire the data from machine with and how that hampers really to do any meaningful analysis of dynamic signals through wireless data acquisition. And of course, another emerging area is monitoring the health by torsional vibration in this ISO standards or mostly in this class we have talked about linear vibration measurements, but recently there have been techniques where people have used torsional vibration measurements to find out faults in machine and unlike the accelerometers which are used to measure the linear vibrations, these torsional vibration measurements by simple optical encoders are very cheap method of finding such analysis. So, now I will come to the very first case study on vibration measurements. By the way to get more references for this course, you can refer to my website where time to time I will have technical updates on condition based maintenance case studies uploaded for anybody to download. So, this website is openly accessible to everybody. So, you can know more about this material and of course, if anybody wants to contact me you can contact me over my email of course, my mobile number is. So, these are the contacts and if anybody needs more information on this course machinery fault diagnostics and signal processing you can either visit this website or contact me over email or a mobile call. So, this is a typical configuration in an industry wherein we have a motor and then which is driving a gearbox. So, motor is the prime mover and this is the mechanically we need which is being driven this gearbox could have been a blower or a fan. So, in this particular example I will just give you a overview this is a plant which is used for raw material handling and this gearbox actually drives a conveyor belt system when raw material at the port is one conveyor system loads done to the ship for export and there is another conveyor system and then another series of conveyor system which brings in raw materials from the ship hull to the stack yard at the port. And as you know in this port you know port of course, next to the sea and then this atmosphere is saline and there is a aggravated corrosion because of the harsh environment. So, such a plant we noticed that the vibration levels were alarmingly increasing and there have been failures in the one of the drives and then we are asked to investigate the cause. So, as a very fast there is no record of any vibration levels in such a system because this was about this was put in a structure which was about 25 meters from the ground and it we only had a narrow ladder to access the maintenance crew only had a narrow ladder to access the gearbox and motor and they were practically not being monitored throughout the life of this plant this raw material handling plant. And once the vibration levels were excessively high we went ahead and instrumented this locations you see 1 through 18 are actually the bearing locations the black ones are the bearing locations. So, like 13 would be an NDE bearing location of the motor that is non non drive end 13 is non drive 16 is drive end if I was to say all the blacks. So, the bearing locations are 13 16 and this is an intermediate stage gearbox. So, that is three stage gearbox. So, the shafts are like this and this is a bevel gear because the direction would be of power transmission is changing. So, 4 9 3 8 1 2 7 17 this is the drive end bearing of the gearbox. So, all the measurements were done at the bearing locations of the gearbox and that would be 17 4 9 3 8 2 and 7 and then we decided to measure some at the foundational locations and these were 14, 15, 12, 11, 5, 10, 1, 6. And another very for just for reference because this was a platform and while in operation this was vibrating we measured the structural vibration close to the ground that was at 18 and they were all measured in different directions. So, this is the orientation and the foundation we had in a different layers of shims. So, we measure at A, B and C and I will show you a figure of this plant. So, this is the motor side end that is the gear coupling which is driving this motor this gearbox and you can see the chalk numbers 9, 8, 10 etcetera. And you can see pretty well because of poor workmanship they have this has warped the base has warped and there is a lot of corrosion in this base because of the harsh saline environment at the port and because of this corrosion there were lot of play and these were these jack bolts which are used to do a local alignment and eventually this kind of corrosion led to the misalignment and this is another view of the shims which were placed underneath the gear box to arrest the to level it and they also corroded. So, misalignment crept into the system and then excessive viruses were noticed and this is another view of from the non-drive end of the motor at the base. You can see how poor the manufacturing is and this has led to corrosion has to cracking and because this is in a most environment and these motors I was made to understand while the plant was been was being commissioned these motors are arrived long before they were put and made to operate. So, these motors were actually stored in the yard and so there was lot of moisture developed and this moisture stayed in the motor and this led to the corrosion of this compound because if the motor was running then there are been lot of heat generation and this problem would not have happened, but since in a yard this motor was stored lot of moisture did come in and then they corroded and then that aggravated the entire corrosion of this plant. And of course, because of these and you can see the motor base is also not in the same level. So, many reasons attributed to high corrosion level because one is corrosion next is corrosion was because of moisture because of saline atmosphere and this led to shims not uniform which in turn led to the misalignment of the system and mind you in such a plant they never ever were measuring the vibrations or monitoring. So, a new plant it took only 6 months to commission, but the motors were stored were stored in open yard under a plastic wrapper under a cover new motors and then they were installed and all these problems happened and then this led to the misalignment and eventually failure of the drive. So, once people noticed a failure and then they get