 This is the very first class in module 4 on the basics of instrumentation. Essentially in module 4 we are going to discuss about the issues of instrumentation, measurements, data, data recording, data storage, data transfer and so on. Because as you know in condition based maintenance, the use of transducers is very important to know the conditions of the machines. Now we had discussed that there are certain parameters which we use in condition based maintenance like as in vibration, temperature, noise, electrical current. So you know you must have studied in an instrumentation because this instrumentation itself is about a 40 hour lecture in any undergraduate program in mechanical or electrical engineering. But today in this class in about an hour's time we are going to overview the basics of instrumentation and how in particular you will see in the subsequent classes. We will discuss about some of the transducers which are used in condition based maintenance to be put on the machines so that we can capture the mechanical parameters of the machine that could be vibration, noise, temperature, etcetera. And then of course very important is we have to be very careful that we do not induce or do bring in an extra noise or error into our measurement because the algorithms of condition based maintenance depend on the data which is been collected by us or by the transducers and provided to the analyst. So if we create noise or bring in artificial errors into the measurement system we will not be doing a good job. So other than knowing the instrumentation the equipment and required to do the signal acquire the signal from the machines we have to be also careful about how by doing a proper instrumentation we can minimize error how we can do the instrument calibration so that we get the exact replication of the phenomena which is happening in the machine. Imagine you go to your doctor and he has a blood pressure meter which is you know which has not been calibrated ok. You can imagine the consequences similarly you know when we want to capture certain parameters from the machine would obviously not like to do a wrong measurement. So with this preamble I would like to start this 16th lecture on basics of instrumentation. So let us see what are the important elements of instrumentation. One of course is the sensing element or the transducer essentially sometimes you know we have been loosely sometimes people say that it is a sensor or a transducer is the very most important element which is kept or placed or connected on our machine. So this is my machine there could be lot of dynamics happening in this machine you know that it could have been having rigid body motions or the rotations. So how do we and then if we have a transducer the idea is to capture the motion around one of this points and essentially this transducer usually gives an analog electrical signal. Now this signal which we obtain from the transducer is dependent on the mechanical parameter. So this electrical signal obtained is proportional to the mechanical parameter which has been measured okay and you all know there is an endless list of mechanical parameters and endless list of sensing element rather than sensors. Sensing element is very very important same mechanical parameter could be sensed by different sensing elements for example either direct or indirect for example I have a body which is having a certain motion at one point because of the motion there will be displacement this displacement could be captured by an LVDT and that is a linear variable differential transformer LVDT or strain gauge or a piezoelectric crystal. So these are the different sensing elements which are used to measure the mechanical parameter could be mechanical motion this is just to give you an example of the body. Now from this sensors I will get an electrical output now you may be wondering yourself well why do we have so many different sensing elements well it is because of the fact that these sensing elements have different characteristics some may have a poor response some may have an excellent response some may not respond at certain ranges some may not work at high temperatures some may not have a linear output so these are characteristics of sensing elements. So a transducer or a sensor a transducer has an essential element which is the sensing element. Sensing element is the most important part of a transducer and this list of sensing element is endless okay it is a very large list but we will try to focus our attention mostly to mechanical motions vibrations noise temperature process parameters and so on. So we will home in towards these few mechanical parameters and see because if you recall I told you in the very few first few classes that the condition based maintenance around the world 70 percent of the cases are by vibration monitoring rest 20 by wear debris analysis and the remaining 10 either by ultrasonics and NDT techniques motor current signature analysis. So we will focus our attention to mostly how do you correctly measure vibrations and how do you correctly measure temperature pressure current and the wear debris parameters so with that we will be kind of looking into these elements. So coming back to our discussions on the sensing element there could be LVDT strain gauges visual electric crystal etc but the between the machine I have certain intermediate step where in I put a transducer I will have some intermediate unit which is essentially a signal conditioning unit and then we will have the either the display or the analysis unit and of course associated this there are lot of secondary devices like a archival device to store the data to plot the data etc we are not going to discuss this. So depending on this transducer output my signal conditioning element could be many I have listed few of them in here in a slide one is definitely sometimes an amplification is required I will give you an example of an amplification which is used mostly in condition based maintenance for example we are using a thermocouple ok. Suppose a thermocouple at a certain voltage certain temperature gives only about 3.5 millivolt and with the if you recall the measurements done by thermocouple when the temperature increases this voltage output will increase 3.5 