38179874 infrared thermography guide revision 3

8/18/2019 38179874 Infrared Thermography Guide Revision 3

1/246

Infrared Thermography Guide

(Revision 3)

Technical Report L

I

C

E N

S E D

M A T

E R

I

A

L

Equipment

Reliability

Plant

Maintenance

SupportReduced

Cost

WARNING:

Please read the License Agreement

on the back cover before removing

the Wrapping Material.


2/246


3/246

EPRI Project ManagerP. Zayicek

EPRI • 3412 Hillview Avenue, Palo Alto, California 94304 • PO Box 10412, Palo Alto, California 94303 • USA800.313.3774 • 650.855.2121 • [email protected] • www.epri.com

Infrared Thermography Guide(Revision 3)

1006534

Final Report, May 2002


4/246

DISCLAIMER OF WARRANTIES AND LIMITATION OF LIABILITIES

THIS DOCUMENT WAS PREPARED BY THE ORGANIZATION(S) NAMED BELOW AS ANACCOUNT OF WORK SPONSORED OR COSPONSORED BY THE ELECTRIC POWER RESEARCHINSTITUTE, INC. (EPRI). NEITHER EPRI, ANY MEMBER OF EPRI, ANY COSPONSOR, THEORGANIZATION(S) BELOW, NOR ANY PERSON ACTING ON BEHALF OF ANY OF THEM:

(A) MAKES ANY WARRANTY OR REPRESENTATION WHATSOEVER, EXPRESS OR IMPLIED, (I)WITH RESPECT TO THE USE OF ANY INFORMATION, APPARATUS, METHOD, PROCESS, ORSIMILAR ITEM DISCLOSED IN THIS DOCUMENT, INCLUDING MERCHANTABILITY AND FITNESSFOR A PARTICULAR PURPOSE, OR (II) THAT SUCH USE DOES NOT INFRINGE ON ORINTERFERE WITH PRIVATELY OWNED RIGHTS, INCLUDING ANY PARTY'S INTELLECTUALPROPERTY, OR (III) THAT THIS DOCUMENT IS SUITABLE TO ANY PARTICULAR USER'SCIRCUMSTANCE; OR

(B) ASSUMES RESPONSIBILITY FOR ANY DAMAGES OR OTHER LIABILITY WHATSOEVER(INCLUDING ANY CONSEQUENTIAL DAMAGES, EVEN IF EPRI OR ANY EPRI REPRESENTATIVEHAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES) RESULTING FROM YOURSELECTION OR USE OF THIS DOCUMENT OR ANY INFORMATION, APPARATUS, METHOD,PROCESS, OR SIMILAR ITEM DISCLOSED IN THIS DOCUMENT.

ORGANIZATION(S) THAT PREPARED THIS DOCUMENT

EPRI

ORDERING INFORMATION

Requests for copies of this report should be directed to EPRI Orders and Conferences, 1355 WillowWay, Suite 278, Concord, CA 94520, (800) 313-3774, press 2 or internally x5379, (925) 609-9169,

(925) 609-1310 (fax).

Electric Power Research Institute and EPRI are registered service marks of the Electric PowerResearch Institute, Inc. EPRI. ELECTRIFY THE WORLD is a service mark of the Electric PowerResearch Institute, Inc.

Copyright © 2002 Electric Power Research Institute, Inc. All rights reserved.


5/246

CITATIONS

This report was prepared by

Nuclear Maintenance Applications Center (NMAC)1300 W.T. Harris Boulevard

Charlotte, NC 28262

This report describes research sponsored by EPRI.

The report is a corporate document that should be cited in the literature in the following manner:

Infrared Thermography Guide (Revision 3), EPRI, Palo Alto, CA: 2002. 1006534.

The enclosed CD contains a PDF file of this report featuring full-color images.

iii


6/246


7/246

REPORT SUMMARY

Costly equipment outages can be reduced by implementing a comprehensive predictive

maintenance program. Infrared thermography (IR), a fundamental component of such programs,uses nonintrusive techniques to monitor the operating condition of equipment and components.

This revised report provides updated information to assist utilities in implementing an effective

IR program.

Background

IR has proven to be an effective predictive maintenance and diagnostic tool. For example, it can be used to identify areas of condenser air in-leakage, bad terminal lugs/connections, leaking

valves, and nozzle blockages in the containment spray ring header. To broaden the range of IR

applications, EPRI sponsored the development of a guide to address IR diagnostic capabilities.This guide was originally published in 1990 and is being revised to incorporate user input and to

update information on IR equipment and vendors.

Objective

! To develop and maintain a guide that provides a consistent approach for using IR as a predictive maintenance tool

ApproachThe EPRI Nuclear Maintenance Applications Center (NMAC) originally worked with AlabamaPower personnel to assess the viability of IR as a predictive maintenance tool in a nuclear plant

application. An initial IR survey and a subsequent follow-up survey identified the effectiveness

of IR for identifying abnormal operating conditions for the surveyed components. Revisions to

the guide include updated information on IR equipment, applications, training, and certification.

ResultsThis guide, which provides a compendium of information rather than definitive standards,

describes IR theory, summarizes existing and potential IR applications, and offers technicalinformation necessary for developing an effective in-house IR program. Key topics that are

included in this guide are:

! The science of thermography

! Selection of infrared instruments

! Inspection techniques

! IR applications

! Basic elements of an in-house program

! Training and certification

v


8/246

This revision provides updated information on commercial infrared sensing and imaging

instruments, IR applications, and training and certification criteria.

EPRI PerspectiveInfrared thermography is a valuable tool in a predictive maintenance program, as has been

demonstrated by those applying the principles described in the Infrared Thermography Guide.Periodic updates of the guide keep the utility thermographer aware of recent developments in IR

equipment technology, criteria for training and certification, and proven IR applications that addvalue to the utility IR program. The guide also serves as benchmark reference for those who

contract their IR inspection services.

Keywords Nuclear power

Infrared thermographyFossil fuel power plants

Predictive maintenance

vi


9/246

EPRI Licensed Material

ABSTRACT

This guide is a valuable reference for the development of infrared thermography (IR) capabilities

as part of a plant predictive maintenance program. The guide includes IR theory, a summary ofIR inspection applications, and the technical information necessary to develop an effective

in-house program. The body of the guide is structured for the general user of IR, and the

appendices provide a more in-depth look at this technology for the advanced user. This thirdrevision of Infrared Thermography Guide contains updated information on IR equipment

technology, IR inspection applications, and training and certification criteria.

vii


10/246


11/246


ACKNOWLEDGMENTS

The Infrared Thermography Guide was produced by the Nuclear Maintenance Applications

Center (NMAC). Extensive information for the original guide was provided by Alabama PowerCompany (the primary demonstration plant) and other electric power generating utilities, and is

gratefully acknowledged. A. E. Hammett from SONOPCO is acknowledged for his efforts,

enthusiasm, and support of this project.

The following utilities are acknowledged for their review of the original guide and their

comments:

Alabama Power Co. Florida Power Corp.Arkansas Power & Light Co. Maine Yankee Atomic Power Co.

Duquesne Light Co. Pacific Gas & Electric Co.

Florida Power & Light Co. Toledo Edison Company

The following utility personnel are acknowledged for their review of Revision 1 of the Guideand their comments:

Larry Shay – Entergy Operations

Scot Stewart – Florida Power Corp.

Joe Connolley – Omaha Public Power DistrictRuss Cabrel – Washington Public Power Supply SystemTom George – Wisconsin Public Service Corp.

Gary Thomas of Florida Power & Light Co. is acknowledged for his contribution of IR

inspection application images for Revision 2 of the Guide.

FLIR Systems Inc. and the Infrared Training Center are acknowledged for their contributions ofIR inspection application images for Revision 3 of the Guide.

In addition, NMAC and EPRI NDE Center staff reviewed Revisions 1, 2, and 3 and offered

comments. NMAC was supported in its efforts to develop this guide by Herb Kaplan ofHoneyhill Technical.