worried what is going wrong with the plant and then these measurements were done. So, this gives you an idea first of all this is an overall RMS level in millimeters per second from a frequency of 10 to 1000 hertz and this is as per the ISO 108163 standard. There are about different parts of the standard depending on the type of motor whether it is a flexible system or overhang system rigid system weight of the, but this is the standard which has to be followed. And there are there are there is to be earlier a German standard even Naya standard is there, but we recommend that this standard gives us the allowable vibration level in a plant or machinery for a certain power of the machine. Of course, the power of the machine is more the vibration level will be more by the way this power of the machine was about 9 about you know 1000 hertz power is something which can you can keep in mind the 1000 hertz power motor. So, you can imagine the size of the system. So, these were the 18 locations and then these were the vibrations measured as velocity in millimeters per second and they are a single number in the band of 10 hertz to 1000 hertz. So, when you have your measurement system always you know of course, nowadays suppose you have this transducer on a machine. So, this is my machine you can have a filter unit band pass from 10 hertz to 1 kilo hertz. And then you can have a RMS display unit and this is an axiolometer this is my machine. So, one has to keep this in mind that the ISO 10816 standard says that this has to be at the very important value it is not any value and many a times I am telling you when you go to the industry to do troubleshooting of machines the engineers many a times will give you numbers you know suppose you know they will say 3.8 and today we are getting 3.8 yesterday we got you know 2.0 3.9. But many of them they say it without assuming that everybody knows that this is in millimeters per second without making sure whether the filters were on or off without even knowing whether it was in acceleration mode or velocity mode or displacement mode. So, these kind of problems do creep in for example, once you are doing a trending because with a simple electronic integrator I can move the measure from acceleration and get the velocity or displacement values. So, one has to be careful about the units and the measurement parameters. So, if somebody is strictly following the standard these errors will not creep in and one has to be careful about it because in such measurements I just showed you for the case of the motor gear box system suppose one particular parameter say vibration level at say motor and e bearing in this example point number 13 and with time in such a plant if somebody was measuring these values every 1 week at every 1 week interval. Now, suddenly unknowingly somebody has changed the parameter units say for example, this was all in this placement in velocity somebody had suddenly moved it to acceleration and it may so happen because see acceleration amplitude is suppose a or suppose the velocity is v times omega and the velocity amplitude is sometimes x times omega or acceleration is actually x times omega square. So, this is a displacement this is velocity this is acceleration as you will see acceleration is linearly proportional to the frequency and what happens suddenly you may think that this machine has increased its velocity has increased because you are always monitoring the velocity, but unknowingly a mistake has happened that the operator instead of monitoring velocity he has changed the knob to acceleration. So, this is going to happen. So, this is the case of a false alarm. So, these kind of scenarios are to be avoided of course, nowadays in the plants with automated data acquisition system such false alarms can be avoided which follows alarms can be avoided. So, in such vibration level monitoring systems in many plants nowadays you know 10 years ago there is to be a scenario where maintenance crew where every day going to different parts of the plant and measuring the vibration by holding by using handheld portable acquisition devices or vibration meters, but just by mistake somebody could change the knob, change the filter settings, change the mode of measurement and this kind of errors can creep in. But over the time people have realized the importance of vibration based monitoring for machinery condition monitoring and then they have realized the payoff they get out of such measurements and then they have put in place such automated systems where the accelerometers are permanently mounted, cables are drawn permanently to the signal analysis unit and on the computer screen you can get the current display, you can pull up data which was logged a few months ago while you are doing any troubleshooting to see if there were any serious changes in that machine. There are alarm levels built in in software when a certain preset level exceeds it will warn the operator or the management that something is wrong machine. So, good robust vibration monitoring system must have these software driven system in place in a plant and in this plant we did find out that the vibration levels in the motor ND bearing were the highest and they were not what they were supposed to and this was attributed to corrosion in the bearing because and then the lot of high impurities you know or the corroded particles are were getting on the bearing were giving rise to this kind of corrosion levels in the motor. So, now I will come to another related problems with bearings because let me tell you many of the times you know these reasons could be very very simple like in the previous example I just told you storing the motor in the yard for 6 months a new motor in a on a on a sea coast where the port was coming up the motors came in before the structures were there were built and then they were stored. So, moisture got into it and saline environment corrosion was aggravated and eventually people install this machine without noticing these corroded parts and once the plant started few months after the new plant started to components started to fail and this is because of sheer negligence of people ignoring the fact that corrosion can be a such harmful and you also saw the poor workmanship of the foundation base because of the fact that