 This lecture is on thermography, this is in the last module on NDT techniques which are used in Machinery Condition Monitoring. So, we will be covering this NDT techniques in about the next four lectures. If I was to less down the NDT techniques which are used for NC or CBM or more. So, for CBM first less than one is thermography, then next is the ultrasonics and we have radiography, acoustic emission and few other techniques like dye penetrant test eddy current. So, in this NDT techniques or what are what is known as non-destructive test techniques about 10 percent of the condition based maintenance which is done throughout the world almost lie in this these areas. And if I was to just recollect our memory about in the whole world about 70 percent of the CBM techniques is vibration based followed by 20 percent being wear debris analysis. And then I was just mentioning that a new technique of the motor current signature analysis is also becoming very prevalent and about you know another 10 percent, but out of this you know 10 percent lot of these are also the NDT techniques. So, in the last module on this course where we have four lectures will be covering mostly thermography, ultrasonics, radiography, acoustic emission and also dye penetrant and eddy current test in about four lectures. Now, thermography is such a technique which essentially is based on this principle that any body gives out infrared radiations and these radiations are a function of the body's absolute temperature in the Kelvin scale. And the energy which is radiated by this infrared from the body is dependent on a factor known as the surface emissivity and somehow if this energy can be captured one can get a good clue about the temperature of the body. In fact, if you think of a body or three dimensional body at a certain temperature in Kelvin. So, it gives out infrared radiations IR or infrared radiations. Basically, this infrared radiations are electromagnetic radiations and they travel at the speed of light, but this wavelength of the infrared radiation is you know the visible light is the wavelength is somewhere from 4000 to about 7000 angstrom where 1 angstrom is 10 to the power minus 10 meters. So, the infrared is somewhere from maybe 9000 to 11000 angstrom is the IR. So, just beyond the visible light the wavelength of the infrared is from 9000 to 11000 angstrom and these infrared radiations give out given out from the body have some clue as to the temperature of the body. Now, there are this devices which can measure the energy radiated from every location and then give us some indication what is the temperature at these locations may be T 1, T 2, T 3. So, then we can get what is known as a thermal map or an IR temperature image or a thermogram. So, before we go in details about this infrared let us see what are the governing expressions and what is the theory of this temperature radiation and how the heat energy is getting transferred and so on. So, if I was to define thermography. So, infrared thermography is the science of thermal acquisition and analysis of thermal information from non-contracting thermal imaging devices. So, some basics about this thermal sciences well these are basic textbook definitions like the amount of heat in an object is the total current technology of the molecules that composes it and the temperature is a measure of the average speed of the molecules and atoms that take up the substance. So, temperature defines the state and object is in relative to other objects. Temperature is not a form of energy, but temperature is an index of the amount of energy in the body. Temperature will rise and fall as energy in an object increases and decreases it is a consequence of more or less energy. So, temperature of the objects will tell us how easy it is for a body to give heat to others or take heat from others. So, now certain basics of heat transfer. Suppose I have one body here body one another body two. There are many modes of heat transfer you know if this is at some temperature T 1 this is at some temperature T 2 may be you know the energy this is that at higher energy than this some sort of an energy transfer occurs. So, that these bodies are in thermal equilibrium. So, the modes of heat transfer between bodies as you all know is conduction, convection and radiation. So, it is this radiation mode of heat transfer which comes to use in thermography. So, the principles of thermal science tell us that the conservation of energy the sum of total energy contents in a closed system is constant. So, there has to be thermal equilibrium. So, heat will spontaneously from a hotter to colder. Therefore, transfer of heat from one body to other will occur. So, temperature will define the existence of heat and when the bodies are in thermal equilibrium there will be no heat transfer. So, we just mentioned about conduction convection radiation. So, heat transfer by emission and absorption of thermal radiation is called radiation heat transfer and I was telling you radiation heat transfer is what we are going to take help of to estimate the temperature of the bodies by thermography. So, thermal radiation is a form of electromagnetic radiation we just mentioned to you these are in the form of this electromagnetic radiation from bodies is used is by sorry by IR waves. So, this thermal radiation