 I welcome you all for the lecture number 3 in module number 10. In this lecture, we will be discussing about the pneumatic comparators. We will study about the need for pneumatic comparators. They are also known as air gaging equipments. We will also study about the working principle of pneumatic comparators and what are the different kinds of circuits available and what are the various components used in pneumatic comparators. We will also study about the commercially available gauge that is Solex gauge and then we will move on to the important characteristics of pneumatic comparators. Then we will discuss about the advantages and disadvantages of pneumatic comparators. Finally, we will see some applications of pneumatic comparators. Now, let us study why there is a need for air gaging circuits or pneumatic comparators. Basically, they are non-contact type of comparators and because of this, they offer the advantages of improved workflow, increased productivity and decreased downtime. They are ideal for measuring dimensions with tolerances smaller than 0.1 millimeter and when gauging the very tight tolerances, a resolution as small as 0.001 millimeter can be achieved. Its non-contact characteristic makes air gaging particularly useful for checking very soft materials, highly polished surfaces, components with highly polished surfaces, the components with very thin walls and other delicate materials. In case of delicate materials and very workpieces with highly polished surfaces, if we use contact type comparators, then the scratches may appear on the workpiece. So in that case, in such cases, non-contact type comparators are desired. So pneumatic comparators offer that particular benefit of not making any scratch on the workpiece surface. Now, let us study about the air gauge principle. So in this diagram, we can see that they have workpiece with the surface of the workpiece and we have a nozzle. So this is the gap between the nozzle and the workpiece. Now when the air gap or the clearance between the workpiece and the nozzle increases, the flow of air through the nozzle increases and when the clearance reduces or the air gap reduces, the pressure increases. So this characteristic is used in the pneumatic comparators. Now let us study about the different types of air gaging circuits that are available. The first one is the back pressure circuit. I can see in this diagram, this is the workpiece, this is the nozzle and this is the air gap or clearance between the workpiece and nozzle and we have the compressed air supply and there is a pressure regulator. So desired pressure can be set using this regulator and there is a restrictor to restrict the flow of air. Now when the gap between nozzle and workpiece is high, the air flow is easy. The air escapes easily into the atmosphere and little pressure is developed in the system. Now when the workpiece moves towards the workpiece or in other words when the size of, when this particular size increases, that means the gap, air gap reduces, the escapement of air is restricted. So the back pressure is developed in the circuit which is indicated in this gauge. So the development of back pressure is used in this, is used to indicate the dimensional feature in this particular circuit. Now there is another circuit in which air flow is measured. Again we have the air plug gauge where in we have two jets. Now say this is the workpiece and then this particular dimension say D is to be checked. This D is to be checked in this pneumatic comparator. Now we have the pressure regulator and then there is a air flow meter. For example, rotometric can be used in such applications. In the air flow meter we have a float. Now when the gap between the plug and the workpiece reduces, the air flow is restricted, that means the air flow reduces, so float level reduces. When this gap increases, air flow will increase, air will escape freely, hence air flow increases, the float level ingredients there will be a scale fixed on the air flow meter. So by knowing the position of the float with respect to the scale we will come to know about the size of the workpiece. Now let us study what are the various components used in pneumatic comparators. Essentially the comparator requires the precision air regulator to provide a constant pressure air supply to the system and then the different kinds of toolings are needed like plugs, rings and other shield depending upon the work to be inspected. These toolings deliver a specific air flow pressure to the surfaces being checked. An amplifier is another essential component used in pneumatic comparator and this amplifier can be an air electronic column or it could be a dial type meter or it could be a flow meter cube for example, the automator. The amplifier provides visual representation of the size being measured, permitting the user to take readings quickly and accurately. Now in this photograph you can see a pressure regulator, this is the pressure regulator with filter to clean the air supply, supplied air and then this is the knob to adjust the air pressure and the adjust what is the level of pressure that is available in the system can be note down by this pressure indicator. And setting masters are used to calibrate the comparator depending upon the system. One or two masters usually in the form of discs or rings are used. Masters are typically made from alloy steel or tungsten carbide. So you can see here one set of setting masters are used to calibrate the system, one for setting the upper limit of the workpiece and other for setting the lower limit of the workpiece. Now this is a close view of setting master. You can see here this is for a particular dimension that is 102.01 millimeter. This is the desired size of the workpiece or the basic size of the workpiece and this particular setting master is used to set the upper limit that is 102.01 plus 0.104 millimeter. This is the upper limit of the workpiece and then we have another setting master for to set the lower limit of the workpiece. So again the basic size is 102.01 millimeter and this particular setting master is used to set the lower limit that is 102.01 minus 0.0094 millimeter, which is the lower limit