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Introduction to Pressure Measurement

FG05W5 Version 1.3© 2010

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Seminar Logistics

• Seminar materials– Downloadable presentation– Question and Answer session (audio and email)– Survey– Earn 1.5 Professional Development Hours (PDH)

• Seminar length– 90 minute total presentation – Three approximately 20 minute instructional presentations– Three approximately 10-minute question and answer sessions

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Audio Instructions

• Please note the following during the seminar:• As a participant, you are in a “listen-only” mode.• You may ask questions via the internet, using your

keyboard, at any time during the presentation. • However, the presenter may decide to wait to answer

your question until the next Q&A Session.• If you have audio difficulties, press *0.

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Audio Instructions for Q & A Sessions

• Questions may be asked via your telephone line. • Press the *1 key on your telephone key-pad. • If there are no other callers on the line, the operator will

announce your name and affiliation to the audience and then ask for your question.

• If other participants are asking questions, you will be placed into a queue until you are first in line.

• While in the queue, you will be in a listen-only mode until the operator indicates that your phone has been activated. The operator will announce your name and affiliation and then ask for your question.

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Introduction of the Presenter

• ISA Presenter– Larry Thompson, CAP– ISA Adjunct instructor since 1984. B.A.A.S Tarleton State

University. Instructor for Texas State Technical College in Instrumentation (1977-1979), Computer Networking and System Administration (1996-1999), E-Commerce Technology (1999-2003). CCST Certificate, FCC Radiotelephone License (General, formerly First Class). Served 20 years USAF primarily in Electronic Encryption Systems. Owned and managed own services business since 1979.

– Designed, developed, taught and maintained industrial controls in many varied applications.

– Author of ISA books: Industrial Data Communications and Basic Electrics/Electronics for Control

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Goals of this Session

• Discuss the measurement principles, instrument technologies, and applications to process conditions for pressure measurement

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Course Objectives

• Define pressure in terms of force and mass• Describe how fluid height/specific gravity affect pressure• Differentiate between absolute and gage pressure• Describe the operation of a manometer• Describe the operation of pressure gages• Describe the operation of electrical pressure transducers• Identify different types of electrical pressure transducers• Describe the operation of pressure transmitters• Describe installation considerations for pressure

instruments• Describe methods of protecting pressure measurement

devices from damage

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Section 1: Intro to Pressure Measurement

• Introduction to Pressure: – Force Exerted by Liquids – Forces Exerted by Gas

• Pressure Measurement: – Units of Measurement – Converting Measurement Units

• Differential Pressure• Specific Gravity

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What is Pressure

• Pressure is force over an area• Work is force through a distance• Therefore, pressure is potential energy

lw

forceArea = l x w

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Liquid Force Over An Area

Area = � r2

Force = Weight of liquid

Increasing

Pressure

Atmospheric Pressure

0

P = F/A

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Gas Pressure Over An Area

A gas (other than a blanket of air – atmosphere) exerts an equal force throughout its constraint (vessel).

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Liquid Pressure

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Common Conversions

Atmospheric Pressure

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Differential Pressure (1)

• All pressure measurement is differential– Gauge is measured as difference between measured and

atmospheric– Absolute is measured as difference between measured and

absolute (complete vacuum)

• In measurement when it is called differential, it means the difference between two pressures of which neither may be absolute or atmospheric.

• Differential simply means “difference between”

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Differential Pressure (2)

High Side Low Side

30 psi 30 psi

30 psi 0 psi 30 psi0 psi

Hi Lo Hi Lo

Positive Pressure Negative Pressure

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Differential Pressure (3)

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Specific Gravity

• Ratio of density of a process material to the density of water or air

• Specific gravity of water = 1• Specific gravity of air = 1• Example:

– Density Mercury = 848.6 lbs/ft3– Specific Gravity = 848.6 lbs/62.4 lbs = 13.6– Density (petroleum) = 54.8 lbs./cu. ft.– Specific Gravity = 54.8 lbs/62.4 lbs = 0.077