Honeyhill Technical Honeyhill Technical

65 Fawn Ridge Lane 11550 Ballylee Terrace

Norwalk, CT 06851 Boynton Beach, FL 33437

ix


12/246


13/246


INTRODUCTION

Many electric generating stations and utilities have integrated the non-contact, nondestructive

capabilities of infrared thermography (IR) for condition monitoring and diagnostics in their predictive maintenance program. The purpose of this guide is to assist the nuclear industry in its

efforts to factor IR into its predictive maintenance program. This guide provides the theory of IR,

a summary of existing and potential applications, and the technical information necessary todevelop an effective in-house program. Also included is a matrix that lists all of the known

manufacturers of IR instruments for a broad range of applications.

IR has been used in commercial applications since the early 1970s. In the early 1990s, at the timethis guide was first completed, the most frequent applications centered on building energy losses,

roof moisture detection, and inspections of major electric equipment. Applications have since

expanded to almost all areas of plant predictive maintenance (PdM), product and process control,

and nondestructive testing of materials. The wide and growing selection of thermal imagers andviewers available for these applications provides both qualitative and quantitative displays of

temperature distribution patterns.

The manufacturers of modern thermal imagers and viewers have kept pace as detector andmicroprocessor technologies have advanced. The capabilities of today’s IR thermal imagers and

viewers have yet to be fully explored and developed for commercial applications. In addition,

computer software programs are now available to store, retrieve, analyze and compare infraredimages.

Much of the information presented in the original guide was developed as a result of ademonstration project at a U.S. nuclear utility. In addition to information gathered through this

demonstration project, all Nuclear Maintenance Applications Center (NMAC) members weresurveyed to provide data on the implementation status of IR technology at their facilities.

This latest revision of the guide (Revision 3) was undertaken to correct text errors, to update the

information on IR products vendors, certification, training, and techniques, and to restructure theguide so that it can become a living document, able to be readily updated to reflect technology

changes. The body of the guide is structured for the general user of IR, and the appendices provide an in-depth look at this technology designed for the more advanced user.

Basic IR Concepts

A target at any temperature above absolute zero will emit infrared radiation in proportion to itstemperature. Thermal imagers develop an electronic image by converting the invisible heat

radiation emitted by that target into electrical signals that can be displayed on a monitor and/or

xi


14/246


recorded on a variety of electronic storage media. By monitoring these targets with thermal

imaging equipment, a visual image of their temperature differentials can be displayed. Thevariations in intensities of the blacks, grays, and whites (or color variations) provide an

indication of the temperature differences. Areas of higher temperatures will appear brighter and

the areas at lower temperatures will appear darker (or appear as different colors). The quantity

and wavelength distribution of the energy that is radiated depends upon the temperature andspectral characteristics of the material, and on that material’s radiation efficiency (emissivity).

Thermal imagers convert the invisible heat radiation into visible images while spot radiometers

convert the heat radiation from a single spot into a number indication on a meter.

The thermographer views the target through an IR instrument, while looking for unexpected or

unusual temperature patterns. A qualitative examination compares the apparent temperature

pattern of one component to that of an identical or similar component under the same or similaroperating conditions.

Temperature differences can be measured quantitatively as well. The achievement of accurate

temperature indications, however, is dependent upon many factors and extreme care must betaken in the selection of variables used in temperature calculations. The thermal images obtained

can be stored on memory sticks, PCMCIA cards, computer hard drives, floppy disks, CDs, ZIP

disks, or video tape.

An advantage of infrared monitoring or testing is that it can be performed with the equipment in

service at normal operating conditions (that is, it will not interfere with normal plant operations).

xii


15/246


CONTENTS

1 THERMOGRAPHY OVERVIEW.............................................................................................1-1

1.1 Advantages of Non-Contact Thermal Measurement....................................................1-1

1.2 Heat Transfer and Infrared Radiation Basics...............................................................1-2

1.2.1 Heat and Temperature........................................................................................1-2

1.2.2 Instruments for Temperature Measurement (Contact and Non-Contact)............1-2

1.2.3 Converting Temperature Units............................................................................1-3 1.2.4 The Three Modes of Heat Transfer.....................................................................1-3

1.3 Measuring and Mapping Temperature Without Contact ..............................................1-7

1.3.1 The Three Elements of a Non-Contact Temperature Measurement...................1-7

1.4 Performance Parameters of Thermal Sensing Instruments.........................................1-9

1.4.1 Point-Sensing Instruments..................................................................................1-9

1.4.2 Line Scanners and Imagers—Qualitative and Quantitative ..............................1-10

1.4.3 Thermal Imaging Software................................................................................1-11

2 A COMPENDIUM OF COMMERCIAL INFRARED SENSING AND IMAGINGINSTRUMENTS.........................................................................................................................2-1

2.1 Classification of Instruments........................................................................................2-1

2.2 Instrument Manufacturers............................................................................................2-2

2.3 Discussion of Instruments............................................................................................2-2

2.3.1 Point Sensors (Radiation Thermometers)...........................................................2-2

2.3.1.1 Probes...........................................................................................................2-2

2.3.1.2 Portable Hand-Held ......................................................................................2-3

2.3.1.3 On-Line Monitoring and Control....................................................................2-3 2.3.1.4 Specials ........................................................................................................2-4

2.3.2 Line Scanners .....................................................................................................2-5

2.3.2.1 Opto-Mechanically Scanned Line Scanners .................................................2-5

2.3.2.2 Electronically Scanned Focal Plane Array Line Scanners............................2-6

2.3.3 Thermographic Instruments ................................................................................2-6

xiii


16/246


2.3.3.1 Thermal Viewers, Opto-Mechanically Scanned ............................................2-7

2.3.3.2 Opto-Mechanically Scanned Imaging Radiometers ......................................2-8

2.3.3.3 Thermal Viewers, Electronically Scanned (Pyrovidicon Imagers).................2-9

2.3.3.4 Focal Plane Array (FPA) Imagers—Qualitative and Quantitative ...............2-10

2.3.3.5 FPA Imager Performance Comparisons .....................................................2-11

2.4 Thermal Imaging Diagnostic Software .......................................................................2-13

2.4.1 Quantitative Thermal Measurements of Targets...............................................2-13

2.4.2 Detailed Processing and Image Diagnostics.....................................................2-13

2.4.3 Image Recording, Storage, and Recovery ........................................................2-14

2.4.4 Image Comparison............................................................................................2-15

2.5 Recording, Hard Copy, and Storage of Images and Data .........................................2-15

2.6 Report Preparation ....................................................................................................2-15

3 THE MEASUREMENT MISSION ...........................................................................................3-1

3.1 Thermal Behavior of the Target ...................................................................................3-1

3.1.1 Emissivity Difference...........................................................................................3-2

3.1.2 Reflectance Difference........................................................................................3-2

3.1.3 Transmittance Difference....................................................................................3-2

3.1.4 Geometric Difference ..........................................................................................3-2

3.1.5 Mass Transport Difference..................................................................................3-2

3.1.6 Phase Change Difference...................................................................................3-3

3.1.7 Thermal Capacitance Difference.........................................................................3-3

3.1.8 Induced Heating Difference.................................................................................3-3

3.1.9 Energy Conversion Difference ............................................................................3-3

3.1.10 Direct Heat Transfer Difference .......................................................................3-3

3.2 Equipment Preparation ................................................................................................3-3

3.2.1 The Mission Checklist .........................................................................................3-3

3.2.2 Equipment Checkout and Calibration..................................................................3-4

3.2.3 Batteries..............................................................................................................3-4

3.2.4 Facility Personnel Participation...........................................................................3-4

3.3 Some Cautions for Correct Instrument Operation........................................................3-4

3.3.1 Start-Up Procedure .............................................................................................3-5