of the workpiece. And then the amplifier or indicators are essentially required. Now this photograph shows a flow meter, a rotor meter. This is a tapered inside surface of this flow meter is tapered like this. Now this is the shape of the flow meter. So inside it is tapered and then a scale, graduated scale is engraved on the outer surface of the glass tube. And then we have a flow which will float inside the tapered tube is a metallic flow. Now when the gap between the work surface and the gauge reduces, air flow reduces and flow level will come down. So it will indicate that the dimension being checked is small. Now when the gap increases, air flow is more. So the float level increases, which will indicate that the dimensional feature is, the dimension of this particular feature is more. So we can always set two limits, upper limit and lower limit using the setting masters. So when the float crosses the upper limit or lower limit and the workpiece is rejected. Now let us see the working of an air gauge operators. Now we are observing the honing operation. The workpiece is clamped and the honing tool is inserted into the bore of the workpiece. The honing tool is adjusted. Now the machine is started. The honing tool is reciprocating and rotating. These reciprocation rate and rotation rates can be adjusted depending upon the surface finish required. Now the operator is removing the workpiece. You can see the coolant flow, flow brick and flow. Now the honed surface is visually inspected for the finish. Now we are observing the pressure regulator and filter. You can see the pressure indicator. Using this we can set the working pressure to required pressure like 3 bar, 4 bar or 5 bar. Now this green area indicates the pressure range in which the air gauge can be used. Now we are observing an indicator which shows the size variation in terms of microns. So one small division is one micron. When we insert the black gauge into the bore of the workpiece, depending upon the clearance between the workpiece surface and the black gauge, the pointer will move and we can note down the reading. Now we can observe the operator is inserting the black gauge into the bore. The bore is rotating the workpiece or gauge to check for roundness and vertical movement to check the salienticity of the bore. Now we can observe the air plug gauge, air jet through which air escapes. In the opposite direction we have air jets. Now we can see the air connection. Via the air gauge the air will flow and it will enter into the air plug gauge. Now holes are provided in the air plug gauge to reduce the weight of the plug gauge. We can set the air gauge. So initial calibration we have to do using the masters and we can set the limiters. We can observe two limiters are there. We can set these limiters to indicate upper limit and lower limit of the bore size. Now the plug gauge is being inserted into the workpiece. Now operator is rotating the workpiece. He is removing the black gauge. So now we can observe the two masters for initial calibration of the air gauge. So this is a plus 0.0104 millimeter from the desired size and this is the lower side minus 0.0094 millimeter. Now we are observing the indicator removed from the air gauge setup. You can see the plunger. When the plunger is moved the pointer rotates. We can see the range 0 to 50 microns on both sides clockwise as well as anticlockwise. Now this is the place where the indicator should be inserted. Now the operator is inserting the indicator and then using masters we can set the indicator. Now let us study a commercially available pneumatic comparator which is known as Solex gauge produced by Solex company. So this Solex company has developed a single and multiple dimensional measuring system. That means a single dimension can be measured at the time or multiple dimensions can be compared simultaneously. These highly versatile systems can be used in many industries such as automotive industries and manufacturing industries, pharmaceuticals and food industries etc. They work on the principle of pressure difference generated by the airflow. That is back pressure is measured which will indicate about the size of the workpiece. The air is supplied at constant pressure through the RFI's and the air escapes in the palm of jets through the restricted space which exerts a back pressure in the system. The variation in the back pressure is then used to find the dimensions of the components. Now let us study how the Solex gauge works. Compressed air is supplied to the system. The pressure of the air will be equal to water head H. We can see here we have a tank here filled with water to a certain level and this H indicates the air pressure. This value of this pressure can be varied by adjusting the depth of dip cube in the water tank. So we can adjust the depth and then we can adjust the pressure in the system and then excess air escapes in the palm of bubbles which we can observe here. The controlled amount of air is passed through the RFI's. So we have an RFI's here and it is connected to the gauge gauge head. The controlled air is connected to the gaging head via the flexible tubes. Due to the restricted area between the gaging head and the workpiece say for example at position A1 the back pressure H is developed because of the restriction here the back pressure H is developed which indicates the size of the dimensional feature. For example diameter the whole diameter in this case. Now we can also determine the roundness of the job and then the cylindicity of the job using this system. To determine the roundness of the job the workpiece is rotated along the jet axis. So this is the jet axis and the workpiece is rotated. If there is no variation in pressure reading H when the job is rotated it indicates that the workpiece is perfectly round at this particular position. So this procedure is repeated at different positions along the length of the hole A2, A3, A4 etc and then we can note down what is the roundness of different positions of the workpiece. Similarly we can measure the cylindicity of the workpieces. The diameter is measured at various positions A1, A2, A3, etc which will give the information about the