Pressure Sensors
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Transcript of Pressure Sensors
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PRESSURE SENSORS
By
Jean Raynell Bello
Khazel Bustillo
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BASIC TERMS
Pressure force applied over a surface area
Fluid any substance that can flow
Pressure sensor devices designed to accurately detect the magnitude of external applications.
Sensitivity measure of the change in output in response to a change in input
Accuracy specifies the maximum error to be expected from a device
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PRESSURE SENSORS
They can alternatively be called
pressure transducers
pressure transmitters
pressure senders
pressure indicators
Piezometers
and manometers, among other names.
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PRESSURE SENSORS
It is important that the pressure sensor used be able
to give accurate and precise readings as needed for a long period of time without need for maintenance
to endure the conditions of the system.
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PRESSURE SENSORS
Several factors influence the suitability of a particular pressure sensor for a given process:
the characteristics of the substances involved in the process
the environmental conditions of the system
the pressure range of the process
the level of precision and sensitivity required in measurements.
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THEORY
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TYPES OF PRESSURE
Absolute Reference
Pre
ssu
re
0
Gage
Pressure Total
Pressure
Reduced (or Vacuum)
Pressure
Absolute
Pressure
Atmospheric Reference
(Standard Atmospheric Pressure)
Barometric
Pressure
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PRESSURE-MEASURING DEVICES
There are two types of measuring devices:
Mechanical Pressure Transducer and elements
Electrical Pressure Transducer and elements
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MECHANICAL
Bourdon-tube
As pressure is applied internally, the tube straightens and returns to its original form when the pressure is released
The tip moves with internal pressure and is converted with a pointer onto a scale
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MECHANICAL
Bourdon-tube
Advantages:
Inexpensive
Wide operating range
Fast response
Good sensitivity
Direct pressure measurement
Disadvantages:
For indication only
Hysteresis on cycling
Sensitive to temperature variation
Vulnerable to shock and vibration
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MECHANICAL
Helix and Spiral tubes
The pressure causes the tube to straighten out
The degree of its uncoiling is linked to a pointer that indicates the pressure reading
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MECHANICAL
Helix and Spiral tubes
Advantages:
Increased accuracy and sensitivity
Advantage over the Bourdon-tube as there are no movement losses due to links and levers
Disadvantages:
Very expensive
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MECHANICAL
Spring and Bellows Bellows made up of series
of folds which allow expansion. One end is fixed while the other moves in response to the applied pressure
Spring opposes the applied pressure and a linkage connects the end of the bellows to a pointer for indication
This device is used for ON/OFF controls
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MECHANICAL
Spring and Bellows
Advantages: Simple construction
Easily maintained
Inexpensive
Disadvantages: Sensitive to temperature
variation
Work hardening of bellows
Hysteresis
Poor over range protection
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MECHANICAL
Diaphragm Used as a means of
isolating the process fluids or for high pressure application
Provides pressure measurement with electrical transducers
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MECHANICAL
DiaphragmAdvantages:
Simple construction
Easily maintained
Inexpensive
Disadvantages: Sensitive to temperature
variation
Work hardening of bellows
Hysteresis
Poor over range protection
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MECHANICAL
Manometer
Pressure measured are applied to the open ends of the tube
Difference in height will be read as the pressure difference
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MECHANICAL
Manometer
Advantages:
Simple operation and construction
Inexpensive
Disadvantages:
Low pressure range
High pressure range requires mercury
Readings are localized
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MECHANICAL
Single and Double Inverted Bell
It measures the pressure difference in a compartment on each side of a bell-shaped chamber
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ELECTRICAL
Strain gauge
Uses semiconductor chip to measure pressure changes
Change in pressure also causes a change in resistance as the metal is deformed
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ELECTRICAL
Strain gauge
Advantages: Wide range
Accuracy of 0.1%
Small in size
Stable with fast response
No moving parts
Disadvantages: Temperature sensitive
Thermo-elastic strain causes hysteresis
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ELECTRICAL
Vibrating Wire Consists of an electronic
oscillator which causes a wire to vibrate at its natural frequency under tension
As the pressure changes on the diaphragm, so does the tension on the wire which affects the frequency on the wire
Frequency changes then cause pressure changes
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ELECTRICAL
Vibrating Wire
Advantages:
Good accuracy and repeatability
Stable
Low hysteresis
High resolution
Absolute, gage, or differential measurement
Disadvantages:
Temperature sensitive
Affected by shock and vibration
Physically large
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ELECTRICAL
Piezoelectric
Pressure sensing is applied to crystals that becomes elastically deformed upon application
When a crystal deforms, it generates an electric charge signals
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ELECTRICAL
Piezoelectric
Advantages: Accuracy 0.0075%
Very high pressure measurement
Small in size
Fast response
Self-generate signal
Disadvantages: Dynamic sensing only
Temperature sensitive
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ELECTRICAL
Capacitance
Pressure measurement involves sensing the change in capacitance that results from the diaphragm movement
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ELECTRICAL
Capacitance
Advantages:
Accuracy 0.01 to 0.2%
Wide range
Linearity
Fast response
Disadvantages:
Temperature sensitive
Vibration
Limited overpressure capability
Costly
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ELECTRICAL
Optical Used to measure the
movement of the diaphragm due to pressure
An opaque vane is mounted to the diaphragm and moves in front of an infrared light beam
As the light is disturbed, the received light on the measuring diode indicates the position of the diaphragm
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ELECTRICAL
Optical
Advantages:
Temperature corrected
Good repeatability
Negligible hysteresis
Disadvantages:
Expensive
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