Understanding infrared thermography reading 7 part 2 of 2

Infrared Thermal TestingReading VII Part 2 of 2My ASNT Level III, Pre-Exam Preparatory Self Study Notes 12 June 2015

Charlie Chong/ Fion Zhang


6. Basic Elements Of An In-house ProgramThe creation of an in-house program to utilize infrared thermography would be customized to each facilitys methods of conducting operations. The basicelements of each program, however, would probably be much the same. Thissection outlines a generic approach to developing and implementing acomprehensive infrared thermography program. A discussion of the basicelements is followed by a sample program.


6.1 Basic Elements An in-house program can be developed by many different approaches. A program that is limited to the use of only qualitative thermal imaginginstruments (as compared to radiometric/quantitative) is likely to be lesscomprehensive. Assuming that a program was created to make full use of aradiometric/quantitative imager and image processing software, the followingtopics would need to be addressed:

Reporting requirements

Qualification of personnel

Scheduling

Equipment matrix

References

Introduction

Definitions

Scope

Responsibilities

Precautions

Prerequisites

Conduct of the Survey

Acceptance criteria


6.1.1 Introduction This section provides a discussion of the purpose and goal of the IR survey.

6.1.2 Definitions In order to put the program in the proper context, the definitions should be at the front. This will allow the reader or reviewer to have an easy reference forthe terminology that follows.

6.1.3 Scope The scope of the program should be very specific as to what is covered and what is not. The applications for infrared thermography are very broad.Inspections of roofs and buildings should not be addressed in a documentthat has inspections of safety-related equipment as its main purpose. Anaddendum to the main procedure should be used to avoid confusion.


6.1.4 Responsibilities This section should clearly delineate who is responsible for the various aspects of the program from administration through corrective action. Themain areas of responsibility are administration, inspection (InfraredThermographer), and corrective action. Most of the difficulty in applying thistechnology is in image interpretation and diagnosis. It might be necessary touse others in this effort and, if so, their role should be specifically identified.

6.1.5 Precautions Many of the infrared inspections necessitate that panels be removed from energized electrical equipment. Precautions as to electrical and personnelsafety should be included.


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6.1.6 Prerequisites All of the prerequisites for conducting the survey should be identified here. This should include the qualification of personnel, calibration of equipment,approvals needed from Operations and/or Management, and the requiredresources (equipment and personnel).

6.1.7 Conduct of the Survey This section could reference or include specific procedures for inspections. Specific techniques and a suggested sequence of inspections could also be included.


6.1.8 Acceptance Criteria All survey results should be compared to either a baseline thermogram or other industry accepted standards. Problems or anomalies should then bereviewed for determination of which corrective action, if any, should beundertaken. The following acceptance criteria provide a generic example butwould need adaptation for component-specific use.

An alternative to the above classification is that used in Military Standard MIL-STD-2194 (1988). The MIL Standard uses four categories as follows:


The main difference between the two methods of problem classification is that the MIL Standard references temperature rise above ambient and the guideclassification relates to a temperature rise above a reference value. Thatreference value could be ambient or, in the case of three-phase electricalcircuits, a temperature rise above an adjacent phase. Each facility shouldadopt criteria that provide a balance between maintenance requirements andoperational considerations.


6.1.9 Reporting Criteria A rigid process should be established when reporting the results of infrared inspections. This rigidity is necessary due to the ease of misinterpretation ofthe thermograms by untrained personnel. A typical quarterly survey ofelectrical equipment might result in 25 to 50 problems in 200 pieces ofinspected equipment. The vast majority of these problems might be minor innature and require corrective action on a low priority. The process that worksbest, based on industry responses, is one that keeps the report distributionand decision-making in the hands of the right people (operations,maintenance, and/or program managers). The format for the report shouldalso be consistent.


At a minimum, it should include the following: Time/date Equipment identification Location Specific problem Corrective action recommended Problem action criteria Visible photograph Infrared photograph Inspectors name and signature


6.1.10 Qualification of Personnel Personnel responsible for conducting the surveys and interpreting the results should be trained in the use of the equipment and certified by their employer.The training and certification criteria, established by the American Society forNondestructive Testing (ASNT), should be adapted and incorporated into theprogram. These criteria are outlined in their document SNT-TC-1A and will bediscussed in more detail in Section 7.

6.1.11 Scheduling The documentation requirements and listing of equipment to be evaluated during the survey should be established in advance so that trends inequipment operation can be translated easily into predictions of future results.This is the key to predictive maintenance. The program must also be flexibleenough to accommodate emergency inspections and inspections duringunplanned outages. Typically, the administrator of the IR program providesthis interface.


6.1.12 Equipment Matrix The equipment to be surveyed, the selection criteria, and the locations and frequency of inspection should be compiled in a matrix. Typically, theelectrical equipment is grouped together, as are the other major componentgroups. An alternate approach would be to list the equipment in a route ofsurvey-format, which might save time for the infrared thermographer.

6.1.13 References References to any helpful information should be provided. These typically include training materials, textbooks on the subject, and equipment operation manuals.

EPRI Licensed Material

Basic Elements of an In-House Program

6.2 Sample Program

This section incorporates the above recommendations and could serve as the basis for a program using infrared thermography as part of a predictive maintenance program.

1.0 INTRODUCTION

1.1 This program is for the administration and conduct of an infrared inspection program of electrical and mechanical equipment. The purpose of this program is to identify equipment that requires maintenance and to improve its reliability through the use of infrared thermography (IR).

1.2 This document contains the recommended scope, frequency, and corrective action criteria for routine and unscheduled infrared surveys.

1.3 Requests for changes to this program and questions relative to it shall be directed to the administrator of the IR program.

2.0 DEFINITIONS

2.1 Infrared Electromagnetic radiation having wavelengths that are greater than those of visible light, but shorter than microwaves. As it applies to IR thermography, the wavelengths are between 3 to 15 micrometers.

2.2 Infrared Survey A comprehensive examination of components and equipment with an infrared imaging system.

2.3 Emissivity The ratio of radiance from a surface to the radiance at the same wavelength from a perfect blackbody at the same temperature. Functionally, this is the radiation efficiency of a surface in the infrared spectrum.

2.4 Radiosity Thermal energy of a surface as seen by the infrared detector.

2.5 Thermogram A recorded, displayed, or hard-copy image of the output of an infrared imaging system.

2.6 Isotherm A thermal contour on a thermogram where all of the spots along it are at the same apparent temperature.

2.7 Infrared thermographer An individual who is trained and qualified to operate infrared imaging equipment and to interpret the images.

3.0 SCOPE

3.1 The requirements of this procedure shall apply to all safety-related components. It shall also be applicable to non-safety-related equipment where financial benefit might be achieved by monitoring (that is, increased plant availability, decreased maintenance costs, and so on).

3.2 This procedure includes guidelines for the following:

Component selection

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EPRI Licensed Material Basic Elements of an In-House Program

Interval selection Determining component acceptability

4.0 RESPONSIBILITIES

4.1 Administrator of IR It is the administrators responsibility to oversee the program. This includes making changes to the procedure. All surveys, whether they are scheduled or conducted on an emergency basis, shall be approved by the administrator or his/her designee. The administrator shall be responsible for budgeting, planning, and interfacing with outside organizations.

4.2 Infrared Thermographer The infrared thermographer is the only person trained and qualified to operate the infrared imaging equipment. He/she is responsible for conducting the surveys, interpreting the images, writing the reports, and acting as a technical resource to other plant departments. The infrared thermographer is responsible for the maintenance and calibration of the infrared imaging equipment.

4.3 Cognizant Engineer At the request of the infrared thermographer, a discipline-cognizant engineer will provide assistance in diagnosing a problem. The cognizant engineer will also suggest corrective action and provide coordination with other plant disciplines.

4.4 Root Cause Determination of root cause and the subsequent applicable action level shall be the responsibility of plant management. When necessary, the infrared thermographer shall request assistance from a cognizant systems or maintenance engineer in determining the root cause or the recommended corrective action.