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Review of Key Points

• Introduction to Pressure: – Force Exerted by Liquids – Forces Exerted by Gas

• Pressure Measurement: – Units of Measurement – Converting Measurement Units

• Differential Pressure• Specific Gravity

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Section 2: Physical Measurement

• Manometers: – Basic Manometers – Types of Manometers

• Mechanical Pressure Transducers: – Principles of Mechanical Pressure Transducers – Types of Pressure Transducers

• Pneumatic Pressure Transmitters

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U-Tube Manometers

U-Tube Manometers (cont’d)

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Hydrostatic Head Pressure

Well Manometers

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Example of Pascal’s Law

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Bourdon, Helical, Spiral, Elements

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Bellows

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Diaphragm

Diaphragm: front side capsule

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Flapper and Nozzle

Pneumatic Transmitters

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Review of Key Points

• Manometers: – Basic Manometers – Types of Manometers

• Mechanical Pressure Transducers: – Principles of Mechanical Pressure Transducers – Types of Pressure Transducers

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Live Question and Answer Session

• During Q&A, questions may be asked via your telephone line. • Press the *1 key on your telephone key-pad. • If there are no other callers on the line, the operator will

announce your name and affiliation to the audience and then ask for your question.

• If other participants are asking questions, you will be placed into a queue until you are first in line.

• While in the queue, you will be in a listen-only mode until the operator indicates that your phone has been activated. The operator will announce your name and affiliation and then ask for your question.

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Section 3: Electrical Pressure Measurement

• Electrical Pressure Elements: – Principles of Electrical Pressure Transducers – Types of Electrical Pressure Transducers

• Electronic Pressure Elements: – Strain Gage – Crystals

• Electronic Pressure Transmitters• Installation Considerations

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Electronic Pressure Element Principles

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Capacitive Pressure Sensor

- lead wires

- isolating diaphragm

- silicon oil

- welded seals

- capacitor plates

- sensing plate

- solid insulation

Current to Pneumatic (I/P) Transducer

• Used to convert current signal to pressure signal

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Strain Gauge

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Load Cell

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Piezoelectric Forces

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Crystal Pressure Sensor

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Typical dP Electronic Transmitter

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Digital Pressure Transmitter

FoundationFieldbusTransmitter

Tag = PIT-010Value = 70.34Units = PsigDevice status = Good/badSensor status = Good/badPV value = Good/badHI/HI alarmHI alarmLO alarmLO/LO alarmTrending

Real Engineering Language

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Pressure Transmitter Installation

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Pig Tail

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Zero Suppression

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Key Points

• Electrical Pressure Elements: – Principles of Electrical Pressure Transducers – Types of Electrical Pressure Transducers

• Electronic Pressure Elements: – Strain Gage – Crystals

• Electronic Pressure Transmitters• Installation Considerations

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How Many People Are at Your Site?

• Poll Slide• Click on the appropriate number indicating the number of

people that are at your site.

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Live Question and Answer Session

• During Q&A, questions may be asked via your telephone line. • Press the *1 key on your telephone key-pad. • If there are no other callers on the line, the operator will

announce your name and affiliation to the audience and then ask for your question.

• If other participants are asking questions, you will be placed into a queue until you are first in line.

• While in the queue, you will be in a listen-only mode until the operator indicates that your phone has been activated. The operator will announce your name and affiliation and then ask for your question.

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Related ISA Courses

• FG07 Introduction to Industrial Automation and Control• TC05 Tuning Control Loops• TS00 CCST Review Course

• All ISA courses are available any time as on-site training • For more information: www.isa.org/training

or (919) 549-8411

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ISA Certifications

• Certified Automation Professionals ® (CAP ®)– www.isa.org/CAP

• Certified Control Systems Technician® (CCST®)– www.isa.org/CCST

• Please visit us online for more information on any of these programs, or call (919) 549-8411.

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Conclusion

This is the end of:

Introduction to Pressure Measurement