 I welcome you for the module 2 lecture 1 of this series. In module 2, we will be discussing about linear metrology, what is linear metrology, what are the various instruments used in linear metrology, those things we will be studying. And then before we start linear metrology, let us try to understand the general care of measuring instruments. When the instruments are in use, how to take care of the instruments and when they are in storage that means for a long time they are not in use and we are storing them and how to store, what type of care we should take so that they are protected from the environment. We will also study about classification of measuring instruments, how the instruments are classified based upon the type of physical quantity that is measured and then based upon whether they are they have graduated scale or no graduations are there and then depending upon the precision and accuracy how they are classified and then very recently nanotechnology has evolved and what type of metrological instruments are used in nanometrology that also we will be studying. And finally, we will be dealing with various kinds of linear measuring instruments. Now, let us try to understand the general care of measuring instruments. Now, whenever the measuring instruments are not in use for a long time, it is very essential that corrosion resistance coating is provided on all working surfaces of the instruments. For example, if you take the micrometer, we should apply the corrosion resistance protective coating like petroleum jelly on the surface of anvil and on the surface of spindle. Similarly, if you take the example of vernier caliper we have to apply petroleum jelly on all the working surfaces wherever there is movement we have to apply wherever there is open surfaces or the machine surfaces are there we have to apply petroleum jelly so that the surfaces are not corroded. And now when we use when we try to use the measuring instruments it is very essential that the protective coating that is applied should be cleaned properly all dust particles should be cleaned protective coating should be cleaned by using maybe some chemical or by using soft cloth we have to clean all surfaces and then we have to check for smooth movement over entire range. For example, if we have vernier micrometer it should the moving jaw should moving head should move throughout its range smoothly there should not be any stick slip motion so that we have to check if necessary we have to make some corrections so that the movement is smooth. And then we should not allow the instruments to fall down so that when they are subjected to impact the working parts of the instrument may get they may bend and it becomes unusable. So, it is very essential that while using lot of care should be taken so that they would not fall. And then whenever we are in doubt how to use we do not know how to use the instruments we should it is always better to consult the manual or consult the experts who know about operation of those instruments so that we should not they are not mishandled. Then it is very essential that whenever we use the instruments we should not over pressurize or we should not apply excessive pressure so that the moving the jaws or anvils or plungers they will not impinge the work surfaces. For example, if you over pressurize the thimble of the micrometer and then the spindle will enter into the workpiece and indentation mark will occur so it may damage the workpiece as well as it may damage the spindle. So such things should be avoided and it is very essential that we should have a proper sense of feeling we should have we should feel before we apply pressure and it is always better if we have instruments where in the application of excessive pressure is avoided. If such system such mechanism is there we should we should try to have such instruments and then we should always check for calibration status whether the calibration is required for that instrument when it is required such things we should see whenever calibration is required we have to arrange for sending it for the calibration purpose. It is also important to avoid direct sunlight and high and low temperatures and high humidity during the storage of measuring instruments and in case of digital instruments it is necessary that we have to remove the battery before storage if we are not using the instruments battery operated instruments for longer duration and then wherever possible we should use protective cover on the instruments to prevent dust settling on the instruments. Now after this let us try to understand how the measuring instruments are classified they are classified based upon the physical quantity that is to be measured for example, length measurement we need to measure length of the workpiece or breadth of the workpiece depth of the workpiece or say diameter of a hole. So, this represents the single dimension quantity. So, when we use the instruments for single dimension measurement then we say they are length measuring instruments then again if the instruments are used for the purpose of measuring angles then we say they are angle measuring instruments for example, bevel protractor is an example for angle measuring instrument. Then there are some instruments which are meant for measuring the surface roughness of working machine surfaces for example, the surface tester used to measure the surface roughness and then in some cases we use the instrument for measurement of form of the workpiece whether there is any out of roughness is there or some drum shape is there or barrel shape is there. So, if we use the instrument to measure such things then we say they are form measuring instruments. Now based upon accuracy and precision also we can classify the instruments as very accurate instruments and not so accurate instruments similarly very precise instruments and not so precise instruments. Then if the instrument is having a graduated scale then we say they are graduated instruments and if there is no scale on the instrument we say non-graduated instrument. For example, a spring caliper is a non-graduated instrument whereas a vernier caliper is a graduated instrument and if the instruments are used to check the character for characterization of nanoparticles then we say such thing such instruments are nanometrology instruments. Now we will study about linear measuring instruments. So, in this type of instrument in this classification the measured quantity is length that means linear measuring instruments they are used for measurement of length, breadth, depth, diameter and such things one dimensional quantities. Now under this first we will study about