OPTICAL COMPARATOR AND ITS WORKING

Optical Comparators have a high degree of precision and magnification is obtained with the help of light beams which have the advantage of being straight and weightless. Optical comparators , therefore, suffer less wear during usage than the mechanical type.

Optical comparators are used to magnify parts of very small size and of complex configuration that require accurate and enlarged profile. So they are widely employed in the inspection of many small parts such as needles, saw teeth , gear teeth , screw threads , etc. Since they check work to definite tolerances , they can be used to study wear on tools or distortion caused by heat treatment.

In an optical or projection comparator which is designed on the same principle as the ordinary projection lantern, an object is placed before a light source , and the shadow of the profile is projected at some enlarged scale on a screen where it is compared to a master chart or drawing. Interchangeable projection lenses which serve to magnify the image give accurate magnifications from 5 to 100 times.

Light is collected from a suitable source by a circular swiveling mirror placed at the left-hand side near the eyepiece. This light which is directed on to the 90 prism shown between H and E illuminates the scale incorporated in E and its image is reflected downwards by the mirror D through the lens onto the mirror B. This mirror , which is carried on a Pivot and rests on the top of the measuring finger A, reflects the image of the scale back the way it came. The mirror is so arranged that the return path offset slightly to enable it to be observed through the eye-piece H . In diagram C represents a fine adjustment ring for vertical position and G a final adjustment for zero setting.

In setting the comparator, the center zero on the scale is level with the zero mark in the eye piece. Any variation of the work causes the measuring finger A to tilt the mirror B and displaces the reflection of the scale from its mid position. The accuracy of measurement of this type of instrument is usually limited to 0.001 mm, and one of such division appears to occupy a space of about 2 mm. The scale movement provided (+) or (-) variation on each side of the zero is about 0.02 mm.

Working of Mechanical optical comparator

Other Common Types of comparators :

* Mechanical Comparators.

* Electrical Comparators.

* Pneumatic Comparators.

Comments

THROTTLE GOVERNING OF STEAM TURBINES

Steam Pressure at inlet to a steam turbine is reduced by throttling process to maintain the speed of the turbine constant at part load and hence this method of governing is called "Throttle Governing". Construction : Throttle governing system consists of a centrifugal governor, a lever , an oil pump , a pilot piston , control valve , a relay piston and a throttle valve. The throttle valve is moved by a relay piston. The relay piston is actuated by pilot piston control valve. There are two piston valves covering ports in the pilot piston control valve without any overlap. These piston valves are operated by lubricating oil supplied by a gear pump at 2 to 4 bar. The oil returns to the drain from this chamber. Working : When the turbine works on full rated load, the throttle valve will remain open. When the load is decreased, the energy output of the turbine becomes in excess and the turbine shaft speed increases. Hence, governor sleeve will lift. The upward movement of the

ELECTRICAL COMPARATORS AND ITS WORKING

Electrical Comparators are used as a means of detecting and amplifying small movements of a work contacting elements. An electrical comparator consists essentially of a pick-up head or transducer for converting a displacement into a corresponding change in current and a meter or recorder connected in the circuit to indicate the electrical change, calibrated to show in terms of displacement. Generally, an amplifier is needed to provide the requisite sensitivity and to match the characteristics of different parts of the circuit. Electrical comparators can be classified according to the electrical principle used in the pick-up head. Most of the comparators use either a differential transformer, an inductance bridge, a strain gauge or a capacitor as a means of detecting movement of the gauging element. There are different types of electrical comparators. One kind called an electrolimit gauge is used to check or measure the outside diameter of a roll. The object to be checked is place

Advantages And Disadvantages Of Air Refrigeration System :

Advantages Of Air Refrigeration : 1. The refrigerant used namely air is cheap and easily available. 2. There is no danger of fire or toxic effects due to leakages. 3. The weight to ton of refrigeration ratio is less as compared to other systems. Disadvantages Of Air Refrigeration : 1. The quantity of Refrigerant used per ton of refrigeration is high as compared to other systems. 2. The COP of the system is very low. Therefore running cost is high. 3. The danger of frosting at the expander valves is more as the air contains moisture content.

Mechinopedia For Mechanical Engineers

Search This Blog