3.3.2 Memorizing the Default Values ...........................................................................3-5

3.3.3 Setting the Correct Emissivity .............................................................................3-5

3.3.4 Filling the IFOVmeas for Accurate Temperature Measurements......................3-12

xiv


17/246


3.3.5 Aiming Normal to the Target Surface................................................................3-12

3.3.6 Recognizing and Avoiding Reflections From External Sources........................3-12

3.3.7 Avoiding Radiant Heat Damage to the Instrument............................................3-12

4 INSPECTION TECHNIQUES .................................................................................................4-1

4.1 Mitigating Inherent Effects ...........................................................................................4-1

4.1.1 Emissivity and Reflectivity...................................................................................4-1

4.1.2 Foot Powder........................................................................................................4-3

4.1.3 Dye Check Developer .........................................................................................4-3

4.1.4 Electricians' Tape................................................................................................4-5

4.2 Proven Inspection Techniques.....................................................................................4-5

4.2.1 Mirrored Surfaces................................................................................................4-5

4.2.2 Thermal Transfer Imaging...................................................................................4-6

4.2.3 Thermal Transients .............................................................................................4-6

4.2.4 Differential Thermography...................................................................................4-7

4.2.5 Using Infrared Transmitting Windows .................................................................4-7

5 EXAMPLES OF INFRARED APPLICATIONS.......................................................................5-1

5.1 Current Applications.....................................................................................................5-1

5.2 Electrical Applications..................................................................................................5-1

5.2.1 High Electrical Resistance ..................................................................................5-1

5.2.2 Induced Currents.................................................................................................5-2

5.2.3 Open Circuits ......................................................................................................5-2

5.3 Mechanical Applications ..............................................................................................5-2

5.3.1 Friction ................................................................................................................5-2

5.3.2 Valve Leakage/Blockage.....................................................................................5-2

5.3.3 Insulation.............................................................................................................5-3

5.3.4 Building Envelopes..............................................................................................5-3

5.4 Miscellaneous Applications..........................................................................................5-3

5.4.1 Containment Spray Ring Header ........................................................................5-3 5.4.2 Hydrogen Igniters................................................................................................5-4

5.4.3 Condensers.........................................................................................................5-4

5.4.4 Thermal Plume Detection....................................................................................5-4

5.5 Applications Summary .................................................................................................5-5

xv


18/246


6 BASIC ELEMENTS OF AN IN-HOUSE PROGRAM..............................................................6-1

6.1 Basic Elements ............................................................................................................6-1

6.1.1 Introduction .........................................................................................................6-2

6.1.2 Definitions ...........................................................................................................6-2

6.1.3 Scope..................................................................................................................6-2

6.1.4 Responsibilities ...................................................................................................6-2

6.1.5 Precautions .........................................................................................................6-2

6.1.6 Prerequisites .......................................................................................................6-2

6.1.7 Conduct of the Survey.........................................................................................6-2

6.1.8 Acceptance Criteria.............................................................................................6-3

6.1.9 Reporting Criteria ................................................................................................6-3

6.1.10 Qualification of Personnel................................................................................6-4

6.1.11 Scheduling .......................................................................................................6-4 6.1.12 Equipment Matrix .............................................................................................6-4

6.1.13 References ......................................................................................................6-4

6.2 Sample Program..........................................................................................................6-5

7 TRAINING AND CERTIFICATION .........................................................................................7-1

7.1 Background..................................................................................................................7-1

7.2 Levels of Qualification..................................................................................................7-2

7.3 Training Requirements ................................................................................................7-2

7.4 Predictive Maintenance (PdM) Level III Certification Program ....................................7-4

APPENDICES:

A THE SCIENCE OF THERMOGRAPHY (PRACTICAL APPLICATION OFTHERMOGRAPHIC AND THERMAL SENSING EQUIPMENT).............................................. A-1

A.1 Introduction ................................................................................................................. A-1

A.2 Heat Transfer and Radiation Exchange Basics for Thermography............................. A-1

A.2.1 Heat and Temperature....................................................................................... A-2

A.2.2 Converting Temperature Units........................................................................... A-2

A.2.3 The Three Modes of Heat Transfer .................................................................... A-7

A.2.4 Conduction......................................................................................................... A-7

A.2.5 Convection ......................................................................................................... A-8

A.2.6 Radiation............................................................................................................ A-9

A.2.7 Radiation Exchange at the Target Surface ...................................................... A-10

xvi


19/246


A.2.8 Specular and Diffuse Surfaces......................................................................... A-12

A.2.9 Transient Heat Exchange................................................................................. A-12

A.3 The Basic Physics of Infrared Radiation and Sensing.............................................. A-13

A.3.1 Some Historical Background............................................................................ A-14

A.3.2 Non-Contact Thermal Measurements .............................................................. A-14

A.3.3 The Target Surface .......................................................................................... A-14

A.3.4 The Transmitting Medium ................................................................................ A-20

A.3.5 The Measuring Instrument ............................................................................... A-23

A.3.6 Introduction to Thermal Scanning and Imaging Instruments............................ A-25

A.3.6.1 Line Scanning............................................................................................ A-25

A.3.6.2 Two-Dimensional Scanning....................................................................... A-26

A.4 Performance Parameters of Thermal-Sensing Instruments...................................... A-29

A.4.1 Point-Sensing Instruments............................................................................... A-29 A.4.2 Scanners and Imagers—Qualitative and Quantitative ..................................... A-35

A.4.3 Performance Parameters of Imaging Radiometers.......................................... A-35

A.4.3.1 Temperature Sensitivity, Minimum Resolvable TemperatureDifference (MRTD) or Minimum Resolvable Temperature (MRT) ............................ A-36

A.4.3.2 Spot Size, Instantaneous Field of View (IFOV), Imaging SpatialResolution, Measurement Spatial Resolution (IFOVmeas) ...................................... A-37

A.4.3.3 Speed of Response and Frame Repetition Rate....................................... A-41

A.4.4 Thermal Imaging Software............................................................................... A-42

B MEASURING EMISSIVITY, REFLECTANCE, AND TRANSMITTANCE.............................B-1

B.1 Introduction ................................................................................................................. B-1

B.2 Measuring Emissivity .................................................................................................. B-2

B.2.1 Reference Emitter Technique ............................................................................ B-2

B.2.2 Reflective Emissivity Technique......................................................................... B-3

B.2.3 Transmittance Measurement ............................................................................. B-5

B.2.4 Generic Emissivity Values.................................................................................. B-6

C QUICK REFERENCE CHARTS AND PLATES.................................................................... C-1

D REFERENCES...................................................................................................................... D-1

E BIBLIOGRAPHY ................................................................................................................... E-1

xvii


20/246


21/246


LIST OF FIGURES

Figure 1-1 Categories of Conditions for Infrared Thermal Measurements.................................1-8

Figure 1-2 Components of an Infrared Sensing Instrument.......................................................1-9

Figure 4-1 Emissivity Improvement by Coating—Setup ............................................................4-4

Figure 4-2 Thermogram of an Uncoated Shiny Metal Container ...............................................4-4

Figure 4-3 Container Has Been Coated to Improve Emissivity—Thermogram NowReveals Fluid Level............................................................................................................4-5

Figure 5-1 Step-Up Transformer High-Resistance Connection .................................................5-8

Figure 5-2 250 kV Transformer................................................................................................5-10

Figure 5-3 Steam Line Leaks...................................................................................................5-12

Figure 5-4 Isophase Bus Bellows ............................................................................................5-14

Figure 5-5 Electric Generator...................................................................................................5-16

Figure 5-6 Regulating Transformer Cooling Oil Migration .......................................................5-18

Figure 5-7 Generator Casing ...................................................................................................5-20

Figure 5-8 Energized Ground Cable ........................................................................................5-22

Figure 5-9 480 V Breaker Connection .....................................................................................5-24

Figure 5-10 Current Transformer .............................................................................................5-26

