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High Pressure and Vacuum Measurement 2007-CHEM-21 Presented to: Sir Naveed Ramzan

High Pressure and Vacuum Measurement 2007-CHEM-21 Presented to: Sir Naveed Ramzan. Pressure. Pressure is defined as force per unit area. P=F/A Pressure exceeding 1,000 psig is considered as High pressure. Pressure below 14.7 psig is considered as vacuum. High Pressure Measurement Devices.

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High Pressure and Vacuum Measurement 2007-CHEM-21 Presented to: Sir Naveed Ramzan

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  1. High Pressure and Vacuum Measurement 2007-CHEM-21Presented to:Sir Naveed Ramzan

  2. Pressure Pressure is defined as force per unit area. P=F/A Pressure exceeding 1,000 psig is considered as High pressure. Pressure below 14.7 psig is considered as vacuum.

  3. High Pressure Measurement Devices • Button diaphragm repeater • Helical bourdon tube • Dead weight tester • Bulk modulus cell • Manganin pressure cell • MgO Interferometric sensor

  4. The bulk modulus cell The bulk modulus cell comprises of • Hollow cylindrical steel probe, • Thick-walled steel cylinder, • The cell body , • Threaded retainer, • Stem. Suitable for ranges from 0-50,000 psi to 0-200,000 psi Hysteresis of 0.5 % and overall accuracy of 1.0 %.

  5. FOXBORO Bulk modulus cell.

  6. MgO Interferometric sensor “A high pressure sensor based on the shift of the interference peaks of MgO etalon” MgO Interferometry is a method based on optical interferometry. Pressure dependencies of the refractive index of MgO is up to 10 GPa.

  7. Typical interference pattern of the MgO etalon inside DAC

  8. Manganin High Pressure Sensor “The Manganin cell depends on the change in the resistance of the coil of wire when it is exposed to high pressure. The change in the resistance is measured by the bridge.” The pressure coefficient may vary as much as 10 % depending on the composition of sample.

  9. Cont… The wire constituting a pressure gauge be free from internal strain. The wire is wound in the form of helix. The wire has a pressure sensitivity of 1.65 X 10-7 ohms/psi and 120 ohm resistance at atmospheric pressure.

  10. Button Diaphragm repeater Pressure repeater which generates an air signal that is about 1/200 of the process Pressure. Ranges 0-150 psig to 0-10,000 psig Accuracy is 0.5 to 1% full scale. Plastic extrusion and synthetic fiber industry

  11. Dead weight tester • Calibration of bourdon gauges. • Absolute measuring device and utilizes Pascal’s law.

  12. Cont… 1.Hand Pump 2.Testing Pump 3. Pressure Gauge to be calibrated 4.Calibration Weight 5.Weight Support 6. Piston 7.Cylinder 8. Filling Connection.

  13. Vacuum Measurement Widely used in the processing of food, drugs, and chemicals. Pressure below 14.7 psig is considered as vacuum.

  14. Methods for measuring low pressure • Momentum gauges • Thermal gauges • Viscosity gauges • Mechanical gauges

  15. Knudsen vacuum gauges Insensitive to the gas Composition. Ranges 10-8 to 10-2 Torr. Fixed plates temperature Tf Movable vane temperature To

  16. Pirani ( Resistive Wire ) Vacuum gauge Measures the vacuum pressure through the change in thermal conductance of the gas. Filament is made up of either tungsten or platinum wire. Range from 10-5 to 1 Torr.

  17. Thermocouple type gauges

  18. Hot cathode Gauges A HCG boils electrons from a hot filament and accelerates them towards a cylindrical grid cage. As the electrons traverse the space enclosed by the grid, which is fully open to the vacuum chamber, they collide with gas molecules ionizing some of them. A fine wire located at the center of ionization volume collects the resulting cations producing a current proportional to the gas density. At constant temperature, the collector current is proportional to the gas pressure.

  19. Cont… Range of a conventional Bayard Alpert gauge extends between 10-3 to 10-10Torr.

  20. Cold-Cathode Ionization gauges All CCG utilize crossed electric and magnetic fields to trap electrons. The electron plasma is responsible for Ionization. At pressure below 10-4 Torr. The discharge is practically pure electron plasma.

  21. Typical operating range of CCG 10-2 to 10-9 Torr

  22. References • Emily Raymond Riegel, “Chemical Process Machinery” Second Edition (1953) Reinhold Publishing Corporation • D. Patranabis, “Principles of Industrial Instrumentation “McGraw Hill Publishing Company New Delhi India • Curtis D. Johnson, “Process Control Instrumentation Technology “Seventh Edition, Pearson Education New Delhi India. • J. M. Lafferty, Ed, “Foundation of Vacuum Science and Technology”, (1988) John Wily and Sons, NY. • R. N. Peacock, N. T. Preacock, and D. S. Hauschulz, “Comparison of Hot Cathode and Cold Cathode Ionization Gauges”, J. Vac. Sci. Technol. A 9(3) (1991) 1977. • Nagamitsu Yoshimura “Vacuum technology: practice for scientific instruments “ Page. 205 • K. Krishnaswamy, S. Vijayachitra, “Industrial Instrumentation” Edition 1st (2005) New Age international Publishers. New Delhi. India

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