 Welcome you all for the module 5 lecture 4, in this lecture we will be discussing about Tom Linsson surface tester which is a contact type of measurement method and then we will move on to non-contact methods, the various non-contact methods like optical systems and then microscope surface measurement using microscopes and then the pneumatic method of surface finish measurement, those non-contact methods we will be discussing. And then we will also see what are the advantages of non-contact methods and then what are the relevant ISO standards pertaining to the surface finish measurement that also we will see and then what are the common mistakes one does during measurement of surface finish we will discuss about those common mistakes and then what care one should take so that the surface finish measuring instrument will be in good condition, so those things we will be discussing. Now let us study how the Tom Linsson surface meter is constructed and how it works in order to measure the surface finish, you can see the diagram we have a vertical lapped steel cylinder to one end of which has a diamond probe, so which will be in contact with the surface to be measured and then the lapped steel cylinder is fastened to the body of Tom Linsson surface meter using a leaf spring and then a spring is provided at the other end of lapped steel cylinder. Now a arm is provided to the cylinder A which is in contact with lapped vertical steel cylinder and the other end of the arm has a diamond scriber which is in contact with smoked glass. Now during the operation the body of the Tom Linsson surface tester is made to move on the workpiece surface and because of the asperities present on the workpiece surface this lapped steel cylinder will move up and down and this motion is converted into rolling action of the arm with the help of this horizontal cylinder A. So the other end of the arm we have this diamond scriber which is in contact with the smoked glass, so when the cylinder moves and up and down the diamond scriber scratches makes scratches on the smoked glass. So the both the horizontal motion of the instrument body and the vertical motion of the lapped cylinder are combined here to get the profile surface profile. So the vertical motion of the lapped steel cylinder is magnified by using a longer arm whereas the horizontal motion is not magnified. Now we can take this profile and if required it can be further magnified and then the various parameters can be calculated. So this is how a Tom Linsson surface meter works. Now let us move on to the various non-contact methods that are available for the measurement of surface finish. Now we should understand here when we say non-contact method the stylus is not present. So the non-contact methods are very much suitable for the normal engineering components as also they are suitable for thin and fragile workpiece measurement of surface on thin and fragile workpieces. So there are different methods of measuring surface finish by non-contact method. We have replica method, we have light reflection method and then we can use microscopes for measuring the surface parameters and then the optical profilers are developed for measurement of the surface along a line or they can be used to measure the surface finish in a particular area and then we will also discuss about the pneumatic assessment of surface finish. Now let us study the replica method. You can see here we have a schematic diagram to show the construction of a setup used to measure surface finish by replica method. So we have a light source and a condensing lens and then this is the specimen, the plastic replica specimen and then light is made to fall on the replica and then it will pass through the specimen and then the transmitted light will fall on the photoelectric cell. Depending upon the intensity of the light falling on the photoelectric cell, the current that is generated will vary and that generated current will supply to electronic circuit for processing and finally we get the roughness parameter. Now due to the asperities that are present on the surface of the replica, the light intensity will vary and hence the current that is generated will also vary. The fluctuations of intensity of transmitted light causes pulsating voltage in the cell circuit which is recorded by the electronic voltmeter and which will directly give the roughness parameters. Now how do we prepare the transparent plastic replica? These replicas are prepared by applying a suitable solvent to the metal surface which is under question and then the solvent is composed of 80% toluene and 20% acetone. It is spread on the surface of metal. A strip of clear plastic film of ethyl cellulose of about 125 millimeter micrometer or 0.125 millimeter thick plastic sheet is pressed on the metal surface which has the coating of the solvent and the solvent softens the side of the film which is in contact with the surface and then a rubber roller is used and it is moved over the plastic film so that plastic film adheres to the surface. The softened plastic flows and conforms under pressure to the minute surface irregularities present on the metal surface. The plastic film dries in about 1 minute and then it is stripped from the surface. Now what is the procedure of getting the surface finish values in this replica method? So initially we have to prepare the plastic replica as explained and then it should be mounted on to the measurement setup and the replica is moved vertically down and there is a light source. So light is made to fall on the photocell passing through the replica. Voltage that is generated by the photocell varies due to the change in the light intensity which is due to the varying geometric characteristic. Now change in the voltage is the