Figure 5-11 Fuse Holder ..........................................................................................................5-28 Figure 5-12 Connection to Fuse Holder...................................................................................5-30

Figure 5-13 Knife Switch..........................................................................................................5-32

Figure 5-14 Motor Control Center Breaker ..............................................................................5-34

Figure 5-15 Motor Control Center Terminal Block ...................................................................5-36

Figure 5-16 Motor Control Center Control Wire .......................................................................5-38

Figure 5-17 Padmount Transformers.......................................................................................5-40

Figure 5-18 Vacuum Leak on Turbine Condenser...................................................................5-42

Figure 5-19 Small Transformer ................................................................................................5-44

Figure 5-20 Motor ....................................................................................................................5-46 Figure 5-21 Shell Relief Valve .................................................................................................5-48

Figure 5-22 Shell Relief Valve (Weeping) ................................................................................5-50

Figure 5-23 Shell Relief Valve (Leaking) .................................................................................5-52

Figure 5-24 Vacuum Leak on Turbine .....................................................................................5-54

Figure 5-25 Steam Trap...........................................................................................................5-56

Figure 5-26 Pump Bearing.......................................................................................................5-58

xix


22/246


Figure 5-27 Office Building ......................................................................................................5-60

Figure 5-28 Building Roof with Water Saturation.....................................................................5-62

Figure 5-29 Induction Motor Air Intake Plenum .......................................................................5-64

Figure 5-30 Generator Step-Up Transformer...........................................................................5-66

Figure 5-31 Printed Circuit Module ..........................................................................................5-68

Figure 6-1 Infrared Survey Results ..........................................................................................6-14

Figure A-1 Conductive Heat Flow ............................................................................................. A-7

Figure A-2 Convective Heat Flow ............................................................................................. A-9

Figure A-3 Infrared in the Electromagnetic Spectrum............................................................. A-10

Figure A-4 Radiative Heat Flow .............................................................................................. A-11

Figure A-5 Radiation Exchange at the Target Surface ........................................................... A-12

Figure A-6 Blackbody Curves at Various Temperatures......................................................... A-16

Figure A-7 Spectral Distribution of a Blackbody, a Gray Body, and a Non-Gray Body........... A-18

Figure A-8 Components of Energy Reaching the Measuring Instrument ............................... A-19

Figure A-9 Aiming the Instrument to Avoid Point Source Reflections ..................................... A-19

Figure A-10 Infrared Transmission of 0.3 km of Sea Level Atmosphere ................................ A-20

Figure A-11 Infrared Spectral Transmission of Glass ............................................................. A-21

Figure A-12 Characteristics of IR Transmitting Materials ....................................................... A-22

Figure A-13 Components of an Infrared Radiation Thermometer........................................... A-23

Figure A-14 Typical Infrared Radiation Thermometer Schematic ........................................... A-24

Figure A-15 Spectral Sensitivity of Various Infrared Detectors............................................... A-25

Figure A-16 Scanning Configuration of an Infrared Line Scanner .......................................... A-26

Figure A-17 Schematic of a Typical Opto-Mechanically Scanned Imager .............................. A-28

Figure A-18 Schematic of a Typical FPA-Based Thermal Imager .......................................... A-29

Figure A-19 Instrument Speed of Response and Time Constant ........................................... A-31

Figure A-20 Fields of View of Infrared Radiation Thermometers ............................................ A-32

Figure A-21 Spectral Filtering for Polyethylene Temperature Measurement.......................... A-34

Figure A-22 Spectral Filtering for Polyester Temperature Measurement................................ A-34

Figure A-23 Test Setup for MRTD Measurement, MRTD Curve ............................................ A-37

Figure A-24 Modulation Transfer Function, Imager Spatial Resolution .................................. A-39

Figure A-25 MRTD and MTF for a System Rated at 1.0 Milliradian ....................................... A-40

Figure A-26 Setup and Curves for Slit Response Function Test ............................................ A-41

Figure B-1 Target Radiosity ...................................................................................................... B-1

Figure B-2 Using the Reference Emitter Technique ................................................................. B-3

Figure B-3 Using the Reflective Emissivity Technique ............................................................. B-4

Figure B-4 Using the Transmittance Technique (Measuring Transmittance)............................ B-5

xx


23/246


LIST OF TABLES

Table 1-1 Temperature Conversion Chart .................................................................................1-4

Table 2-1 Instrument Characteristics .......................................................................................2-16

Table 2-2 Equipment Manufacturers........................................................................................2-29

Table 2-3 Compilation of Typical Industrial Applications of Thermal Imaging Instruments......2-33

Table 3-1 Table of Normal Spectral Emissivities .......................................................................3-6

Table 3-2 Emissivity for Wavelengths of 8–14 µm at 0°C ........................................................3-10

Table 4-1 Normal Emissivity Values of Common Materials .......................................................4-2

Table 5-1 Composite List of Infrared Applications .....................................................................5-5

Table 5-2 List of IR Application Examples .................................................................................5-6

Table A-1 Temperature Conversion Chart ................................................................................ A-4

Table B-1 Normal Emissivity Values of Common Materials...................................................... B-6

xxi


24/246


25/246


1THERMOGRAPHY OVERVIEW

Temperature and thermal behavior of plant machinery, power generation and distribution

equipment, control systems, and related materials are the most critical factors in the maintenanceof operations. For this reason, temperature is frequently considered the key to successful plant

maintenance and is, by far, the most measured quantity. Although conventional methods of

temperature measurement using thermometers and thermocouples are still commonly used for

many applications, infrared thermography (IR) sensors have become less expensive, morereliable, and electrically interchangeable with conventional thermistors and thermocouples. Non-

contact measurement using infrared sensors has become an increasingly desirable alternative

over conventional methods. Now, with the proliferation of innovative computer hardware andsoftware, computer-aided predictive maintenance is feasible and efficient.

1.1 Advantages of Non-Contact Thermal Measurement

The four most commonly stated advantages of non-contact thermal infrared measurement over

contact measurement are that it is non-intrusive, remote, much faster than conventional methods,and that it measures the temperature at the surface of the target (test subject) not the surrounding

air. Any one, or a combination of the following conditions, warrants the consideration of a non-

contact sensor:

! Target in motion – When the target to be measured is moving, it is usually impractical tohave a temperature sensor in contact with its surface. Bouncing, rolling, or friction can cause

measurement errors and the sensor might interfere with the process.

! Target electrically hot – Current-conducting equipment and components present a hazard to personnel and instruments alike. Infrared sensors place both out of harm's way.

! Target fragile – When thin webs or delicate materials are measured, a contacting sensor canoften damage the product.

! Target very small – The mass of a contacting sensor that is large with respect to the target being measured will usually conduct thermal energy away from the target surface, thus

reducing the temperature and producing erroneous results.

! Target remote – If a target is very far away from, or inaccessible to, contacting sensors,

infrared measurement is the only option.

! Target temperature changing – Infrared sensors are much faster than thermocouples. Infrared

radiant energy travels from the target to the sensor at the speed of light. A rapidly changingtemperature can be monitored by infrared sensors, with a millisecond response or faster.

1-1


26/246


Thermography Overview

! Target destructive to thermocouples – When the high mortality rate of thermocouples due to jarring, burning, or erosion becomes a serious factor, an infrared sensor is a far more cost-

effective alternative.

! Multiple measurements required – When many points on a target need to be measured, it is

usually more practical to re-aim an infrared sensor than it is to reposition a thermocouple or

to deploy a great number of thermocouples. The fast response of the infrared sensor isimportant.

There are, of course, limitations to the non-contact approach—conditions that might make itimpractical or ineffective. These will be covered as the discussion progresses.

1.2 Heat Transfer and Infrared Radiation Basics

Infrared thermography is based on measuring the distribution of radiant thermal energy (heat)emitted from a target surface and converting this to a surface temperature map or thermogram.

