It is essential to the well-being and growth of most meaningful emerging high technologies to have some professional forum for the exchange of information within their user community. The Thermosense conference series has grown in scope to a point where it can now serve the entire industrial and commercial user community of thermal infrared sensors as a primary forum for the exchange of information. For perspective the history of the Thermosense conferences is traced from its initial interest in diagnostics of building envelopes for energy conservation to its present broad scope of interests involving general infrared sensing for diagnostics and control. A breakdown of associated business activities suggests the scope of the Thermosense VI Conference encompasses a $100M industry.
Just as your companies screen and monitor the market place to determine demand and the public's perception of product need, the power company is constantly faced with studying and forecasting the potential for load growth within it's franchised areas. This study and it's resultant forecast for growth has placed the power industry in a hot spot.
An overview of process control including system types, control algorithms and industrial categories is presented. Use of infrared sensors in process control is discussed. Noncontact temperature sensing is compared with contact measurement. Acquisition of sensor data through point, line scan, and imaging radiometer techniques is discussed. The focus is on current inroads, future potential and challenges these methods offer to the process control industry.
A novel method of thermal scanning a large number of vertical structures has been operational for the past eight years. The technique utilizes an imaging line scan system to create continuous thermograms of high spatial resolution and thermal sensitivity. Moreover, VANSCAN® continuous mobile thermography has a very high data acquisition rate, making it suitable for large scale surveys. This paper describes the evolution of continuous mobile thermography for a laboratory prototype to a fully integrated operational system employing near real-time hardcopy output. The various instrument configurations are documented as they were developed for scanning industrial/institutional facilities, petrochemical complexes, and residential communities. Signal processing techniques to portray a wide range of radiant temperatures in a color-coded hardcopy format are also addressed in this paper.
A field study was carried out to investigate the accuracy of using high-resolution radiometers to determine the in situ thermal resistance of building components having conventional residential construction. Two different types of radiometers were used to determine the thermal resistances of the walls of six test buildings located at the National Bureau of Standards. These radiometer thermal resistance measurements were compared to reference thermal resistance values determined from steady-state series resistance predictions, time-averaged heat-flow-sensor measurements, and guarded-hot-box measurements. When measurements were carried out 5 hours after sunset when the outdoor temperature was relatively steady and the heating plant was operated in a typical cyclic fashion, the following results were obtained: for lightweight wood-frame cavity walls, the radiometer procedures were found to distinguish wall thermal resistance 4.4 h.ft2- Ã‚Â°F/Btu (0.77 m2•K/W) systematically higher than corresponding reference values. Such a discrimination will per-mit insulated and uninsulated walls to be distinguished. However, in the case of walls having large heat capacity (e.g., masonry and log), thermal storage effects produced large time lags between the outdoor diurnal temperature variation and the heat-flow response at the inside surface. This phenomenon caused radiometer thermal resistances to deviate substantially from corresponding reference values. This study recommends that the ANSI/ASHRAE Standard 101-1981 be modified requiring the heating plant to be operated in a typical cyclic fashion instead of being turned off prior to and during radiometer measurements.
Building envelopes often contain numerous highly conductive heat flow paths, called thermal bridges, which are major sources of heat loss and deterioration of building materials due to moisture condensation. Some examples of thermal bridges occurring in office buildings are presented. Infrared thermography was used to identify the locations and magnitudes of thermally defective areas resulting from inadequate construction, design, or substandard workmanship in existing buildings. Due to the large thermal inertia of building components and transient conditions caused by fluctuating outdoor and indoor temperatures, long measurement periods are required. This makes thermography impractical for quantifying the heat loss. In order to estimate the heat loss rate from thermal bridges and to obtain a better understanding of the physical processes involved, a two-dimensional heat flow model has been developed for transient heat conduction within the exterior wall/intermediate floor systems. The calculated results from the mathematical model are compared with available experimental data. An in-situ measurement technique, which is currently under development at NBS for quantifying the energy loss due to thermal bridges, is described.
Rising energy costs have placed a heavy burden on multifamily complex managers in recent years. To reduce energy expenditures these managers are then faced with making difficult decisions as to which building retrofits will prove to be most cost-effective. The Building Energy Research Group at Princeton University has embarked on the development of analysis procedures that will provide these managers with a prioritized list of energy conservation opportunities (ECOs). The case studies presented here illustrate the importance of thermography in this analysis procedure, its impact on the inspection time, and the value of the information gained. The infrared scan often eliminates large areas of the thermal envelope from further inspection and aids the analyst in locating energy losses through construction that would otherwise be difficult to find. Not only does thermography guide us in the choice of ECOs but it also provides us with information that should lead to the construction of better buildings in the future.