will easily pass through most gases, but will pass with difficulty or be blocked by most liquids and solids. So, very easily and objects will emit thermal radiation as a consequence of the temperature. Since, all objects have a temperature all objects will emit thermal radiation the higher the temperature the more thermal radiation will be emitted. So, in fact, anybody it is if it is more than the absolute if anybody's temperature is more than the absolute 0 it is going to emit IR, but only thing that in thermography we have to find out a way to capture this IR, but it is not so simply said that now everybody will irradiate heat by IR that is fine, but the amount of energy which is emitted depends on few other things like the surface emissivity we will define what this is and so on. So, there is actually I will come to the law later, but so heat transfer by emission and absorption both objects emit and absorb radiation net heat transfer is the difference between the two. Now, if I will just to give you an idea regarding the electromagnetic spectrum I just mentioned to you about the visible range somewhere from 4000 to 7000 angstrom and then somewhere here is the infrared wavelength and the higher the wavelengths will get into microwave and radio. So, we are talking beyond the visible this is the infrared and this band is where we are taking advantage of in this thermal radiation measurements. So, thermal radiation occurs in part of the electromagnetic spectrum that begins somewhere within UV band and continuous throughout all of the visible infrared wave bands visible is about 4000 to 7000 angstrom near IR, short wave IR and long wave IR. So, these are the ranges of the wavelengths of the infrared waves which are emitted from the body. Now, when radiation is incident on a body from a source some of it will get absorbed some will get reflected some will get transmitted ok. Now, this reflection transmission and absorption depend on the body type the surface type and so on. So, this reflection which is coming out of the body is what we are going to measure. So, of the total accident radiation from a target a certain portion will be emitted from the object itself reflected from a source in front of the object transmitted from a source behind the objects. So, one has to be careful that are we able to capture the right kind of wave. So, certain things I will be telling you later on as to the total energy is some of them is emitted some of them is reflected some of them is transmitted. So, if I take the ratios they are given by this term should be equal to 1 and this expression is always true from the principle of conservation of energy. So, now if the object or the body is giving out radiation I can have a device which can capture this radiation and then try to get a sense as to what the temperature is and that is the essential principle behind this thermal radiation or thermography principle. Now, let us see there is a certain physical law and there is a scientific law which relates temperature to the radiant energy and this tells us how much radiation a black body a certain temperature will emit and this is called as the Stephen Boltzmann law. So, based on the Stephen Boltzmann law the amount of energy which is getting transmitted or sorry getting emitted can be estimated and for a perfect black body that means, which only the energy given out is given by where I will give an expression here this is known as the emissivity in many books you know they write this is delta or sigma. So, this temperature is in the Kelvin scale and this is the fourth power and the value of the Stephen Boltzmann constant is 5.67 it is not 10 to the power minus 8. So, this value is 5.67 into 10 to the power minus 8 watt per meter square times Kelvin to the power 4 that is the Stephen Boltzmann constant. So, any body which radiates heat energy can be estimated by this expression where this is a parameter for black body this happens to be 1 for other bodies we will see what the values are. So, black body is a theoretical term and in practice we encounter only real bodies. So, these are known as cameras only get radiation from the real bodies. So, what if our target is not black body, but a real body then it will less emit less radiations emissivity of not black bodies or real bodies this emission is less than 1.0. So, we have to keep that in mind for every material if this emissivity is known to us then we can plug in the emissivity value and then we can measure the temperature, but many times what happens the emissivity is not known, but sometimes this can be found out by a simple calibration and I will explain you how this calibration particularly for infrared imaging is done and that is a very handy concept which is to be used in the field because if I have a thermal camera how do I believe that whatever temperature it is giving is correct. So, that calls for a in situ field calibration. So, this is the Stephen Boltzmann law. So, emissivity is the ratio of the radiation emitted by a real body compared to the radiation emitted by a black body at the same wavelength and same temperature real body. Now, sometimes this IR camera before I go into this let me tell you what this IR cameras are actually. So, now I know that some IR waves are incident. So, what I can have I can have a lens system which will make