lec09 pressure measurement yap1 - inc.kmutt.ac.thinc.kmutt.ac.th/course/inc336/pressure_336.pdf ·...

MEASUREMENTMEASUREMENTPRESSUREPRESSURE

By Dr. By Dr. DiewDiew KoolpiruckKoolpiruckRevised by Revised by WanchakWanchak 20082008

INC 336 Industrial process measurement, 2005INC 336 Industrial process measurement, 2005


TABLE OF CONTENTSTABLE OF CONTENTS

A.A. INTRODUCTIONINTRODUCTION

B.B. MANOMETERMANOMETER

C.C. ELASTICELASTIC--ELEMENT MECHANICAL PRESSURE GAGESELEMENT MECHANICAL PRESSURE GAGES

D.D. ELECTRONIC PRESSURE SENSORSELECTRONIC PRESSURE SENSORS

E.E. DIFFERENTIAL PRESSURE SENSORSDIFFERENTIAL PRESSURE SENSORS

F.F. HIGH PRESSURE MEASUREMENTHIGH PRESSURE MEASUREMENT

G.G. LOWLOW--PRESSURE (VACUUM) MEASUREMENTPRESSURE (VACUUM) MEASUREMENT


INTRODUCTIONINTRODUCTION

ความดัน PRESSURE• หมายถึง แรง (force; F) ตอ หนวยพื้นที่ (area; A)

• ใน SI unit ความดันมีหนวย เปน ปาสคาล (Pa) หรือ• นิวตันตอตารางเมตร ( ) หรือ • กิโลกรมัตอเมตรตอวินาทีกําลังสอง ( )• สวนความดันในหนวย มิลลิเมตรปรอท (mmHg)

หนวยความดัน• 760 mmHg = 101325 Pascal หรือ 1 atm = 101325 Pa = 101.325 kPa

แตอยางไรก็ตามความดันในหนวย mmHg ไมใช SI unit แตก็อนุโลมใหใชคาความดันในหนวย mmHg หรือ ความดันบรรยากาศเปนหนวยความดนัมาตรฐาน

• 1 atm = 101325 Pa = 101.325 kPa = 1.01325 bars = 760 mmHg • 1 psi = 0.068947 bar• 1 atm = 1.01325 bar


INTRODUCTIONINTRODUCTION

ความดันเกจ ( Gage Pressure)• คือเปนคาความดันที่อานจากมาตรวัดความดัน ในกรณีที่เปนความดันที่

สูงกวาความดันบรรยากาศ เนื่องจากมาตรวัดความดันสวนใหญจะตองเปรียบเทียบคาความดันที่วัดกับคาความดันบรรยากาศรอบๆขางขณะนั้น ทําใหคาที่อานออกมาไดนั้นเปนคาความแตกตางระหวางความดันที่วัดและความดันบรรยากาศขณะ

ความดันสุญญากาศ ( Vacuum Pressure, P vac )• กรณีที่เครื่องวัดอานคาความดันที่ต่ํากวาความดันบรรยากาศจะไดวา

ความดันสุญญากาศ = ความดันบรรยากาศ - ความดันสัมบูรณหรือ


INTRODUCTION :INTRODUCTION :Standards and Calibration Standards and Calibration

Deadweight testingDeadweight testing

Pressure is defined as force per unit area. Dead-Weight Pressure Testers use these measurements of force and area to produce a pressure to calibrate instrument with great accuracy. The force is derived from weights and the area is that of a piston in a cylinder


Pressure Calibrator

INTRODUCTION :INTRODUCTION :Standards and CalibrationStandards and Calibration

Secondary pressure testingSecondary pressure testing


MANOMETERSMANOMETERS


ELASTIC TRANSDUCERSELASTIC TRANSDUCERS


ELASTIC TRANSDUCERS : ELASTIC TRANSDUCERS : Bourdon tubesBourdon tubes


ELASTIC TRANSDUCERS : ELASTIC TRANSDUCERS : Bellows pressure gageBellows pressure gage


ELASTIC TRANSDUCERS : ELASTIC TRANSDUCERS : Diaphragm pressure gageDiaphragm pressure gage

Diaphragm pressure gageDiaphragm pressure gage

A diaphragm is a sheet of a semi-flexible material anchored at its periphery and most often round in shape. It serves either as a barrier between two chambers, moving slightly up into one chamber or down into the other depending on differences in pressure, or as a device that vibrates when certain frequencies are applied to it


ELECTRONIC PRESSURE SENSORS : ELECTRONIC PRESSURE SENSORS : Strain gaugeStrain gauge

Major types of resistance strain gages

• Bonded foil strain gages(metallic)

• Bonded semiconductor strain gages

• Thin film strain gages

• Diffused semiconductor strain gages



Bonded foil strain gages



Bonded foil strain-gage pressure transducer



Strain gauge transducer with diaphragm element

Wheatstone circuit



Diaphragm-type strain-gage pressure pickup



Diffused semiconductor strain-gage transducer

Diffused semiconductor strain gages represent a furtherimprovement in strain gagetechnology because they eliminatethe need for bonding agents.