5.0 PRECAUTIONS

5.1 Many of the components that are being inspected represent potential plant trip hazards; exercise extreme care.

5.2 All safe work practices as outlined in the plant safety manual, shall be followed. These practices include exhibiting caution near energized electrical equipment, rotating equipment, and hot pipes. All surveys shall be conducted from a safe stable location.

5.3 Infrared surveys within the Radiological Controls Area shall be conducted within the guidelines of the Health Physics Department. In areas of potential contamination, the infrared thermographer shall be responsible for covering the equipment with plastic as directed by Health Physics.

5.4 When practical, surveys in areas of airborne contamination should be avoided. When this is not possible, a thin piece of polyethylene or plastic can be placed over the lens. If this is done, the transmittance of the covering must be taken into account.

6.0 PREREQUISITES

6.1 Personnel The infrared thermographer and one craft person constitute the minimum personnel necessary to conduct a survey when the operating or opening of equipment is necessary.

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6.2 Approvals The required approvals to conduct a survey shall be coordinated with the IR administrator. The control room should be notified both prior to the start of the survey and at its end. If requested, the infrared thermographer will inform the control room prior to opening equipment that presents a possible plant trip hazard.

6.3 Emergencies In cases where requests for surveys are done on an emergency basis, the infrared thermographer shall fulfill the duties of the IR administrator and provide the necessary coordination.

7.0 CONDUCT OF THE SURVEY

7.1 The equipment survey matrix shall identify the equipment to be surveyed and the frequency of the survey.

7.2 The sequence of the survey is not important unless specifically stated in the procedure or requested by either Maintenance or Operations. All equipment on the matrix must be surveyed unless it is not in operation or conditions dictate otherwise. The infrared thermographer shall note any exceptions in the inspection report.

7.3 Standard practice is to videotape all surveys and to include an audio track for verbal identification and discussion.

7.4 The thermal images must be of sufficient resolution to identify the components and any problem areas.

7.5 When problems are identified, the thermographer shall reposition the imager and obtain more than one view. This is done to eliminate the possibility of apparent problems being caused by reflections from hot objects. The hard-copy images should be obtained from the position that provides the best image.

7.6 All problems are to be photographed in the visible as well as in the infrared. This is to allow proper and easy identification of the problem areas, which will facilitate maintenance activities.

7.7 The problems shall be customarily reported as a temperature rise. This rise can be calculated from ambient, thermal baseline data, or made by comparison in the cases where similar equipment exists.

7.8 When absolute temperatures are requested or required, the infrared thermographer shall determine and use the target's effective emissivity to assure accuracy. A standard table of effective emissivities will be developed by measurement and will be maintained by the infrared thermographer.

7.9 Important information relating to test conditions, such as load, flow, and pressure shall be noted by the thermographer if it is available. This information will be used in component trend analysis.

7.10 The components shall be inspected with the imager aimed along a line normal (perpendicular) to the target surface whenever possible, to minimize the potential for errors due to reflections.

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7.11 During the infrared inspection, the components must also be inspected visually and any discolorations, questionable noise, or smell should be reported.

7.12 In cases where precise measurements must be obtained, the instrument background radiation effects must be taken into account. Instrument background temperature can be determined by placing a good diffuse reflector (such as a piece of aluminum foil that has been crumpled and re-flattened) in ambient air and measuring its apparent temperature with the imagers emissivity set to 1.0.

7.13 Where external optics, such as telescopic and wide-angle lenses are used, the transmittance of the optics must be taken into account. The information that corrects the effects of these devices is supplied by the manufacturer and is entered directly into the imager software.

7.14 When measurements are being made on targets, the size of the target and the distance must be known. The IFOVmeas (Instantaneous Field of View for measurement) of the instrument must fit comfortably within the required target spot at the measurement distance. If these criteria are not satisfied, the instrument must be moved closer to the target and/or a higher magnification lens must be used. (See section 3.3.4 for a more detailed discussion of this subject).

7.15 The survey should be done with the imager scanned at a speed that does not cause blurring of the image so that acceptable thermograms can be obtained from the videotape on playback.

7.16 If requested or desired, a second (backup) measure of temperature can be obtained through the use of contact thermocouples or spot radiometers. (Care should be used in evaluating the results of measurements that are not calibrated.)

7.17 In general, equipment shall be surveyed when in a normal operational state. In cases where equipment is not energized or running normally, the thermographer shall note it in the IR inspection report.

7.18 Equipment such as batteries shall be surveyed during both normal operation and during discharge tests.

7.19 Requests for equipment operation for the sole purpose of an infrared inspection shall be coordinated with operations by the IR administrator. In most cases, this should be avoided.

7.20 All infrared inspections, whether done by on-site personnel or outside contractors, will be performed under the guidance and procedures listed in this program. Special tests outside of the normal inspection shall be reviewed and approved in advance by the IR administrator.

8.0 ACCEPTANCE CRITERIA

8.1 Subsequent to an initial thermal baseline, the following action levels are to be used to classify each problem:

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Advisory (Level 1) 1F to 15F rise

Intermediate (Level 2) 16F to 50F rise

Serious (Level 3) 51F to 100F rise

Critical (Level 4) in excess of 100F rise

8.2 When indications on components fall into levels 2, 3, 4, section 9 of the program shall be followed for reporting.

8.3 To determine acceptability of the inspection, the results and final report shall be compared against the criteria set forth in this program.

9.0 REPORTING REQUIREMENTS

9.1 Every scheduled and unscheduled infrared inspection shall be documented and reported in accordance with the requirements of this section (see Figure 6-1).

9.2 At a minimum, the report shall contain the following:

Summary of inspection and findings

Equipment list

Data sheets with IR and visible photographs of anomalies

Root cause analysis and corrective action

Comments 9.3 The report shall be issued to the IR administrator within five working days of the

completion of the survey.

9.4 A verbal report shall always be given to the on-site IR administrator upon completion of the survey.

9.5 The reporting of problems that fall within the four acceptance action levels are as follows:

Advisory (Level 1) Normal cycle of corrective maintenance.

Intermediate (Level 2) High priority during an unscheduled shutdown.

Serious (Level 3) Alert Operationspotential failure. Correct ASAP.

Critical (Level 4) Alert Operations, Management. Remove from service ASAP.

9.6 Items classified as serious are to be immediately reported to the IR administrator who will advise Maintenance and Operations.

9.7 Items classified as critical are to be immediately reported to Operations, Maintenance, and the IR administrator.

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10.0 QUALIFICATION OF PERSONNEL

10.1 The infrared thermographer shall be qualified by examination and certified by the plant to conduct the survey.

10.2 The qualifying examination and training shall meet the guidelines of ASNT SNT-TC-1A (current edition).

10.3 In addition to the ASNT qualifications, the thermographer shall be knowledgeable in the following areas:

Equipment-specific operation Infrared theory Heat transfer modes Safety practices

10.4 Certification of the thermographer shall be made through a written and a practical examination.

10.5 The plant Training Department shall administer the initial and re-qualification training.

11.0 SCHEDULING

11.1 The IR administrator is responsible for scheduling all routine infrared inspections.

11.2 The Equipment Matrix (Program, section 12.0) lists the frequency of inspection for each component.

11.3 Inspections on an emergency basis or for a special test shall be scheduled and coordinated by the IR administrator.

12.0 EQUIPMENT MATRIX

12.1 Component Selection Criteria

12.1.1 The components that are to be included in the thermographic analysis program should be selected based on the perceived or documented benefit of thermography on the type of equipment and the following criteria categories:

A. Critical: Critical equipment shall be defined as:

Equipment whose function is necessary and must be available at all times.

Equipment upon which thermography has been used to deviate from a specific vendor-recommended preventive maintenance activity.

Equipment necessary to maintain full-power generating capabilities (that is, non-redundant).

B. Vital: Vital equipment shall be defined as those components whose function is necessary but that, through redundant design, do not have to be available at all times.

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C. Vendor Recommended: Vendor-recommended equipment whose manufacturer or vendor recommends the periodic monitoring of the equipment with infrared thermography.