millivolt will never become 10 volts ok but this goes you know 3.5 maybe you know maybe 2 volts and so on. So the range given by the sense the output produced by the sensing element may be from 0 to 2 volts ok that may be very very small compared to the range of display which I could have or for example recall back to the lectures on data acquisition is the minimum voltage data acquisition unit can sense is say 1.5 millivolt or let me take this say 5 millivolt and this is an hardware requirement a characteristic of the data acquisition unit. Now if my thermocouple output in this example is 3.5 millivolt obviously my display or analysis unit because data acquisition unit is actually sitting in your analysis unit I am not able to capture or sense the thermocouple output that is the problem I have. So obviously I need to amplify so amplify amplification is a solution to the problem ok maybe I will increase it by a gain of 10 gain usually written by multiplied by 10 x 10 or multiplied by 10 that means this becomes 35 millivolt ok. So one such intermediate unit or signal conditioning unit is an amplifier or an amplification unit but this may sound very easy you know I have increased the voltage again by 10 volts but I also am amplifying the noise ok this is an associated problem. So how do you remove it? So there are issues ok once this noise has increased I could always you know for example to begin with you know my signal in the time domain look something like this certain voltage if I increase it by a factor of 10 maybe this will all ok this becomes by 10 and this is my original signal the black one is the original signal ok I have amplified the noise but then you will see sometimes you know there are detectors if I put a detector that you sense only the peaks I should be able to sense the peaks this is in time domain but sometimes here it is seen sometimes we can do certain filtering because in the frequency domain I know my signal is in this band I can put a band pass filter. So it is going to eliminate the noise in the bands which are not of interest. So this is my f lower and f upper and this will have a center frequency fc depending on you know you recall your understanding of filters whether it is an octave filter one third octave filter it is a linear band pass filter we can decide on this or whether it is a notch filter particularly when we do measurements in mechanical systems wherein there is an electrical power supply there is a problem of what is known as an electrical ground ok this is very very very important particularly in many measurements when we do at site on condition based maintenance what happens suppose I have one machine and another machine ok and they require an say an AC power supply ok they require an AC supply machine 1, machine 2 right and suppose physically this is the ground potential of this ideally it should be 0 voltage but you would have seen in many cases suppose this is a 2 volt instead of a perfect ground this is a 2 volt and that is 0 volt. So if I do lot of instrumentations I and I conduct each one by wires ok there will be a flow of current because the potential difference is only 2 volts is good enough for a current to flow and this current will flow at the supply frequency of 50 hertz. So any measurements if I have put a transducer here if I put a transducer here T 2 T 1 and then I go to my analysis common analysis unit you will see because of the potential difference because this has a separate power supply this has a separate supply power supply and one is at a different ground you know we may very notionally say well they are all at the same ground but in real life between rooms you would have seen one is not a perfect ground that is perfect earthing even if a 2 volt is there this is large enough for a current to flow and whenever we do the analysis you will see in the frequency domain you may be doing a vibration measurements you know all the vibration measurements will come but they will be a strong 50 hertz signal ok. This is a real problem with instrumentation and once we go to the field we have to avoid ground loop ok well I will just tell you some of the tricks to avoid ground loop one is wherever possible use DC power supply battery source next is keep common common common ground that means if all the potentials all all are common then this will be no potential difference and then there will be no flow or make sure earthing is proper. Sometimes I have seen earthing voltage is of 10 volts very poor earth and this is responsible for because this signal carrying cables are actually metal conductors. So there is path for the electrons to flow and they get buried in the signal which is being captured by the transistor ok. So this could be done by having a proper intermediate element which is a signal filter I could the next one I could have number 4 is a notch filter that means from the signal it is going to remove the 50 hertz component ok. So 50 hertz effect will be removed few more amplification units are see linearization particularly sometimes in some strain gauges etcetera the outputs are not linear ok. Suppose my output with time or with certain range is some x and y parameter this is my output. So I could because if you imagine because this was my mechanical parameter and this was the corresponding electrical voltage you see lot many oscillations ok. So either through a device either analog or digital I could linearize the response while we are doing the measurements if you have my transducer the intermediate unit and the display unit these are all analog signals. So there are analog linearizers or linearization units these are my transducers and the readout unit ok. So because the signals are analog we have to have certain sets of electronics to do the linearization. But again I will just tell you because we had courses on digital signal processing had I given you this red signal on a computer you could have very easily linearize it now which you all are doing while you plot an excel graph or do a regression analysis ok. So you can imagine the power of digital signal processing think of the days when digital signal processing were not available where computers were not available how were people getting linear output of a lot of sensing elements