 I welcome you all for the series of lecture on metrology, so now we will start the lecture series on module 10 in which we will be discussing about the comparators, topics covered in this module are interaction to comparators, the various features of comparators and how the comparators are classified, various types of comparators will be discussed as also advanced comparators will be discussed. Now we will start the first lecture in this module number 10, topics covered in this first lecture are interaction to comparators and the various features of the comparators and how they are classified, we will learn about the classification of comparators and also the users of comparators. Let us start the introduction to comparators. Now these comparators indicate the differences in size between the standard and the workpiece being measured, there is an integral display unit with sufficient magnification, that means it does not indicate or it does not measure the actual dimension of the workpiece, but it indicates how much it differs in size from the basic desired dimension. However, the comparators can be used for direct measurement within its range of operation, for example the range of the direct indicator is 0 to 10 millimeter, within this range the comparator can be used for direct measurement of the workpiece. Now this picture shows the basic system of the mechanical indicator, so we have a stage where in the standard and the workpieces can be placed and there is an arrangement, there is a column to which the comparator can be mounted and the differences, initially we have to place the standard on the table and we should set the reading of the comparator to 0 and then we have to remove the standard and we have to place the workpiece of unknown size between the table and the spindle and the dial indicator of the mechanical comparator shows the reading which will be difference from the basic size. These comparators are the instruments calibrated by means of end standards, for example slip gauges to quantify unknown dimensions. The purpose of a comparator is to detect and display the small differences between the unknown dimensions and the standard. The difference in the dimensions is detected as displacement of the sensing probe, for example the contact probe in the dial indicator, the movement of the contact probe in the dial indicator and the difference in dimension is also detected by comparison of shadow with a chart gauge which we will be discussing after some time. The important and essential function of the instrument is to magnify the small input displacement so that it is displayed on an analog or distal scale. Comparators are used in mass production to inspect the components to very close tolerances with high degree of position and speed. Quickly we can inspect the workpieces and we can segregate as acceptable workpieces and not acceptable workpieces. Use of line standards such as linear caliper and micrometers require considerable skill in the use of these instruments whereas use of comparator is relatively easy and quick. Multiple dimensions can be checked in a very short time using comparators. Let us study the basic features of comparators. Any comparator consists of a sensing device which faithfully senses the input signal and there is a magnifying system to amplify the signal input signal to suitable level. For this magnification different methods are used like mechanical methods, optical method, pneumatic method, hydraulic method or electronic method of magnification and any comparator will essentially consist of a display system commonly a scale and a pointer is used. Now what are the desirable features of comparators? Now the scale of the comparator should be linear within its operating range. There should be wide range of wide range for comparison so that it can be used for within a wide range of application. There should not be any backlash and friction between the moving part should be very very less and inertia of the parts various parts should be less. It should be very precise and it should contain should have good measurement accuracy and the indicator should be very much clear so that we can easily take the reading. The indicator can be analyzed as shown here so I can see the analog indicator. So it starts from 0, 0, 1, 2, 3, 4, 5 again in the counterclockwise 1, 2, 3, 4, 5. This is the contact probe and we have the pointer and you can see the markings on the scale are very much clear so that we can easily read and this shows a digital indicator so that we can easily take the reading. As also we can transfer the data via some communication systems to the computer system. Now the other desirable features are it should be easy to operate it should not require much skill of operation and no zero error the there should not be any pointer oscillations oscillations it should move smoothly over its range and the system should be robust in design so that it withstands the reasonable yield usage and the measuring pressure should be very low and it should be uniform throughout the operation and there should be inbuilt compensation for temperature effects. So you can see here a system which has a comparator system with the base and there is a column you can see the threaded column so that this measuring head can be moved up and down this height between the table and the probe can be adjusted depending upon the workpiece size and also these tables are replaceable depending upon the application. We can change the tables and this is the sensing probe and the output this is an example for electronic comparator and LVDT the when we place the workpiece between the table and the probe the probe will move and the signal is sent to the indicator and the pointer will move on the scale corotary scale we can select the desired range and sensitivity of operation. Now how these comparators are classified depending upon their design they are classified as mechanical comparators electrical and electronic comparators pneumatic comparators optical comparators which uses optical system fluid displacement comparators multi-check comparators in which multiple dimensions can be checked at a time and then automatic gauging machines. Now let us start the discussion on mechanical comparators now let us study the different displacement amplification systems what are the different types of amplification systems used in the mechanical comparators and what are the various types of mechanical comparators different types are available like dial indicator read type mechanical