D. Non-Vital: Non-Vital equipment shall be defined as:

Equipment whose replacement cost versus periodic monitoring cost does not differ greatly and does not fall into category A or B above.

Components that are used very infrequently and do not fall into category A or B.

12.1.2 The IR administrator shall maintain a listing of all of the components in the thermographic analysis program, the category to which they belong, and their monitoring interval.

12.1.3 Equipment in category D that has a failure history relating to thermography might be included in the program in order to determine root cause, or to prevent failure recurrences or significant inconveniences. Otherwise, equipment in category D should be omitted from the program.

12.1.4 The above recommended component selection criteria should be applied predominantly to electrical equipment such as: Motor control centers Load centers Transformers Switchgear Battery chargers Switchyard equipment Large motor termination

12.1.5 The above criteria can also be applied to:

Pumps/motors Steam traps Valves

12.2 Performance Intervals

12.2.1 The selection of performance intervals should be based upon several factors, such as:

The impact of the component on plant operation and personnel safety if an

unexpected failure were to occur.

The speed at which a component fault manifests itself into a stage of degradation, which affects the components operability.

Vendor/manufacturers recommendations.

The category of the component as stated in section 12.1.1 of the program.

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12.2.2 When considering the vendors recommended frequency for thermography, the application of the equipment should be taken into consideration (that is, the run time experienced by the equipment in this installation versus what the vendor expects for typical run times). Also, if the component falls into categories A or B of 12.1.1, then the most limiting interval (between the vendor-recommended interval and the recommended interval in section 12.2.3 of the program) shall be used for the monitoring of the equipment.

12.2.3 The following recommended intervals for the given categories should be used:

A. Critical Equipment

Monitor quarterly for those components that are operated continuously or are op-tested at least quarterly.

Monitor semi-annually for those components that are operated continuously or are run-tested at least semi-annually.

At start-up, monitor when the component is placed on-line, is at a stabilized temperature, and has not been monitored for at least one monitoring interval.

Equipment less than 240 V does not require periodic monitoring.

B. Vital Equipment

Monitor equipment greater than 480 V quarterly. Monitor equipment greater than 240 V but less than 480 V semi-annually. Equipment less than 240 V does not require periodic monitoring.

12.2.4 Changes to monitoring intervals should be reviewed carefully prior to making changes in order to ensure that maximum component availability and program efficiency is provided.

12.2.5 At a minimum, documentation for interval changes shall be maintained, by the IR administrator.

12.2.6 Components need not be operated for the sole purpose of collecting thermography data.

13.0 SUGGESTED PROGRAM REFERENCES

13.1 Infrared Thermography Guide (Revision 3), (formerly NP-6973)

13.2 Plant Administrative Procedures Manual

13.3 Plant Safety Manual

13.4 Plant Training Manual

13.5 Plant Quality Assurance Procedures Manual

13.6 Plant Systems Training Manual

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13.7 Infrared Imager Instruction Manual

13.8 Plant Predictive Maintenance, INPO Good Practice 89-009.

13.9 Wolfe, W. L. and Zissis, G.J., The Infrared Handbook. Environmental Research Institute of Michigan (1996).

13.10 Mil-Std-2194, Infrared Thermal Imaging Survey Procedure Electrical Equipment.

13.11 American Society for Nondestructive Testing Standard Practice SNT-TC-1A, Qualifications Guidelines.

13.12 American Society for Nondestructive Testing Infrared and Thermal Testing Handbook, 2001.

13.13 American Society for Nondestructive Testing Level III Study Guide: Infrared and Thermal Testing Method, 2001.

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Figure 6-1 Infrared Survey Results

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7. TRAINING AND CERTIFICATIONThis section deals solely with the efforts of the American Society of Nondestructive Testing (ASNT) in the training and certification of infraredthermographers. The purpose is to provide guidelines for training individualswho will be able to deliver the best level of service possible. It is important tounderstand that certification via the ASNT Certification Program, does notimply authorization or licensing of the certificate holder to perform infraredthermography tasks. It is solely the employer's responsibility to review theindividuals qualification records for completeness and to authorize individualsto perform infrared thermography tasks.


7.1 Background Commercially available infrared imagers are quite easy to both use and misuse. Many small, independent contractors, from electricians to engineers, provide a wide range of services to many different industries. In the absence of formal training, most of these people have learned on the job while working with more experienced individuals. At the request of many ASNT members, a committee was formed in the fall of 1989 to propose modifying ASNT Recommended Practice No. SNT-TC-1A, the qualification guideline for nondestructive testing, to accept and recognize infrared thermography as a valid nondestructive examination method. At this writing, all of the training, qualification, and certification guidelines are in place and SNT-TC-1A has been updated (1996) to include the T/IR (Thermal Infrared) method. Two additional ASNT publications were released in 2001 to support training and certification:

ASNT Infrared and Thermal Testing Handbook, 2001 ASNT Level III Study Guide: Infrared and Thermal Testing Method, 2001


Recommended training and certification guidelines for infrared thermographers are summarized in the ASNT Infrared and Thermal Testing Handbook on pages 15 -18, and are explained in detail in SNT-TC-1A.

The ASNT training program is intended to supplement equipment-specific training that might be offered by the manufacturers. Certification is theresponsibility of the individual employer. SNT-TC-1A states the followingin this regard:

Written Practice. The employer shall establish a written practice for the control and administration of nondestructive personnel training, examination and certification. The employers written practice should describe the responsibility of each level of certification for determining the acceptability of materials and components in accordance with applicable codes, standards, specifications and procedures.


7.2 Levels of QualificationThe recommended Levels of Qualification for infrared thermographers follow those of traditional NDE methods. These levels are as follows:

Level I A Level I infrared thermographer shall be qualified to perform specific IRinspections in accordance with detailed written instructions and to record the results; the Level 1 infrared thermographer shall perform inspections underthe cognizance of a Level II or Level III. The Level I shall not independentlyperform nor evaluate inspection results for acceptance or rejection when suchinspection results are for the purpose of verifying compliance to code orregulatory requirements. (if the result is not for the purpose of verifying compliance to code or regulatory requirements; then the Level I could independently perform and evaluate inspection result?)


Level II A Level II infrared thermographer shall be qualified to set up and calibrateequipment, conduct inspections, and to interpret inspection results in accordance with procedure requirements. The individual shall be familiar with the limitations and scope of the method employed and shall have the ability to apply techniques over a broad range of applications within the limits of their certification. The Level II shall be able to organize and report inspection results. A Level II must have the ability to correctly identify components and parts of components within the scope of the IR inspection.

Level III A Level III infrared thermographer is capable of designating a particular inspection technique, establishing techniques and procedures, and interpreting results. The individual shall have sufficient practical background in his/her area of expertise to develop innovative techniques and to assist in establishing acceptance criteria where none are otherwise available. The individual shall have general familiarity with other nondestructive evaluation (NDE) methods and inspection technologies. The Level III individual shall be qualified to train and examine Level I and Level II personnel for qualification and certification as an infrared thermographer.


7.3 Training Requirements The training requirements for each level of the infrared thermographer qualification parallel those for the other traditional NDE methods in that on-the-job training, educational background, and classroom work all count toward qualification. There are qualification examinations and annual re-qualification requirements at all levels. It is up to the utilities training organization and individual employers to implement the appropriate recommendations of the training program set forth in SNT-TC-1A.


The experience and education recommendations for the three levels are: Level I A high school diploma (or equivalent) or 6 months of experience Level II A two-year college or technical degree or 18 months of experience Level III A four-year technical degree from a college or university or 5

years of experience

The required classroom training is as follows: Level I 40 hours of instruction, 50-question written examination, classroom

experiment Level II 40 hours of instruction, 75-question written examination,

classroom experiment Level III 40 hours of instruction, 75-question written examination,

procedure preparation for classroom experiment


The classroom training is based on the body of knowledge reviewed, adopted, and updated by ASNT, summarized in ASNT Recommended Practice No.SNT-TC-1A, and reviewed in ASNT Level III Study Guide: Infrared andThermal Testing Method, 2001. The depth that is covered by these areascorresponds to the level of the training. This translates into more extensivetraining at Level III than Level I, even though the classroom hours are thesame. The four areas for training and associated practical aspects are listedbelow. At the conclusion of training, the trainee will:

A. Radiosity or Target Exitance Understand the concepts of radiosity and associated parameters. Be able to measure emissivity, reflectance, transmittance, background

temperature, foreground temperature, and target temperature. Be cognizant of potential errors in the measurement of the above

parameters, caused by variation across the target surface.