this was done at a platform which was 25 meters from the ground. So, all the crews and equipment were not easily accessible at that location and whatever were done and there was no post weld heat treatment you know many a times failures weld failures happen because improper post weld heat treatment and this is something which is not to be ignored. So, when welding is done there are many ASME welding standards to be followed. So, that this kind of problems do not happen material become do not become weak and then they fail because of excessive loads. Now, I will come to the second case study bearing seat damage in VFD drives. So, this is just a figure I had explained this in one of the earlier lectures, but I will just tell you in a VFD drive in a motor because lot of high frequency sparks are generated between the motor shaft and the bearing. So, lot of high frequency sparks are generated in this gap. So, these sparks are responsible for the spark erosion of material. So, this again leads to another problem if the materials get worn out on the shaft like you see here. This is the normal rest setup and this is because of the materials were removed because of such sparks erosion and the sparks are generated because of the VFD drives. So, to protect such VFD drives you know such sparkings not to occur these are actually there is a brush and which is responsible for which is ground shaft is ground through a carbon brush. So, these sparks never occur because it will be at ground potential and this can be avoided, but the consequence of this is the bearings there will be lot of clearances and there will be looseness and the bearings will get damaged while rotating at high speeds. And this was the case of a motor which had a power of 72 kilowatt and these are the typical bearing and the shaft was now or thing connection was there, but the shaft motor shaft was not rounded because of the VFD drive. So, the VFD drive when so whenever we use VFD drive variable frequency drives we have to be careful about this parts which are generated. So, we should not allow them to erode the particles. This was an example which I was I am showing you in the laboratory what we did. This is a motor in one case which was not driven by VFD drive, but a normal power supply. So, you can see a nice low amplitude voltage at 50 hertz that is the running supply frequency, but whenever we change the power supply through a VFD you can see high levels of peaks occurring because of such VFD drives and this is what we are measuring between the shaft and the ground. This kind of peaks to happen. So, this has to be avoided and these are responsible these are high frequency peaks signals and these are responsible for spark erosion of the bearing seats and now I will come to another technique which is wireless data acquisition system which is to be used in machineries which where we can avoid long cables and these are I will just fill it up. We require various applications by a remote monitoring of wind turbines, nuclear reactors, pumps of oil wells, large power plants. So, imagine it in all these locations it is not possible for anybody to draw wires both of course the present standard is at least we have to monitor these parameters in a routine manner their RMS levels, but there to do diagnosis I require not just the RMS level, but the entire time history of some signal x t it could be vibration or anything. So, this signal has to be acquired the present day technology is that they send this information in packets. So, they will take a certain time window. So, this is n times delta t is the total time where the successive points are sampled at an interval of delta t and they will take the sample do at that location do an overall RMS value some parameters some overall parameter some parameter x p which could be its RMS value mean value cotosis value and this x p is transmitted through wireless this is the present state of the art. So, every machines x p is known to me like sending an information in through SMS on your mobile is one way I just machine it has an transmitter and it sends some information of x p to another receiver that is the present state of the art like we use our mobile phones over the wireless networks we can have, but the problem happens when we have to access the data at high speeds when the sampling frequency is high data transfer limitation by wireless. So, this is one device wherein we can have an data accuracy device right on the machine and then we can analyze the data. So, these are certain terms which are used in Wi-Fi the data rate is nothing, but accuracy rate resolution and then we can find the total rate encoding range etcetera. So, in the laboratory what we did is we had an device and Wi-Fi D A Q device and then we have a receiver and then we did data transfer over the LAN ok. And in the same lab we tried to move this through by increasing this distance and there were limitations to this and this is how the system looks like this is an accelerometer which is connected to an wireless data accuracy unit and then we have the wireless transmitter and you can capture the other end through a wireless receiver. This is one example in the laboratory wherein we have a blower whose vibration is being measured by an D A Q device and this transmits and there is another laptop you will notice that there is no cable coming from the accelerometer at this side to the analysis unit here and then we can capture this data. So, this is the time signal of the data captured over the wireless and then we can analyze it and then we could find out the supply frequency a little less than 48.36 hertz. So, this kind of captured wireless data can be analyzed through such systems. I will come to the last case study wherein we can do the rotational speed measurements or the rotational vibration measurements. See many a times this rotational vibration measurements if you look at the 2 accelerometers which are kept side by side in the rig I can measure the angular vibration you call it angular displacement theta as the difference between these 2 vibrations X A X B and the length. If these are known we can find out the rotational vibration art in a system, but this is cumbersome this is contact type. So, nowadays people use the 2 channel Doppler effect laser vibrometers wherein we have 