Understanding the physical principles of electromagnetic radiation will help you avoid the pitfalls and develop a scientific, problem-solving approach to new applications in the growing field of thermography. The goal of this paper is to link working approximations to the formal theory, illustrating that an understanding of the origin of these approximations can be crucial to your success. In addition, a glossary of terms is presented to improve our literacy in this fascinating field of thermography.
A state-of-the-art survey of portable thermal infrared instrumentation used for building diagnostics, plant maintenance and industrial process control is presented. The thermal infrared instrumentation is divided into three generic classes with a description of each class, its advantages and limitations and typical applications. Photographs of typical thermal infrared devices and systems in each class are presented.
This presentation will begin with an historical background of the application of non-contact infrared instruments to the solution of a variety of industrial problems. It will go on to provide a present-day summary of the more generally accepted applications for these instruments. Finally, some predictions will be made of the future of these types of instruments in solving industrial problems.
Moisture is the big enemy of compact roofing systems. Non-destructive nuclear, capacitance and infrared methods can all find wet insulation in such roofs but a few core samples are needed for verification. Nuclear and capacitance surveys generate quantitative results at grid points but examine only a small portion of the roof. Quantitative results are not usually provided by infrared scanners but they can rapidly examine every square inch of the roof. Being able to find wet areas when they are small is an important advantage. Prices vary with the scope of the investigation. For a particular scope, the three techniques are often cost-competitive. The limitations of each technique are related to the people involved as well as the equipment. When the right people are involved, non-destructive surveys are a very effective method for improving the long-term performance and reducing the life-cycle costs of roofing systems. Plans for the maintenance, repair or replacement of a roof should include a roof moisture survey.
Attendees of early Thermosense (TS) conferences were predominantly researchers, entrepreneurs, and equipment suppliers with interests in aerial scanning, ground imaging, and spot radiometer measurements, but all applied to buildings. While buildings are still strongly represented in TS V, the range of interests has broadened. Plant facilities and services were introduced as topics to the TS IV audience, and are being expanded upon in TS V. Industrial processing applications are new to TS V.
Thermographic techniques have for years been used to locate minor interlaminar faults in the stator cores of steam turbine-driven generators. The technique has been largely employed in a quality control or routine maintenance function. However similar thermo-graphic techniques can be used to detect interlaminar faults and monitor repairs of an extensively damaged stator core of a large hydroelectric generator.
Abnormal temperature increases in refinery process equipment are usually indicative of a condition that will eventually result in serious operational problems or equipment failure. Infrared instruments are available that provide both thermal imaging and temperature measurement capabilities. Several examples of the application of infrared thermal imaging in refineries are described. The examples are chosen to show the capabilities of the infrared instruments, the diversity of application, and the techniques required to obtain meaningful information.
Sensitive infrared thermography is widely used to locate potential problems in industrial equipment. Thermographic inspection-based predictive maintenance programs can have highly favorable payback ratios. Industrial inspections should be conducted at least annually for optimum payback.
Thermal infrared imagers provide reliable and timely non-destructive inspection capa-bilities to persons responsible for the operation and maintenance of mechanical systems. This discussion reviews the fundamental principles of mechanical systems, outlines the steps taken in designing a thermographic inspection of a mechanical system and presents a sampling of thermograms from various mechanical applications for thermography.
Given the technological age that we have now entered, the purpose of this paper is to relate how infrared scanning can be used for an electrical preventative maintenance program. An infrared scanner is able to produce an image because objects give off infrared radiation in relationship to their temperature. Most electrical problems will show up as an increase in temperature, thereby making the infrared scanner a useful preventative maintenance tool. Because of the sensitivity of most of the scanners, .1 to .2 of a degree, virtually all electrical problems can be pinpointed long before they become a costly failure. One of the early uses of infrared scanning was to check the power company's electrical distribution system. Most of this was performed via aircraft or truck mounted scanning devices which necessitated its semi-permanent mounting. With the advent of small hand held infrared imagers, along with more portability of the larger systems, infrared scanning has gained more popularity in checking electrical distribution systems. But the distribution systems are now a scaled down model, mainly the in-plant electrical systems. By in-plant, I mean any distribution of electricity; once it leaves the power company's grid. This can be in a hospital, retail outlet, warehouse or manufacturing facility.