indicator sigma comparator Johansson micro theater and internal group comparators. Now the displacement amplification systems used in the mechanical comparators are illustrated here different amplification systems are used in the mechanical comparators like rack and pignon and gear train you can see this is the spindle contact spindle which contacts the workpiece so when the workpiece is placed between the table and the spindle the spindle will move in so spindle is connected to the rack and rack we have the rack on this rack cut on the spindle and we have a pignon here when the spindle moves that is rack moves pignon will rotate. So this rotation of the pignon is amplified using the gear trains finally the motion is transmitted to the pointer and pointer will move on a rotary scale and then we can take the reading now this is a very simple gear train with 10 is to 1 ratio and we have another simple gear train with rack you can see the rack which contains the contact probe so when the rack moves up and down this gear train will rotate and we get an amplification of 10 is to 1 ratio and then we have compound gear train with rack so this is the rack and then we have a compound gear train which will give us 100 is to 1 magnification ratio and then we have length of indicator indicator hand F so this is the length of indicator as the length of indicator increases there also we get some amplification now another amplification mechanism used is lever mechanism so this is a simple lever with 10 is to 1 ratio you can see here this is the contact point and this is the pivot the distance between the contact point and pivot is 1 millimeter here one unit and distance between pivot and the in tip of pointer is 10 so that the signal displacement signal is amplified by 10 times now this shows a compound lever wherein we get an amplification of 256 times so this is the contact point and this is the pivot and this is here we have another secondary lever so totally we get an amplification of 256 times so another mechanism is cam and gear train this is the measuring the splinter with the cam and then we have a set of gears so using this we get the amplification of the signal and this is another system with which uses lever with gear using lever system we get some amplification and using the gear train we get added amplifier further amplification of the signal but these are other systems to amplify the input signal this is the lever and gear so this is the lever and gear and the twisted strip and this is the lever combined with the band bound around the drum we have a drum here and a band is bound around this drum so there also we get amplification of the signal now let us study a very common type of mechanical indicator that is dial indicator so this dial indicator measures change in length and it does not measure the length itself however within this range of operation it measures the actual length of the workpieces for example if the range of the dial indicator is 0 to 10 millimeter the range is 0 to 10 millimeter and if the workpiece size is say 5 millimeter so the mechanical dial indicator can be used directly to measure the length of the workpieces so various names are used for dial indicators depending upon the type and purpose including dial gauge probe indicator test indicator dial test indicator drop indicator plunger indicator etc now this picture shows the arrangement of the dial indicator this is the table on which the standard or workpieces are placed so this is the reference point and this is the standard for example slip gauge can be used as standard to set the desired distance between the plunger and the reference point now they say we want a desired height of 10 millimeter this is the basic dimension then we use a slip gauge of 10 millimeter dimension we keep it between the plunger and the table that is the reference point and we set the dial indicator to read 0 we adjust the height of the dial indicator so that it is 0 now we remove this standard and we place the workpiece whose height is to be checked that is placed workpiece is placed between plunger and the reference point if the size of the workpiece is greater than the standard size that is 10 millimeter then this is the error or difference from the basic size so this difference in size can be measured using this dial indicator arrangement now let us study the basic operation of the mechanical indicator dial indicator this is the dial indicator and we have a granite table or cast iron table this which is the reference point and then we have a column on which we have we have an arrangement for mounting the dial indicator the dial indicator height can be adjusted by moving this bracket or it can be dial indicator itself can be more up and down and then it can be clamped using this knob now this is the height this height can be adjusted depending upon the workpiece height now initially we have to adjust the height of the indicator to accommodate the workpieces of different heights and then we have to insert this gauge between the spindle and the reference point between the contact probe and the reference point that is surface on top surface of the reference table and we should set the indicator to read zero now we should remove this gauge and insert the workpiece standard should be removed at workpiece whose heights are to be inspected they should they are inserted between the table and the plunger and then if the size is different from the standard size the pointer will move and that will show the change in the difference difference so that is recorded now let us study the construction of the dial indicator there are many parts in the dial indicator this is the indicating hand and then we have a rotary scale with markings and there's a dust cap to protect the rack and we have a bezel to protect the pointer and the scale bezel clamp and then we have this stem connected to the body of the dial indicator and then there is a rack or spindle and then the contact probe is connected mounted on the rack now there is a mounting lug using this this can be mounted to the stand now this shows a dial indicator wherein you can see we have a pointer and then we have a revolution counter and this is the scale you can see this is zero and this is 10 so this zero to 10 we have 10 markings each small marking represents 0.01 millimeter so when the pointer moves from 0 to 10 so the displacement of the plunger will be 0.01 into 10 that is 0.1 millimeter so like that if the pointer completes one revolution so it will