measure of surface roughness and proper calibration is to be made so that the replica method can be used and standard specimens can be used for calibration of the setup. Now this photograph shows the setup replica surface analyzer setup. This is the light source through which light will, so there is a window through which light will move out and then we have a condensing lens. So light is made to fall on to the specimen. This is the specimen. So this specimen size will vary depending upon the surface that is to be tested. So if we require very long surface to be inspected then we have to take a very long plastic film and the replica should be prepared and then it is mounted in this setup. Now we can see here there is a electric motor and then there is a belting arrangement for moving the replica up and down. Now the light will pass through the replica and it will fall on the photocell. So this is the photocell. Depending upon the intensity of light falling on the photocell the current that is generated will vary and that is passed to the electronic circuit and finally there is an electronic meter which will give us the surface characteristic and this shows a micrograph obtained from plastic replica. This is actually the plastic replica, the magnified view of the plastic replica and you can see the asperities and then the tool marks lay etc. We can clearly see in this replica. Now what are the features of this replica method? It is very easy to maintain the permanent record of the surface finish. So the plastic replicas can be stored for a longer period and then rapid average evaluation of considerable length and width of the surface. If longer length and longer width, a big area is to be analyzed then we can prepare the replicas for the requirement and then the evaluation, the parameters can be calculated easily and quickly. The operation is very simple and there is no presence of personal factor, no operator skill is required and the preservation of surface replica for a longer duration is possible and replica may be prepared in one locality and it can be transported to the place where the analyzer is present. We need not have to transport the workpiece itself. We can prepare the replica and replica can be transported to the place where it is analyzed. So this is very useful in evaluating the surfaces which are not readily accessible with other methods. For example, say we have a workpiece like this and now we need to analyze the surface roughness of this bottom surface. This is a very deep hole. Say the depth is something like 50 millimeter or 60 or 100 millimeter. So the normal instrumentation with the normal instrument is not possible to measure the surface finish. In that case, we can prepare the replica and then replica can be removed from this place and then it can be analyzed. Now we will move on to the various optical methods under the non-contact method. We have surface assessment by light reflection. Now you can see here we have two types of reflections, specular reflection of light wherein the angle of incidence of light is equal to angle of reflection of light. So this condition is satisfied then we say it is a specular reflection of light. So this is possible if we have an absolute smooth surface like a mirror surface. So if you have a mirror very fine polished surface then all the most of the light falling on the surface gets reflected back and it will pass to the viewer yes and no light will fall on the viewer D. Now if the surface is rough, we have say we have a rough surface and then the light gets scattered. So this is known as diffuse reflection of light in all direction, the light gets scattered and some light will fall on the viewer yes and some light will fall on the D. Now the ratio of specular to the diffuse reflection is the measure of finish of the surface. That means what is the amount of intensity that is collected here and what is the amount of light that is intensity of light that is collected here. If you take the ratio, so that is the measure of surface finish. So in this way we can use optical method to check the quality of surfaces. Now based on this light reflection we will see a simple experiment to see how we can measure the roughness of surfaces. So in this photograph you can see we have a laser tube, gas laser tube, this is helium neon laser with 5 milliwatt laser source and then I can see here we have a detector photo detector and we have the optical lens to focus the light on to the photo detector. So this is the power supply for the helium neon source and the detector output is connected to the milli volt meter. And you can also see we have to calibrate this setup light reflection method setup using some standard surfaces. So you can see here we have 2 surfaces with N3 and N5 finish. Using these standard surfaces we can calibrate the setup and then we can put the surface to be tested here and the amount of light that is falling on photo detector will vary depending upon the scattering. Now the laser will fall on the surface to be tested. So here initially we have to keep the standard surface here and for N3 surface what is the amount of light intensity and what is the corresponding milli volt we have to record. Similarly we have to use some 2-3 standard surfaces and then depending upon the roughness the light intensity, light falling on the photo detector changes and accordingly the milli volt will vary. Now we have to remove the standard surface and we have to keep the surface to be tested here and then if it is rough the light will scatter like this and some amount of light will fall on the photo detector and what is the output shown in the milli volt meter that should be recorded. Now say for N2 surface so we have some X1 milli volts and similarly and then we