they had to have some electronic hardware to do that ok. But gone are those days now it is I will just get the signal from a transducer by having a proper data acquisition take it in the computer put a software do the linear output ok. And the next element of this instrumentation of the last element very important is the data presentation element ok. Because finally either you can call it as data presentation or data further analysis or because you know once the signal has come from the transducers through the signal conditioning element to the data presentation element we have to now see the format in which the data has to be presented. Sometimes once the data presentation is done we have to do the data analysis. Now this presentation is in a proper format this format could be if you are just doing a measurement and reporting it it has to be as per the format of the report or a standard. Now this presentation whether it is analog display or a digital display whether this data which has been presented whether it needs to be archived or stored it may go to a database. Because finally or CBM software or technique it will be working from this data only I can store them if the data is large should I store them in ASCII characters or binary because the storage space is very important. If I am doing all these measurements I imagine you know you can complicate you have a small laptop hand held laptop and you have to do the measurements all around the plant and capture all the data into your laptop imagine in one day you are going to fill up your hard disk ok. So the format of storing the data if there are certain image files we cannot be storing large image files. So that is why all these formats of JPEG, TEF all those compression formats have come up you must have heard of JPEG files because only the process is to compress the data. So binary method of storing data is much much useful in the sense that the memory requirement will be less when you are storing digital data. Earlier there is you know if you if you go to any plant control room particularly if you go to the plant control room of an electrical power station you will be noticing that there are there are few engineers or operators looking at the wall full of dials because they have many critical components which they will be recording. In fact many of the you know steel plants cement plants etcetera around the clock when their production the shift in charge do nothing but they will be maintaining a log ok and the next day morning the in charge is going to come take a look at it. But these are done about decade ago. Nowadays everything is automatically data log and if there is an deviation you will either get an alarm may be on your mobile phone. If you are sleeping at your house you will get a mobile phone such and such bearing in a plant has become abnormally hot and this is the state of the art nowadays. I mean earlier days 30 years ago 20 years ago steel plant what they were doing the control room in the night they were just logging down in every half an hour. This is the temperature of the that blast furnace this is of that coolant pump this is of this gear was that gear was temperature pressure flow rate all this. And this was being done manually when all the computer aided data acquisition systems were not available. Nowadays you need not worry it is totally manpower less there is no manning ok everything all from all the data transducers are put permanently around the instruments signal analysis units are there data is being logged into your computer and data if if the sudden data suddenly some data are there which are abnormal which are not as per the prediction models you will get enough alarms. Alarms could be right there at the plant alarms could be right there on your mobile phones also ok and that is what is the present state of the art ok. So, well essentially all this you know which you have discussed so far are the elements of instrumentation and to summarize the three elements of instrumentation are the most important is the sensing element then is the signal conditioning the intermediate equipment or analysis unit and then the data presentation element ok. Now, let us see what are the different transducer elements available to us to do measurements. If you look at the two broad classifications one is the analog transducers and other is the digital transducers. In analog transducers we have the electromechanical type basically a resistance type and inductive type a capacitive type or a strain displacement type ok. So, this is this is the technique I mean I am not these are not the mechanical parameters mechanical parameters could be anything, but by having this sensing sensing elements I can measure the mechanical component I will just give an example here. So, for example all of you know what a strain electrical resistance strain gauge is it measures strain, but you see this strain gauge could be used to measure a mechanical parameter displacement another mechanical parameter as a load or a force which are actually load cells. Suppose I have a because of certain force this member is either going to get an axial pull or compressive and then if I put electrical resistance strain gauges here because of this load compressive load I will get a strain. So, by measuring the strain knowing the parameters of this member in terms of the cross sectional area the Young's modulus the length I can indirectly measure what the force load is and that is what is a load cell. So, an electrical resistance strain gauge is this sensing element, but the mechanical parameter could be load could be displacement could be pressure for example there are diaphragm types of pressure gauges and these are held in this is a thin membrane and there is certain pressure here P and this of course, this is there in housing etcetera because of this what is going to happen is this membrane is going to have a deflection. Now, on this membrane suppose there are certain strain gauges attached. So, because of the pressure this membrane is going to deflect because of the deflection the membrane will have a strain and that is again sensed by the strain gauges. So, strain gauge has become a sensing element mechanical parameter could be pressure instead of strain gauges I could