be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and 1mm so if pointer completes one revolution the movement of the plunger will be 1 millimeter like that you can see the pointer can rotate 10 10 strand revolutions so we have 10 markings here 0, 1, 2, 6, 7, 8, 9, 10 so the range of this dial indicator is 0 to 10 millimeter and least count is 0.01 millimeter now let us see the internal construction of the dial indicator this is a mechanical type dial indicator you can see the contact plunger stem and the back cover is open this is the spindle varying the rack so rack is cut and rack is connected is contact with the pinion and then we have a set of gear trying and there is a spring to bring back the spindle back to initial position when we remove the workpiece so this is a digital dial indicator you can see the display display and then we can set the tolerance limits upper limit and lower limit we can also set we can select the display range for example 0 to 10 millimeter, 0 to 20 millimeter, 0 to 30 millimeter so the range can be selected now the magnified view of the internal structure you can see the spindle on which rack is cut and the pinion is in contact with the rack and there is a spring to bring back the rack when the workpiece is removed and this is the guide for the rack and the spring and there is a gear train for amplification of the signal gear train amplification is the most common method used to magnify the dial indicator motion that is the plunger motion because its accuracy meets the requirements of comparison measurement in use the sensitive contact probe is part of a rack in which a series of three to five years magnifies and transmits the movement of the contact probe to the pinion gear on which the indicator hand is mounted now we can see the dial indicator back cover is opened I am pressing the plunger we can see the movement of the plunger we have a guide for the movement of the plunger and the guide rod we can also see the rack and pinion we can also see a spring now different types of dials are used this is a dial with continuous clockwise markings 0 to 90 markings and this is a continuous counter clockwise markings and this is the balanced type that is in the clockwise we have 0 to 50 markings and then in the counter clockwise we have 0 to 50 markings and then we have flat and round contact points so we have this is the flat contact point and this is the anvil of the table on which workpiece is mounted a workpiece with a flat surface a round workpiece okay now it is very essential that the surface of the flat contact point should be parallel to the anvil surface otherwise the it will give error and we can see here round contact points now when we use round contact points and when we are checking the round parts it is essential that the contact point contacts the maximum size of the workpiece for example the diameter of the workpiece if we place the cylindrical object like this then we get the error in reading so readability of the dial indicator is another important thing I can see here commercial dial indicator where in markings are there and they are very much clear so reading is very easy also one can have a digital indicator so wherein you can select the system at a system or in this system now the measurement errors in dial indicator I can see here in this picture we have the table on which the workpieces are placed now we have this dial indicator mounted on this arm now when we insert the workpiece what happens if this arm is not rigid enough it will bend and then we get a wrong reading so how do we eliminate this deflection of this support we should use a very rigid very strong arm or else we have to minimize the overhang of this dial indicator it should be moved as close to the column as possible also we can minimize the deflection of these supports using the extra support cash one here now what are the uses of dial indicator so it is used in the turning work to check whether the whether we have achieved the proper size of the workpiece it can be used to check the wobbling of the rotating surfaces it can also be used to check the roundness of the work parts you can see the workpiece is mounted on the block and then the rotation is given to the workpiece so it is rotated and then readings of the dial indicator are taken if this is not round then this will indicate what is the amount of error also it is used to check the wobbling in the rotary source the amount of magnification of an indicator depends on its use and desired resolution dial indicators can have gear trains that amplify the movement anywhere from 40 is to 1 to 1500 is to 1 that means a magnification of 1500 times is possible this can give a dial indicator a discrimination or resolution of 0.02 millimeter 2.001 millimeter the total travel or reading capacity of the dial indicator commonly ranges from 0.075 millimeter to 50 millimeter or more so in the case of long range indicators for example 0 to 100 millimeters 0 to 105 150 millimeters the gear train drives revolution counters you can see here we have this pointer the main scale and then a revolution counter you can see here which tells how many revolution the pointer has rotated the revolution counters that tell the user the number of times the hand has traveled around the dial and thus the range of indicators displacement can be known these dial indicators are calibrated using slip gauges or using dial gauge calibrators so you can see here a calibrated span which is used to calibrate the dial indicators dial indicator which is to be calibrated is mounted and you can see there is a disc with markings and then we have to note down what is the reading given by this standard calibrator and what is the reading given by the dial indicator and then we can we'll come to know what is the amount of error in the dial indicator so this is another calibrator which is a distant time now let us study how we can use a dial indicator as a comparator we can see we have a slip gauge box the slip gauges are used as a reference to set the basic size the dial indicator now we have the round the workpiece and a linear caliper to measure the diameter of the workpiece with close view of the workpiece now we can observe the dial indicator fixed to the scan now we can we are observing the replaceable table these replaceable tables can be changed depending upon the workpiece we can see the slot in the stand to accommodate the table the dial indicator is fixed in the bracket the least count of the dial indicator is 0.01 millimeter and range