various accessories used for the measurement and then we will go for studying different kinds of linear instruments. Now the cast iron surface plate is a very very important accessory whenever we want to conduct the measurement process. Now this figure shows a cast iron surface plate we can see the top surface of the cast iron surface and we can also see different kinds of ribs are there on the sides and then there is provision for inserting the handles on both the sides we can insert the handles so that we can easily lift the lift and move the cast iron surface plate. So, normally they are placed on steel frames as shown in the figure. Now over to blackboard we can see the under surface of the cast iron surface plate there will be lot of ribbing provided so that the surface plate will not bend due to the weight of the instruments kept on the surface plate. Now this table shows what are the various sizes available for example 300 millimeter by 300 millimeter is a square shaped cast iron surface plate. Similarly 400 by 400 is again a square shaped cast iron surface plate and then we have we can have rectangular shaped surface plates also we can get surface plate of size 3000 millimeter by 1200 millimeter size they are available in different grades grade 0 grade 1 and grade 2 grade 2 is normally used for used in the workshop for regular inspection of the work pieces whereas grade 0 is used in the calibration and the standards room for calibration purpose. Now IS the cast iron surface plates are made as per IS 2285 2003 standard. Now this table shows that these figures they indicate the maximum deviation from flatness over the entire area for example for grade 0 and the cast iron surface plate of 300 by 300 the maximum deviation from flatness is 4 micrometer. So meaning of this is if we have 2 parallel plane planes separated by a distance of 4 micrometer then all the points on the cast iron surface plate top surface all the points should lay within this gap of 4 micrometer. So that is the meaning of that flatness over the entire area of the cast iron surface plate for grade 2 for the serial number 1 that is 300 by 300 millimeter sized cast iron plate for grade 2 the flat deviation from flatness is 15 micrometer. Now these surface plates they are made out of cast iron and they are also available in glass as well as granite. The advantages of glass and granite is they are not subjected to corrosion whereas cast iron plate is subjected to corrosion if not properly protected. So whenever the surface plates are not in use it is necessary that they should be covered with a wooden cover. Now another advantage of glass and granite surface plate is when a solid object whenever piece falls on the surface plate in case of glass and granite plate no burr is formed. So a dent will be formed which will not affect the measurement process whereas in the case of cast iron burrs will be formed which may affect the measurement process. We may get some measurement error due to the burr formed. Now we have some other accessories like angle plate. Now I am showing an angle plate which is a very important accessory used along with the surface plate. Now you can see the shape of the angle plate. This is the L shaped and this is the bottom working surface and this surface is again a working surface which is perpendicular to the bottom surface. So this is the length of the angle plate and then this is the height of the angle plate and then this is the breadth of the angle plate. Now it is very essential that this bottom surface and this surface should be square. Now IS 2554 1963 specifies the various sizes and what are the accuracies needed for angle plate. For example if the size is 125 by 100 and for this particular size the flatness of this working surface should not exceed 5 micrometer. Similarly this working surface also for the same size of 125 millimeter by 75 millimeter by 100 millimeter the flatness of this bottom surface should not exceed 5 micrometer. Then the squareness of this working surface with the bottom surface for a height of 100 millimeter the squareness of this surface with the bottom surface should not exceed 10 micrometer and then for the same size the parallelism of opposite faces. That means if this also working surface deviation from parallelism should mean this surface and this surface should not exceed 13 micrometers. Now we can just see the other side of the angle plate. Now we can see there is a rib between the vertical plate and the horizontal plate. So that the angle plate will be rigid. We can also see three slots here and we have two horizontal slots used for clamping of work pieces. And then we have V block which is another accessory used for the measurement process. Now we can see a cast iron V block. We can see the V channel and then we have V channel on both the sides. So this is the top surface and this is the side working surface and this is the end surface. It is necessary that all these surfaces are square to each other. And now these V blocks are used for clamping cylindrical objects and for marking center of cylindrical objects. We can always clamp the work pieces using this type of clamp. So in between the V channel and the screw we can place the cylindrical object and we can clamp it. Now there is another accessory known as universal surface gauge. This is used for scribing lines on the work surfaces. This inclination can be changed by operating this mechanism so that any height can be adjusted and parallel lines can be scribed on the work piece surface. So we have another accessory known as engineers square. Now this is engineers square. We have the bottom surface and we have the vertical surface here. This is used to check squareness of the work pieces. These are made as per Indian standard 2103 1972. And different grades are available A grade, B grade and C grade depending upon the type of work whether it is used for used in the machine shop or whether it is used in the standards room. We need to select appropriate grade. It is very essential that this surface and the bottom surface should be square to each other. Now these squares engineers squares are used to check squareness of the work pieces. Now let us assume that this is the work piece and I want to check whether this surface is square with the datum surface. So for that we have to keep the engineers square like this and then we have to take a thin paper and we have to insert the paper between engineers square and the work piece. If it enters it indicates that there is some error. If it does not enter then it indicates that squareness is ok. Now it is not entering so squareness of the work piece is ok. Now we have a steel