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Question and AnswerSubject: Instrumentation1. Define Absolute pressureThe force exerted by the fluid per unit area of the wall of the container is called the absolute pressure. 2. Define Gauge pressureIt is the difference between the absolute and the local atmospheric pressure.3. Define vacuum pressureVacuum pressure?is the amount by which atmospheric pressure exceeds the absolute pressure.4. Give some units of pressurePascal,psi,kg/cm2,bar etc.5. What are the types of manometers?U – tube manometerWell type manometerInclined type manometerRing balance manometerMicro manometer6. State the principle of U- tube manometerThe?U-tube manometer?is the simplest measuring instrument used for gauge pressure measurement by balancing the pressure against the weight of a column of liquid.7. What are the types of elastic pressure gauges?Bourdon tubesBellowsDiaphragms8. Explain the principle of Bourdon tube pressure gaugeBourdon tube is a device that senses pressure and converts the pressure into displacement. Since the bourdon tube displacement is a function of the applied pressure it may be amplified and indicated by a pointer.9. What are the advantages and disadvantages of bellows?Advantages:Simple constructionModerate priceUseful for measurement of low, medium, high pressures.Used to measure absolute, gauge, differential pressuresDisadvantages:Not suited for dynamic measurements.Errors will occur10. State the principle of DiaphragmsThe pressure to be measured is applied to the diaphragm, causing it to deflect. That deflection is being proportional to the applied pressure.11. What are the types of diaphragms?Flat typeCorrugated type12. State the principle of LVDT and STRAIN GAUGELVDT:The differential output voltage of the secondary winding of the?LVDT?is proportional to the displacement experienced by the mass caused due to acceleration on the Core; the differential output voltage becomes a measure of acceleration.Strain Gauge:When the?strain gauge?is stretched or compressed, its resistance changes on the account of the fact that both length and diameter of the strain gauge changes. This change in resistance will be proportional to the torque in the shaft.13. State the principle of capacitive pressure transducerThe output of a parallel plate capacitor depends on the gap between its movable and fixed plates. Due to pressure, if the gap between the plates is altered, its capacitance also changes. This change in capacitance becomes a measure of pressure.14. Write the advantages and disadvantages of capacitive pressure transducerAdvantages:Simple constructionUseful for measurement of low, medium, high pressures.Used to measure absolute, gauge, differential pressuresDisadvantages:Errors will occur15. State the principle of piezo-resistive pressure sensorWhen a wire is subjected to pressure from all sides its electrical resistance changes. This change in resistance occurs due to the distortion produced in the crystal when subjected to external pressure.16. What are the applications of piezoresistive pressure sensor?Household appliances – washing machine, vacuum cleanerAutomotive appliances – oil level, gas levelBiomedical appliances – blood pressure measurement17. State the principle of Mc leod gaugeCompression of a sample of the low pressure gas to a level which is sufficiently high so that it can be read with the use of a simple?manometer.18. What are the advantages and limitations of Mc leod gaugeAdvantages:?Independent of gas compositionLinear relationship existsDisadvantages:It should obey boyle‘s law.It cannot give a continuous output.19. State the principle of thermal conductivity gaugesWhen a?conductivity wire?gets heated electric current flows through it. The rate at which heat is dissipated from this wire depends on the conductivity of the surrounding media.20. What are the types of thermal conductivity gauge?Pirani gaugeThermocouple type conductivity gaugeIonization gauge ................
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