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Utsav mmm
This document describes the working principle and components of a pneumatic comparator. A pneumatic comparator uses differences in air pressure to precisely measure dimensions. It works by supplying compressed air through an orifice, where it escapes through restricted spaces and exerts back pressure. Variations in back pressure correspond to changes in dimensions as small as 0.002mm. The comparator has advantages like low cost, lack of mechanical wear, and ability to detect tapers and oval shapes. However, it is sensitive to temperature/humidity and requires auxiliary equipment.
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Utsav mmm
- 1. MECHANICAL MEASUREMENT AND METROLOGY PNEUMATIC COMPARATORS BY: UTSAV SHARMA 150010102059
- 2. CONTENT • INTRODUCTION • WORKING •ADVANTAGES • DISADVANTAGES
- 3. PRINCIPLE • It workson the principle of pressure difference generated by the air flow. Air is supplied at constant pressure through the orifice and the air escapes in the form of jets through a restricted space which exerts a back pressure. The variation in the back pressure is then used to find the dimensions of a component.
- 5. WORKING • As shownin Figure (a) the air is compressed in the compressor at high pressure which is equal to Water head H. The excess air escapes in the form of bubbles. Then the metric amount of air is passed through the orifice at the constant pressure. Due to restricted area, at A1 position, the back pressure is generated by the head of water displaced in the manometer tube
- 6. WORKING • To determinethe roundness of the job, the job is rotated along the jet axis, if no variation in the pressure reading is obtained then we can say that the job is perfectly circular at position A1. Then the same procedure is repeated at various positions A2, A3, A4, position and variation in the pressure reading is found out. Also the diameter is measured at position A1 corresponding to the portion against two jets and diameter is also measured at various position along the length of the bore.
- 7. WORKING • Any variationin the dimension changes the value of h, e.g. Change in dimension of 0.002 mm changes the value of h from 3 to 20 mm. Moderate and constant supply pressure is required to have the high sensitivity of the instrument.
- 8. ADVANTAGES 1. It ischeaper, simple to operate and the cost is low. 2. It is free from mechanical hysteresis and wear. 3. The magnification can be obtained as high as 10,000 X. 4. The gauging member is not in direct contact with the work. 5. Indicating and measuring is done at two different places. 6. Tapers and ovality can be easily detected. 7. The method is self cleaning due to continuous flow of air through the jets and this makes the method ideal to be used on shop floor for online controls.
- 9. DISADVANTAGES • Disadvantages: 1. Theyare very sensitive to temperature and humidity changes. 2. The accuracy may be influenced by the surface roughness of the component being checked. 3. Different gauging heads are needed for different jobs. 4. Auxiliary equipments such as air filters, pressure gauges and regulators are needed. 5. Non-uniformity of scale is a peculiar aspect of air gauging as the variation of back pressure is linear, over only a small range of the orifice size variation
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