This paper presents fundamental principles for the utilization of infrared thermography in quantitative studies. Step-by-step procedures are described for basic field measurement technique without the need for extensive ancillary equipment. Both temperature and emissivity measurements are discussed, and a graphical measurement technique is introduced.
Thermography, or temperature maping, is a useful preventative maintenance and maintenance tool. Although thermography is a useful tool, it is a very expensive equipment investment and requires a highly skilled person to apply the thermoscanning equipment effectively. One of the concepts of preventative maintenance, or maintenance application, is to develop temperature maps depicting thermal levels at various geographic locations. This concept provides a number of advantages. One advantage is that after the maping is completed a less sophisticated and expensive piece of equipment can be used by operating or maintenance personnel to measure temperatures. By comparing the temperatures to the geographic maping, an evaluation of the mill's material condition can be made. If thendll's material condition has deteriorated, the information would help direct a corrective opera-ting procedure away from the weak spots to slow down the deterioration process until maintenance can be performed. Another advantage is that the record of regular checks, made with the less sophisticated equipment done by operating or maintenance personnel, would eventually aid in determining a life cycle of high thermally-stressed areas of the mill. With this collective information it is possible to forecast failure in critical areas, and schedule, at an operationally convenient time, a mill shutdown for repair.
A unique insulating grout used to repair refractory failures in blast furnace stoves can contribute to energy conservation. Infrared thermography techniques identify where refrac-tory failures occur and a closed-circuit television system allows monitoring of the thermal image by the repair crew. With infrared thermography the complete repair can be assured and maximum energy conservation achieved.
Die surface temperature and internal die thermal balance are critical to the quality of semi-permanent mold die castings. Measurements of the surface temperature are currently made using either hand-held contact temperature probes or optical pyrometers. Neither measurement technique provides a thermal map of the entire die surface. This paper discusses the use of infrared thermography for die surface temperature measurement. Using infrared thermographic techniques, scans were made over the surface of an experimental 302 CID semi-permanent mold cylinder head die during several casting cycles. The results obtained were in reasonable agreement with the temperature measurements made using optical pyrometers and the contact probes. In addition, using gray-level conversion the IR technique provided a measure of the temperature gradient over the surface of the die. Such thermal mapping has not been practical using optical or contact temperature probes.
The increasing use of composite materials in military and commercial aircraft requires the development of improved quality control and nondestructive inspection techniques to assure their structural integrity and reliability. Infrared thermography is particularly useful for rapid scanning and detection of manufacturing inhomogeneities and inservice damage states in composites. The relationship between the surface thermal patterns and the interior damage is governed by the type of damage, thermal conductivity of the material and the distance between the surface and the damaged region. Applications of real-time thermography as a quality control technique for processing fiber reinforced composites, and as a nondestructive technique for monitoring growth and development of defects in composite laminates and rotor blades during low-frequency, high amplitude fatigue tests will be discussed. Applications of high frequency vibrothermography for characterizing composite structures will also be presented. This latter technique involves the use of high-frequency, low amplitude ultrasonic excitation of a sample.
Glass processing is always performed at high temperatures and many fabrication operations are done with glass in a semi-fluid condition where non-contact methods of sensing are desirable. There are also a number of other areas of temperature measurement - such as mold temperature, tempering of already hardened glass - which could be done the best by non-contact methods.
A detailed study of four multiple hearth sludge incinerators was undertaken to determine the cause of observed outer wall deterioration. A qualitative inspection revealed little evidence of existing or developing structural defects. A subsequent quantitative analysis determined surface heat losses, effective R-values and temperature profiles for incinerator wall components. From this data it was hypothesized that extensive areas of saturated insulation was present within the incinerator walls and the saturating material was causing the shell deterioration. This hypothesis was proven by subsequent tests.
This article reviews the recent developments in thermographic standards for the inspection of the building envelope. A general overview of the present standards and standards activities is given. The purpose of the standards is explained, their general content outlined and how they are to be used is discussed. The results of a field evaluation of the accuracy of thermographic inspectors in locating insulation voids in cavity walls are summarized. The reasons for the observed inconsistencies in the results of the inspections of the same building by differnent thermographic inspectors are given. In general, at present, it must be concluded that improvements in existing inspection techniques are needed before thermographic inspections can be considered accurate.