rule which is the most common instrument for measurement of linear dimensions. Now you can see here this steel rule is made out of stainless steel and then it is hardened. Now the range of this scale is it starts from 0 and then we have 20 centimeter. So 0 to 20 centimeter is the range of this and then coming to the resolution we can see here up to 10 centimeter we have a very fine resolution of 0.5 millimeter and then from 10 centimeter to 20 centimeter we have a resolution of 1 millimeter. Now depending upon the accuracy required we can use this portion where in resolution is 1 millimeter or if finer accuracy is required we can use 0 to 10 where in resolution is 0.5 millimeter and then graduations are marked on both the edges and then the graduations are available on both sides also. So any side we can use. Now before using this steel rule it is very essential to check whether this end is proper or not. Sometimes this may be worn out in that case we should not use this edge. We should start from one marking and then we should use it and then we should not forget to deduct this 1 centimeter from the reading obtained. Now I will show how to use this to measure the length of a workpiece. Now I can see here I have a workpiece it is butt against the angle plate. Now I am keeping this steel rule on the workpiece and now we can read. So this edge is the reference wherein the reading is 0 and then on the other side we have the measurement point. So now the reading is 35 millimeter that means length of this workpiece is 35 millimeter. Now it is very essential to read the steel rule normal to the steel rule otherwise parallax error may creep in. Now in case this edge is worn out then how to use this steel rule. I will just show how to use the steel rule when the edge is worn out. Now you can see number 1 is coinciding with one edge of the workpiece. This is the reference point and then on the other side we have 45. Now you can see the observation is not normal to the scale. So there is some parallax error. Now the reading is difference between the measurement point and reference point is 35 millimeter. Now I will just show how the cosine error creeps in. I can see we have the workpiece and then we need to measure the length of the workpiece for that I am using this steel rule. The one end of the steel rule is coinciding with this edge. So this is the reference point and then this is the measurement point. Now it is reading 40 millimeter. Now the steel rule is parallel to the physical quantity to be measured that is length. Now when there is some angle like this now we can see the steel rule is not parallel to the physical quantity to be measured. So this is the length of the workpiece but we have placed the steel rule at some angle theta. So because of this there will be cosine error. So actually when we measure we get now this is around 41 millimeter it is showing 41 millimeter whereas the actual length will be L cos theta. So this cosine error can be avoided by keeping the steel rule parallel to the quantity to be measured like this. Now I am explaining how to use a steel rule for outside diameter measurement. Now I am keeping one edge of the steel rule at this place. So this is the reference point and then I am slowly adjusting the steel rule so that I am measuring the diameter not the chord. So now the measurement point is at this place and it is showing 4 centimeter. So the diameter of the workpiece is 40 millimeter. So this is an example for direct measurement wherein we can directly get the size of the physical quantity and there is no need to have any calculations. Now I am showing a few non-graduated instruments. This one is a spring caliper, outside spring caliper for measurement of outside dimensions. This is inside caliper for measuring inside dimensions. These are the legs of the caliper and we have a screw and we have a net and this is the spring which provides necessary tension to the legs. So similarly we have 2 legs here for the inside caliper and a screw, a knurled net. By rotating this we can adjust the distance between these 2 measuring points. Now these edges are hardened to nearly 600 wicker hardness so that they do not wear much. Now let me demonstrate how we can use an inside caliper for measurement of inside diameter. Now we have to insert the caliper both the legs of the caliper inside the hole and then we have to adjust the screw till we get the diameter. So slowly we have to rock the inside caliper till we get the minimum dimension. If we take the dimension in this position, inclined position there are chances of getting cosine error. So we should get the minimum dimension and always the instrument should be perpendicular to the workpiece like this. So now I am getting the minimum dimension. Now we have to remove the instrument from the workpiece and then we have to transfer this distance on to the steel drill. Now we can see one point is coinciding with it, graduation mark 10 and then graduation mark 12 is coinciding with this point. So the distance between these 2 is 20 millimeter. So the diameter of the hole is 20 millimeter. Now let me explain how this outside spring caliper is used to get the diameter of the workpiece. Now we have to keep the workpiece on the surface plate and we have to hold the caliper like this. We have to rotate the nut so that 2 tips come in contact with the workpiece. Now we should take care that the 2 tips are in contact at the diameter and now we have to remove this spring caliper from the workpiece and then we have to use the steel rule. Now we can see this tip is in contact with the edge of the steel rule and we have this is the reference point and this is the measurement point. Now we can take the reading so it is giving 40 millimeter. That means the diameter of the workpiece is 40 millimeter. Since the spring calipers do not have their own graduated scale they are used only for transferring the distances. Now let me conclude this session. In this session we learnt about general care of the measuring instruments and then how we can classify the measuring instruments. Also we learnt about linear measuring instruments wherein we discussed about the different kinds of accessories like surface plate and then angle plate and then engineers square and then we studied about some of the linear measuring instruments that is steel rule how to use steel rule for length measurement, how to use steel rule for inside diameter measurement and outside diameter measurement and then how to use spring caliper for transferring the distance from the object to the steel rule. We will continue with the other kinds of instruments used for linear measurement. Thank you.