3237 Jos Ee Instr_S108 05 Tekanan

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

3237 Jos Ee Instr_S108 05 Tekanan

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