have for N2 surface N3 grade surface say we have X2 milli volts and then for N4 grade surface say we have X3. Now we have to keep the surface which is to be tested here and say the voltmeter reading is between this X1 and X2 then that indicates that the surface finish is between N2 and N3. So like this initially we have to calibrate and then we can use this setup. Now we will conduct an experiment to show how the laser setup can be used to evaluate the surfaces. Now let me explain how we can use the laser system to measure the roughness of surfaces. Now you can see the various components of the laser system. We have this long tube this is the gas laser helium gas laser of 5 milli watts and this is the power supply for the gas laser and you can see the tube is placed in the stand ok. There is a stand to keep the laser tube now we can see the standard specimen. So standard specimen we have to use for calibrating the system. So we have two surfaces here one is N3 grade surface and another one is N5 grade surface. Using these two standard surfaces we can calibrate the laser system here. So one is N3 and another one is N5 and then you can see here we have a reflecting mirror. So which will reflect all the surface all the light. So it has a very smooth surface. So all the light falling on this incident light will be reflected back that is a specular reflection. And now you can see the work pieces we have to measure the roughness of these ground surfaces for which we are using the laser system. And you can also see the multimeter the photo detector output is given to this multimeter and then we can read the voltage that is generated by the photo detector in terms of milli volts. And this is the place where we have to keep the standard work piece this is the reflecting surface we have to keep the standard surfaces here for calibration purpose. And then we have to remove the standard surface and then we have to keep the work pieces whose surface finish is to be measured and the light will fall laser will fall on to this reflecting surface the surface to be tested and then it is reflected and then it will pass through the collimating lens and then the reflected light will fall on the photo detector. So depending upon the light intensity falling on the photo detector it will generate the voltage which is connected to the multimeter and we can read what is the amount of voltage that is generated which is dependent on the surface finish. If the surface is very fine like mirror so the intensity that is falling on the photo detector is maximum and we get the maximum reading here. If you put a very rough surface more scattering will be there and only little light is falling on the detector so the voltage generated is less. So once we calibrate the system using standard surfaces we can inspect the surfaces whose surface finish is to be measured. Now we can see the angle we have to adjust so that the light will fall on this and then it gets reflected on to the detector. So now I am adjusting the angle. Now we can see the light is falling on the collimating lens and then it is falling on the detector. Now we can see the detector. Now light is falling on the detector. So once the light falls on that since we are using a mirror the maximum intensity will fall on the detector and you can see the voltage generated is maximum that is 0.395 milli volts. So light is falling on the photo detector solid state photo detector. Now I have removed the reflecting surface put the workpiece to be inspected light we have to adjust the inclination so that light will fall on the detector. So proper alignment is very very essential in this case. I am calibrating the system using the standard surfaces. We can see we have two surfaces N3 and N5. I am keeping the standard surface in position and I am adjusting the inclination so that light falls on the detector. I can see the laser light it is spread it is scattered because of the surface roughness. Now I am doing the alignment. Light is falling on the collimating lens and then on to the photo detector. I am adjusting the orientation of detector. I am adjusting the height of the detector so that light falls on the detector. Now we can see the reading is 0.266 milli volts 0.263 milli volts. Now again I have adjusted the alignment. Now it is 0.288 milli volts 0.313 milli volts 0.314 milli volts. Now it is N5. N5 surface is kept in position. Now N5 is rougher than N3 so more scattering will be there. So now the voltage milli voltage is 0.294. You can see I am taking the surface which is to be inspected. I am keeping that in position. I am adjusting the orientation. You can see the light scattering because of more rough surface. I am doing the alignment. We have to adjust the height and inclination of these various elements so that maximum light falls on the detector. I am adjusting the height of detector. Now we can see light is falling on the detector and you can see the voltage that is generated 0.306 milli volts. Now we will move to another method of non-contact method of surface finish measurement. We can use microscopes for measuring the quality of the surfaces. So this is known as Schumelge Profile Microscope. The arrangement is like this. This is the workpiece for which we have to measure the finish of this particular surface. And now a thin film of light is made to fall on the workpiece surface. We can have a very thin slit here and then light is made to pass through that slit and it will fall on the workpiece surface. And now the light gets reflected. So reflected light will show the surface profile and this reflected light is magnified and observed through eyepiece. So the eyepiece contains a scale which is used to measure the surface roughness. That means what is the distance between peak