have put piezoelectric crystals they would have produced in charge. So, some of the for example, microphones in a microphone we have 2 membranes or 2 desks rather and they are maintained at a certain potential let me draw it in another page here is a very thin membrane like a metallic foil and then this is another base plate metallic. So, if there is a pressure fluctuation this pressure has become because of the acoustical waves which are being incident. So, what is going to happen this membrane is going to deflect as per the pressure waves which are incident. So, what is going to happen? So, this is going to happen this gap is going to change because this gap has changed its capacitance has changed. So, by sensing the capacitance change in the capacitance because the capacitance has changed the charge produced will be changed and because they are maintained at a particular voltage this plates are maintained at a particular voltage. Now, the capacitance has changed because the gap has changed and then we will get a charge which is corresponding to the mechanical pressure P. So, these are what are what I mean are the sensing elements resistance inductance capacitance strain etcetera and these are used as sensing elements in mechanical systems to measure the mechanical parameter instead of strain gauges and we are also nowadays using piezoelectric crystals. In fact, in CBM some of the instruments which you are going to discuss are basically nowadays having piezoelectric crystals as the sensing element. And some of the other type of transducers are the digital transducers they will generate the frequency generating type or the digital digital encoder types wherein we will get a pulse strain and by measuring the pulse width we will get the frequency estimation and these are used in particularly in CNC machines lathe etcetera to find out the speed fluctuation etcetera. Now, based on these sensing elements certain transducers are built manufactured and then we use them in CBM, but then these sensing elements so if I was to go back to the discussion of the pressure gauge. So, input so in the measurement chain in an electromechanical transducer are these three one is the physical variable. Physical variable could be the load force in the case of a load cell pressure in the case of a pressure gauge, but the primary sensor is that mechanical displacement or strain it was that membrane which deflected and on that membrane I had kept a strain gauge I could have kept a piezoelectric crystals as that was my primary sensor and then I will get an output which corresponds to the characteristic or deflection of these sensing element strain gauge or piezoelectric crystal and finally, I will get an output. So, everything to put together is a electromechanical transducer. So, now a transducer is a little bigger superset of the sensing element excuse me. Now, once we have understood what these transducers are let us see how do you know the whether we are measuring them correctly. So, some of the static characteristics because the primary mechanical parameter as a function of time mechanical parameter could be anything it could be either static not varying with time example temperature in this room almost static or the parameter is changing with time maybe the. So, this is the dynamic examples vibration of a structure voice signal in this classroom example here in static case is the temperature. So, the mechanical parameter is either a static or a dynamic character has been a dynamic characteristics. So, that means static means it is not changing with time it has a DC value it is not having any frequency or dynamic means it is varying with time. So, it has a frequency content now what are the frequency static characteristics of an equipment or a transducer. For example, I know I will give you an example I know that this is my actual quantity which is to be measured. But each time I measure I am reporting these values this is one case another case could happen this is my target of the bull side another is these are the cases another could be I am all over the place and another could be I will just this is my target in this case I am precise in the in the sense that I am always measuring around a particular value here here I am accurate, but not quite in this case I am both accurate and precise and this I am neither accurate or precise the best would be this kind of instrument wherein I always measure accurately and precisely in the first scenario there is an error there is an actual offset. So, this offset if I know this value I can always remove this offset and get the correct measurement. So, this is the measurement has been biased constant shift. So, this is the case of a bias error and here in the case of accurate if I did more averages and more measurements and did many averages I could be perhaps close to the target. So, this is the case of an random error here I have both random and bias errors and here I have removed both the random error and bias error. So, you get a feel that in any measurement this happens, but my CBM wants only this we have to be both accurate and precise. So, today if you go to the market to buy a thermometer you will get a thermometer for 5 rupees, you will get a thermometer for 20 rupees, you will get a thermometer for 2000 rupees ok. Not that the cost is towards the profit margin of the supplier, but it is for these values you know the same amplifier, same vibration meter which we use for accurate scientific measurements and R and D are very very costly same microphones now which I am using here could be you know 100 rupees, but then there are microphones which are 100000 rupees doing the same thing, but they are more accurate and precise because of this scenario. So, accuracy and precision go hand in hand and then as CBM we have to remove this bias error and random error and this is done by random error reduced by doing more averages, bias error by doing a calibration ok. And some of the important other characteristics are the resolution, sensitivity, range, hysteresis, impedance etcetera. Resolution is the least value with my measurement system can measure and so on. And so in a static instrument which we use for measurements we have to be very careful about whether it is accurate, whether