B. Spatial Resolution the concept of spatial resolution. Understand the difference between

image resolution and measurement resolution. Understand the effect on measurement of the distance between the

instrument and the target. Be able to calculate measurement spot size. Be able to exploit equipment- pecific aids to determine measurement

adequacy.


C. Heat Transfer Understand the fundamental concepts of heat transfer including

conduction, convection, and radiation. Understand the difference between steady state and transient heat flow

and application dependence. Understand the effect of the environmental conditions of sky temperature,

view factor, wind velocity, and surface orientation. Understand the potential problems if evaporation or condensation occur at

the target surface.


D. Equipment Operation Be able to set up and operate the necessary equipment. Understand dynamic range and its implication in image acquisition. Demonstrate good data acquisition practices. Demonstrate the use of accessories. Understand how to compensate for external optics. Understand the implications of system spectral response.

The written examination is derived from a pool of 200-300 questions that are reviewed and approved by the ASNT T/IR committee members. During training, practical exams are conducted through classroom experiments and are focused on one particular concept, such as transient thermal heat transfer. The actual practical exam is determined by the trainer and is conducted within the guidelines for each particular level. Infrared thermography was adopted as a nondestructive inspection method in the fall of 1991.


7.4 Predictive Maintenance (PdM) Level III Certification Program Recognizing that there are areas of specialization within the infrared thermography discipline, the ASNT T/IR committee has promoted thedevelopment of specialty certification. The Predictive Maintenance Level IIICertification Program has been developed by ASNT in response to this effort.Developed to meet the needs of the predictive maintenance sector of theindustry, this program incorporates the vibration analysis (VA) andinfrared/thermal (IR) test methods. A PdM-specific body of knowledge,including knowledge of the Recommended Practice No. SNT-TC-1A and theANSI/ASNT CP-189 standard, is used for the two-hour PdM basicexamination. The VA and IR method tests are the same as those used in theASNT NDT Level III program. A separate and distinct PdM Level III certificateis issued for this certification.


The PdM basic examination is more specific than the ASNT NDT Level III basic examination, and thus, PdM certificate holders wishing to gain traditional NDT Level III certification will still be required to sit for the ASNT NDT Level III basic examination, as well as taking an ASNT NDT Level III method test.

Certification via the ASNT PdM Level III Certification Program, as with the ASNT NDT Level III program, does not imply authorization or licensing of the PdM certificate holder to perform PdM tasks. It is solely the employers responsibility to review the individuals qualification records for completeness and to authorize individuals to perform PdM.

The Expert!


Appendix-AThe Science Of Thermography (Practical Application Of Thermographic And Thermal Sensing Equipment)


A.1 Introduction This appendix is presented as a reference guide to provide the practical thermographer with an understanding of the science behind themeasurements. It is intended as an aid in performing and understanding non-contact thermal and thermographic measurements using infrared sensingequipment. The deployment and operation of infrared sensing instrumentswas, at one time, cumbersome and difficult. Thermographers were oftenrequired to perform on-the-spot calculations in order to reduce theirmeasurement data and determine actual temperature values; this is no longerso. Modern instruments are light in weight, portable, and rugged.

Menu-driven on-board software now makes it relatively simple to operate equipment and to gather data directly in terms of target temperature. Because of this very ease of operation, it is also relatively simple to misinterpret the results so easily and quickly obtained.


Erroneous conclusions can have an extremely negative effect on themeasurements program and on the credibility of the thermographer.

A solid understanding of the basis on which thermographic measurements are made will go a long way toward minimizing operator error and ensuring the success of the thermographic program.

The subject matter in this appendix begins with a discussion of heat transfer and how radiative heat transfer is the basis for infrared thermography. The basic physics of infrared radiation and how it applies to instrument performance is explained. Finally, the performance parameters of infrared point-sensing and imaging instruments are discussed, including how to select, calibrate, and evaluate the performance of the instrument that is best suited to your application.


A.2 Heat Transfer and Radiation Exchange Basics for ThermographyThis section is to provide the reader with an understanding of how heat transfer phenomena affect non-contact infrared thermal sensing andthermographic measurements. Infrared thermography depends on measuringthe distribution of radiant thermal energy (heat) emitted from a target surface,thus, the thermographer requires an understanding of heat, temperature, and the various types of heat transfer as an essential prerequisite in preparing to undertake a program of IR thermography.


A.2.1 Heat and TemperatureWhat is often referred to as a heat source (like an oil furnace or an electric heater) is really one form or another of energy conversion; the energy storedin one object is converted to heat and flows to another object.

Heat can be defined as thermal energy in transition. It flows from one place or object to another as a result of temperature difference, and the flow of heat changes the energy levels in the objects.

Temperature is a property of matter and not a complete (that means it need other input to completely quantify the internal energy) measurement of internal energy. It defines the direction of heat when another temperature isknown. Heat always flows from the object that is at the higher temperature to the object that 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 temperature and, hence, the heat flow remains constant.


A.2.2 Converting Temperature UnitsTemperature is expressed in either absolute or relative terms. There are two absolute scales called degree Rankine (English system) and Kelvin (metric system). There are two corresponding relative scales called Fahrenheit (English system) and Celsius or Centigrade (metric system). Absolute zero is the temperature at which no molecular action takes place. This is expressed as zero Kelvins or zero Rankines (0 K or 0 R). Relative temperature is expressed as degrees Celsius or degrees Fahrenheit (C or F). The numerical relations among the four scales are as follows:

T Celsius = 5/9 (T Fahrenheit - 32 )T Fahrenheit = 9/5 T Celsius + 32T Rankine = T Fahrenheit + 459.7T Kelvin = T Celsius + 273.16Absolute zero is equal to -273.1C and is also equal to -459.7F.


To convert changes in temperature or delta T between the English and Metric systems, the simple 9/5 (1.8 to 1) relationship is used:

T Fahrenheit (or Rankine) = 1.8 T Celsius (or Kelvin)Table A-1 is a conversion table to allow for the rapid conversion of temperature between Fahrenheit and Celsius values. Instructions for the use of the table are shown at the top.

(T temperature interval)


Table A-1 Temperature 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.


A.2.3 The Three Modes of Heat TransferThere are three modes of heat transfer: (1) conduction, (2) convection, and (3) radiation (and nothing else) . All heat transfer processes occur by one or more of these three modes. Infrared thermography is based on themeasurement of radiative heat flow radiation (and nothing else) and is, therefore, most closely related to the radiation mode of heat transfer.

A.2.4 ConductionConduction is the transfer of heat in stationary media. It is the only mode of heat flow in solids, but can also take place in liquids and gases. It occurs asthe result of molecular collisions (in liquids) (fluid, both liquid and gas) and atomic vibrations (in solids), whereby energy is moved one molecule at a time, from higher temperature sites to lower temperature sites. Figure A-1 is an illustration of conductive heat flow. The Fourier conduction law expresses the conductive heat flow through the slab shown in Figure A-1.


Figure A-1 Conductive Heat Flow


The Fourier Conduction Law:

Q/A = K (T1 - T2) / L

Q = KTA / LWhere:Q/A = the rate of heat transfer through the slab per unit area

perpendicular to the flowL = the thickness of the slabT1 = the higher temperature (at the left)T2 = the lower temperature (at the right)K = the thermal conductivity of the slab material


Thermal conductivity is analogous to electrical conductivity and is inversely proportional to thermal resistance, as shown in the lower portion of Figure A-1.The temperatures, T1 and T2, are analogous to voltages V1 and V2, and theheat flow, Q/A, is analogous to electrical current, I, so that: if:

R electrical = V1 - V2/ I

then:

R thermal = T1 - T2 / Q /A = L/K

Heat flow is usually expressed in English units. K is expressed in BTU/hrftF and thermal resistance (1/K) would then be expressed in Fhrft/BTU.