The thermographer requires an understanding of heat, temperature, and the various types of heattransfer as an essential prerequisite in preparing to undertake a program of IR thermography.This section is an overview discussion to provide the reader with a basic understanding of how

heat transfer phenomena affect non-contact infrared thermal sensing and thermographic

measurements. For a more detailed discussion of temperature and heat transfer basics, see

Appendix A.

1.2.1 Heat and Temperature

Heat is defined as thermal energy in transition, flowing from one place or object to another as aresult of temperature difference, with the flow of heat changing the energy levels in the objects.

All of the energy must be taken into account because energy can neither be created nordestroyed. What we often refer to as a heat source (like an oil furnace or an electric heater) is

really one form or another of energy conversion; the energy stored in one object is converted to

heat and flows to another object. Temperature is a property of matter and not a completemeasurement of internal energy. It defines the direction of heat flow when another temperature is

known. Heat always flows from the object that is at the higher temperature to the objectthat is at the lower temperature. As a result of heat transfer, hotter objects tend to become

cooler and cooler objects become hotter, approaching thermal equilibrium. To maintain a steady-state condition, energy needs to be continuously supplied to the hotter object by some means of

energy conversion so that the temperatures and, hence, the heat flow, remain constant.

1.2.2 Instruments for Temperature Measurement (Contact and Non-Contact)

Conventional temperature measuring instruments use various contact sensors. A mercury

thermometer works on the principle of expansion with heat: the mercury expansion is calibrated based on its known characteristics and the reading is an indication of the temperature at the site

of the mercury reservoir. Thermometers using thermocouples, thermopiles, and thermistors are

based on the electrical-thermal characteristics of these sensors and produce a reading based on

1-2


27/246



the temperature of the object with which the sensor is in contact. Infrared thermal instruments

are non-contact devices and produce readings based on the surface temperature of objects

at which the instrument is pointed.

1.2.3 Converting Temperature Units

Temperature is expressed in either absolute or relative terms. There are two absolute scalescalled Rankine (English system) and Kelvin (metric system). There are two correspondingrelative scales called Fahrenheit (English system) and Celsius or Centigrade (metric system).

For a detailed discussion of temperature units and formulas for converting from one scale

to another, see Appendix A.

Table 1-1 is a conversion table to facilitate the rapid conversion of temperature betweenFahrenheit and Celsius values. Instructions for the use of the table are shown at the top. For

convenience, Table 1-1 is repeated in Appendix A (Table A-1). For quick reference, the

conversion factors are summarized in Appendix C, Plate 1.

1.2.4 The Three Modes of Heat Transfer

There are three modes of heat transfer: conduction, convection, and radiation. All heat transfer

processes occur by one or more of these three modes. Infrared thermography is based on themeasurement of radiative heat flow and is, therefore, most closely related to the radiation mode

of heat transfer. For a detailed discussion of heat transfer modes and the relationship

between infrared measurements and radiative heat flow, see Appendix A.

1-3


28/246



Table 1-1Temperature Conversion Chart

Instructions for Use:

1. Start in the Temp. column and find the temperature that you wish to convert.

2. If the temperature to be converted is in °C, scan to the right column for the °F equivalent.

3. If the temperature to be converted is in °F, scan to the left column for the °C equivalent.

°C Temp. °F °C Temp. °F °C Temp. °F

-101 -150 -238 -36.7 -34 -29.2 -26.7 -16 3.2

-95.6 -140 -220 -36.1 -33 -27.4 -26.1 -15 5

-90 -130 -202 -35.6 -32 -25.6 -25.6 -14 6.8

-84.4 -120 -184 -35 -31 -23.8 -25 -13 8.6

-78.9 -110 -166 -34.4 -30 -22 -24.4 -12 10.4

-73.3 -100 -148 -33.9 -29 -20.2 -23.9 -11 12.2

-67.8 -90 -130 -33.3 -28 -18.4 -23.3 -10 14

-62.2 -80 -112 -32.2 -26 -14.8 -22.8 -9 15.8

-56.7 -70 -94 -31.7 -25 -13 -22.2 -8 17.6

-51.1 -60 -76 -31.1 -24 -11.2 -21.7 -7 19.4

-45.6 -50 -58 -30.6 -23 -9.4 21.1 -6 21.2

-40 -40 -40 -30 -22 -7.6 -20.6 -5 23

-39.4 -39 -38.2 -29.4 -21 -5.8 -20 -4 24.8

-38.9 -38 -36.4 -28.9 -20 -4 -19.4 -3 26.6

-38.3 -37 -34.6 -28.3 -19 -2.2 -18.9 -2 28.4

-37.8 -36 -32.8 -27.8 -18 0.4 -18.3 -1 30.2-37.2 -35 -31 -27.2 -17 1.4 -17.8 0 32

1-4


29/246



Table 1-1 (cont.)Temperature Conversion Chart


-17.2 1 33.8 -2.8 27 80.6 11.7 53 127.4

-16.7 2 35.6 -2.2 28 82.4 12.2 54 129.2-16.1 3 37.4 -1.7 29 84.2 12.8 55 131

-15.6 4 39.2 -1.1 30 86 13.3 56 132.8

-15 5 41 -0.6 31 87.8 13.9 57 134.6

-14.4 6 42.8 0 32 89.6 14.4 58 136.4

-13.9 7 44.6 0.6 33 91.4 15 59 138.2

-13.3 8 46.4 1.1 34 93.2 15.6 60 140

-12.8 9 48.2 1.7 35 95 16.1 61 141.8

-12.2 10 50 2.2 36 96.8 16.7 62 143.6

-11.1 12 53.6 2.8 37 98.6 17.2 63 145.4

-10.6 13 55.4 3.3 38 100.4 17.8 64 147.2

-10 14 57.2 3.9 39 102.2 18.3 65 149

-9.4 15 59 4.4 40 104 18.9 66 150.8

-8.9 16 60.8 5 41 105.8 19.4 67 152.6

-8.3 17 62.6 5.6 42 107.6 20 68 154.4

-7.8 18 64.4 6.1 43 109.4 20.6 69 156.2

-7.5 19 66.2 6.7 44 111.2 21.1 70 158

-6.7 20 68 7.2 45 113 21.7 71 159.8

-6.1 21 69.8 7.8 46 114.8 22.2 72 161.6

-5.6 22 71.6 8.3 47 116.6 22.8 73 163.4-5.0 23 73.4 8.9 48 118.4 23.3 74 165.2

-4.4 24 75.2 10 50 122 23.9 75 167

-3.9 25 77 10.6 51 123.8 24.4 76 168.8

-3.3 26 78.8 11.1 52 125.6 25 77 170.6

1-5


30/246



Table 1-1 (cont.)Temperature Conversion Chart


25.6 78 172.4 54.4 130 266 193 380 716

26.1 79 174.2 60 140 284 199 390 73426.7 80 176 65.6 150 302 204 400 752

27.2 81 177.8 71.1 160 320 210 410 770

27.8 82 179.6 76.7 170 338 216 420 788

28.3 83 181.4 82.2 180 356 221 430 806

28.9 84 183.2 87.8 190 374 227 440 824

29.4 85 185 93.3 200 392 232 450 842

30 86 186.8 98.9 210 410 238 460 860

30.6 87 188.6 104 220 428 243 470 878

31.1 88 190.4 110 230 446 249 480 896

31.7 89 192.2 116 240 464 254 490 914

32.2 90 194 121 250 482 260 500 932

32.8 91 195.8 127 260 500 288 550 1022

33.3 92 197.6 132 270 518 316 600 1112

33.9 93 199.4 138 280 536 343 650 1202

34.4 94 201.2 143 290 554 370 700 1292

35 95 203 149 300 572 399 750 1382

35.6 96 204.8 154 310 590 427 800 1472

36.1 97 206.6 160 320 608 454 850 1562

36.7 98 208.4 166 330 626 482 900 165237.2 99 210.2 171 340 644 510 950 1742

37.8 100 212 177 350 662 538 1000 1832

43.3 110 230 182 360 680 566 1050 1922

48.9 120 248 188 370 698 593 1110 2012

621 1150 2102 843 1550 2822 1066 1950 3542

649 1200 2192 871 1600 2912 1093 2000 3632

677 1250 2282 899 1650 3002 1149 2100 3812

704 1300 2372 927 1700 3092 1204 2200 3992

732 1350 2462 954 1750 3182 1260 2300 4172

760 1400 2552 982 1800 3272 1316 2400 4352

788 1450 2642 1010 1850 3362 1371 2500 4532

816 1500 2732 1038 1900 3452

Conversion Factors °C = (°F - 32) x 5/9 0 Kelvin = -273.16°C°F = (°C x 9/5) + 32 0 Rankine = -459.69°F

