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7/22/2019 3237 Jos Ee Instr_S108 05 Tekanan
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1Instrumentasi Sistem Pengaturan - 05
Sistem Instrumentasi
Pengukuran Tekanan
(Measurement of Pressure)
Ir. Jos Pramudijanto, M.Eng.
Jurusan Teknik Elektro FTI ITSTelp. 5947302 Fax.5931237
Email: [email protected]
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Where do we need pressure
measurements?Pressure driven equipment (IC engines, turbines, etc.)
Pneumatic or Hydraulic mechanical elements
Biomedical applications (Blood Pressure, Barometric Chambers)
Losses in pipes and ducts energy efficiency
Atmospheric conditions (weather forecast, altitude)Indirect measurement of flow rate or velocity
Scuba diving
Many, many more ...
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Pressure Terminology (1)
Tekanan Gage (Gage Preasure)
Tekanan yang diukur relativ terhadap tekanan atmosfir.
Tekanan Absolut (Absolute Preasure)
Pengukuran tekanan relativ terhadap titik nol tekanan.
Vacum (Reduced Vacuum)
Vacum diukur relativ terhadap tekanan atmosfir.
Tekanan Differensial
Pengukuran Tekanan relativ terhadap referensi tekanan.
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Pressure Terminology (2)
Tekanan Statis
Tekanan termodinamik yang proporsional dengan
tumbukan pada molekul fluida (sensor pada kecepatan lokalfluida).
Tekanan Dinamis
Tekanan pada permukaan atau objek sesaat padatumbukan fluida (1/2!V2)
Tekanan Stagnasi/Tekanan Total
Jumlah Tekanan Satis dan Dinamis
Ptotal = Pstatis+ Pdinamis
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Various types of pressure
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Bagaimana memilih Tranduser Tekanan?
Lingkungan KerjaRange required
Absolute, gage, differential or vacuum
Burst strength and overpressure limitsWorking fluid chemical compatibility
Operating temperature
Temperature compensation
AkurasiSensivitas
Kecepatan Respons/Frequency Response
Output Sinyal yang dibutuhanAnalog, digital, manual
Biaya?
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Types of pressure transducers
Gravitational
Liquid Columns Manometers, pistons and weights
Mechanical
Bellow, bourdon tubes, diaphragms (equipped withdisplacement or strain sensors)
ElectricalPiezoelectic, Semiconductor elements (directly convertstress into voltage)
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Liquid Column ManometersU-tube and inclined manometers aresimplest pressure sensing devices.
Micromanometers
AdvantagesSimple
Inexpensive
Can be highly sensitive (inclined)
DisadvantagesPoor dynamic response
No remote sensing
Limited pressure range
Not practical over 100 psi
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U Tube & Well Manometers
p gh!" #
U tube manometer Well-type manometer
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Liquid Column Manometers, continued
sinp gh gL! ! $" # #
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Elastic Type Manometers
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Dial-type Manometer
Dial-type Manometer as a mini measurement system
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Bellows Gages
Bellows (Accurate to 0.5% FS)
Bellows gage not adequate for transient
measurements Typically used for small pressures
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Diaphragm Gages
Can be used for very small to very large pressure differences.
Can have rather fast response.
Can use a strain gage or displacement sensor to have a voltage
output.
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Strain gauges used with Diaphragm
Foil strain gage
Strain gage is attached toelastic membrane.
Narrrow span sensors
Rugged sensors
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More Elastic types...
Two dummy gages
mounted elsewhere
Why do we not put 4 active gages?
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LVDT used with Diaphragm
Linear Variable DifferentialTransformer (LVDT)
Operates under inductance ratio
principleMagnetic coupling depends onposition of coil.
As iron core changes position
voltages changeRestricted to low vibrationapplications
0.5 % FS accuracy available
Operating ranges from 0 to 10,000psi
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CapacitiveThe displacement between two platesproduces a change in capacitance.
Wide operating range (vacuum to10,000 psi)
Differential pressures as low as 0.01inches H2O
Fast response time
0.01% FS accuracy and 0.25%temperature effect
Capacitive used with Diaphragm
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Static Calibration
2
cyl
mgp
%" #
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Semiconductor-type Sensors
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Silicon used with Diaphragm
Silicon piezoresistiveDisplacement compresses a siliconcrystal. A charge is developed (lasting
only a few seconds) which isproportional to the applied pressure.
High frequency applications (400 kHz)
Not well suited for static pressure
measurements because chargedecreases rapidly.
Large pressure range (2 to 20,000psi)
Accuracy is typically 1% FS