A.2.5 ConvectionConvective heat transfer takes place in a moving medium and is almost always associated with transfer between a solid and a moving fluid (such asair). Forced convection takes place when an external driving force, such aswind or an air pump, moves the fluid. Free convection takes place when thetemperature difference necessary for heat transfer produces density changesin the fluid and the warmer fluid rises as a result of increased buoyancy. Inconvective heat flow, heat transfer takes effect by means of two mechanisms,(1) the direct conduction through the fluid and (2) the motion of the fluid itself.

Figure A-2 illustrates convective heat transfer between a flat plate and a moving fluid. The presence of the plate causes the velocity of the fluid to decrease to zero at the surface and influences its velocity throughout thethickness of a boundary layer. The thickness of the boundary layer depends on the free velocity, V, of the fluid. It is greater for free convection and smaller for forced convection. The rate of heat flow depends on the thickness of the convection layer, as well as the temperature difference between Ts and T (Ts is the surface temperature, T is the free field fluid temperature outside of the boundary layer.)


Newtons cooling law defines the convective heat transfer coefficient:

(h is expressed in BTU/hr-ft-F)rearranged:

= Thwhere:Rc = 1/h and is the resistance to convective heat flowRc is also analogous to electrical resistance and is easier to use when determining combined conductive and convective heat transfer.


Figure A-2 Convective Heat Flow


A.2.6 RadiationRadiative heat transfer is unlike the other two modes in several respects:

1. It can take place in a vacuum.2. It occurs by electromagnetic emission and absorption.3. It occurs at the speed of light.4. The energy transferred is proportional to the fourth power of the

temperature difference between the objects (T4 or T4?) .The electromagnetic spectrum is illustrated in Figure A-3. Radiative heattransfer takes place in the infrared portion of the spectrum, between 0.75 m and about 100 m (0.1mm) , although most practical measurements can be made out to 20 m. ( or m stands for micrometers or microns. A micron is one-millionth of a meter and is the measurement unit for radiant energy wavelength.) (radiative heat only take place at the aforementioned portion of spectrum?)


Figure A-3 Infrared in the Electromagnetic Spectrum


A.2.7 Radiation Exchange at the Target SurfaceThe measurement of thermal infrared radiation is the basis for non-contact temperature measurement and thermal imaging (or thermography). Theprocess of thermal infrared radiation leaving a surface is called exitance orradiosity. It can be emitted from the surface, reflected off of the surface, ortransmitted through the surface. This is illustrated in Figure A-4. The totalradiosity is equal to the sum of the emitted component (E), the reflectedcomponent (R), and the transmitted component (T). The surface temperature is related to E, the emitted component only.


Thermal infrared radiation impinging on a surface can be absorbed, reflected, or transmitted as illustrated in Figure A-5. Kirchhoffs law states that the sum of the three components is always equal to the received radiation (the percentage sum of the three components equals unity):

A (absorptivity) + R (reflectivity) + T (transmissivity) = 1

( + + = 1)When making practical measurements, the specularity or diffusivity of a target surface is taken into effect by accounting for the emissivity of the surface. Emissivity is discussed as part of the detailed discussion of the characteristics of infrared thermal radiation in section A.3.


Figure A-4 Radiative Heat Flow


Figure A-4 Radiative Heat Flow

W = Te4W = Tr4W = Tt4


Figure A-5 Radiation Exchange at the Target Surface


A.2.8 Specular and Diffuse SurfacesIt should be noted that the roughness or structure of a surface will determine the type and direction of reflection of incident radiation. A smooth surface willreflect incident energy at an angle complementary to the angle of incidence.This is called a specular reflector. A rough or structured surface will scatter ordisperse some of the incident radiation; this is a diffuse reflector.

No perfectly specular or perfectly diffuse surface can exist in nature. All real surfaces have some diffusivity and some specularity.


Specular or Diffuse Surfaces


Specular or Diffuse Surfaces Diffuse Reflector

Specular Reflector?

http://www.hunantv.com/v/3/56616/f/750962.html?f=lb#


Specular and Diffuse Surfaces

Diffuse Reflector

Specular Reflector?


Specular and Diffuse Surfaces

Confused

Specular Reflector?


Specular or Diffuse Surfaces


Specular reflection is the mirror-like reflection of light (or of other kinds of wave) from a surface, in which light from a single incoming direction (a ray) is reflected into a single outgoing direction. Such behavior is described by the law of reflection, which states that the direction of incoming light (the incident ray), and the direction of outgoing light reflected (the reflected ray) make the same angle with respect to the surface normal, thus the angle of incidence equals the angle of reflection 2 = 1 in the figure), and that the incident, normal, and reflected directions are coplanar.


Reflections off Specular and Diffuse Surfaces


A.2.9 Transient Heat Exchange The discussions of the three types of heat exchange in sections A.2.4, A.2.5, and A.2.6 deal with steady-state heat exchange for reasons of simplicity and easier understanding. Two fixedtemperatures are assumed to exist at the two points between which the heat flows. In many applications, however, temperatures are in transition, so that the values shown for energy radiated from a target surface are the instantaneous values from the moment that measurements are made. There are numerous instances where existing transient thermal conditions areexploited in order to use thermography to reveal material or structural characteristics in test articles.


The thermogram of the outside surface of an insulated vessel carrying heated liquid, for example, should be relatively isothermal and somewhat warmer than the ambient air. Insulation voids or defects will cause warm anomalies to appear on the thermogram, allowing the thermographer to pinpoint areas ofdefective or damaged insulation. Here a passive approach can be takenbecause the transient heat flow (or it is a steady state heat flow?) from the liquid through the insulation to the outside air produces the desired characteristic thermal pattern on the product surface. Similarly, watersaturated areas on flat roofs will retain solar heat well into the night; long after the dry sections have radiated their stored heat to the cold night sky, the saturated sections will continue to radiate and exhibit distinct anomalies to the thermographer. When there is no heat flow through the material or the test article to be evaluated, an active, or thermal injection, approach is used to generate a transient heat flow.

Comment: In general steady state heat flow always lead to thermal equilibrium, for IRT, transient heat flows are exploited to reveal abnormalities.


This approach requires the generation of a controlled flow of thermal energy across the laminar structure of the sample material under test, thermography monitoring of one of the surfaces (or sometimes both) of the sample, and a search for anomalies in the thermal patterns that will indicate a defect inaccordance with established accept-reject criteria. This approach has been used extensively and successfully by the aerospace community in the evaluation of composite structures for impurities, flaws, voids, disbonds, delaminations, and variations in structural integrity. Most recently, time-based heat injection methods have been applied successfully to measure the depthof voids, as well as their location. This is effective because thinner sections of a given material will heat more rapidly than thicker sections.


Steady-state conductionSteady state conduction is the form of conduction that happens when the temperature differences T driving the conduction are constant, so that (after an equilibration time), the spatial distribution of temperatures (temperature field) in the conducting object does not change any further. Thus, all partial derivatives of temperature with respect to space may either be zero or have nonzero values, but all derivatives of temperature at any point with respect to time are uniformly zero. In steady state conduction, the amount of heat entering any region of an object is equal to amount of heat coming out (if this were not so, the temperature would be rising or falling, as thermal energy was tapped or trapped in a region).

For example, a bar may be cold at one end and hot at the other, but after a state of steady state conduction is reached, the spatial gradient of temperatures along the bar does not change any further, as time proceeds. Instead, the temperature at any given section of the rod remains constant, and this temperature varies linearly in space, along the direction of heat transfer.