1-6


31/246



1.3 Measuring and Mapping Temperature Without Contact

All targets radiate energy in the infrared spectrum. The hotter the target, the more energy that is

radiated. Very hot targets radiate in the visible spectrum as well as in the infrared. As targetscool, they no longer glow but they continue to radiate. The radiation can be felt on a hand placed

near the target's surface, but the glow can't be seen because the energy has shifted from red toinfrared. Infrared detectors can sense infrared radiant energy and produce useful electrical

signals proportional to the temperature of target surfaces. Instruments using infrared detectorsallow a fast and highly sensitive target surface temperature measurement without contact.

Instruments that combine this measurement capability with the capability of scanning a target

surface area are called infrared thermal imagers. They produce thermal maps, or thermograms,where the brightness intensity or color of any spot on the map is representative of the surface

temperature of that spot. In other words, they extend non-contact point temperature

measurements to non-contact thermography.

1.3.1 The Three Elements of a Non-Contact Temperature Measurement

In using infrared instruments for making non-contact temperature measurements, three sets ofcharacteristics need to be considered:

! Target surface

! Transmitting medium between the target and the instrument

! Measuring instrument

Figure 1-1 shows how the instrument is aimed at the target and makes the measurement through

the medium.

1-7


32/246



Figure 1-1 Categories of Conditions for Infrared Thermal Measurements

Every target surface above absolute zero radiates energy in the infrared. The hotter the target, the

more radiant infrared energy is emitted. The physical laws that define this behavior are discussed

in detail in Appendix A, along with a detailed discussion of medium and instrumentcharacteristics. Emissivity is a very important characteristic of a target surface and must be

known in order to make accurate non-contact temperature measurements. Methods for estimatingand measuring emissivity are discussed throughout this guide, and the emissivity setting that is

needed to dial into the instrument can usually be estimated from available tables and charts. The

proper setting needed to make the instrument produce the correct temperature reading can be

learned experimentally by using samples of the actual target material. This more practical settingvalue is called effective emissivity.

Although the transmitting medium is usually air, non-contact temperature measurements can be

made through a vacuum, gas, or certain solid materials. The characteristics of the medium need

consideration and a detailed explanation of this is included in Appendix A. Figure 1-2 shows thenecessary components of an infrared radiation thermometer that makes a single point non-contact

temperature measurement on the target surface. Collecting optics (that is, infrared lenses, etc.) isnecessary in order to focus the energy radiated from the target onto the sensitive surface of an

infrared detector. The detector converts this energy into an electrical signal that is representative

of the temperature of a spot on the target. Adding scanning elements between the target and the

detector (also shown in Figure 1-2) allows the instrument to scan the target surface and to produce a thermogram. Most currently available infrared thermal imagers incorporate

1-8


33/246



multi-detector focal plane array (FPA) sensors that are electronically scanned and that eliminate

the requirement for an opto-mechanical scanning mechanism.

When an infrared radiation thermometer (point-sensing instrument) is aimed at a target, itcollects energy within a collecting beam, the shape of which is determined by the configuration

of the optics and the detector. The cross-section of this collecting beam is called the field of view(FOV) of the instrument and it determines the size of the area (spot size) on the target surfacethat is measured by the instrument. On scanning and imaging instruments this is called the

instantaneous field of view (IFOV) and becomes one picture element on the thermogram.

Figure 1-2Components of an Infrared Sensing Instrument

1.4 Performance Parameters of Thermal Sensing Instruments

This section previews the performance parameters of point-sensing instruments and scanning and

imaging instruments. For a detailed discussion of these parameters and how to specify and testthe performance of instruments, please refer to Appendix A.

1.4.1 Point-Sensing Instruments

Point-sensing instruments are defined by the following performance parameters:

! Temperature range – The high and low limits over which the target temperature might vary

! Absolute accuracy – As related to the NIST (National Institute of Standards and Technology)standard

! Repeatability – How faithfully a reading is repeated for the same target

1-9


34/246



! Temperature sensitivity – The smallest target temperature change that the instrument needs todetect

! Speed of response – How fast the instrument responds to a temperature change at the target

surface

!

Target spot size and working distance – The size of the spot on the target to be measured andits distance from the instrument

! Output requirements – How the output signal is to be utilized

! Spectral range – The portion of the infrared spectrum over which the instrument will operate

! Sensor environment – The ambient conditions under which the instrument will operate

1.4.2 Line Scanners and Imagers—Qualitative and Quantitative

The parameters used for assessing the performance of infrared thermal line scanners and imagers

are more complex because a thermal line-scan or image is made up of a great number of discrete point measurements. Many of the performance parameters of infrared thermal line-scanners andimagers, such as accuracy, repeatability, and spectral range, however, are the same as those of

radiation thermometers. Others are derived from, or are extensions of, radiation thermometer

performance parameters.

Some types of thermal imagers show comparative temperatures and not actual temperaturemeasurements. For users of these thermal viewers (see section 3), parameters dealing with

accuracy and repeatability do not apply. Parameters exclusive to thermal line-scanners and

imagers are as follows:

! Total field of view (TFOV) – The thermogram image size, in terms of scanning angle.

(example: TFOV=20° Vertical x 30° Horizontal) The TFOV of a line scanner is consideredto be the TFOV of one scan line.

! Instantaneous field of view (IFOV) – The spot size represented by one detector element atthe target plane: Imaging spatial resolution.

(example: IFOV= 2 milliradians) (1° = 35 milliradians)

! Measurement spatial resolution: (IFOVmeas) – The spatial resolution that describes theminimum target spot size on which an accurate temperature measurement can be made.

(example: IFOVmeas = 5 milliradians)

! Frame (or line) repetition rate – The number of times every point on the target is scanned in

one second.(example: Frame rate = 30/second or 30 Hz; Scan rate = 60 lines/second)

! Minimum resolvable temperature (MRT) – The smallest blackbody equivalent targettemperature difference that can be observed: Temperature sensitivity.

(example: MRT=0.1°C @ 30°C target temperature)

1-10


35/246



! Other parameters such as spectral ranges, target temperature ranges, accuracy andrepeatability, and focusing distances are essentially the same as those for point-measuring

instruments.

1.4.3 Thermal Imaging Software

In order to optimize the effectiveness of thermographic measurement programs, the

thermographer needs a basic understanding of the thermal image processing techniques. The

following is a list of broad categories of thermal image processing and diagnostics currentlyavailable. A discussion of each of these categories is included in Appendix A. A detailed

description of currently available thermal imaging and diagnostic software is provided in

section 2.

Thermal imaging software can be categorized into the following groups:

! Quantitative thermal measurements of targets

! Detailed processing and image diagnostics

! Image recording, storage, and recovery

! Image comparison

! Archiving and database*

*Although data and image database development is not an exclusive characteristic of thermalimaging software, it should be considered an important part of the thermographer’s tool kit.

1-11


36/246


37/246


2A COMPENDIUM OF COMMERCIAL INFRARED

SENSING AND IMAGING INSTRUMENTS

This chapter begins with a classification of infrared sensing and imaging instruments by type andapplication. The list includes commercially available instruments, from single-point thermal probes to on-line control sensors, to high-speed, high-resolution thermal imaging (thermography)systems [1].

