 Hello, students. I am Dr. Prakash Sarunke from Valtran Institute of Technology Mechanical Engineering Department. Today, let us discuss mechanical comparators. At the end of this session, students will be able to explain principle and working of dial gauges or dial indicator, which is one of the mechanical comparator. Dial gauge or dial indicator is one of the most widely used mechanical comparator. We can refer one. Yes, figure one. So, this is the dial indicator. So, if we see that say it uses this dial and this rotating pointer as a display unit, hence the name is given as dial gauge. It has a sensing device in the form of a plunger or stylus, which senses normally a linear displacement, again with reference to say this figure. So, this is the cement plunger. So, that is a sensing element and that will be sensing a displacement, linear displacement. It employs some mechanical means such as gears or levers, so which is not seen in the figure. So, that is inside the casing. So, that gears or lever mechanism is used for magnification. And say normally the dial gauge is mounted on some stand or some suitable base. Now, it is not shown in this particular figure. According to IS2092, dial gauges have been divided into two categories, type one and type two. And this categories are made for general engine purposes depending upon the movement of the plunger. So, let us see. Type one dial gauge has the plunger movement parallel to the plane of dial as shown in figure two. So, this is figure two. So, this is the plunger, this is the plunger in two views. This motion of the plunger, so that is parallel to the plane of dial. So, this is the plane of dial. And in type two, say this motion of the plunger is perpendicular to dial, perpendicular to dial. I hope you understood the difference. Now, these dial gauges are manufactured in two grades, grade A and grade B with total plunger movement or lift of 3, 5 and 10 mm. So, these are the three, of course, different ranges. Now, normally working of the dial gauges may have either, dial gauges, I mean display element, may have either sector shaped or circular shaped. There are several mechanisms used for magnification of the displacement. Lever type, gear type or combination of these two. So, these are very common. This mechanism of the instrument is housed in a metal casing we have seen already this construction. Normally there are two pointers and two circular scale. Large scale is graduated in 100 divisions. Each division, say for a typical dial gauge is of 0.01 mm. However, for more accuracy, for more accurate gauges it may be 0.001 mm. And there is a small circular scale and small pointer say that indicates the number of revolutions completed by the large pointer. Now, dial indicator with gear and pinion mechanism. So, which are these are very commonly used. So, we are studying this particular mechanism. As seen in figure 4, this type of dial indicator consists of a plunger sliding in bearings and carrying a rack on it. So, let us refer figure 4 then we will understand. Yes. So, this is the plunger, this is the plunger. So, this is of course figure of mechanism only inside. So, this is the plunger and it is sliding in say this particular cement bearings, in this particular bearings. And here if you see a rack teeth are cut on the plunger or that is attached to the plunger. So, this is the plunger. This is a plunger which moves in this particular cement direction. The rack meshes with pinion P1. Now, let us try to understand what will be the function of this rack and pinion. So, this here, this is pinion P1. So, which meshes with this particular rack. Now, what is the function of rack and pinion? Can you tell anybody of you just think? Yes. So, rack and pinion. So, this particular mechanism is used say to convert the linear motion of the plunger into rotary motion of the pinion. So, that will be convenient. Now, this pinion P1 drives gear G1 and the motion is further amplified through series of gears. We can see here that say this is the gear G1. So, that will mesh with another cement pinion. So, that pinion is mounted on a shaft on which one more gear is there. So, this gear will in turn again drive one more pinion. So, likewise say there will be amplification through series of gear turns, series of gear turns. And in each stage, say there will be magnification in the ratio of say Ng1 divided by Np1. So, where N indicates the number of tooth number of tooth or there can be you can also take diameter of that particular gear. So, that will be having a larger diameter as compared to pinion. Then again gear 2 and say Ng2 divided by Ng1. So, like that. So, gear pairs. So, that every pair. So, that will add multiply in the magnification. So, as we go on adding number of pairs. So, there will be multiplication say in the magnification magnification. Now, apart from these gear trains say there is one coil spring that you can see at the bottom. So, which is attached to the cement pointer. So, that restores the say it is attached to the plunger sorry. So, that is that restores the cement position of the cement plunger. So, let us see say here yes. So, this is the coil spring. So, this will say as the plunger moves upwards say this particular I mean a kind of diaphragm. So, that will push say this spring and the spring will be in tension that will again bring back the plunger it is in its original or initial position. Similarly, there is one more spring here which is called as hair spring hair spring edge. Now, this spring say that is attached to those gears. So, this will help reducing the backlash. So, that will cement that will be working in this I mean plane in motion circular and say that will press the gears against the I mean another machine gear and that backlash will be removed. So, rag guide. So, that is one more element in this kind of mechanism. So, it ensures linear motion of the plunger as well as preventing the rotation. So, if we see this rag guide yes. So, this is the guide. So, this is the rag guide. So, this I mean rod. So, that will pass through the guide. So, that will ensure linear motion of the this plunger as well as say that sometimes plunger will try to rotate in this same direction. So, that rotation is also some in prevented due to this rag guide. Now, last pointer is mounted on the last pinion in the gear train. If we see here say this is the last cement pinion say pointer last pointer. So, that will be so that will have a maximum motion. So, that will be mounted on this last cement pinion of the cement gear train and small revolution contour pointer will be mounted on some of the cement pinion here or here. So, in so which will have certain correct ratio say bearing to this I mean one complete revolution of this pointer will move one division of this particular pinion like that ok. So, this is the working mechanism of gear and cement pinion type of dial gauge. Now, there are some constructional features of dial gauge let us try to understand them. So, one is rotatable bezel if we see any dial gauge you will find say this particular bezel. So, this is rotatable this is rotatable bezel. So, this bezel will enable us to I mean adjust the motion of the I mean position of the pointer to 0 pointer at any position. So, we can rotate and that say 0 can be adjusted to say this particular position. Then the contact points the plunger has at the end has the contact point which is normally spherical hardened steel contact point. So, to have I mean lesser wear and sometimes it may be detachable. So, it can be replaced with another. Then there are tolerance pointers. So, there are two pointers which are not rotating which are not rotating. However, they can be moved say along the dial independently my beans of the knobs independent means two tolerance pointers can be moved independent of each other. So, they can be set as upper limit and lower limit depending upon the tolerance values. So, by specifying the limits on both sides of the 0 the dial gauge can also be used as a limit gauge. So, for fast operations now lever attachments. So, these attachments enable to make internal measurements and to enable gauge some awkward corners and grooves etcetera say with ease. Apart from that there are stands and holders. So, this help in positioning and clamping of dial gauge as limitations say I have taken the references from textbook of metrology by Mahajan and Nanpatra and company private limited thanks to them and thank you.