and valley? Those things can be measured using the eyepiece. Now we will move to another optical method known as optical profiler. This is also known as confocal microscope or confocal scanning microscope since the scanning process is used in this microscopic method. Now the arrangement is shown here. So we have two lenses. This is the objective lens L1 and then we have a light source helium laser light source. And then there are collimating lens to collimate the light source. So light will pass through the pinhole 1 and then using this beam splitter light is made to fall on the objective lens and then it gets focused somewhere here. And then they say this is the workpiece surface to be tested. If the workpiece surface is exactly at the focal point of the objective lens then the light gets reflected and then it will pass through the pinhole number 2 and then it will fall on the detector. If the workpiece surface is exactly at the focal point then maximum intensity of light will fall on the detector. Now if the workpiece surface is at a place other than the focal point say it is somewhere here at position C. So now it is not focused. So reflected light will get scattered and only a small quantity of light will fall on the detector. So intensity of light will be less if the surface is not at the focal point. Now by moving the objective in this direction we can always make the light to focus on the workpiece surface. We can either move the lens or we can either move or move the surface to be tested. So it is easy to move the lens. So in order to move the objective lens a PZT is used. So the amount of movement that is needed to focus the light on the workpiece surface is measured using this PZT. Now what we can do is we should understand that this is a system wherein at a time one point is inspected. That means after getting the light intensity for a particular point then the workpiece is moved. For that we can use an XY table or if we have a cylindrical surface the surface of the cylinder is to be checked. So in that case we can use a motor, electric motor to rotate the workpiece and then the light is made to fall on the surface. So after taking the reading the workpiece is rotated and again the other point is inspected. Like this point by point we have to get the data. So the dimensional data that is gathered from a particular area is clipped together and it is processed to get the various parameters like roughness parameters or waveiness parameters or the form error of the workpiece can be computed. Now this is the functional block diagram of the profiling system. We can see the various components involved in this setup. So we have the XY table for moving the workpiece and for moving the workpiece we have motion controller and then we have air bearing rotary stage to rotate the cylindrical object. Air bearing is required so that it runs smoothly and with least amount of runout. And there is a motor to rotate the cylindrical object or if it is XY table then we will be having two motors one for x direction and one for y direction movement. And now we can see here we have the objective lens which is fixed to the PZT. So for focusing the light on to the surface we use the PZT and using PZT the lens can be moved up and down for focusing purpose and this PZT movement it is connected to the computer via this PZT interfacing circuitry. And then we have the gas laser source and then the beam splitter and then another lens the light will pass through this pinhole and it will fall. Reflected light will pass through the pinhole and it is made to fall on the detector via the lens L2 and then the light intensity is measured in terms of micro watts. So there is a power meter to measure the light intensity in terms of wattage. So again it is connected to the computer. And then for moving the stage and then for rotating the workpiece we have a stepper motor driver board. So this shows the various components of the profile meter. Now so we have hardware components like photo detector and then XY table and then motor to rotate the workpiece and air bearing for smooth rotation of the workpiece. And then all these are integrated to the computer via proper interfacing devices and then there is a data acquisition card. And then the software consists of data acquisition software and processing and manipulation of data in order to find in order to compute the various parameters. And then we can get visual and numerical characterization of 2D and 3D surface topography of flat surfaces as well as cylindrical surfaces. So we can get the if it is flat surface a particular area can be scanned and then what is the roughness of this particular roughness or flatness or form error in this particular area can be calculated in terms of various parameters. If it is a cylindrical surface then also we can find what is the cylinder city, what is the error in the form. So some 3 dimensional parameters also we can get by using these profile meters. Now in this method we have two methods one is called auto focus method and other one is called light intensity method. In this auto focus method the objective lens is focused on to the surface. You can see here we have the surface which is to be tested and we have three conditions. So here the surface to be tested is above the focal point that means the light reflected will have little amount of intensity and here the surface to be tested is beyond the focal point again the light intensity will not be equal to maximum whereas in this case the surface to be tested is exactly at the focal point of the objective lens. So in order to focus the light on to the particular point on the surface we need to move the objective lens using PGRT. So measurement of lens displacement by what amount lens moves up and down