For many midwest and northeast states, the cost of energy is an important consideration in their efforts to achieve economic recovery. Certainly this is true of Michigan. Eighty-seven percent of Michigan's 1981 energy needs were purchased from out-of-state sources. In 1982, the Energy Administration estimates that about $9 billion will leave the state to pay for energy imported from other states and countries, providing investment capitol and jobs there, rather than in Michigan. While containing energy costs makes a great deal of sense in Michigan, the problem of how to do it on a scale large enough to make a convincing difference has been difficult. This paper describes a current effort by the Energy Administration, Michigan Department of Commerce, which, we believe, represents a breakthrough in marketing energy conservation.
Rhode Islanders Saving Energy (RISE) is a non-profit corporation founded in 1977 to provide Rhode Island residents with a variety of energy conservation services. Since January of 1981, it has been performing energy audits in compliance with the Department of Energy's (DOE) Residential Conservation Service Program (RCS). One aspect of the RCS program is the performance of inspections on energy conservation activities completed according to RCS installation guidelines. This paper will describe both the use and results of thermographic inspections within the RISE program. The primary objective of these inspections has been to assure the quality of the building envelope after completion of retrofit measures. Thermal anamolies have been detected that vary in size, location and probable cause. Approximately 37% of all jobs performed through RISE in conjunction with the RCS program have required remedial work as a result of problems that were identi-fied during the thermographic inspection. This percentage was much higher when infra-red inspections were conducted on "Non-RCS" retrofits. Statistics will be presented that provide an interesting insight on the quality of retrofit work when performed in associa-tion with a constant inspection process.
There have been many presentations of thermographic residential building analyses at the past ThermosInse conferences. A number of these papers have dealt with evaluation of insulation voids and more recently a few have described air leakage detection 2,3 during the colder winter months. This paper will focus on the thermographic application in the House Doctor instrumented energy analysis approach as developed by Princeton University. The central theme will be the application to a year-round research or commercial activity. Some of the conditions that could create thermographic problems, as well as techniques that may be used to lessen these difficulties, thereby extending the thermographic "season" is discussed. Our experiences in summer thermography with and without the use of a building pressurization system is also covered.
Infrared thermography is the technique of using non-contact scanning equipment that detects invisible infrared radiation (heat) and converts this energy to visible light. To record the real-time images produced by these infrared scanners, we use conventional silver-halide films with conventional cameras to produce hard-copy photographs, or thermograms (a picture of heat). This paper presents the equipment, films, cameras and procedures needed to produce thermograms. We deal exclusively with two infrared thermal imaging viewers, the AGA Thermovision110 and the Hughes Probeyel which present their images through a monocular eyepiece. But much of the information presented can be applied to recording the images of other infrared scanners.
Infrared thermography has proven to be a valuable tool in the detection of heat loss in both commercial and residential buildings. The field of residential thermography has needed a simple method with which to report the deficiencies found during an infrared scan. Two major obstacles hindering the cost effectiveness of residential thermography have been 1) the ability to quickly transport some high resolution imaging system equipment from job site to job site without having to totally dismount the instruments at each area, and 2) the lack of a standard form with which to report the findings of the survey to the customer. Since the industry has yet to provide us with either, we believed it necessary to develop our own. Through trial and error, we have come up with a system that makes interior residential thermography a profitable venture at a price the homeowner can afford.
Insulation voids, or defects can be instantly spotted with the use of a thermal imaging system under the proper conditions. A special hand-held device was developed that enables the thermographer to carry the equipment from house to house without the need to dismantle and set up at each stop. All the necessary components are attached for a total weight of about 40 pounds. The findings are then conveyed to a form we have developed. The form is simple enough that the client without special training in thermography can understand. The client is then able to locate the problems and take corrective measures or give it to a con-tractor to do the work.