2 laser beams incident at point 2 different points on the rotating shaft and then from the mathematics from the geometry you can find out the Doppler shift are between these 2 frequencies as this and then this omega can be known if you know the D because the 2 channel Doppler effect rotational laser vibrometer come with these 2 lasers fixed at a particular distance you know it could be about 25 mm, 10 mm etcetera and depending the wavelength lambda we can find out the frequency shift and then we can know the rotational speed or the rotational vibration. This is one optical motor attack which is being used to measure the rotational speed of a device which is right here, but the photo attack does not work on the principle of the laser vibrometer here only it sense a pulse of light and it has a transmitter and a receiver on a photo cell. So, depending on the time period between these 2 pulses you can find out the rotational speed, but these rotational speeds are very gross in the sense suppose a shaft is rotating at a certain rpm I can know over the period over the time what is the mean omega or n. However, because of a defect in the system if the shaft within one rotation there is a speed fluctuation how does one capture that and that is where I mean this is another view of the rotational laser vibrometer which is focused on a rotating shaft. So, coming back to the measurement of a rotational speed fluctuation we can use what is known as an optical encoder for condition based monitoring where gears are inversely used in rotating machinery they have been applied from household appliances as the vacuum cleaner owners. A lot of fault detection procedures have been done in finding on faults in gear, but the possible way for gear box fault regression is the instantaneous rotational speed. So, this is known as IAS this has been used to find out faults in gear boxes faults in IC engines and so on. I will not go into details of these much here the details can be found in my website and some of our papers. This is how an optical encoder looks like and is held to the end of the shaft and this is on that same gear box which I have used quite often in this class that is the set up which we have in our laboratory and then the driven by a motor we use this for motor current signature analysis. Now, we are doing it for the optical rotational speed measurements and this is the setup of the gear box and which I had told earlier in many of my classes this is the control panel for the same this is the gear box which I had shown earlier and this is how this optical encoder is put at the end of the generator which is loading the gear box right here this is the gear box and this is the optical generator and the optical encoder is mounted here. This is how this optical encoder looks like this is another view of the optical encoder and then parallel view also measure the vibration. So, a typical optical encoder actually has slots on the periphery and when a light beam passes through them it will generate a pulse and the spacing of the pulse is a measure of the instantaneous speed and this is perhaps not clear in the slide this omega is nothing but d phi by d t. So, we can measure the instantaneous angular speed. So, this encoder has to be captured the data from the encoder has to be captured at very high frequency about 20 megahertz and then we can measure the rotational speed and this is the minimum measurable speed these are given in some of the references and this is the power flow from the gear box and we could capture the different frequencies of the gear box this were known to us beforehand. So, in a multi stage gear box these were the input shaft speeds and this is the lathe shaft and this is the gear missing frequencies and the interesting part was you know we had the healthy gear the one-tenth missing case and the data were acquired over the entire pulse duration and this pulse spacing would change and these are indications of the I s that the speed is changing and then this data this is a lot of signal processing is required and this is the vibration spectrum of that same gear box as measured by the transducer and the most important thing here is to notice that the I s amplitude in rpm which are measured from the pulses in the optical encoder the c is the variation is not much only 0 to 3.5 if I fail this is the I s and this variation is only 0 to 3 rpm. However, this small f 2 f 1 etcetera. However, this small fluctuations are captured by this optical encoder and which is not possible with a normal mechanical tachometer it is not possible. So, by I s we can capture this phenomena and the best part about this optical encoders is that they are relatively very very cheap and it all they require is a high frequency data equation unit. So, that the signal are captured at higher rate they can be analyzed with the signal processing unit and then we can find out the fault in the system because we are able to detect the gear box defect frequencies just by monitoring the I s or the instantaneous angular speed which is measured by from the pulses recorded by the optical encoder. So, by signal processing of the pulses we have to capture them at very very high frequencies and then just by doing a derivative of the pulse strain we can find out the instantaneous angular speed and these speeds are not varying much even 0 to 3 rpm when some machine is running at say 1440 rpm. For a fraction of a second if this small variations is there because of a load because of a fault and if that can be captured that gives us a telltale sign as to what is defective in the system and this has been very popular with IC engines and at our laboratory in IIT Kharagpur we have been using them to find out faults in gear box systems and they are a cheap replacement to normal vibration measurements by rotational laser vibrometers. Laser vibrometers cost us in millions of rupees whereas, this is a very few thousands of rupees and this are the high frequency gear box viruses which again we could capture through viruses and with this I would like to conclude this course on machinery fault diagnosis and signal processing. Hope you had an enjoyable teaching and learning lesson in this class and if there are any issues you can contact me over email or at my website or my phone numbers. Thank you.