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Technology Training that Workswww.idc-online.com/slideshare
Pressure Measurement
By Steve Mackay –
Dean of Engineering: En...
Technology Training that Workswww.idc-online.com/slideshare
EIT Micro-Course Series
• Every two weeks we present a 35 to
4...
www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare
Topics
• Principles
• Pressure Sources
• Pressu...
www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare
Principles
• Pressure = Force per unit area
• U...
www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare
Pressure Sources
• Static Pressure
Due to weigh...
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Static Pressure
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Dynamic Pressure
Pressure VariationsPressure Va...
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Total Pressure
• Total Pressure = Static Pressu...
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Pressure Transducers - Mechanical
•Bourdon Tube...
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C-Bourdon Tube
• Bent tube will change its shap...
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C-Bourdon
• Advantages
– Inexpensive
– Wide Ope...
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C-Bourdon Pressure Element
Limitations
•Use air...
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Helix and Spiral Tubes
• With one end sealed, p...
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Helix and Spiral Tubes
•Spiral Bourdon Element
...
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Spiral/Helix tubes
Increased accuracy and sensi...
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Spring and Bellows
• Expandable element
• Free ...
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Spring and Bellows Switch
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Technical Terms
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Spring and Bellows Gauge
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Diaphragm, Bellows or Piston?
• Pressure applie...
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Refrigeration Applications
• Pulsation generate...
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Refrigeration Applications
• Simple constructio...
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Diaphragm
• Sensor measurement dependent on def...
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Simple Corrugated Diaphragm
Diaphragm Sensors
•...
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Advantages - Diaphragm
• Provide isolation from...
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Manometer
• Simplest form is U-shaped, liquid f...
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Simplest Form of Manometer
Atmospheric Referenc...
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Typical Applications
• Mainly spot checks or ca...
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Manometer
Advantages
Disadvantages
Simple opera...
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Single and Double Inverted Bell
• Measures pres...
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Inverted Bell d/p Detector
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Pressure Transducers and
Elements - Electrical
...
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Strain Gauges
• Metal wire or semiconductor chi...
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Wheatstone Circuit for Strain
Gauges
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Typical Application
• Force
Applied to diaphrag...
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Strain Gauges
• Wide range, 7.5kPa to 1400MPa.
...
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Vibrating Wire
• Electronic oscillator circuit ...
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Vibrating Wire
• Good accuracy and repeatabilit...
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Piezoelectric
• Crystals elastically deformed w...
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Piezoelectric
• Accuracy 0.075%
• Very high pre...
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Cross Section of the Rosemount
d-CellTM Sensor
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Capacitance
• Diaphragm movement causes capacit...
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Capacitance Measurement
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Capacitance
• Inaccuracy 0.01 to 0.2%
• Range o...
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Linear Variable Differential
Transformer
• Mech...
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Linear Variable Differential
Transformer
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Optical
• Opaque vane mounted to the diaphragm
...
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Optical Pressure Sensor
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Optical
• Temperature corrected
• Good repeatab...
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Installation considerations
• Location of Conne...
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Location of Process Connections
• Top of proces...
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Use of Impulse tubing
Test and Drain Valves
• B...
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Sensor Construction
Wheatstone bridge often use...
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Remote Diaphragm Seals
Corrosion is possible
Fl...
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Remote Diaphragm Seals
Large diameter minimises...
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Process Flanges
•Coplanar flange
- Becoming mor...
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Additional Hardware
• If pulsation dampeners ar...
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Overall Control Loop
•Impact
Longer response du...
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Thank You For Your Interest
If you are interest...