is 0 to 10 millimeter now we can adjust the height of the dial indicator to accommodate workpieces of different heights by rotating this nut we can adjust the height of the bracket we can raise it or lower it in the column now I am measuring the diameter of the workpiece using the linear caliper the diameter of the workpiece is 19 millimeter now I have to select 19 millimeter slip gauge I am setting two slip gauges one nine millimeter thick and the other one 10 millimeter thick after cleaning the surfaces of slip gauges we have to ring them properly to build a pile of the desired thickness now we can see a slip gauge pile of 19 millimeter thickness after ringing we can use this pile to set the basic size the dial indicator we have to insert the slip gauge pile between the table surface and the dial indicator so this is the desired size 19 millimeter is the desired size so we have to set the dial indicator to read 0 by rotating the bezel now the dial indicator is reading 0 that means when the gap between the spindle and the table surface is equal to 19 millimeter indicator shows 0 millimeter now we have to remove the slip gauge pile now the reading is zero we have to remove the slip gauge pile and then we have to insert the workpiece which is to be inspected so I am inserting the cylinder which is to be inspected and we have to rotate it slowly so that we get the maximum reading so and we have to slowly rotate or roll the workpiece I can see the pointer is moving so we have to note down the maximum reading so the maximum reading is three divisions that means the least count is 0.01 millimeter so it is giving five divisions so the workpiece size workpiece diameter is greater than the desired size by five divisions that means 0.05 millimeter that means the size of the cylinder is 19.05 millimeter now we have another type of dial indicator known as dial test indicator we can see the photographic view of dial test indicator we have a lever which moves in this fashion so the lever moves in this fashion the pointer will move actually it will indicate the movement of this stylus so whenever we want to measure the displacement for example we have a workpiece like this placed on the surface plate now depending upon the height of the workpiece stylus will move up and down so the movement of this stylus is amplified by using this lever so we have a pivot ball bearing we have a pivot here and then we have a lever at the end of the lever we have a gear sector and which is in engagement with this is the gear sector this is in engagement with a pinion so pinion will also rotate so the rotation of the pinion will be transferred to the pointer to the pointer by means of the gear arrangement and the pointer will move on the scale and we can note on the reading so we can amplify the displacement of this stylus by means of this lever arrangement now we will move to another type of mechanical comparator known as read type mechanical comparator this sketch shows the arrangement of read type mechanical comparator we have a member two members so member a this is the movable member which will move up and down and there is a fixed member these two are connected by means of horizontal reads we have a horizontal read here and we have another horizontal read here so these two are the horizontal reads named R1 now we have a set of vertical reads R2 so one vertical read is connected to the movable member and another vertical read is fixed to the fixed member now when the component is inserted between the surface plate and the plunger the plunger will move so this x is the input displacement depending upon the height of the component plunger will move up and down and then movable member A will also move up and down the two vertical reads they are joined at the top and then a pointer is fixed at this point so since the two vertical reads are joined when the plunger moves up and down the read will tilt in this fashion and hence the pointer will also move and then we can note down the reading displacement reading a linear motion of the spindle moves the free block vertically causing the vertical read on the floating block to slide past the vertical read on the fixed block now as these vertical reads are joined at the upper end the two reads are joined at the upper end instead of slipping the movement causes both reads swing through an arc and the pointer swings through a much wider distance the amount of pointer swing is proportional to the distance the floating block has moved but of course very much magnified now this shows the amplified view of the fixed block and then the vertical reads this is the spindle which is fixed to the movable member and two vertical reads are joined together at the end of at the top end we have the pointer so now a is the displacement depending upon the height of the workpiece the a can be positive or negative and then when the height of the workpiece is greater than the standard of the desired height this spindle will move in this direction and the pointer will swing in this direction if the height is smaller than the desired height then this wing will be in this direction and pointer will swing like this and then we can go down the reading there these comparators are available in magnifications ranging from 500 to 1000 comparators of this type have sensitivities of the order of 0.002 millimeter per scale division now again we have read type comparator wherein the mechanical pointer is replaced with an optical lever so this is the top end of the reader reads vertical reads and we have a lamp and a lens so we get a light beam here so light beam will go will move in this direction we have a mirror so light is reflected back so when the top end of the read moves swings in this fashion the reflected light will also move on the scale and hence we can note down the displacement of the spindle so in this case magnification is of time by the length of this vertical read as also the magnification is further magnification is obtained by this optical arrangement now we are coming to the end of the lecture 1 in module 10 in this lecture we learnt about the basics of dial indicators what are the basic features or characteristics of the mechanical comparators what are the purposes of comparators what are the uses of comparators what are the various types of comparators and then we also learned about the construction and working of mechanical type dial indicator now we will stop here and we will continue the discussion on other types of comparators in the next lecture thank you