that measurement yields the vertical or radial surface displacement and the surface roughness can be determined by rotating or moving the surface below the focus spot. Now in the intensity method the objective lens is fixed it is not moved and due to the variations of the asperities on the workpiece surface the lens is fixed. If a particular point is at exactly at the focal point and the maximum all the reflected light intensity will be maximum. If the point a particular point is not at the focal point you can see this is the focal point is somewhere here whereas the point on the surface is somewhere here. So the reflected light intensity will not be maximum. So depending upon the asperities the light reflected light intensity falling on the detector will vary. So those variations in the light intensity they tell us they give us the height variations on the surface of the workpiece. Now what we have to do is we have to collect all the measured intensities reflected intensities and then we have to manipulate those data and then we can find the roughness parameters. So now the system software that is used in the profiler like this have five modules. So there is a measurement system control and data equation element of the software and then various filtering filters are used to remove the unwanted elements. So if you want only roughness the waviness can be eliminated if we require only waviness parameter then roughness parameters can be eliminated. So for that various different kinds of filters are used. A datum characterization algorithm is also used in the software and analysis and numerical characterization is possible using the software and then visual characterization such as 2D and 3D plots can be obtained. We have a very high data equation rate of 40,000 to 60,000 data per hour is possible. So the optical method of measuring the roughness will be quick. Now what is the measurement range and accuracy in such a system? So this measurement range is determined by the maximum possible displacement of the objective lens. In other words what is the maximum amount of movement of the PJT that is used. So typically 0.5 micrometer ranges are available and the maximum peak to valley height of the surface should not exceed this range. That means if peak to valley height roughly we know accordingly we have to select appropriate profile meter which will accommodate that range. Then the instrument it is very essential that we should calibrate the profile of meters with standard specimens and these systems can be calibrated to an accuracy of 10 nanometer. The accuracy of the measurement method depends on the z scanning step size of the PJT. Now scanning step sizes varies between 5 and 320 nanometer. So if we require very finer step size then appropriately we have to select the PJT that is used. So what is the resolution of this setup? The vertical resolution depends on the sensitivity of the PJT that is used. So vertical resolutions of 5 and 40 nanometer are possible with PJTs of sensitivities 5 micrometer per 1000 volt and 40 micrometer per 1000 volt respectively. So if we use this a PJT with sensitivity of 5 micron per 1000 volt then the vertical resolution that means the least value by which the objective lens can be moved will be 5 nanometer. So the lateral resolution depends upon the size of the focus spot. So now we have the objective lens and then we get the focus spot focus. So the lateral resolution it depends upon what is the focus spot. So typically 0.5 micrometer spot sizes are available. If the size is too big then the lateral resolution will also be less. So this is something like the stylus in a probe in a stylus type instrument. So we have the conical stylus with radius of maybe 5 micrometer or 10 micrometer. If the aspect value is the width between 2 value is less than say 5 micrometer and if the stylus size is 5, stylus radius is 5 micrometer then it will not enter. So same thing happens in this, this is analogous to the size of tip radius. Now it is very essential that before using such a system we have to calibrate the system. Here we can see the calibration is carried out using a standard groove with a groove height of 9 micrometer. So this is the calibration result obtained by optical profiler and then this is the calibration curve obtained by a stylus instrument. Now we know that the groove size is 9 micrometer. Now we can see here after measuring that groove we can see here. So this depth is 9 micrometer. Similarly in the stylus type instrument this is approximately equal to 9. So there is a small amount of error here. And then the reflected light intensity is measured in terms of micro vat. You can see here the reflected light intensity in terms of micro vat it varies from 1 micro vat to micro vat like this and corresponding height of the point corresponding height of the point. So depending upon the light intensity as the light intensity varies the height of the point also varies. So like this we have to initially calibrate the system and then we can use for assessment of the surface. Now this is one result obtained by the optical profiler meter. Now this is surface profile of a standard ground surface obtained by autofocus method. Now the x axis is a distance in terms of 1000 micrometer 20,000 micrometer like that. So small division indicates 100 micrometer and this is the peaks and valleys on the surface. So after the manipulation after processing the data the RA value was calculated to be 0.03 micrometer and RT value is 0.38 micrometer and RZ value is 0.28 micrometer. Now the same surface was checked with stylus instrument and then the comparison was made. So you can see here comparison of optical profiler and stylus instrument values. So these are the results obtained by optical profiler. This