it is an accurate instrument, whether it is a precise instrument or transducer and you will see because how accuracy and precision can hand for your results. And now let us come back to the dynamic characteristic of an equipment ok. By the dynamic characteristic of an equipment I mean or a transducer that means if my mechanical parameter which is to be measured is varying at a certain rate it is varying at a certain frequency is not it. Now imagine that means high frequency means it is varying at a high rate. So, my measurement system cannot be slower than the mechanical system is not it. Suppose every instance the vibration is changing I cannot come with a transducer which will measure vibrations only at intervals of ten minutes. So, I am going to lose this phenomena is not it. So, my instrument has to be has to react faster than the quantity or the mechanical parameter which I am measuring that is very very important. I use the word react quicker because of the fact every mechanical transducer has inertia has stiffness has a natural frequency. And if you recall this natural frequency is nothing, but stiffness by mass if mass is low then natural frequency is low ok. So, if I want a very sensitive equipment in terms of very fast response its mass has to be less I will give you another related example. You know many of you must have seen the jockeys riding the horses on the horse track ok. Have you seen why the jockeys are very less weight the person was riding the horses. Because my objective there the horse has to go from the starting point to the finishing point quickly. And jockey is loading the horse ok. The horse should not become sluggish or should not react late because it has got loaded ok. So, that is why jockeys are of lesser weight. Same token here if I am mass is very heavy the transducer will be having a very very poor frequency response they cannot react faster ok. You would have we all cut jokes with you know persons who are overweight they do not have they have a poor reaction time. Because of this similarly transducers which are heavy and bulky they cannot respond fast the mechanical parameters which are sensing ok. So, we have to have sensing elements which will react faster or which will have a response quicker to them. So, now going back to the transducers because the transducers because they have natural frequencies if I was to plot the natural frequency response of a transducer may be certain parameters. So, this is the natural frequency of the transducer. So, I should not have to have to be doing my measurements in the band much much away from the frequency response of the frequency natural frequency transducer. So, this is my useful range. So, if I was to define the frequency response of an instrument that is the response of the output to the input in the frequency domain usually given in the transducer. Because if my input is having a certain characteristic the output should be identical. So, this in the decibel scale will become 0 decibel because if I come to these ranges my output is getting affected by the natural frequency of the transducer. Because we have to live with it the transducer has a natural frequency. So, my output cannot be getting amplified because I am measuring in this frequency range. So, every transducer has a useful frequency range wherein the output to input ratio is 1 or in log scale this becomes 0 decibels. Similarly, we have the time constants. So, here I will direct you to my website w w w dot i i t noise dot com. In this website if you go to the student resources page there is a tab on virtual labs. So, if you go to the experiment number 2 in this virtual labs that is the response of mechanical systems you can have an understanding of the response of first order, second order systems. So, you know you all can go to this place and just for your cell study look into this website. So, well you must be wondering why do you always use electrical signals because of these inertia and friction effects are absent, amplification can be obtained with relative ease and recording from a remote distance is also possible because electrical signals I can transfer it to a large distances which is not possible by mechanical systems. I cannot have linkages and relays and bars for large distances and that is why in a transducer traditionally we have been using all the sensing elements and we get an electrical output. And then we just had discussed about this measurement errors you know the bias error and the random error. And of course, they can be removed by having proper calibrations. So, calibrations and measurements of course, measurements have to be done as per the international standards because once we report our vibration measurements done in lab A to lab B we should ensure that the same standards from standards equipments are calibrated. So, that the data is reproducible and data can be exchanged between different communities and groups. So, when we have the frequency response of the transducer and in an entire measurement chain when you are talking about a transducer having a good frequency response of 10 kilohertz and I put a signal conditioning unit of a response up to 5 kilohertz and digital display of only 2 kilohertz. I cannot say that I have a 10 kilohertz bandwidth of measurement and that is the important mistake people do and we will discuss that in the subsequent classes when we talk about the transducer. So, we have to keep in mind that the frequency range and the dynamic range of the measurement chain and dynamic range is nothing but the ratio of the highest to the lowest values which the same sensing element can sense. We will as now with this kind of background with this instrumentation we will now be specific would discuss about the specific transducers in the subsequent classes. And in particular some of these are the transducers which we will be discussing because these are the mechanical parameters vibration noise rotational speed current temperature flow rate and thickness and these are the transducer which are conventionally used like accelerometers microphones, key phasors, photo tech, RTDs, flow meters or resonant thickness gauge and these the principles behind this equipment we will be discussing in the subsequent classes. Thank you.