In steady state conduction, all the laws of direct current electrical conduction can be applied to "heat currents". In such cases, it is possible to take "thermal resistances" as the analog to electrical resistances. In such cases, temperature plays the role of voltage, and heat transferred per unit time (heat power) is the analog of electrical current. Steady state systems can be modelled by networks of such thermal resistances in series and in parallel, in exact analogy to electrical networks of resistors. See purely resistive thermal circuits for an example of such a network.

https://en.wikipedia.org/wiki/Thermal_conduction


Transient conductionIn general, during any period in which temperatures change in time at any place within an object, the mode of thermal energy flow is termed transient conduction. Another term is "non steady-state" conduction, referring to time-dependence of temperature fields in an object. Non-steady-state situations appear after an imposed change in temperature at a boundary of an object. They may also occur with temperature changes inside an object, as a result of a new source or sink of heat suddenly introduced within an object, causing temperatures near the source or sink to change in time.

When a new perturbation of temperature of this type happens, temperatures within the system change in time toward a new equilibrium with the new conditions, provided that these do not change. After equilibrium, heat flow into the system once again equals the heat flow out, and temperatures at each point inside the system no longer change. Once this happens, transient conduction is ended, although steady-state conduction may continue if heat flow continues. If changes in external temperatures or internal heat generation changes are too rapid for equilibrium of temperatures in space to take place, then the system never reaches a state of unchanging temperature distribution in time, and the system remains in a transient state.

An example of a new source of heat "turning on" within an object, causing transient conduction, is an engine starting in an automobile. In this case the transient thermal conduction phase for the entire machine is over, and the steady state phase appears, as soon as the engine reaches steady-state operating temperature. In this state of steady-state equilibrium, temperatures vary greatly from the engine cylinders to other parts of the automobile, but at no point in space within the automobile does temperature increase or decrease. After establishing this state, the transient conduction phase of heat transfer is over.

https://en.wikipedia.org/wiki/Thermal_conduction


A.3 The Basic Physics of Infrared Radiation and SensingAll targets radiate energy in the infrared spectrum. The hotter the target, the more energy is radiated (T4). Very hot targets radiate in the visible as well, and our eyes can see this because they are sensitive to light. The sun for example, at about 6000 K, appears to glow white-hot; a tungsten filament, at about 3000 K, has a yellowish glow, and an electric stove element, at 800 K, glows red. As the stove element cools, it loses its visible glow but it continues to radiate. We can feel it with a hand placed near the surface but we cant seethe glow because the energy has shifted from red to infrared. Infrareddetectors can sense infrared radiant energy and produce useful electricalsignals proportional to the temperature of target surfaces. Instruments thatuse infrared detectors and optics to gather and focus energy from the targetsonto these detectors are capable of measuring target surface temperatureswith sensitivities better than 0.1C, and with response times as fast asmicroseconds. Instruments that combine this measurement capability withcapabilities for scanning the target surface are called infrared thermal imagers.


They can produce thermal maps or thermograms where the brightnessintensity or color hue of any spot on the map is representative of thetemperature of the surface at that point. In most cases, thermal imagers canbe considered as extensions of radiation thermometers or as a radiationthermometer with scanning capability. The performance parameters ofthermal imagers are extensions of the performance parameters of radiationthermometers.


A.3.1 Some Historical BackgroundThe color of a glowing metal is a fair indication of its temperature (the higher the temperature, the whiter the color). The ancient sword-maker andblacksmith knew from the color of a heated part when it was time to quenchand temper. This technique is still in use today; precision optical matchingpyrometers are used to match the brightness in color of a product with that ofa glowing filament. The brightness of the filament is controlled by adjusting aknob that is calibrated in temperature. The next logical step is to substitute aphotomultiplier for the operators eye and, thus, calibrate the measurement.Finally, a differential measurement is made between what the brightness ofthe product is and what it should be (the set point), and the differential signalis injected into the process and used to drive the product temperature to theset point. With the advent of modern infrared detectors, the precisionmeasurement of thermal energy radiating from surfaces that do not glowbecame possible. Measurements of cool surfaces, well below 0C, areaccomplished routinely with even the least expensive of infrared sensors.


A.3.2 Non-Contact Thermal MeasurementsInfrared non-contact thermal sensing instruments are classified as infrared radiation thermometers by the American Society of Testing and Materials(ASTM), even though they dont always read out in temperatures. The laws of physics allow for the conversion of infrared radiation measurements totemperature measurements. This is done by first measuring the self-emittedradiation in the infrared portion of the electromagnetic spectrum of targetsurfaces, and then converting these measurements to electrical signals. Inmaking these measurements, three sets of characteristics need to beconsidered:

The target surface The transmitting medium between the target and the instrument The measuring instrument


A.3.3 The Target SurfaceThe chart of the electromagnetic spectrum (Figure A-3) indicates that the infrared portion of the spectrum lies adjacent to the visible. Every targetsurface above absolute zero (0 Kelvins or -273 Centigrade) radiates energyin the infrared. The hotter the target, the more radiant energy is emitted.When targets are hot enough, they radiate or glow in the visible part of thespectrum as well ( and beyond that, again becoming invisible again, example UV & ray) . As they cool, the eye becomes no longer able to see the emitted radiation and the targets appear to not glow at all. Infrared sensors are employed here to measure the radiation in the infrared, which can be related to target surface temperature. The visible spectrum extends from energy wavelengths of 0.4 m for violet light to about 0.75 m for red light. ( or m stands for micrometers or microns. A micron is one-millionth of a meter and is the measurement unit for radiant energy wavelength.) For practical purposes of temperature measurement, the infrared spectrum extends from 0.75 m to about 20 m.


The visible spectrum extends fromenergy wavelengths of

0.4 m for violet light to about 0.75 m for red light. For practical purposes oftemperature measurement, the infrared spectrum

extends from 0.75 m to about 20 m.

for my ASNT Exam


Figure A-6 shows the distribution of emitted energy over the electromagnetic spectrum of targets at various temperatures. The sun, at 6000 K, appearswhite hot because its emitted energy is centered over the visible spectrumwith a peak at 0.5 m. Other targets, such as a tungsten filament at 3000 K, ared-hot surface at 800 K, and the ambient earth at 300 K (about 30C), arealso shown in this illustration. It becomes apparent that, as surfaces cool, notonly do they emit less energy, but the wavelength distribution shifts to longerinfrared wavelengths. Even though the eye becomes no longer capable ofsensing this energy, infrared sensors can detect these invisible longerwavelengths. They enable us to measure the self-emitted radiant energy fromeven very cold targets and, thereby, determine the temperatures of targetsurfaces remotely and without contact.

Keypoints: The visible spectrum extends from energy wavelengths of 0.4 m for violet light to about 0.75 m for red light. For practical purposes of temperature measurement, the infrared spectrum extends from 0.75 m to about 20 m.


Figure A-6 Blackbody Curves at Various Temperatures

Charlie C

hong/ Fion Zhang

Charlie Chong/ Fion Zhang http://www.nasa.gov/centers/goddard/news/topstory/2004/0107filament.html

m = b/T = (2897/T m)


Two physical laws define the radiant behavior illustrated in Figure A-6:

The Stephan-Boltzmann Law (1):

W = T4and Wiens Displacement Law (2):

m = b/T = (2897/T m)Where: W = Radiant flux emitted per unit are a (watts/cm) = Emissivity (unity for a blackbody target) = Stephan-Boltzmann constant = 5.673 x10-12 watts cm-2T = Absolute temperature of target (K)m = Wavelength of maximum radiation (m)b = Wiens displacement constant = 2897 (mK)


According to (1), the radiant energy emitted from the target surface (W) equals two constants multiplied by the fourth power of the absolutetemperature (T4) of the target. The instrument measures W and calculates T.

One of the two constants, , is a fixed number. Emissivity () is the other constant and is a surface characteristic that is only constant for a given material over a given range of temperatures.

For point measurements, one can usually estimate the emissivity setting needed to dial into the instrument from available tables and charts. One can also learn, experimentally, the proper setting needed to make the instrument produce the correct temperature reading by using samples of the actual target material. This more practical setting value is called effective emissivity (e*).