Proc. SPIE 0371, Practical Method For Applying Building Diagnostic Techniques To High Volume Urban Energy Auditing And Retrofit Quality Control: Results From Total Surveys In Three Major Swedish Cities, 0000 (21 March 1983); doi: 10.1117/12.934473
Within the last two (2) decades there have been numerous introductions of "new technology" building materials that have gained widespread use in all sectors of construction. This phenomenon is particularly relevant in the industrial and commercial building industries and no single component of these buildings has undergone more changes in recent years than that of the roofing system. As a result of the many changes in building design considerations, roofing systems have become a very costly, complex, and potentially troublesome item that building owners must now contend with.
The premature failure of a costly insulated built-up roofing system is a major concern to every facility manager, military or civilian. Because of the interrelated and critical relationship existing between the various components of the roofing system, it is essential that these roofs be inspected twice a year and repaired, as necessary. The bi-yearly inspection not only requires a comprehensive evaluation of the surface area, but an in-depth look into the interior of the system to determine if moisture has penetrated the system and has begun to deteriorate the layer of insulation. Infrared (IR) thermography has proven to be a very successful nondestructive method of detecting moisture in the layer of concealed insulation.
The US Army Facilities Engineering Support Agency (FESA), located at Fort Belvoir, Virginia, has the responsibility for providing technical engineering assistance for the operation, maintenance, and repair of Army facilities throughout the country. As a troubleshooter for solving built-up roofing problems, FESA uses a roofing evaluation concept that incorporates a detailed visual inspection with a nighttime IR scan. Within the last two years, the two FESA teams have surveyed more than 281 buildings at 30 Army installations. Incredible as it may seem, wet insulation was detected during the IR scan in more than 31 percent of the roofs surveyed. This paper describes the visual and infrared concepts and techniques used during the FESA surveys.
Infrared scanners are quite successful in finding wet roof insulation, especially boards of rapidly absorbing insulations like perlite, wood fiber and fibrous glass. But wet areas develop more slowly and nonuniformly in the cellular plastic insulations, such as urethane, which are commonly used in new roofs. These differences can affect the outcome of an infrared survey of new roofs. To determine the feasibility of detecting incipient wet insulation, several recently constructed roofs were examined thermographically. It was usually more difficult to find moisture in new roofs containing cellular plastic insulations than in new roofs with more-absorbent insulations. This increased difficulty is due to the slower rate of wetting and to the nonuniform manner of wetting of some of the cellular plastics. Perlite, wood fiber and fibrous glass insulations tend to become uniformly wet throughout an entire board, whereas moisture initially concentrates at the perimeters of boards of some cellular plastic insulations. However, eight to ten months after construction, enough moisture can accumulate in most cellular plastic insulations to be visible to aninfrared scanner. Since this moisture is concentrated in a small portion of each insulation board, much of it would probably be overlooked by a nuclear or capacitance grid survey.
The use of infrared thermography for detecting wet insulation in built-up-roofs provides an added dimension in planning roof maintenance programs. Early detection of wet insulation reduces roof maintenance costs.
At a time when rising fuel costs and energy conservation are of prime concern, roof thermography is a vitally important test method for reducing energy costs, particularly when you consider that 70% of heat loss from the skin of most single storey buildings occurs through the roof. Empirical data indicates that the use of thermography for analyzing the thermal integrity of roofs and detecting subsurface moisture is, for the most part, substantially more effective when utilized on the roof than in aerial (airborne) survey work. However, the method selected will depend on the problems being investigated and the information desired.
An aerial infrared survey of a community was made using quantitative techniques designed to measure the roof surface temperature and the net heat flux from the roof structure. The aerial heat loss values were computed on over 1,000 structures from which a subset of 100 were selected for additional analysis using an on site visit. The aerial and structural data (i.e., insulation levels and inside air temperature) obtained from the on site visits are shown to correlate quite well with residual errors of less than 7 watts/m2 . These results indicate that meaningful measurement of different levels of heat loss can be quantitatively measured using wholely airborne aerial survey techniques. The technique described accounts for atmospheric and emissivity effects on the thermogram data as well as convective and radiational losses from the roof surface.