this IR beam convert converge on a semiconductor device semiconductor device and which gives us certain EMF based on the thermal energy incident on them. So, this is essentially a semiconductor material device and you can think of them as in a grid and there will be pixel after pixel. So, this could be know some pixel 320 640 depending on. So, so many pixels can be there. So, depending on the resolution each of these pixels will give us an EMF. So, if I have a body which is giving out IR waves I can have a camera system and which will essentially this is an IR image on the camera where depending on the temperature the voltage at each pixel location gives the thermal image. That is something we have to keep in mind. So, depending on the body I will I will be showing you examples wherein this thermography how it is useful in condition monitoring for quick measurements of the surface temperature of large bodies these are very very handy. Imagine in many times to measure temperature we normally use thermocouples RTDs thermistors thermometers even for that matter. But imagine a large body say for example, the wall of a blast furnace would like to find out if the blast furnace refractory lining in the inside has weakened or got damaged. So, that the blast furnace wall temperature at that point would increase to do to find out such places we can do a quick survey. So, coming to the applications of this technique. So, that you know we appreciate that why at all we are using this technique in CBM. Let us talk about large blast furnace some sort of a furnace with there is this is the refractory lining and this is the blast furnace wall. So, if there is some place where this has got damaged. So, I can shoot. So, I mind you all these are everything is giving out IR waves IR. So, if I have a camera IR camera it is going to capture this IR waves and then it will give us a picture that if you look at the side view of this blast furnace maybe this is the area because this got damaged the temperature has shot up this temperature is much much higher than the normal temperature. And this gives us a quick way to find out that this area in the blast furnace is damaged. So, this should normally not have been possible by conventional temperature measuring imagine a large blast furnace about to know 20 meters and height 1 of 4 meters and diameter imagine I mean you just cannot put thermocouples and keep measuring. These are some of the areas and another example I will tell you how this has helped us in CBM. For example, you know in electrical circuits the heat radiation is because of I square r. And if the current increases the heating effect of the current produces these temperature and imagine you have a control panel particularly in ships this is used. So, this is the control panel and behind it there are lot of electrical cables which are going around these are all electrical. So, if the one particular cable is carrying high current for some reason may be a higher increase in the load or something this temperature has increased or the entire cable the temperature has increased. So, what can happen by an IR image we can quickly find out that where is the source of the increase in temperature. So, these are the places where the thermography is applicable in CBN. If I was to briefly say it is used for a quick survey tool in CBM to detect on usual temperature rise or any abnormal heat source. So, this is where CBM is of use. Now, this IR cameras are calibrated to black bodies. So, only black body radiation can be converted to temperature. Hence, we must compensate for real body radiation by the most important is the emissivity. Reflected temperature relative humidity atmospheric temperature because these factors will affect the infrared waves which are incident which are being emitted from a body. But most importantly let us look into this emissivity. So, when the camera is calibrated it will look at a number of black bodies and corresponding temperatures are recording accordingly. The signal strength of real bodies will be less than a black body the compensation of the signal is calculated like heat is the energy exchange between systems having different temperatures. So, when there is temperature difference the temperature does not show any contrast and there is no possible analysis. So, if there is no temperature difference I cannot find out any contrast and thus I cannot possibly do thermography. So, there has to be a temperature difference to find out any significant information. So, something about this emissivity. So, thermal and electrical insulators are excellent emitters. Measurement is not a problem like on woods, plastic, soil, paper, painted surface, building materials, porcelain concrete, but metals are poor emitters unless heavily oxidized emissivity is rare superior to only 0.25. Measurement is difficult when we have lot of metals copper, steel, iron, soil, sorry iron coil actually soil, zinc, aluminum, chromium, brass, nickel, lead etcetera ok. Now, how do I know while we are doing calibration how do I know that I am doing the right kind of measurement. So, what typically people do is some of the rules which will follow, but a good thermal imaging procedure requires that I first capture a good image when it is out of focus the measurement is wrong how much nobody knows, but it is