According to (2), the wavelength at which a target radiates its peak energy is defined as simply a constant (b = 2897 3000) divided by the target temperature (T) in Kelvins. For the 300 K ambient earth, for example, the peak wavelength would be (max = 2897/300) or 10 m. This quickcalculation is important in selecting the proper instrument for a measurement task, as will be discussed in section A.4.

Target surfaces can be classified in three categories: (1) black bodies, (2) gray bodies, and (3) non-gray bodies.

The targets shown in Figure A-6 are all blackbody radiators (or black bodies). A blackbody radiator is a theoretical surface having unity emissivity at all wavelengths and absorbing all of the energy available at its surface. This would be an ideal target to measure because the temperature calculation within the instrument would be simply mechanized and always constant. Fortunately, although blackbody radiators do not exist in practice, the surfaces of most solids are gray bodies, that is, surfaces whose emissivities are high and fairly constant with wavelength.


Figure A-7 shows the comparative spectral distribution of energy emitted by a blackbody, a gray body, and a non-gray body (also called a spectral body), allat the same temperature. For gray body measurements, a simple emissivitycorrection can usually be dialed in when absolute measurements are required.For non-gray bodies, the solutions are more difficult. To understand thereason for this, it is necessary to see what an instrument sees when it isaimed at a non-gray target surface.

Keywords:non-gray body (also called a spectral body)


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


Figure A-8 shows that the instrument sees three components of energy: first, emitted energy (); second, reflected energy from the environment (); andthird, energy transmitted through the target from sources behind the target ().The percentage sum of these components is always unity (1). The instrumentsees only , the emitted energy, when aimed at a blackbody target because ablackbody reflects and transmits nothing. For a gray body, the instrumentsees and , the emitted and reflected energy. The instrument sees all threecomponents when aimed at a nongray body because a non-gray body ispartially transparent.

Keywords:because a non-gray body is partially transparent.(?)


Figure A-8 Components of Energy Reaching the Measuring Instrument


If the emissivity of a gray body is very low, as in the case of polished metal surfaces, the reflectance becomes high (reflectance = 1 - emissivity) and can generate erroneous readings if not properly handled. Reflected energy from a specific source can generally be redirected by proper orientation of theinstrument with respect to the target surface, as shown in Figure A-9. Thisillustrates the proper and improper orientation that is necessary to avoidreflected energy from a specific source.


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


Under certain conditions, an error in temperature indication can occur as the result of a high temperature background, such as a boiler wall (behind theinstrument), reflecting off of a reflective target surface and contributing to theapparent temperature of the target. Most instrument manufacturers provide abackground temperature correction to compensate for this condition. Often, inpractice, the troublesome component is T, the energy transmitted through anon-gray target from sources behind the target. A discussion of solutions tothis type of problem is included in section A.4.

Non-Gray body An object whose emissivity varies with wavelength over the wavelength interval of interest. A radiating object that does not have a spectral radiation distribution similar to a blackbody; also called a colored body or realbody. Glass and plastic films are examples of non-graybodies. An object can be a graybody over one wavelength interval and a non-gray body over another. http://www.infraredtraininginstitute.com/thermography-terms-definitions/

Charlie Chong/ Fion Zhang http://www.moistureview.com/resources/infrarods-blog/page/4

Blackbody, Graybody & Non-graybody (colored body or real body)


EXAM score!

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Non-graybody(colored body or real body)


A.3.4 The Transmitting MediumThe transmission characteristics of the medium in the measurement path between the target and the instrument need to be considered in making non-ontact thermal measurements. No loss of energy is encountered whenmeasuring through a vacuum. For short path lengths, a few feet for example,most gases including the atmosphere, absorb very little energy and can beignored (except where measurements of precision temperature values arerequired). As the path length increases to hundreds of feet, or as the airbecomes heavy with water vapor, the absorption might become a factor. It isthen necessary to consider the infrared transmission characteristics of theatmosphere.


Figure A-10 illustrates the spectral transmission characteristics of 0.3 km of ground level atmosphere (what is the object to detector distance in tabulating the chart? or this is not a factor as the transmittance is given as a ratio (%) with respect to transmittance in vacuum (Transmittance in vacuum=100%)).

Two spectral intervals can be seen to have very high transmission. These are known as the 1.5 m and the 8.14 m atmospheric windows, and almost all infrared sensing and scanning instruments are designed to operate in one or the other of these windows. (unless) Usually, the difficulties encountered with transmitting media occur when the target is viewed by the instrument through another solid object such as a glass or quartz viewing port in a process.

Keywords:These are known as the 1.5 m and the 8.14 m atmospheric windows.


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


Figure A-11 shows transmission curves for various samples of glass and quartz. Upon seeing these, our first impression is that glass is opaque at 10m where ambient (30C) surfaces radiate their peak energy. This impressionis correct and, although in theory, infrared measurements can be made of30C targets through glass, it is hardly practical. The first approach to theproblem is to attempt to eliminate the glass, or at least a portion of it, throughwhich the instrument can be aimed at the target. If, for reasons of hazard,vacuum, or product safety, a window must be present; a material thattransmits in the longer wavelengths might be substituted.


Figure A-11 Infrared Spectral Transmission of Glass


Figure A-11 shows transmission curves for various samples of glass and quartz. Upon seeing these, our first impression is that glass is opaque at 10m where ambient (30C) surfaces radiate their peak energy (?). This impression is correct and, although in theory, infrared measurements can be made of 30C targets through glass, it is hardly practical. The first approach to the problem is to attempt to eliminate the glass, or at least a portion of it, through which the instrument can be aimed at the target. If, for reasons of hazard, vacuum, or product safety, a window must be present; a material thattransmits in the longer wavelengths might be substituted.

Charlie Chong/ Fion Zhang http://www.technicalglass.com/fused_quartz_transmission.html


EXAM score!

Glass is opaque > 5m at 30C?

for my ASNT exam


Figure A-12 shows the spectral transmission characteristics of several ofthese materials, many of which transmit energy past 10 m. These materialsare often used as lenses and optical elements in low-temperature infraredsensors. Of course, as targets become hotter and the emitted energy shifts tothe shorter wavelengths, glass and quartz windows pose less of a problemand are even used as elements and lenses in high-temperature sensinginstruments.


Figure A-12 Characteristics of IR Transmitting Materials

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i

e

C

h

o

n

g

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F

i

o

n

Z

h

a

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The characteristics of the window material will always have some effect on the temperature measurement, but the attenuation can always be correctedby pre-calibrating the instrument with a sample window placed between theinstrument and a target of known temperature. In closing the discussion of thetransmitting medium, it is important to note that infrared sensors can onlywork when all of the following spectral ranges coincide or overlap:

1. The spectral range over which the target emits2. The spectral range over which the medium transmits3. The spectral range over which the instrument operates

123


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A.3.5 The Measuring InstrumentFigure A-13 shows the necessary components of an infrared radiation thermometer. Collecting optics (an infrared lens, for example) is necessary inorder to focus the energy emitted by the target onto the sensitive surface ofan infrared detector, which, in turn, converts this energy into an electricalsignal.


Figure A-13 Components of an Infrared Radiation Thermometer

Thermal or photon detector, single element or FPA.


When an infrared radiation thermometer (point-sensing instrument) is aimed at a target, it collects energy within a collecting beam, the shape of which isdetermined by the configuration of the optics and the detector.

The cross- section of this collecting beam is called the field of view of the instrument, and it determines the size of the area (spot size) on the target surface that is measured by the instrument.

On thermal imaging instruments, this is called the instantaneous field of view (IFOV) and becomes one picture element on the thermogram.

Comment: for single element detector; FOV = IFOVfor FPA multi element detector; IFOV (D) = (rad) x dWhere, d= focal to object distance


Infrared optics are available in two general configurations, refractive and reflective;

Refractive optics (lenses), which are at least partly transparent to the wavelengths of interest, are used most often for high- temperature applications where their throughput losses can be ignored.

Reflective optics (mirrors), which are more efficient but somewhat complicate the optical path, are used more often for low-temperature applications, where the energy levels cannot warrant throughput energy losses.