cylindicity. For example, so we have a workpiece with the axis of the workpiece and then we are using the gaging head to check the diameter. Now we insert the gauge here and then what is the reading hatch at this position A1 is noted down. Then gauge is moved and then reading is taken at position A2 and then at K3 like there is a different position so the reading hatch is taken. If there is any variation that will indicate whether the hole or the workpiece is tapered or double tapered like this or the bore is barrel shaped or bell mouth shaped so such cylindrical features we can check using these gauges. Now let us study why two jets are you can observe here two jets are used in this particular gaging head. What happens if we use a single jet. I can observe here this is the workpiece part being inspected and the gaging head or it is also known as the spindle with single jet. Now when the spindle is rotated keeping the job fixed this clearance is varying from angular position to angular position. So because of this the float will move up and down. So this will indicate that the diameter is varying from angular position to angular position. Even though the inside bore is round because of this use of single jet since the float moves up and down so it will give a false information about the roundness of this bore. Now what happens if we use a double jet in the opposite faces. So when we rotate the spindle with two opposite jets the sum a plus b this clearance and this clearance or this clearance and this clearance some of a plus b will remain constant any angular position. So the float remains constant. So when the spindle is rotated this will not move up and down because the summation a plus b remains constant. So it will indicate that the hole is round. So this is the advantage of using the dual opposite jets it will give the correct information about roundness of the bore. Now let us study what are the important characteristics of air gauging. The air gauging operators are available with very high magnifications or amplifications as high as 10,000 times. It can be used to measure the parameters like diameters, length of the component, squareness, parallelism, concentricity, tapered measurement is possible, center distance between two holes also can be checked using a gauging. As there is no physical contact between the gauging head and the work part the accuracy will not be lost because of the gauge wear. For this reason air spindle and air snap gauges last very long. Also very soft parts can be gauged without any chances of getting scratched. The internal dimensions of the components can be readily measured not only with respect to the tolerance limits but also with respect to the geometric form. Geometrical aspects such as taper, straighteners, camber and bell mouth can be easily checked. These air gauges they are independent of operator skill. Any unskilled operator can easily use these air gauges for checking the components. High pressure air gauging can be done with cleansing of the parts which helps to eliminate errors due to the dirt and foreign matter. Gaging pressures can be kept sufficiently low as low as some three bar or four bar to prevent part deflection. In general high pressure gauges are suitable for those parts in which tolerance are relatively large and low pressure air gauges are preferable for highly precise work. Dimensional variations throughout the length of shaft or cylinder bore can be explored for out of roundness, taperness, concentricity and similar other conditions. That means if you have a cylinder bore like this we can insert the air gauges into the bore and the bore can be checked throughout the length for circularity errors, taperness, concentricity etc. Not only it measures the actual size but it can also be used for salvage of over sized work pieces for rework or to sort out for selective assembly. That is pneumatic gauging is very much suitable for variable inspection that is for the measurement of size and also for attribute inspection to segregate the work pieces into acceptable and unacceptable work pieces. Now let us study what are the advantages of pneumatic comparators. The gauging member does not come in contact with the part to be measured and hence practically there is no wear of the gauging member also there are no chances of scratches on the surface of the work piece. It has usually very small number of moving parts thus the accuracy is more due to less friction and less inertia. Measuring pressure is very small it can be as low as 3 to 4 bar and the jet of air helps for cleaning of the work surfaces. We can also have very high magnification as high as 10,000 times the indicating instrument can be removed from the measuring unit. These air gauges are very much suitable for measuring diameter of holes where the diameter is very small compared with the length. For example, deep holes like the gun barrels can be easily checked with these gauges. It is possibly the best method for detecting the the mobility and taperness of circular boards. So, we can check whether there is any taperness or some bell mouth shape or some barrel shape in the hole. So, such things can be easily checked using these gauges. A row of multiple column amplifiers can be scanned in one glance. So, you can see here many column amplifiers are available and we can observe the reading multiple readings are multiple features of the work piece at a time. So, that the work pieces can be checked with can be checked at a faster rate. That means, the checking time or inspection time can be greatly reduced by using multiple gauging. These amplifiers they provide visual representation of the checked feature. It permits the operator to take readings quickly and accurately. Either back pressure system can be used or flow systems which uses flow meter tubes can be used for visual representation. And parallel stacking of columns or flow meter tubes puts all the readouts into the same vertical relationship making comparison very much simpler. For example, multiple dimensions like this can be checked using multiple gauging operators and their relationship can be easily understood by using multiple amplifiers. Relationships for