wrong. So, first thing is we have to focus it. So, sometimes this IR cameras if you can think of this IR cameras are little sophisticated than your and your normal video cameras or you can say sophisticated. IR cameras can be still or you can record them in a video mode, but the most important characteristics of this IR camera is we have a semiconductor backing or focusing plane which gives out voltage. Sometimes laser are provided on such IR cameras to focus on a particular target, desired target must cover this spot and that is why sometimes we have to use a laser and do not aim with an angle greater than 45, 50 degree, but sometimes you know what happens if you are perpendicular to the body you may be also reflecting and choose a zone of high emissivity to do the measurements. So, these are the some things you have to keep in mind. So, for example whenever you are measuring on a shiny metal I will show you an example where we had a refrigerator and I was trying to measure this is a shiny surface and if you are measuring in front of it. So, your reflections are going to come across. So, this is to be avoided avoid this kind of this kind of a scenario and never be perpendicular if you are perpendicular you know. So, always stand at an angle and this angle is usually between 45, 50 degrees. So, essentially three things must be taken care of while doing an thermography. One is the temperature range, focusing and the image composition. So, you should not be too far away or too close to the target your distance from the object is such that it covers the critical points you wanted to cover. So, it depends on the focusing area and the depth of coverage. If you are close by you can only get this if you are far off get this. So, depending on this distance and this area and of course, there is no end to this distance. For example, I will just give you an example many times you know you have seen thermal imaging is used for security surveillance. So, what happens suppose there are shrubs and there is a intruder. So, you can always you must have seen this can from maybe from a helicopter you can you can shoot an IR camera. So, you can identify hot bodies and here what I mean to say your depth of coverage will depend on how high up from the ground you are and there is no end to the length you can cover and of course, with more the length you are this area of coverage will increase. But most important factor which you have to keep in mind is this emissivity. Now, all these cameras have an microprocessor based circuit. So, for example, one quick rule of calibration people do is suppose this some known temperature T and they will try to shoot from an IR camera and suppose they measure a temperature T star with a particular emissivity. So, in this camera there is an option to change emissivity some of this hand held cameras. So, you can change the value of emissivity. So, that T star equal to T provided T is known and you can do that with couple of temperature and that is a very quick way you can do a field calibration that is one. Next is you can do a black body calibration in the sense I will make a body and I will put some black patch black tape so that emissivity becomes one and then because the emissivity of this IR camera is set to one I will measure the temperature accurately this is one. But in the field it is always good to change emissivity so that your known temperature is equal to whatever you are measuring by T star in the camera this is something you have to keep in mind. So, the reflected temperature is a problem while doing IR measurements. So, reflected apparent temperature is the apparent temperature of object that results in reducing that is reflected by the target and into the camera to avoid reflections we should not be right in front of the cameras and we should be away from it. So, make sure that what is reflecting in your target not a spot source, but on an event apparent temperature set emissivity to one and then you can find out the average temperatures. So, one way to measure emissivity is select a sample put a place of electrical tape with known emissivity heat the sample focus and note the temperature at tape move your measurement function to the sample surface change the emissivity and then till you get the previous and that is what I told you in the method. So, you can change the emissivity till you get the right temperature that is what people follow in the field. These are some examples which I am going to show you for example, many times in the switch gear there because of loose contact you can find out by thermal imaging that how this kind of temperature can be measured and which is not possible by particularly imagine a high voltage circuit it is not humanly possible for them to mount any temperature. By the way some of this images from the or from the FLIR website. In fact, in our laboratory we have an FLIR camera and I will be showing that to you and this is particularly in electrical motor it is again a thermal image this is the near the bearing of the electrical motor you can see how the temperature has increased particularly in few petrochemical applications this is in the steel mill this is the temperature difference a very very high temperature and rotating objects we cannot possibly measure the thermography or temperature measurements. So, in CBM the