An infrared interference filter is often placed in front of the detector to limit thespectral region or band of the energy reaching the detector. The reasons for spectral selectivity will be discussed later in this section.


The processing electronics unit amplifies and conditions the signal from the infrared detector and introduces corrections for such factors as (1) detector ambient temperature drift and (2) target surface emissivity. Generally, a meter indicates the target temperature and an analog output is provided. The analog signal is used to record, display, alarm, control, correct, or any combination of these.

Figure A-14 illustrates the configuration of a typical instrument employing all of the elements outlined. The germanium lens collects the energy from a spoton the target surface and focuses it on the surface of the radiation thermopile detector. The 8.14 m filter limits the spectral band of the energy reaching the detector so that it falls within the atmospheric window. The detector generates a dc emf proportional to the energy emitted by the target surface. The auto-zero amplifier senses ambient temperature changes and prevents ambient drift errors. The output electronics unit conditions the signal and computes the target surface temperature based on a manual emissivity setting. The analog output terminals accept a 15 - 30 VDC loop supply and generate a 4 - 20 milliampere signal, proportional to target surface temperature.


All infrared detector-transducers exhibit some electrical change in response to the radiant energy impinging on their sensitive surfaces. Depending on the type of detector this can be (1) an impedance change, (2) a capacitance change, (3) the generation of an emf (voltage), or (4) the release of photons.

Detectors are available with response times as fast as nanoseconds or as slow as fractions of seconds. Depending on the requirement, either a broadband detector or a spectrally limited detector can be selected.

Keywords:Depending on the type of detector this can be (1) an impedance change, (Z) (thermal detector?)(2) a capacitance change, (C) (thermal detector?)(3) the generation of an emf (voltage), (Emf) (thermal detector?)(4) the release of photons. (E=h) (photon detector?)


Sequences of Events:

1. The germanium lens collects the energy from a spot on the target surface2. focuses it on the surface of the radiation thermopile detector. 3. The 8.14 m filter (pass) limits the spectral band of the energy reaching

the detector so that it falls within the atmospheric window. 4. The detector generates a dc emf proportional to the energy emitted by the

target surface. (thermal detector)5. The auto-zero amplifier senses ambient temperature changes and

prevents ambient drift errors. (electronic)6. The output electronics unit conditions the signal and computes the target

surface temperature based on a manual emissivity setting. (W = T4)7. The analog output terminals accept a 15 - 30 Volt, DC loop supply and

generate a 4 - 20 milliampere signal, proportional to target surface temperature.


Figure A-14 Typical Infrared Radiation Thermometer Schematic


Germanium Len


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Thermopile Detector

https://www.adafruit.com/products/2023


Thermopile DetectorThe Grid-EYE 64-thermopile infrared array sensor from Panasonic adds state-of-the-art sensing technology to Avnet Abacus' passives portfolio. Based on Panasonics advanced MEMS technology, the 8x8 grid format infrared array sensor combines a built-in thermistor and an integrated circuit for temperature sensing in a small SMT package measuring only 11.6x4.3x8.0mm. Grid-EYE enables contactless temperature detection over the entire specified area. It can use passive infrared detection to determinetemperature differentiation allowing it to detect multiple objects simultaneously. It is able to measure actual temperature and temperature gradients, providing thermal images and identifying the direction of movement of people or objects. The devices 64 pixel range yields accurate temperature sensing, within the range of -20C to 100C, over a viewing angle of 60 provided by a silicon lens. It uses an external IC communication interface, enabling temperature measurement at speeds of 1 or 10 frames/s. An interrupt function is also available. The operating voltage of the device is 3.3 or 5.0V.

http://www.electronics-eetimes.com/en/64-thermopile-infrared-array-sensor-available-from-avnet-abacus.html?cmp_id=7&news_id=222915463


Thermopile Detector

http://www.electronics-eetimes.com/en/64-thermopile-infrared-array-sensor-available-from-avnet-abacus.html?cmp_id=7&news_id=222915463


Thermopile Detector - DR46 Thermopile DetectorFeatures- A two-channel or a one-channel compensated thin-film thermopile in a TO-8 package. Each active area is 4mm x 0.6mm. Offers high output with excellent signal-to-noise ratio. An internal aperture minimizes channel-to-channel crosstalk increasing sensitivity. Applications: Gas analysis, non-contact temperature measurement, fire detection / suppression.

http://www.dexterresearch.com/?module=Page&sID=dr46


The IR DetectorsInfrared detectors fall into two broad categories:

thermal detectors, which have broad, uniform spectral responses, somewhat lower sensitivities, and slower response times (on the order ofmilliseconds), and photodetectors, (or photon detectors), which have limited spectral responses, higher peak sensitivities, and faster response times (on the order of microseconds).

Thermal detectors will generally operate at or near room temperature, whilephotodetectors are generally cooled to optimize performance. The mercury-Cadmium-telluride (HgCdTe) detector, for example, is a photodetector cooledto 77 K for 8.14 m operation and to 195 K for 3.5 m operation. Because ofits fast response, this detector is used extensively in high-speed scanningand imaging applications.


The radiation thermopile, on the other hand, is a broadband thermal detector operating uncooled. It is used extensively for spot measurements of cool targets. It generates a dc emf proportional to the radiant energy reaching its surface and is ideal for use in portable, battery powered instruments. Figure A-15 illustrates the spectral responses of various infrared detectors.


Figure A-15 Spectral Sensitivity of Various Infrared Detectors


Thermal Detectors & Photon Detectors

ThermalDetector

PhotonDetector


The Mercury- Cadmium-telluride (Hgcdte) Detector,


DiscussionSubject: Why there are many curves for HgCdTe.

http://irassociates.com/index.php?page=hgcdte


The Mercury- Cadmium-Telluride (HgCdTe) Detector FPAWISE Mercury Cadmium Telluride Focal Plane Mount Assembly (HgCdTe FPMA). This picture shows one of the four WISE detectors. The sensitive area shows as green and contains 1 million pixel elements.

http://wise.ssl.berkeley.edu/gallery_detector.html


The Mercury- Cadmium-Telluride (HgCdTe) Detector FPA

http://spie.org/x91246.xml


The Mercury- Cadmium-Telluride (HgCdTe) Detector FPAOctober 24, 2011 - All Eyes on Oldest Recorded SupernovaThis image combines data from four different space telescopes to create a multi-wavelength view of all that remains of the oldest documented example of a supernova, called RCW 86. The Chinese witnessed the event in 185 A.D., documenting a mysterious "guest star" that remained in the sky for eight months. X-ray images from the European Space Agency's XMM-Newton Observatory and NASA's Chandra X-ray Observatory are combined to form the blue and green colors in the image. The X-rays show the interstellar gas that has been heated to millions of degrees by the passage of the shock wave from the supernova.



DiscussionSubject: Why it wasnt pixel-like correspond to the spatial resolution of 106?



The Mercury- Cadmium-Telluride (HgCdTe) Detector FPASept 29, 2011 - Portrait of Two Asteroids in Different Light - This animation illustrates the benefits of observing asteroids in infrared light. It begins by showing two artistic interpretations of asteroids up close. They are about the same size but the one on the right is darker. The animation zooms away to show how a visible-light telescope would see these two space rocks, located at the same distance millions of miles away from Earth, against a background of more distant stars. The one on the left would be much easier to see because it reflects more visible light from the sun. The animation then transitions to an infrared view of the same two objects. Both asteroids are equally as bright because the telescope is picking up infrared light coming from the bodies themselves, as a result of being heated by the sun. The measurements are not strongly affected by how light or dark an asteroid is, a property called albedo. Instead, the brightness is more directly related to an asteroid's size. Therefore, infrared telescopes like WISE are better at both finding the small, dark asteroids and determining asteroid sizes.



Sept 29, 2011 - Portrait of Two Asteroids in Different Light - This animation illustrates the benefits of observing asteroids in infrared light.

http://

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Understanding infrared thermography reading 7 part 2 of 2

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