Results were presented from ground-based infrared thermographic studies performed by the National Bureau of Standards (NBS) on eight federal office buildings. Infrared thermography was utilized to observe the thermal anomalies in those buildings, as part of a diagnostic program to evaluate the thermal integrity of building envelopes. Thermographic data were collected via complete exterior scannings and selected interior scannings at regions where thermal defects were identified or suspected during the outside inspections. Analysis from thermographic inspections with examples of defects found in some of these buildings are also included. The potential applications of the diagnostic procedures to both new and existing buildings are discussed.
Many design and construction details can affect building energy consumption in unex-pected ways. Further, design and construction errors can increase building energy consumption, result in discomfort to building occupants and cause structural damage to the building. Infrared inspections can easily evaluate the energy efficiency of various aspects of a building's design and identify flaws that might otherwise be detected as a result of occupants' complaints or damage to the building's mechanical or structural systems. Infrared thermography can be used by the architect to evaluate his designs and by the contractor to control the quality of construction. This paper discusses a number of issues that can help determine the effectiveness of infrared building surveys. Following this, three case stud-ies will be presented to illustrate design flaws that were detected through infrared build-ing surveys.
Of the five primary heat transfer mechanisms revealed in today's commercial buildings by thermography, air flow is the largest single threat to a structure's thermal integrity. Also, it is generally the one condition which, when corrected, offers the owner the quickest payback. The following presentation deals with one modern building's air flow problems and the building envelope investigations that led to cost savings solutions. The purpose of the initial study was to evaluate a recent infiltration retrofit and to identify entry points of uncontrolled air into the structure at the second floor mechanical room level. This investigation later broadened into locating exfiltration of conditioned air from the total building enclosure (Figure la).
Correct interpretation of thermal anomalies detected during an infrared roof moisture survey depends upon a working knowledge of the types of thermal signatures exhibited by moisture-damaged roofing insulation. The paper discusses four characteristic thermal patterns indicative of moisture-damaged insulation, resulting from the different moisture absorption characteristics of different roof insulations. Appropriate survey conditions for detecting each type of signature are discussed, and example thermograms for each type of pattern are presented.
In low sloped roofing systems using porous insulation, the presence of water can significantly degrade thermal performance. Because of the different thermal characteristics of wet and dry insulation, there is often a surface temperature differential between areas of wet and dry insulation. Under the right circumstances, the areas of wet insulation can be detected by means of infrared sensing techniques. To better define the conditions under which infrared techniques can distinguish between areas of wet and dry insulation, a mathematical model was developed. This model is a one-dimensional, transient heat transfer model of a roofing system. The model considers conduction through the roof, insolation, radiant exchange between roof and sky, convective heat transfer between the roof and air, and the influence of moisture trapped in insulation. For one particular roof system, a parametric study was undertaken using this model to determine the influence of moisture content, outside air temperature, wind speed, insolation, sky temperature, and other factors on the roof surface temperature. Preliminary recommendations for employing thermal sensing techniques to locate wet insulation are developed.
Prior research by the Corps of Engineers has shown aerial thermography to he useful as a reconnaissance tool for finding wet roof insulation. This conclusion was based on findings from thermal line scanners flown at about 1000 feet in military fixed-wing aircraft and from hand-held thermal imagers flown at about 500 feet in military helicopters. During the spring of 1983 a comprehensive aerial to on-the-roof infrared comparison study was conducted on several roofs at Fort Devens, Massachusetts. These recent studies confirm our earlier opinion that oblique thermography is generally of reconnaissance value only. However, "straight-down" thermography from either fixed-wing aircraft or from helicopters can be used to produce reasonably accurate maps of wet roof areas. The most accurate maps were produced by thermal imaging systems in a helicopter hovering as close as 200 feet above a roof. This study suggests that some forms of airborne thermography can be of more value than just a reconnaissance tool in finding wet roof insulation. Of course, a visual examination of each roof along with a few core samples are still needed before recommendations for maintenance and repair can be made.
The energy crisis of the past decade focused tremendous resources on investigating new methods for detecting heat loss. Thermal infrared sensing techniques were recognized as an efficient tool for providing timely and informative data for analysis of heat loss from buildings and heat carrier lines. Facility managers responsible for the operation of large buried steamline systems also see airborne linescanning as a mapping tool for line maintenance programs. Accurate mapping of the buried lines results in effective deployment of the overhaul and replacement crews reducing both the spread of line deterioration and the man-hours required for line excavation. The mobility and speed of quantitative linescanners mounted in fixed wing aircraft results in significant cost reductions and ensures collection of thermal infrared data during desireable environmental and operational conditions. LINEMAP: An Airborne Infrared Survey, was developed by INTERTECH to provide facility managers with a comprehensive detection and mapping service for maintenance programs.