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Pressure Measurement

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Pressure Measurement

  1. 1. Technology Training that Workswww.idc-online.com/slideshare Pressure Measurement By Steve Mackay – Dean of Engineering: Engineering Institute of Technology
  2. 2. Technology Training that Workswww.idc-online.com/slideshare EIT Micro-Course Series • Every two weeks we present a 35 to 45 minute interactive course • Practical, useful with Q & A throughout • PID loop Tuning / Arc Flash Protection, Functional Safety, Troubleshooting conveyors presented so far • Upcoming: – Electrical Troubleshooting and much, much more….. • Go to: http://www.idc-online.com/slideshare • You get the recording and slides
  3. 3. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Topics • Principles • Pressure Sources • Pressure Transducers - Mechanical • Pressure Transducers - Electrical • Installation • Impact on overall loop • Selection Tables • The Future
  4. 4. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Principles • Pressure = Force per unit area • Units of psi, mm Hg and kPa • Absolute Pressure referenced to a vacuum • Gauge Pressure referred to one standard atmosphere • Differential Pressure compares two different pressures
  5. 5. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Pressure Sources • Static Pressure Due to weight of the molecules “pressing down” • Dynamic Pressure Relative movement when a body is moving through air
  6. 6. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Static Pressure
  7. 7. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Dynamic Pressure Pressure VariationsPressure Variations
  8. 8. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Total Pressure • Total Pressure = Static Pressure + Dynamic Pressure
  9. 9. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Pressure Transducers - Mechanical •Bourdon Tube •Helix and spiral tubes •Spring and Bellows •Diaphragm •Manometer •Single and Double Inverted Bell
  10. 10. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare C-Bourdon Tube • Bent tube will change its shape when exposed to variations in internal or external pressure • Orientation dependent for correct results • Vertical mounting • Wide Operating range
  11. 11. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare C-Bourdon • Advantages – Inexpensive – Wide Operating Range – Fast response – Good sensitivity – Direct Pressure measurement Disadvantages – Primarily intended for indication only – Non-linear transducer – Hysteresis on cycling – Sensitive to temperature variations – Limited life when subject to shock and vibration
  12. 12. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare C-Bourdon Pressure Element Limitations •Use air if calibrated for air •Use in liquid if calibrated for liquid •Bleed air from the liquid lines •Limited where there is input shock •If for Oxygen, device cannot be calibrated for oil
  13. 13. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Helix and Spiral Tubes • With one end sealed, pressure causes the tube to straighten out • Spiral suitable up to 28000 kPa • Helical suitable up to 500000 kPa
  14. 14. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Helix and Spiral Tubes •Spiral Bourdon Element •Helix Bourdon ElementHelix Bourdon Element
  15. 15. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Spiral/Helix tubes Increased accuracy and sensitivity Higher overrange protection •Disadvantages Very Expensive •Advantages
  16. 16. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Spring and Bellows • Expandable element • Free end responds to pressure • Spring used to oppose force • Linkage connects end to pointer for indication • Primarily for ON / OFF control • Provides clean contacts for electrical circuits • Responds to pneumatic or hydraulic pressure changes
  17. 17. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Spring and Bellows Switch
  18. 18. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Technical Terms
  19. 19. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Spring and Bellows Gauge
  20. 20. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Diaphragm, Bellows or Piston? • Pressure applied to actuator - Diaphragm, bellows or piston type • Piston used for hydraulic fluids at high pressure • Not used for air or water as accuracy is limited
  21. 21. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Refrigeration Applications • Pulsation generated by reciprocating refrigeration compressors • Require additional pulsation dampening
  22. 22. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Refrigeration Applications • Simple construction • Easily maintained • Inexpensive • Sensitive to temperature variations • Work hardening of bellows • Hysteresis • Poor overrange protection Advantages Disadvantages • Range into vacuum required where settings approach 0 psi • Surges of pressure can occur prior to steady state condition • Bellows and fittings are specially prepared for oxygen and nitrous oxide Application Limitations
  23. 23. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Diaphragm • Sensor measurement dependent on deflection of diaphragm • Flexible disc • Flat or with concentric corrugations • Sheet metal with high tolerance dimensions
  24. 24. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Simple Corrugated Diaphragm Diaphragm Sensors • Two main types : – Motion balanced – Force balanced
  25. 25. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Advantages - Diaphragm • Provide isolation from process fluid • Good for low pressure • Inexpensive • Wide range • Reliable and proven • Used to measure gauge, atmospheric and differential pressure
  26. 26. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Manometer • Simplest form is U-shaped, liquid filled tube • Reference and measured pressure applied to ends of tube • Difference in pressure causes difference in liquid level between sides
  27. 27. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Simplest Form of Manometer Atmospheric Reference •For water 1.0 Pa (Pascal) = 0.9807 mmH2O •For mercury 1.0 Pa (Pascal) = 133.3 mmHg
  28. 28. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Typical Applications • Mainly spot checks or calibration – Modern calibration using electronic meters • Low range measurements – Higher measurements require mercury - toxic, therefore hazardous
  29. 29. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Manometer Advantages Disadvantages Simple operation and Construction Inexpensive Range (water) Higher pressure range requires mercury Readings are localised Application Limitations Size limits operation to low range Difficult to integrate into continuous control system