A detailed overview of performance characteristics and features follows, along with a discussion

of the typical thermographic display approaches that are used by various imager manufacturers.This is followed by a discussion of currently available thermographic image processing softwareand image hard-copy recording accessories. Finally, a tabulation of currently availableinstruments by category and manufacturer is appended, including a digest of performancecharacteristics and features. A current index of manufacturers' addresses, phone numbers, Websites (where available), and/or e-mail addresses is also included.

2.1 Classification of Instruments

Infrared sensing instruments are traditionally classified into three groups: point-sensing, line-scanning, and thermographic (two-dimensional scanning). Point-sensing devices (commonly

called Infrared Radiation Thermometers) collect radiant energy from a spot or area on thesurface of an object to be measured (the target ) and provide an output indication, usually interms of target temperature. Line-scanning instruments provide an output, generally an analogtrace, of the radiant energy (or, in ideal cases, temperature) distribution along a single straight-line projection from the target surface. Thermographic instruments (imagers) provide an imageof the energy distribution over a scanned area on the target surface. This is presented in the formof an intensity-modulated black and white picture or a synthesized color display called athermogram.

Point sensors, line scanners, and imagers can be further divided into sub-groups. This sectionwill review commercially available instruments along the lines of this breakdown:

Point-Sensing

! Probes and IR thermocouples

! Portable (hand-held)

! On-line monitoring and control

! Specials

2-1


38/246


A Compendium of Commercial Infrared Sensing and Imaging Instruments

Line-Scanning

! Opto-mechanically scanned

! Focal plane array (FPA), electronically scanned

Thermographic! Opto-mechanically scanned imagers

! Electronically scanned pyrovidicon imagers

! Electronically scanned focal plane array imagers

2.2 Instrument Manufacturers

Particularly in the point-sensing category, there are many companies offering the sameinstrument under different private label arrangements. In order to avoid duplication, the originalmanufacturer or prime (U.S.) distributor will be listed in the material that follows.

At the end of Section 2, a comprehensive list of instruments is included (Table 2-1), for whichdescriptive literature was available at the time of the preparation of this text. The performancecharacteristics are summarized rather than presented in detail. The listed manufacturer should becontacted for detailed performance information.

A listing of current addresses, phone numbers, Web sites, and/or e-mail addresses, for the listedequipment manufacturers, is included in a separate table (Table 2-2) at the end of Section 2. Inaddition, a third table is included, which summarizes proven industrial applications for thermalimaging instruments (Table 2-3). The information that follows will highlight the applications forwhich each instrument category and group is particularly suited, based on configuration or

performance characteristics.

2.3 Discussion of Instruments

2.3.1 Point Sensors (Radiation Thermometers)

2.3.1.1 Probes

Temperature probes are characterized by low price (from less than $100 to about $1,000),

pocket-portability, and wide-collecting angle. They are battery-powered and are generallyoptically pre-adjusted for minimum spot size at a short working distance (a 1/4" (6.35 mm) spotat a 3/4" (19.05 mm) working distance is typical). Some models are designed to operate into aconventional multi-meter and some incorporate their own readout box with a liquid crystal diode(LCD) display. They usually feature disposable batteries and some models have ac adapters.Temperature ranges are from about 0°F, or slightly below, to 600°F, and a sensitivity of +/- 1°Fis easily achieved. Emissivity adjustments are available on some models. Probes are ideal for

2-2


39/246



close-up measurements and are used in circuit board analysis, troubleshooting of electricalconnections, the inspection of plumbing systems, and in application to biological and medicalstudies.

2.3.1.2 Portable Hand-Held

With few exceptions, these instruments are pistol-shaped and designed for middle-distancemeasurements. They are usually optically pre-adjusted for infinity focus. A typical 2° field ofview resolves a 7.5-cm (3-inch) spot at a 150-cm (60-inch) working distance, and a 30-cm (1-foot) spot at a 9-m (30-foot) working distance. Prices range from about $100 to more than$3,500. Sighting and aiming methods vary from simple aiming notches to enclosed illuminatedreticles. There are instruments with extremely narrow fields of view (0.5°) that include a riflestock and telescopic sight. Most instruments in this group incorporate emissivity adjustments andsome include microcomputers with limited memory and data-logging capabilities. Most areavailable with a recorder output, although this feature is seldom used. A meter is always

provided and, with one exception that reads in BTU/ft²-h, the readout is always in temperatureunits. Analog displays are still available, although they are decreasing in popularity. Digitalreadouts featuring light emitting diodes (LEDs) were introduced first but the LCD display,introduced more recently, is now used almost universally because its tiny power drain extends battery life. For this reason, the more recent instruments offer replaceable rather thanrechargeable batteries and battery life approaches one year. Some instruments in this group havezeroing adjustments, but all of the newer instruments include auto-zeroing features. Temperatureranges are, typically, from 0°C to 1500°C. Temperature sensitivity and readability are usually1°C (or °F) or 1% of scale, although sensitivities on the order of 0.1°C (or °F) are achievable.

This instrument group is particularly suited to applications where spot-checking of target

temperatures is sufficient and continuous monitoring is not required. A typical use would be for periodic maintenance checks of rotating machinery to detect whether or not bearings are beginning to overheat. These instruments, over the past few years, have become an important part of many plant energy conservation programs. Although many of these instruments provideextremely accurate readings, accuracy, like the recorder output, is less important to most usersthan repeatability, ruggedness, portability, reliability, and ease of use. Some newer modelsincorporate microcomputers with special features such as a data-logger, which has the capabilityto store as many as 60 readings for future retrieval and printout.

2.3.1.3 On-Line Monitoring and Control

These instruments are primarily used for monitoring and control of manufacturing processes.The one feature that distinguishes this instrument group from the others is dedicated use. Theinstrument is generally mounted where it can measure the temperature of one specific target, andit remains there for the life of the instrument or the process. With few exceptions, theseinstruments operate on line power. The output signal of the instrument can be observed on ameter, used to operate a switch or relay, feed a simple or sophisticated process control loop, or itcan be used in any combination of these functions.

2-3


40/246



Early on-line instruments consisted of an optical sensing head and an electronics/control readoutunit at the other end of an interconnecting cable. This configuration still exists to some extent, but most of the newer units feature sensing heads that are more stable electronically and, hence,more independent of the remote control units. The trend is for these new sensors to mate withuniversal indicator/control units that accept input from various types of industrial sensors.

This instrument group is selected to perform a specific task, so the manufacturer provides a shopping list ordering format to the customer, enabling them to purchase all required features.

Manufacturers offer sensing head features such as variable or fixed focus, sighting tubes, light pipes, water-coolable housings, air purge fittings, air curtain devices, and see-through aimingwith target-defining reticles. The shopping list for the indicator/controller unit might includedigital readout, binary coded decimal (BCD) output, analog output, single, double, or proportional set point, rate signals, sample and hold, peak or valley sensor, and data-loggerinterface. Emissivity controls, located in a prominent place on a general-purpose instrument, aremore likely to be located behind a bezel on the sensor on these dedicated units, where they are

set one time and locked.

Spectral characteristics are worth mentioning separately, although, technically, they are part ofthe sensing head shopping list . The spectral interval over which the sensing head operates isselected to optimize the signal from the target, to reduce or eliminate the effect of an interferingenergy source, or to enable the instrument to measure the surface temperature of thin films ofmaterial that are largely transparent to infrared energy. This last application has made theseinstruments important factors in the manufacture of thin film plastics and also of glass.

2.3.1.4 Specials

There are several special categories of spot-measuring instruments that are worth mentioning,although they might, by strict definition, fit into one or more of the above categories.