example, squareness can be easily checked using gauges. For example, say we have a bore like this whether this bore is perpendicular to the face that such features can be easily checked. Air gauging is very much economical. Once the basic system is purchased relatively inexpensive additional tooling such as the gauging heads can be purchased and used for a wide variety of applications. Since air gauge tooling has less moving parts and most of the cases no moving parts it is virtually immune to trapping. That means, the gauge will not get trapped in the work part. Now, let us study what are the disadvantages of air gauging systems. It requires a very elaborate auxiliary equipment such as pressure gauges or required pressure regulators or required air filters are needed for filtering the dust particles. So, like this it requires elaborate auxiliary equipment. The scale is not generally uniform when indicating device is the glass tube for example, a manometer then very high magnification is necessary in order to avoid the miniscuous errors. The operators is not easily portable since it is bulky they should be placed at one place and is rather elaborate for many industrial applications. Now, different gauging heads are required for different dimensions. For example, when the bore size changes we have to have a different set of gauging heads. For example, for 10 mm bore size we need one gauging head and for 12 mm bore size we need another gauging head. So, like this as the dimension changes we need to purchase the unnecessary gauging heads. The accuracy may be influenced by the surface roughness of the component which is being checked. That means, the surface roughness will also affect the reading. They are very sensitive to temperature and humidity changes. So, sometimes it becomes necessary to control the working environment where the air gauges are used. Now, let us study what are the various applications of air gauging. These air gauges they are used for dimensional control of aerosol spray nozzle and they are used to control the gun barrels. They are also used to control the dimensions of knee prosthesis. They are very much used for dimensional control of mechanical parts such as bore size and bore shape faults can be detected. That means, straightness of tubes for hydraulic cylinders. For example, we have a hydraulic cylinder with a bore. So, whether the bore is straight or whether the bore is perpendicular with respect to face or not such things can be checked. They are used to check the core shock absorbers and perpendicular to the bore to face. So, such features can be easily checked using the air gauges. And dimensional control of mechanical parts such as engine cylinder linings can be checked. These engine cylinder internal surfaces they require very good and fine surface and no scratches should appear on the internal surface of the liners. So, in such cases since the air gauge is non-contact type they are very much used to inspect the lining cylinder lining internal surfaces. Now, it is possible to measure the multiple bores at a time and distance of the bore from a face. For example, we have a bore and then we have a surface here. So, what is the distance between this surface and the bore distance between bore and this face can be checked and it is possible to measure the average diameter by having multiple jets. It is possible to get the average size of the bore and these air gauges they are used for inspection of castings, injection molded or welded parts, tanks, piping and hydraulic nozzles and brake system components are checked by using air gauges. They are also used to check spark plates, gas appliance valves, sunlight valves, fire valves, stationary and rotating joints etc. Testing of carburetor and gas appliance jets, injectors, injection molding nozzles are checked by using air gauges, burners and nozzles are checked, shock absorber nozzles are checked by air gauges, cast iron and injection molded transfer channels, outlets of complex bores are easily checked by air gauging systems and mean diameters of extruded tubes, cigarettes etc. they are inspected by using air gauges. Adjustment of pneumatic and hydraulic operators, needle regulating the flaps and piston cylinder play such things are checked by using air gauges. So, in this picture we can see a cigarette gauge, cigarette is placed here and it is checked for its dimensions. Now, we can see some of the applications the what is the height of the component can be easily checked by using air gauges and we can check the whether the plate is straight or not whether there is any curvature in the surface such things can be checked and here we can see a system where in the we can easily check the squareness of bore to face whether this bore is perpendicular to the face can be checked and the squareness whether this vertical surface is square with the bottom surface such things can be checked and then what is the depth of bore in the depth of blind hole in the workpiece can be easily checked and tubing straightness can be checked by inserting the gauging gate into the tube and short bore squareness can be checked outside diameters can be easily checked squareness the bore with the face can be checked taper in the component can be checked the flatness crew width inside diameter outside diameter such things can be easily checked using air gauges and this shows a system where in the two point out of roundness can be checked and here this three point out of roundness can be checked now you can see here the measurement of groove width so this what is the groove width can be easily checked using air gauges and this is a air plug for measuring the taper you can see the jets air jets here and the connections ports for connecting the pressurized air and this shows two nozzle air plug so there will be two nozzles in the opposite sides width masters one master to set upper limit and other master to set the lower limit of the component so this set can be used for measuring the inside diameter in the component now custom made gauges are available based upon the particular application these air gauges are made and you can have plug gauges and also ring gauges which can be