  30. 30. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Single and Double Inverted Bell • Measures pressure difference between sides of bell shaped compartment • The bell instrument is used where very low pressures are to be measured, typically 0 - 250 Pa •To reference to surrounding conditions Lower compartment vented to outside Gauge pressure measured
  31. 31. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Inverted Bell d/p Detector
  32. 32. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Pressure Transducers and Elements - Electrical • Strain gauge • Vibrating wire • Piezoelectric • Capacitance • Linear Variable Differential Transformer • Optical
  33. 33. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Strain Gauges • Metal wire or semiconductor chip • Change in resistance as metal is deformed by pressure • Temperature sensitive – Temperature compensation required – Often use Wheatstone bridge
  34. 34. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Wheatstone Circuit for Strain Gauges
  35. 35. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Typical Application • Force Applied to diaphragm Through silicone fill fluid To polysilicon sensor • Reference side exposed to atmospheric pressure for gauge transmitters
  36. 36. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Strain Gauges • Wide range, 7.5kPa to 1400MPa. • Inaccuracy of 0.1% • Small in size • Stable devices with fast response • Most have no moving parts • Good overrange capability Disadvantages • Unstable due to bonding material • Temperature sensitive • Thermoelastic strain causes hysteresis Advantages
  37. 37. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Vibrating Wire • Electronic oscillator circuit causes natural frequency oscillation of wire • Wire under tension in diaphragm • Pressure changes causes changes in natural frequency
  38. 38. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Vibrating Wire • Good accuracy and repeatability • Stable • Low hysteresis • High resolution • Absolute, gauge or differential measurement • Temperature sensitive • Affected by shock and vibration • Non-linear • Physically large Advantages Disadvantages
  39. 39. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Piezoelectric • Crystals elastically deformed when force applied • Measure rate of change of deformation • Electrical output proportional to applied acceleration
  40. 40. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Piezoelectric • Accuracy 0.075% • Very high pressure measurement, up to 70MPa. • Small size • Robust • Fast response, < 1 nanosecond • Self-generated signal •Disadvantages • Dynamic sensing only • Temperature sensitive • Advantages
  41. 41. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Cross Section of the Rosemount d-CellTM Sensor
  42. 42. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Capacitance • Diaphragm movement causes capacitance change • Sensor energised by a high frequency electrical oscillator • Relative capacitance measured by bridge circuit
  43. 43. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Capacitance Measurement
  44. 44. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Capacitance • Inaccuracy 0.01 to 0.2% • Range of 80Pa to 35MPa. • Linearity • Fast response • Temperature sensitive • Stray capacitance problems • Vibration • Limited overpressure capability • Cost Advantages Disadvantages
  45. 45. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Linear Variable Differential Transformer • Mechanical wear • Vibration • Movement of high permeability material within transformer coils • Pressure transferred via diaphragm, bellows or bourdon tube Disadvantages
  46. 46. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Linear Variable Differential Transformer
  47. 47. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Optical • Opaque vane mounted to the diaphragm • Vane moves in front of infrared beam • Received light indicates position of the diaphragm
  48. 48. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Optical Pressure Sensor
  49. 49. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Optical • Temperature corrected • Good repeatability • Negligible hysteresis Advantages Disadvantages • Expensive
  50. 50. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Installation considerations • Location of Connections • Isolation Valves • Impulse Tubing • Test and Drain Valves • Construction • Temperature • Remote Diaphragm Seals • Precautions with Remote Diaphragm Seals • Process Flanges • Additional Hardware
  51. 51. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Location of Process Connections • Top of process line for gases • Side of lines for other fluids Isolation Valves Between process fluid and measuring equipment if device is to be taken out
  52. 52. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Use of Impulse tubing Test and Drain Valves • Blowdown valve needed for toxic or corrosive fluid Impulse piping • Short as possible • Self draining by sloping lines towards the process
  53. 53. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Sensor Construction Wheatstone bridge often used to compensate for temperature effects Temperature Effects Mechanical and thermal isolation Position in neck of electronics housing Away from process flange
  54. 54. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Remote Diaphragm Seals Corrosion is possible Fluid viscosity may cause clogging Process temperature is outside normal operating temperature of transmitter Fluid may solidify Fluid needs to be flushed Maintaining sanitary or aseptic conditions Making density or other measurements. NEEDS
  55. 55. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Remote Diaphragm Seals Large diameter minimises temperature effects Short capillary reduces temperature effects In two seal system use same diaphragm diameter capillary length Transmitter below lower tap when using vacuum Fluid to cope with extremes, ie: temp and pressure Fill and process fluids compatible Precautions fluid
  56. 56. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Process Flanges •Coplanar flange - Becoming more standard •Traditional flange - Traditional biplanar configurations •Level flange - Permits direct process mounting
  57. 57. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Additional Hardware • If pulsation dampeners are required the material and fill fluids must be compatible with the process fluid • Siphons of correct material required for vapours above 60oC
  58. 58. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Overall Control Loop •Impact Longer response due to material build-up on sensing element Over-ranging causing incorrect readings
  59. 59. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Thank You For Your Interest If you are interested in further training, please visit: IDC Technologies Short Courses: Two-day practical courses available to the public: http://www.idc-online.com/slideshare

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