is for a particular milled steel surface. RA value was 3.25 micrometer and RQ value was 4.12 micrometer and RT is 21.35. My same surface was checked using a stylus instrument. You can see here RA value is almost the same 3.2 here and 3.11 with a stylus instrument and RT value is 21 and here it is 19.81. So like this we can always compare the different systems. So how they behave that can be checked. Now we will move on to another non-contact method of measurement of surface finish. So this is a pneumatic method. So wherein compressed air is used for measurement of surface finish. The working principle is like this. So we will be having a nozzle like this and then the compressed air is supplied here with a supply pressure of PS and there will be a control orifice and then now this is the workpiece surface which is to be tested. So the nozzle gap between the nozzle and the workpiece surface is xi. If the gap xi is very small then the back pressure here will increase. If the gap is more pressure will be less, if the gap is less pressure will be more. So the variation of the back pressure is dependent on the surface characteristic. If the gap is less then pressure will increase. So this pressure variation can be monitored or measured using a piezoelectric pressure transducer and the variations in the pressure frequencies, pressure pulsations are given to the computer for analysis purpose. So this is the working principle. So the surface, the pressure pulsation depends upon the gap between the nozzle and the workpiece surface. So Pb is proportional to the xi, it is proportional to the xi and xi is proportional to the surface quality, surface quality Q. Now this photograph shows the working setup. You can see here for calibrating the system, the standard surfaces are used here, different surfaces like surfaces made by turning and then vertical milling. So like that with varying roughness, they are used to check the working of the setup. Once the setup is calibrated, it can be used for measuring the surface finish of unknown surfaces. Now the nozzle diameter is 1.5 millimeter. So this is the nozzle through which there is discharge of air. So nozzle diameter is 1.5 millimeter and control orifice diameter is 0.84 millimeters and the supply pressure is approximately 140 kilo Pascal and then the standoff distance xi is 50 micron. So this will be varying depending upon the variations in the surface and nozzle feed rate is 0.4 meters per minute. Either the nozzle is moved or the workpiece is moved for conducting the measurement. Now these pictures show the comparison of stylus and pneumatic signals from milled and turned surfaces. So you can see here milled surface and then turned surface of roughness 3.2 micrometer RA. So standard surfaces are used for calibration purpose. So these are the results obtained by using stylus instrument and these are the results obtained by pneumatic surface instrument. So output is in terms of voltage and this can be converted into roughness value. Now instead of using a piezoelectric transducer, we can always use a rotometer. So this is the rotometer with a float. So air is allowed to flow like this and then air escapes from here and then we have the nozzle here with the surface with the control orifice. This is PB, this is PS and this is PB. So now if the gap is less, then the flow rate, flow of air is restricted. If gap increases, then there is free flow of air, air flow increases and then float moves up and the position of the float indicates the roughness value on the surface. Now let us see what are the various advantages of non-contact methods. So since there is, since no contact stylus is present in these non-contact methods, there is no surface damage occurring on the surface. In the contact type, what happens is we move the very sharp stylus on the workpiece surface. So there is possibility of a scratch appearing on the surface. So in non-contact methods such problems are not there and then there is no filtering effect since the stylus is absent. In the conventional stylus type, due to the size of the stylus, so this is having a diameter of say 5 to 10 microns. Because of this, it will not enter into the very narrow valleys. So there is a sort of filtering, mechanical filtering effect in conventional stylus type methods. So in the non-contact methods, such problems are not there. In process assessment of the surface is possible. Since there is no contact between the setup and the workpiece, so when the machining is going on, we can check the surface finish. Soft surfaces like paper, plastic etc. can be measured for surface finish. So if we try to check the surface finish of soft surfaces using stylus, so the surface may get destroyed. And then assessing and averaging over large areas can be assessed, evaluated and averaging can be performed. And these non-contact methods are methods with high speed. Now let us see what are the various ISO standards available on the surface finish. So we have ISO standards which will tell us about the indication, how to indicate the surface texture on the technical drawings and then normal characteristics of contact type instruments and then what are the various terminologies, definition and surface texture parameters. So these standards, they explain the various roughness parameters, waviness parameters and motif parameters and then the hybrid parameters etc. etc. They all definitions are given in these standards. And then we have standards for rules and procedures for assessment of surface texture. That means how to set up the instrument, how to set the workpiece, how to select the various parameters like cut-off length, assessment length etc. etc. And then how to calibrate the instruments, what are the various measurement standards that