applications of thermography are for quick industrial survey lot of energy audits are done by using thermography like you can find out electrical connections you can find out hot machine areas like bearings, couplings, tight brake drums particularly automobiles. Building if a building has become damp or water seepage. So, these are few industrial service, but if I was to go down to rotating machines in our laboratory in fact, we have been able to find out detect misalignment detection in shots. I will tell you how this happens for example, we have a bearing we have maybe this is driven by a motor and then I have a disc on the shaft and then I have another bearing and then there is a coupling between the motor and the shaft. So, this is the coupling this is the motor and this is bearing drive and bearing this is the N D non drive and bearing this is the rotor and this is the disc. So, if this shafts were misaligned to some extent what happens there will be forces on the coupling forces on the coupling then what happens because of the forces the couplings this bearings and if you think of a bearing these are the rolling elements and there is certain clearances between them and they are allowed to move. So, there will be some sort of an extra force I am writing them as delta force and because of this force there will be increase in the friction the friction force will increase and this is going to be the source of heat generation. So, once and while they are rotating and there will be lubricant. So, heat will be generated in the bearings because of such forces and sometimes this couplings also have some flexible elements. So, flexible elements in coupling will also get heated up because there is a sliding of this flexible elements in the coupling because of the forces and heat is being generated. So, couplings will become hot couplings will become hot bearings will become hot and when a machine is rotating by noticing the change in the coupling temperature I mean to measure the coupling temperature at a difficult thing because the rotating device. So, if somehow by IR image I can record the coupling temperature this will fall on exponential curve being a first order system. The rate of rise of this temperature is going to this is T this is capital T. So, sorry so d T by is will be proportional to amount of amount of shaft misalignment and. So, this has to be measured by an infrared thermal imaging camera wherein we have to sample them at temperatures often at intervals of may be every 1 second. So, this cameras also have the provision to capture image frames you know depending on the format may be 30 image frames per second and then store it to a computer where you can do further image analysis. So, all those this kind of things can be done with thermal imaging and this is another example wherein in a cement plant you can see the kiln becoming hot in a paper mill you can see the rolls getting hot this is the break drums that become hot this is from the electronics you can see the I C chips bearing hot defense these are some of these figures are from the FLIR website as I am mentioning to you coal mines. And this is what I was telling you regarding the infrared imaging or laboratory wherein this my student holding this FLIR camera and you have the bearings this is the coupling. So, the rate of temperature rise we can artificially introduce misalignment in this system this is the coupling. So, this this is the drive end bearing this is the non drive end bearings and motor behind it. So, this is a flexible element coupling. So, through IR imaging you can see the temperature rise this is a single stationary shot, but this can be put in a tripod and the samples can be taken at 30 image frames per second and they can this such videos can be made and they can be stored on a computer where you can do image analysis and looking at the rate of temperature rise you can find out the temperature. And this is another example in the laboratory wherein we have a refrigerator and this is the compressor of the refrigerator just to correlate we can see this yellow cables. There are actually all thermocouples put on the compressor of the refrigerator this is in our laboratory and we and this is a shiny metal surface though this is a black dull surface. Through thermal imaging you can see the temperature of the refrigerator compressor and this we are doing because we are trying to reduce the noise of this refrigerator through some treatment and then we do not want the compressor temperature to rise abnormally and that is why we took the advantage of this thermal imaging. So, that in one go we can get a quick image and I can see these are the thermocouple cables you know these lines are thermocouple cables. So, quickly in one single shot you can get the view of an image. So, this is the video image this is the thermal image of the same thing. So, as I was telling you thermography has a lot of applications in engineering particularly in condition based maintenance for a quick survey which can be done to find out the areas which have hot spots and then you can do detailed analysis on the thermal imaging depending on the interest or depending on the severity of the problem and this is quick this is very fast and not only qualitative, but also you get a quantitative estimate of the temperature rise. Thank you.