Solving engineering problems sometimes depends on detailed quantification. Many such problems can be solved readily, even without quantification, once their existence is known. Over a one-year period, Western Electric evaluated one qualitative thermographic system for screening of problems in roofs and electrical systems. The surveys were provided at the corporate level to support in-house engineering, and to focus maintenance efforts at specific locations. Limited-scale evaluations have been performed of building envelopes with favorable results. The portability, simplicity of operations, and low instrument cost have figured heavily in performing surveys at geographically remote locations. Key factors to successful applications are operator understanding of thermography, equipment limitations, systems to be surveyed, and the acceptance by end users of the operator's interpretations.
The deterioration of sewer systems and their associated infrastructure is one of the most serious problems facing city, state, federal, and world authorities. As an example, three large sewer voids in the St. Louis Metropolitan area caused over $2,000,000 in repair costs in only one year. The detection of voids in and around underground sewer lines, as well as the detection of effluent leakages is necessary when determining the priority of structures for repair. At the present time sewer voids are sometimes detected by manual methods which are expensive, time consuming, and not extremely accurate. Most of the time, the void is not detected until the street caves in. Infrared thermography has been found to be capable of detecting voids around underground sewer systems because under certain conditions, temperature differentials exist between various types of materials, effluents, and cavities. This paper describes the problem of deteriorating sewer systems, the field tests used to detect sewer voids, the equipment used in the field tests, the theories used to design the tests, various complicating factors, and anticipated future refinements on the procedure.
This paper compares results of aerial infrared, infrared walkover, and Air Force visual inspection techniques for assessing the condition of built-up roofing systems. The two infrared techniques focus on locating thermal signatures indicating subsurface moisture damage. The visual inspection method rates visible surface defects, which may represent current or potential sources of moisture damage. The subject in this case was an 8.8-acre factory/warehouse roof in Danville, Illinois. Results of aerial and walkover infrared inspections corresponded strongly for large anomalies, but diverged on smaller ones. Roof Condition Index ratings from the visual inspection did not correlate significantly with the percentage of roof area judged suspect by either the aerial or walkover infrared inspection.
Particulates present in the firebox of a process furnace influence radiometric measurements mde for the., purpose of deriving furnace tube temperatures. It is hypothesized that they influence the radiometric data as an exponential function dependent upon the pathlength in the firebox. Initial radiometric data is used to establish rough parameter values for the hypothesized mathematical relationship.
The industrial use of non-contact temperature-measurement instruments or radiometers began in the 1920's and, for the next sixty years, increased substantially with a major surge occurring during the past ten years. To coin a phrase, "radiometers do not measure temperatures, they solve temperature-measurement problems". Therefore, to solve such problems, Process and Plan engineers must first acquire a basic knowledge of radiometry to be able to correctly match the instrumentation to the specific application. This paper provides some basic principles of radiometry, instrument design features, and application considerations.
Thermographic inspection, through the use of portable infrared imagers, has been performed on over two thousand pumping units in several active Permian Basin oil fields in the past two years. An infrared imager with camera adaptability was used to inspect saddle bearings, equalizer bearings, wrist pin bearings, exterior gearbox bearings, electric motor and related switch gear on each beam-type pumping unit. In some instances, transformers were also scanned for thermal differentials. This technique detects and isolates abnormal variations in the radiant energy emitted from the bearings, motor and switch gear. Thus, qualitative and quantitative data on each problem bearing or electrical component was precisely established. Thermograms and photographs were taken to document the condition.
A feasibility study was performed to determine if infrared thermography could be used to detect perturbations in the arc welding process which result in defects. Data were gathered using an infrared camera with a resolution of .2°C which was trained on the molten metal pool during welding. Several defects were then intentionally induced and the resulting thermal images were preserved on film. These images revealed that different types of weld defects induce different characteristic changes in the thermal image by detectably altering the temperature field around the weld. These perturbations in the temperature field can be used to identify and locate defects such as arc misalignment, plate gap, puddle impurities etc. Macrostructural examinations permitted investigations into the relationships between weld puddle penetration depth and the temperature field. Using computer aided processing of these thermal images, it is expected that the welding process can be controlled to a higher degree than is presently possible.
An infrared thermal imaging technique that comprehensively verifies electronic component derating temperatures is described. Derating sources are listed and case histories are utilized to illustrate the value of the technique. Imaging of printed wiring assemblies (PWA) is covered at length, including corrections for emissivity, cooling, and ambient translation.