are available and calibration aspect of the instruments and what are the various imperfections on this surface, their definitions and parameters are also explained in these standards. And there are standards to cover the motif parameters and then regarding calibration of stylus instruments, the standards are available. So like this, the various ISO standards are available which will help us in assessing the surfaces. Now let us see what are the common mistakes made during surface finish measurement. As per the standard, we should not include the flasks during measurement of surface. Say for example, say we have a surface like this and somewhere here there is a flaw like maybe there is a burr or there is a crack or there is a blowhole. So initially we should visually we should check the surface. If necessary we should use a magnifying lens and we should check the surface. If there are surface flasks like this, such area should not be used for assessing the surface roughness. We should select a surface where no visible surface defects are present. If we include the flasks, then we get some result which will not be useful. Then not paying attention to positioning and leveling of the workpieces. So positioning of the stylus on the workpiece and the leveling of the stylus on the workpiece, they are very, very important. If we do not level the stylus or the probe onto the surface properly, then we will get erroneous results. So this is very important in the case of tapered workpieces. For example, say we have a workpiece like this and this is a surface finish we want to measure. Then now if we allow the stylus to move like this, then instead of measuring the surface finish it will measure the taper. So what we have to do is we should properly align the position of the tapered workpiece like this so that the surface is parallel to the moment of the stylus. So for that various fixtures, work folding devices are available and we should use them and properly we should position and level. Not taking into consideration the environmental conditions like thermal conditions, say we have we want to measure the finish of a engineering component which is just made that it is machined just now and now it is in the very hot condition. So we should allow the component to cool down to the normal temperature and then we should go for surface assessment. If the workpiece in hot condition and if we try to measure surface finish what happens is this is due to the heat it is expanded workpiece is expanded. So in such case we should not take the result. We should allow the workpiece to cool sufficiently and then only we should clean the surface properly and then we should use appropriate instrument instrument to check the surface. Similarly, the external vibrations say we are conducting the measurement at some place where in some external vibrations are induced maybe in the next room we have a forging machine or some machine is making lot of noise and vibration. So those things will also be included if we measure if we measure the surface in the vibrating conditions. So we should see that proper vibration isolators are used before we conduct the measurement and then the all the instrument should be calibrated properly at regular intervals using the standard specimens then only we should use the surface finish testers. Otherwise the if in the if the work tester is in the uncalibrated status and then if we try to use then the measurement result will not be of any use and then insufficient cleaning of components that is the surface is very oily and it is very dirty. If that is the case we should not go for measurement we should thoroughly clean the surface of the workpiece maybe using some chemicals and we should allow it to dry and then only we should take the measurement. Now what type of care one should take so that the instrument sophisticated measuring instruments or surface finish testers will be in good condition. So use of dust covers will not in use say the surface tester is not used for maybe for one week or one month it is in the unused condition then we should use dust covers so that dust will not fall on the instrument and then use of proper calibration practices and conducting the periodic calibration this is very very important so that the instrument will be in good condition. And whenever we transport the instrument from one place to the another place they should be packed properly all the moving parts should be properly clamped maybe we should follow the instructions given by the manufacturer of the instrument and as per the instruction we should properly clamp them. If the moving parts are not clamped then what happens is during transit the moving parts may move in and out and because of that they may get bent so they become useless so to avoid such things proper care should be taken while transporting the instruments and always servicing of the instrument should be carried out by authorized persons unauthorized persons should not be allowed to do the servicing of the instruments and always this is very essential that impacts between work surface and stylus should be avoided we should not allow the stylus to fall rapidly on the surface the diamond point may get destroyed may break so such things should be avoided. Now with this let me conclude the session in this session we discussed about Tomlinson surface tester and various other non-contact methods of measurement of surface also we studied about various ISO standards available on the surface finish and then we learnt about the common mistakes done by the operators while using the surface measuring instruments and what are the care to be taken to see that the work pieces or the instruments will be in good condition so with this let me conclude the session thank you.