Two-color or ratio pyrometers are one special case of an on-line instrument. These are particularly useful in high-temperature applications and in measuring small targets. The effectiveemissivity of the target need not be known, providing that it is constant and that reflections arecontrolled. The target need not fill the field of view, provided that the background is cool,constant, and uniform. Impurities in the optical path that result in broadband absorption, do notaffect the measurement because the measurement is based on the ratio of energy in two spectral bands. Ratio pyrometers are, generally, not applicable to measurements below 500°F.

Another special case is the fiber optic-coupled thermometer. With this instrument, inaccessibletargets can be measured by replacing the optic with a flexible or rigid fiber optic bundle. This, ofcourse, limits the spectral performance and, hence the temperature range, to the higher values, but it has allowed temperature measurements to be made when none were possible.

The infrared microscope is a third special case. This instrument is configured like a conventionalmicroscope. Through the use of reflective microscope objectives and beam splitters, it enables

2-4


41/246



the operator to simultaneously view and measure targets down to 0.0003" (.00762 mm) indiameter with an accuracy and resolution of about 0.5°F.

Another special case, known as the laser pyrometer , has also become available. This instrumentuses the reflected energy of an active laser to measure target reflectance. A built-in

microcomputer calculates target effective emissivity and uses this to provide a corrected truetemperature reading. The laser pyrometer is useful for high-temperature diffuse target surfaces.

Prices of instruments in the on-line control instrument group vary from less than $1,000 for aninfrared switch, to more than $15,000 for infrared microscopes and on-line instruments equippedwith many control features. Generally speaking, the price goes up when sensitivity, small spotsize, and speed of response are all required and, of course, when many shopping list items, oradditional features, are added.

2.3.2 Line Scanners

The purpose of spatial scanning is to derive information concerning the distribution of radiantenergy over a target scene. Quite often, a single straight line scanned on the target is all that isnecessary to locate a critical thermal anomaly. In the newer line scanners, the single-elementdetector is replaced by a multi-element single-line focal plane array (FPA) and the opto-mechanical scanning element is eliminated. Probably the first approach to line scanning that wasadopted commercially was in an aerial-type thermal mapper in which the line scanner wasmounted on a moving aircraft and scanned lines normal to the direction of motion. The outputsrepresenting these individual scan lines were intensity-modulated and serially displayed inshades of gray on a strip map. This display represented the thermal map of the surface beingoverflown by the vehicle.

2.3.2.1 Opto-Mechanically Scanned Line Scanners

The earliest process-monitoring line scanners (many of which are still in use) employed a single-element detector and a single scanning element, usually a mirror. The instantaneous position ofthe scanning element is usually controlled or sensed by an encoder or potentiometer so that theradiometric output signal can be accompanied by a position signal output and be displayed on achart recorder, an oscilloscope, or some other recording device.

One portable, battery-powered line scanner, still used commercially, scans a single line on target,develops a visible temperature trace using light emitting diodes and, by means of optical beam-

splitting techniques, superimposes this trace over the visible scene viewed by the operator. Theoperator selects the line to be scanned by aiming the instrument's horizontal centerline. Photo-recording of the composite scene is accomplished by aiming a conventional instant color camerathrough the eyepiece of the scanner. This instrument has no recorder output and is, therefore, notsuited for process control applications. Unlike most thermal viewers, however, absolutetemperatures are obtainable with this device. Good applications for this line scanner includeelectrical switchgear and transmission lines, the troubleshooting of plumbing systems, and web- process profiling.

2-5


42/246



2.3.2.2 Electronically Scanned Focal Plane Array Line Scanners

The newest high-speed on-line commercial line scanners employ linear focal plane detectorarrays that are electronically scanned. They develop high-resolution thermal maps by orientingthe linear array along an axis normal to the motion of a moving target such as a paper web, a

rotating kiln, or a strip steel process. The output signal information is in real-time computer-compatible format and can be used to monitor, control, or predict the behavior of the target. The best applications for this scanner are in on-line real-time process monitoring and control.

In significant recent developments, families of line cameras have been made available with awide selection of linear focal plane array detectors based on the speed, resolution, and spectralsensitivity requirements of the process being monitored.

2.3.3 Thermographic Instruments

An important advantage of radiation thermometers over contact thermometers is their speed of

response. The measured energy travels from the target to the sensor at the speed of light. Theresponse of the instrument can then be in milliseconds or even microseconds. This importantfeature has allowed the field of infrared radiation thermometry to expand into real-time thermalscanning and thermal mapping. When problems in temperature monitoring and control cannot besolved by the measurement of one or several discrete points on a target surface, it becomesnecessary to spatially scan (that is, to move the collecting beam (instantaneous field of view) ofthe instrument relative to the target). The detector output is intensity-modulated in proportion tothe total exitant radiant energy at each point scanned on the target surface. The image producedis presented in monochrome or color, where the gray shades or color hue are intended torepresent a thermal level at the target surface. These thermal images are called thermograms.

The purpose of spatial scanning is to derive information concerning the distribution of infraredradiant energy over a target scene. Scanning can be accomplished either opto-mechanically orelectronically.

Opto-mechanical scanning can be done by moving the target with the instrument fixed, or bymoving (translating or panning) the instrument, but is most practically accomplished by insertingmovable optical elements into the collected beam. Although an almost infinite variety ofscanning patterns can be generated using two moving elements, the most common pattern isrectilinear. This is most often accomplished by two elements that each scan a line normal to theother. A typical rectilinear scanner employs two rotating prisms behind the primary lens system(refractive scanning). An alternate configuration uses two oscillating mirrors behind the primary

lens (reflective scanning). This is also commonly used in commercially available scanners, as arecombinations of reflective and refractive scanning elements.

Electronic scanning involves no mechanical scanning elements—the thermal pattern of thesurface is scanned electronically. The earliest method of electronically scanned thermal imagingis the pyrovidicon (pyroelectric vidicon) or thermal video system. With this method, charge proportional to target temperature is collected on a single pyroelectric detector surface, within anelectronic picture tube. Scanning is accomplished by an electronic scanning beam. Although

2-6


43/246



many of these devices are currently in use in the field, manufacturers have all but discontinuedoffering them in favor of instruments based on solid-state focal plane array technology.

Most recently, electronically scanned thermal imaging is accomplished by means of an infraredfocal plane array (IRFPA), whereby a two-dimensional staring array of detectors collects radiant

energy from the target and is digitally scanned to produce the thermogram.

All of the above approaches to producing an infrared thermogram will be discussed.

Commercial thermal imaging systems fall into the following categories and sub-categories:

! Thermal viewers, opto-mechanically scanned

! Imaging radiometers, opto-mechanically scanned

! Thermal viewers, electronically scanned (pyrovidicon imagers)

! Focal plane array (FPA) imagers, qualitative (thermal viewers), and quantitative (imaging

radiometers)

A comprehensive list (Table 2-1) of all known, commercially available thermal-imaginginstruments, on which descriptive literature was available at the time of the preparation of thisdocument, is included at the end of Section 2. Performance characteristics are also brieflysummarized. A listing of current addresses, phone numbers, Web sites, and/or e-mail addresses,of the listed equipment manufacturers, is included in a separate table (Table 2-2) at the end ofSection 2. In addition, a third table is included, which summarizes proven industrial applicationsfor thermal imaging instruments (Table 2-3). The information that follows will highlight theapplications for which each instrument category and group is particularly suited, based onconfiguration or performance characteristics.

2.3.3.1 Thermal Viewers, Opto-Mechanically Scanned

Note: Although they are being replaced gradually by focal plane array imagers (see section

2.3.3.4), at the time of this writing, opto-mechanically scanned thermal viewers are still in wideuse commercially. For this reason, the following operational description is provided.

Opto-mechanically scanned thermal viewers are inexpensive battery-powered scanninginstruments producing a qualitative image of the (thermally associated) radiant exitancedistribution over the surface of a target. The battery packs are rechargeable and usually prov

38179874 infrared thermography guide revision 3

Documents