Thermites are solid chemical heat sources that react exothermically by the following equa-tion: Metall + Metal2 Oxide -* Metall Oxide + Metal2 + Heat. This thermite reaction produces a high calorific output that can be used when a concentrated heat source is required. Dynamic evaluation of the thermal profiles generated during thermite reactions requires infrared thermography. The results of this analysis and the technique involved will be discussed.
Thermal images result from temperature differences and/or emissivity differences (apparent temperature differences) in a scene or target. It is the function of a thermal-imaging system to reproduce an acceptable visible image of the scene or target from its thermal content. Thus, a thermal-imaging system is required to resolve spatial differences of temperature and emissivity. The performance of a thermal-imaging system may be specified by means of the fundamental performance measures, noise-equivalent temperature difference (NEAT), minimum-resolvable temperature difference (MRTD), and/or minimum detectable temperature difference (MDTD). Noise-equivalent temperature difference is a convenient measure of an imaging system's thermal sensitivity to a broad-area target (extended source); however, by itself it is no indicator of imaging capability. On the other hand, both minimum-resolvable temperature difference and minimum-detectable temperature difference address the imagery, which includes the human factor; i.e., the image observer. Thus, MRTD is a measure of the compound system-observer capability to spatially resolve temperature differences in a standard periodic-bar target by observing its display on a video monitor. The minimum-detectable temperature difference is similar to the MRTD, except the target geometry differs in being an aperiodic square. The measurement and the significance of each of these performance measures is discussed.
Impacting polymer foams results in a thermal pattern on the surface of the polymer due to energy dissipation and transmission affects. Five polymer foams were tested using two types of ballistic pendulums as impact devices. The transient thermal pattern was recorded on video tape using an infrared scanner. Differing internal energy dissipation mechanisms were detected depending on the type of foam. Temperature distributions were indicative of pendulum penetration, energy dissipation, shock attenuation and transmittance.
The infrared emittance of semi-transparent glazing materials used in passive solar building construction was measured over the temperature range -5.6°C to +15°C at 2 - 5.6 μm wavelength. A table of measured apparent emittance values is presented. Absolute values of emittance are not provided due to the conclusion that no adequate model describing three-dimensional emittance in terms of thickness, rectilinear transmittance, and broadband detector sensitivity has yet been formulated. A rough rule-of-thumb for thermographers appears to be that a high emittance value can be assumed for most thick sheets of these materials but the emittance of thin films drops rapidly below a certain critical thickness.
A spacecraft's deployment hardware on the solar array must not be subjected to temperatures above those it will experience in orbit prior to deployment. Also, the solar array must not be exposed to higher temperatures than those experienced in space. As a consequence, a nondestructive, noninterference method of monitoring the temperature of the solar panel during solar illumination testing is desirable. It was found that the AGA Thermovision system is a viable means of achieving this type of testing, and a thermocouple/ Thermovision comparison was performed on a typical panel.
The use of infrared technology in evaluating all facets of electrical machinery, static and rotating, has enabled the user to pin-point and accurately evaluate problem areas. The application of this technology has enabled the user to develop "predictive maintenance" programs which are superior to any preventive maintenance programs of the same scope ever before devised.
Several instrumented steam traps of all common types were tested to evaluate the thermal measurement technique as a way of determining steam trap performance. The results indicate that the thermal technique is not consistent in pinpointing faulty traps.
Modern electronic equipment presents new challenges for troubleshooting and repair to the manufacturing and test community. Higher circuit density and increased device sophistication requires that innovative new methods be developed for troubleshooting and repair. Expensive and delicate printed circuit boards cannot survive numerous part removal and replacement actions. Component and board defects must be isolated quickly, accurately and efficiently so that repairs may be made with minimum disruption to the board circuitry. Infrared digital thermography offers the promise of helping to solve some of these problems.
Schottky barrier infrared charge coupled device sensors (IR-CCDs) have been developed. PtSi Schottky barrier detectors require cooling to liquid Nitrogen temperature and cover the wavelength range between 1 and 6 μm. The PtSi IR-CCDs can be used in industrial thermography with NEAT below 0.1°C. Pd Si-Schottkybarrier detectors require cooling to 145K and cover the spectral range between 1 and 3.5 μm. 11d2Si-IR-CCDs can be used in imaging high temperature scenes with NE▵T around 100°C. Several high density staring area and line imagers are available. Both interlaced and noninterlaced area imagers can be operated with variable and TV compatible frame rates as well as various field of view angles. The advantages of silicon fabrication technology in terms of cost and high density structures opens the doors for the design of special purpose thermal camera systems for a number of power aystem and industrial applications.
