Measurement Pressure
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A presentation On Pressure Measurement By D K Dey Asstt Professor , JIPT
description
pressure measurement
Transcript of Measurement Pressure
A presentation On
Pressure Measurement
By D K DeyAsstt Professor , JIPT
U Tube invented by Christian Huygens in 1661
Liquid column gauges consist of a vertical column of liquid in a tube whose ends are exposed to different pressures
The difference in fluid height in a liquid column manometer is proportional to the pressure difference.
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Pressure Measurements
The Pressure Measurement in Thermal Power Station ranges from less than atmospheric at condenser to hydraulic test pressure of boiler.
Pressure Measurement is made for :a. Steam / Water Pressure b. Fuel oil / Lubricating Oil Pressure c. Air Flue Gases Pressure d. Hydrogen Pressure etc
Pressure Measurement Many Techniques used
Types of Measurement• Absolute Pressure• Guage Pressure• Differential Pressure
Pressure Measurement Static pressure is uniform in all directions, so pressure
measurements are independent of direction in an immovable (static) fluid. Flow, however, applies additional pressure on surfaces perpendicular to the flow direction, while having little impact on surfaces parallel to the flow direction. This directional component of pressure in a moving (dynamic) fluid is called dynamic pressure.
An instrument facing the flow direction measures the sum of the static and dynamic pressures; this measurement is called the total pressure or stagnation pressure. Since dynamic pressure is referenced to static pressure, it is neither gauge nor absolute; it is a differential pressure.
Pressure Units
• Pascal • Bar• Atmosphere
1 Pa = 1 N/m2
1 Atm = 101325 Pa= 1.01325 Bar
Types of Pressure Sensors Absolute pressure sensor
measures the pressure relative to perfect vacuum pressure (0 PSI or no pressure).
Gauge pressure sensorpressure relative to a given atmospheric pressure
Vacuum pressure sensormeasure pressure less than the atmospheric pressure
Differential pressure sensormeasures the difference between two pressures
Pressure Sensing Technology
Force collector type : use a force collector (such a diaphragm, piston, bourdon tube, or bellows) to measure strain (or deflection) due to applied force (pressure) over an area.
Piezoresistive Type : Uses the piezoresistive effect of formed strain gauges to
detect strain due to applied pressure.
Capacitive Type : Uses a diaphragm and pressure cavity to create a
variable capacitor to detect strain due to applied pressure.
Pressure Sensing Technology
Optical Type : use of the physical change of an optical fiber to detect strain
due to applied pressure.
Potentiometric Type : Uses the motion of a wiper along a resistive mechanism to
detect the strain caused by applied pressure..
Resonant frequency Type : Uses the changes in resonant frequency in a sensing
mechanism to measure stress, or changes in gas density, caused by applied pressure.
Pressure Sensing Technology
Thermal Conductivity Type : Uses the changes in thermal conductivity of
a gas due to density changes to measure pressure. A common example of this type is thePirani gauge.
Ionization Type : Measures the flow of charged gas particles
(ions) which varies due to density changes to measure pressure. Common examples are the Hot and Cold Cathode gages
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Pressure Sensors Measures pressure , typically of
gases or liquids
Usually acts as a transducer
Generates an electrical signal as a function of the pressure imposed.
used for control and monitoring of everyday applications
Are also called pressure transducers, pressure transmitters, pressure senders, pressure indicators and piezometers, manometers, among other names.
Pressure Guages McLeod gauge
Isolates a sample of gas and compresses it in a modified mercury manometer until the pressure is a few mmHg
Useful range: above roughly 10-2 Pa as high as 0.1 mPa
0.1 mPa is the lowest direct measurement of pressure that is possible with current technology
Pressure Guages Aneroid gauge
"Aneroid" means "without fluid,"
Can be used to measure the pressure of a liquid as well as a gas
Pressure sensing element may be a Bourdon tube, a diaphragm, a capsule, or a set of bellows, which will change shape in response to the pressure of the region in question
Useful range: above roughly 1 Pa
Pressure Switch Makes electrical
contact when a certain set pressure has been reached on its input
Types :a. Pneumatic b. Hydraulic
Pressure Transmitters• Translate low-level electrical outputs from pressure sensing devices to higher-level signals that are suitable for transmission and processing
• Can produce several types of electrical signals, including analog voltage and analog current.
• These output signals can be encoded via amplitude modulation (AM), frequency modulation (FM), or some other modulation scheme such as sine wave or pulse train.
Pressure Transmitters
All ST 3000 transmitters can provide a 4-20 mA output, Honeywell Digitally Enhanced (DE) output, HART output or FOUNDATION Fieldbus output when digitally integrated with Honeywell’s Experion® Process Knowledge System.Honeywell’s high-performance ST 3000 S100 transmitters lead the industry in:•Accuracy•Stability•Reliability•Rangeability•WarrantyIncludes Lifetime Transmitters:•Accuracy = +/-0.0375%•Stability = +/-0.01% per year•Reliability = 470 years MTBF•Rangeability = 400 to 1Lifetime Warranty = 15 years
Venturi TubesVenturi Tubes are used widely for measurement of Differential Pressure(DP) in industries were accurate DP is required.
• Venturi Tubes are designed as per BS142 on the basis of customers given fluid, flow. Temperature pressure details.
• Venturi tube has two pressure tappings of ½” BSP (f).
• M.O.C. as per fluid requirement
• Indicating instrument optional
Differential Pressure Guage
Specifications
Accuracy :± 2% ofthe FSD (Ascending)Migration :Minor from high to low portRange :0-0.25 to 0-70 bar First marking on the scale :20% of the FSDSensing element :PistonWetted parts :Body material, SS 302 spring, Case material :Stainless steel (SS 304)Dial size in inch /mm :2",2.5",3.5",4",4.5", 6” Mounting :Direct, front flangeMaximum working pressure:200/400 bar. 200 bar for Alu, Brass & 400 bar for SS bodyMaximum process temperature :8o°c /175° FBody material :Aluminum, Brass, SS 316 & Protection :IP 65/ NEMA-4
Communication protocols
a. Ethernet, DeviceNet,
b. FOUNDATION Fieldbus,
c. Process Fieldbus (PROFIBUS®), (PROFIBUS is a registered trademark of PROFIBUS International )and d. Highway Addressable Remote Transmission (HART®). HART is a registered trademark of the HART Communication Foundation.
e. RS232 and RS485 are serial, digital protocols.
f. Parallel protocols include the general-purpose interface bus (GPIB), a standard which is also known as IEEE 488.