manufactured as per the specifications of taper air jet ring gauges can be made multi diameter a jet ring gauges can be made for simultaneous measurement of several concentric boards so we can see here hand caliper gauges so adjustable hand caliper gauges we can keep the port piece here and we can check whether the size is ok or not so these are adjustable hand caliper gauges they are available with they can be made in different sizes 5 to 38 millimeter size 32 to 60 years so like this with different ranges these can be manufactured and you can see here air ring gauges for measurement of external diameter so we can see the port for connecting the compressed air and you can see the jets here air jets so what piece can be inserted and the external size measurement can be easily made now this shows air ring with guide post for guiding the gauge now here I can see a special type of air gauging system wherein inside we have two portions one is the outside portion outside ring which is made out of aluminum outer ring and inside portion is made out of carbide in the ring so this outer ring is made by aluminum to reduce the weight of the gauge now for external measurement of the external feature measurement u block gauges are available they will be like this so this is the body of u block gauge and it's the table on which the workpiece can be mounted and here we have jets so we can have jet here so where air will escape and air connection can be made here and here we can place the workpiece depending upon the clearance we can get the reading from the float position or if we are using back pressure type the pressure gauge will indicate what is the size so this is a u block gauge air gauge for external feature measurement now you can see some air plug gauges for internal measurement here so these plug gauges they are inserted into the bore and air escapes here depending upon the clearance we can get the reading so the air plug gauges with different sizes are available and we can have air plug gauges in this range 3 to 160 millimeter even bigger says gauges are available we can see a special air plug gauge so we have a split type air plug gauge so where in the weight of the plug gauge can be reduced accuracy between 25 to 200 micrometer is possible with such air plug gauges now let us study about another type of comparator which is known as fluid displacement comparator so we can see the construction of fluid displacement comparator in this diagram there is a chamber in which low viscosity liquid is filled one end of the fluid chamber is having a dag front to which a plunger is fixed at the other end of the fluid chamber we have a fine bore capillary tube when the diaphragm deflects the liquid rises in the capillary tube and there is a scale to note down the level of liquid in the capillary tube we can also have two pointers to indicate upper limit of the workpiece and lower limit of the workpiece now during the usage of fluid displacement comparator what we have to do is we have to insert the workpiece between the table and the plunger depending upon the actual size of the workpiece whether it is greater than the desired size or lower than the desired size this plunger will move up and down accordingly the liquid level in the capillary tube will rise or fall now if the workpiece size is equal to the desired size then the level of the liquid in the capillary tube in the tube will be in the middle position to indicate that that is the that is the desired position that means the deviation of the workpiece from the desired size is zero now when the size of the workpiece is smaller than the desired size then the plunger will move down and the capillary the level of liquid in the capillary tube will move down if the size of the workpiece is greater than the desired size then the liquid level in the capillary tube will move up if the liquid level in the capillary tube is beyond the upper limit or lower than the lower limit then the workpiece is rejected now the magnification of such a system is a chamber cross-sectional area divided by capillary tube cross-sectional area by adjusting these values we can construct fluid displacement comparator of the desired magnification now let us study what are the various applications of fluid displacement comparator so these comparators are used in mass production for quick inspection the operators will insert the workpieces between plunger and table and then they will just observe what is the level of liquid in the capillary tube and then they take the decision whether the workpiece is acceptable or not it can be used as a laboratory standard from which working gauges or inspection inspection gauges can be set these fluid displacement comparators are used for inspecting newly purchased gauges they can also be used as working gauges to prevent workpiece spoilage during the manufacturing of the workpieces to maintain the required tolerances on the workpieces these can be used in the selective assembly of parts where parts are graded in three or more groups depending upon their tolerance now let us conclude the module 10 lecture 3 in this lecture we discussed about the different aspects of pneumatic comparators we discussed about the need of year gauging systems and working principle of year gauging systems we also discussed about the different circuits circuits used in gauges such as back pressure circuit or the fluid flow circuit we also discussed about the various components used in the year gauging systems such as amplifiers and then different types of gauges and different types of amplifying systems and we also discussed about a commercially available solids gauge system we discussed about the various important characteristics of year gauging systems what are the advantages and disadvantages of the year gauging systems we also discussed about the various applications of year gauging systems and the different fields like manufacturing field and how they can be used to check prosthetic toolings also we discussed like a plug and ring gauges we also saw about the fluid displacement comparator and what are the uses of fluid displacement comparator so with this we will conclude module 10 lecture 3 thank you