ELECTRONIC PRESSURE SENSORS : ELECTRONIC PRESSURE SENSORS : Diffused sensor Diffused sensor

Diffused sensor transducers and auto reference techniques



• Sensors to be deposited directly onto conductive and non-conductive components. No mounting cements or adhesives needed.

• Minimal process intrusion. Structural modifications of components typically not necessary. Will not disrupt gas flows.

• Fast time response. Adds neglible amount of mass to system and made with thermally conductive materials.

• Harsh environment capability. Can be made to withstand temperatures in excess of 1000oC.

• Sensors to be placed on 3 dimensional parts. Thin film conductive traces can route leads around corners and edges.

Thin-film strain gages


ELECTRONIC PRESSURE SENSORS : ELECTRONIC PRESSURE SENSORS : CapacitiveCapacitive


ELECTRONIC PRESSURE SENSORS : ELECTRONIC PRESSURE SENSORS : PotentiometricPotentiometric


ELECTRONIC PRESSURE SENSORS : ELECTRONIC PRESSURE SENSORS : Resonant wireResonant wire

A wire is gripped by a static member at one end, and by the sensing diaphragm at the other. An oscillator circuit causes the wire to oscillate at its resonant frequency. A change in process pressure changes the wire tension, which in turn changes the resonant frequency of the wire. A digital counter circuit detects the shift. Because this change in frequency can be detected quite precisely, this type of transducer can be used for low differential pressure applications as well as to detect absolute and gauge pressures.


ELECTRONIC PRESSURE SENSORS : ELECTRONIC PRESSURE SENSORS : PiezoelectricPiezoelectric

A piezoelectric sensor is a device that uses the piezoelectric effect to measure pressure,acceleration, strain or force by converting them to an electrical signal. It measures dynamic pressures. They are generally not suited for static pressure measurements


ELECTRONIC PRESSURE SENSORS : ELECTRONIC PRESSURE SENSORS : MagneticMagnetic

Linear variable differential transformer

Linear reluctance transducer


ELECTRONIC PRESSURE SENSORS : ELECTRONIC PRESSURE SENSORS : ElectroElectro--OpticalOptical


DIFERENTIAL PRESSURE TRANSDUCERSDIFERENTIAL PRESSURE TRANSDUCERS


DIFERENTIAL PRESSURE TRANSDUCERSDIFERENTIAL PRESSURE TRANSDUCERS

Diffused strain-gage differential-pressureTransmitter (Honeywell Inc.)


HIGH PRESSURE MEASUREMENTHIGH PRESSURE MEASUREMENT

Very-high-pressure transducer


LOW PRESSURE MEASUREMENTLOW PRESSURE MEASUREMENT

Vacuum gage types and ranges



McLeod gage

A McLeod gauge is a scientific instrument to measure very low pressures, down to 10-7 Torr.The torr (symbol: Torr), defined as 1/760 atm.

1 Torr; ≈ 1 mmHg

Today, these gauges have largely been replaced by electronic vacuum gauges. McLeod gaugescontinue to be used as a calibration standard for electronic gauges


Pirani gageThermocouple gage

Thermal Conductivity gauges rely on the fact that the ability of a gas to conduct heatdecreases with pressure*. In this type of gauge, a wire filament is heated by running currentthrough it. A thermocouple or Resistance Temperature Detector (RTD) can then be used tomeasure the temperature of the filament. This temperature is dependent on the rate at whichthe filament loses heat to the surrounding gas, and therefore on the thermal conductivity. A common variant is the Pirani gauge which uses a single platinum filament as both the heatedelement and RTD. These gauges are accurate from 10 Torr to 10−3 Torr.

*If the gas pressure is reduced, the cooling effect will decrease


DYNAMIC EFFECTS OF VOLUMES AND TUBINGDYNAMIC EFFECTS OF VOLUMES AND TUBING

Transducer installation types


DYNAMIC EFFECTS OF VOLUMES AND TUBINGDYNAMIC EFFECTS OF VOLUMES AND TUBING

Fill Fluid : The fill fluid will affect the safety of process, accuracy and response time of the measurement. The following four points need to be considered:

• Temperature limitations• Expansion coefficient• Process compatibilty• Viscoscity

Temperature Effects : Three variables can be changed to reduce the errors caused by temperature effects

• Diameter of capillary• Choice of fill fluid• Diaphragm size


ACCESSORIESACCESSORIES

Gauge cock and gauge valves areapplied to the temporary stoppage ofmeasuring fluid for the purposes ofpressure gauge maintenance,inspection

and repair

These joints are applied to the connectionbetween diipe diameters.

This dampener is of variable type beingable to adjust pressure amplitude andapplied to the decrease in pressure pulsation.

Gauge cock Gauge valve

Connecting joint

Dampener


ACCESSORIESACCESSORIES

This pipe siphon is applied tomeasuring steam pressure orthe case where thetemperature of measuring fluidis high

This tank siphon is appliedto the sulstitutionmeasuring fluid and thecase where oil is forbidden.


INSTALLATION GUIDELINESINSTALLATION GUIDELINES


SMART PRESSURE TRANSMITTERSSMART PRESSURE TRANSMITTERS


SUMMARYSUMMARY

lec09 pressure measurement yap1 - inc.kmutt.ac.thinc.kmutt.ac.th/course/inc336/pressure_336.pdf ·...

Documents