The minimum resolvable temperature difference in quantitative thermographic imaging is essentially determined by photo-detector noise processes. In fast scan devices the overall detector noise envelope may be ±0.5°C. When imaging quasistatic thermal scenes, integration of successive frames (signal averaging) can be used to reduce the effect of detector noise. However, many interesting thermal scenes are rapidly changing, such as the thermal pattern resulting from a laser pulse or from radio frequency energy applied to tissues, and frame integration cannot be applied. In the transient temperature measurement case, some smoothing operator must be used to improve the minimum resolvable temperature difference. Linear smoothing operators, such as averaging and gaussian filters, all have the undesirable side effect of smearing the few edges and other small details in the thermal image. Median filters offer the potential of filtering detector noise while preserving edges and other details. Because the median operator is inherently nonlinear, its effect on the accuracy of measured temperatures cannot be predicted a priori. For the photodetector studied, photoconductive mercury-cadmium-telluride, the detector noise process was determined to have a symmetrical probability density function. Thus the median filter yielded an excellent estimate of the uncorrupted signal with no degradation of edges or other details. The median filter is compared to a triangular window function.
The methodology for inferring temperature from optical radiation exitent from an opaque surface is described. Beginning with the measurement equation, the output of the radiation thermometer is related to radiant flux reaching the detector. Characteristics of blackbody radiators are reviewed and the effects of surface emissivity, reflected irradiances and the atmosphere are presented. Applications to a reheat furnace and a direct-fired process heater illustrate the practical importance of these effects and point out the need for a firm understanding of the physics of thermal radiation to properly interpret radiation thermometer observations.
Infrared sensing may seem a relatively new scientific discipline but in reality the existence of infrared was noted as early as 1800 when Sir William Herschel wrote on the subject. He discovered the "invisible rays" as he called them while developing filters for protecting his eyes while observing the sun. Herschel described this effect in 1801 in two papers. The term "infrared" was not coined until the 1880's. The author of the term is not known but in Latin infra means below or beneath, possibly implying beneath the red. Using a prism and a sensitive mercury - in glass thermometer, William Herschel measured the radiation from fires, candles, and kitchen stoves demonstrating a detector able to measure radiation in this infrared region and raising questions about the connection between light and heat. In 1840, Herschel's son John developed a radiation detection process based on the differential evaporation of a thin film of oil to form a "heat picture." This process was improved by Czerny in 1929 and is still in use today as the "evaporagraph." In 1843 Becquerel found that certain materials phosphoresced when exposed to infrared radiation. During the 1880's several highly sensitive new detectors were developed most notable being the Langley bolometer. In 1901 Langley and Abbot reported the use of a bolometer that could detect the heat from a cow at a distance of 1/4 mile. Case in 1917 developed the thallous sulfide detector, the first use of the photoconductive effect in the infrared. Development continued in detector technology especially by the Germans during World War II. Following the war the efforts were on,radiometry. During the 1950's non-military applications for these devices grew rapidly'. Now, point radiometry is an established quantitative technology with thousands of units in place for remote temperature measurement and control. The instruments are calibrated for temperature with appropriate scale, emittance correction, voltage output, and internal reference. Infrared imaging systems have developed in the 60's and are currently approaching tne quantitative level as they are being integrated into computer processing. Technology improvements provide on-line video tape recording, quantification, computer interfacing, and graphics. Instrument improvement is an on-going active process being pushed by military, space, and industrial applications. Associated with the new technology must be the development of an educational process which provides the user with information sufficient to properly assimilate the information derived from the instrument.
This paper will begin with a classification of infrared sensing instruments by type and application, listing commercially available instruments, from single point thermal probes, to on-line control sensors, to high speed, high resolution imaging systems. A review of performance specifications will follow, along with a discussion of typical thermographic display approaches utilized by various imager manufacturers. The paper will conclude with a brief update report on new instruments, new display techniques and newly introduced features of existing instruments
The results of the laboratory evaluation of three high resolution infrared imaging systems are presented. The systems were evaluated for their minimum resolvable temperature difference (MRTD) at spatial frequencies from 0.02 to 0.16 cycles per milliradian and at ambient temperatures in the range of -7° C to 20° C. The results of these tests are compared with the predicted dependence of the MRTD given in the ASHRAE Standard 101-83. It is shown that the dependence on temperature of the MRTD of two of the systems is predicted well by the theory given in the ASHRAE standard. The calibration curves of the infrared imaging systems are given. These are in good agreement with those given by the manufacturers of the equipment.