The state of the art of quantitative infrared thermography is addressed. We are asking more and more of thermography in the field of energy conservation. An energy and dollar conscious public wants to know how much heat is being lost and how much money can be saved by retrofit. Many mission oriented approaches have been developed to address these questions. However, many fundamental questions about how thermography works and how far its capabilities can be pushed have not been addressed. In addition, the theoretical and practical limits of doing benefit cost studies with thermography have not been seriously addressed. This paper discusses the limitations of the current technology and describes many unanswered but important questions facing the future use of thermography for quantitative heat loss analysis.
Thermal mapping with infrared imagery is a very useful test technique in continuous flow wind tunnels. Convective-heating patterns over large areas of a model can be obtained through remote sensing of the surface temperature. A system has been developed at AEDC which uses a commercially available infrared scanning camera to produce these heat-transfer maps. In addition to the camera, the system includes video monitors, an analog tape recording, an analog-to-digital converter, a digitizer control, and two minicomputers. This paper will describe the individual components, data reduction techniques, and typical applications. *
A NASA program, the SILTS experiment (Shuttle Infrared Leeside Temperature Sensing) will utilize an infrared scanning system mounted at the tip of the vertical stabilizer to remotely measure the surface temperature of the leeside of the space shuttle during entry from orbit. Scans of the fuselage and one wing will be made alternately. The experiment will correlate real full scale data to ground-based information. In order to quantitatively assess the temperature profile of the surface, an algorithm is required which incorporates the space shuttle shape, location of specific materials on the surface, and the measurement geometry between the camera and the surface. This paper will discuss the algorithm.
Recently the British have unveiled details of a new Mercury Cadmium Telluride (HgCdTe) "SPRITE" detector that performs time delay and integration within the material itself. This paper presents the concept of the SPRITE detector and analyzes and explains its unique features as applied to commercially available systems. Finally, announcement is made of a new generation of closed-cycle linear resonant cryogenic coolers for infrared systems with a unique guaranteed 2500 hours MTBF.
The elements composing a complete imaging radiometric system are reviewed. The basis for a generalized radiometric equation is developed with expressions for four special simplifying conditions. A method for measuring the emittance of a surface is presented. Measurements made using two special test targets illustrate the significance of the four simplifying special measurement conditions. Digital image processing techniques illustrate statistically a few uncertainties associated with radiometric studies.
With the many commercial and industrial and notwithstanding scientific applications of thermal imaging systems, the trend is and will be "more for less". Increased performance will be characterized by greater thermal and spacial resolution, less spectral sensitivity; quantitative outputs in standardized video format, image storage, digital control, image processing, analysis and interfacing. Ergonomically, systems will demonstrate increased portability, ease of operation, and internal means of detector cooling.
Science and art merge in the optical systems, and hence, the developments are evolutionary as opposed to revolutionary so the areas of keenest interest are detection and signal processing systems.
All of these emerging developments will interestingly result in thermal imaging systems which cost no more than existing systems and, it is suspected by the author, that some will bare a smaller price tag.
A brief description is given of a facility for evaluating infrared imaging systems for building applications being constructed at the National Bureau of Standards (NBS) under sponsorship of the Department of Energy's Oakridge National Laboratory. This paper discusses the functions that the infrared image system evaluation facility is to fulfill, its design criteria , how it is to support the thermographic standards being developed, the tests which the facility will be able to perform and a decription of its major components.
The analysis of vibratory and acoustical signals from rotating machinery has been used successfully for several decades to determine the adequacy of rotating machine design or operation. Certain vibration or acoustical signals are characteristic of machines encountering problems or near failure. Likewise the thermal signature from a rotating machine may have significant diagnostic value. Friction, damping and material deformations are typical sources of thermal energy easily detected by thermal measurements. Thermocouple thermography has been used to determine rotating machine temperatures. However, point measurements are difficult to obtain because of signal coupling problems with the rotating machine. In the past temperatures could only be obtained by stopping the machine and quickly taking temperature measurements hoping that the temperature information would not dissipate by transient affects. Infrared thermography has solved some of these problems by offering a noncontact thermal measurement along with a display of. temperature fields which facilitates the location of hot spots. Several examples of rotating machinery are reviewed such as couplings, power transmission belts, gears and rotors. The significance of the temperature distribution on the power transmission component is discussed. Infrared thermography appears to be a useful tool in diagnosing problems in rotating machinery.