Correct emittance value is one of the necessary inputs for accurate radiometric temperature measurement. Modern Infrared cameras and/or radiometric software programs typically have default emittance tables built-in allowing the operator to simply select the appropriate material and its corresponding emittance value. Unfortunately, many of these values, while perhaps accurately obtained in a laboratory setting, are typically not appropriate for use in a real-world field environment. There are many reasons for this which include: the deposition of dust, dirt and grease; the unknown thickness of oxide layers; the use of invisible (to the human eye) coatings, the unknown nature of the exact material or alloy; an incorrect value in the table itself due to wavelength or test method; and the effect of surface roughness, geometry, cavity radiation, spatial resolution, angle of view or temperature. In many situations incorrect selection of emittance value results in two miscalculations which can magnify the temperature measurement error significantly: calculation of surface reflectance value which in-turn calculates the amount of background signal to be subtracted from the radiance signal; and correction of the remaining signal attributable to radiant spectral exitance to that of the blackbody equivalent signal determined by the camera calibration. This paper will discuss these issues in depth, provide practical considerations for the field use of emittance, and present a simple method to determine measurement errors due to the unknown variance of emittance.
This paper presents a synopsis and status of the various national and international standards relevant to thermal imaging and thermographers developed for the building, electrical, industrial, medical, and non-destructive testing industries. Particular detail will be given to newer and/or relevant to thermal imaging and thermographers within a wide variety of applications and disciplines. Common to most standards and guidelines are minimum performance requirements for the instrument, qualifications for the operator, and limitations of how thermal imaging should be applied.
This paper will summarize by discussing those areas and applications where development is still required. re-written standards that have come to be in the past 7 years, or are currently in development. These documents cut across a wide variety of agencies and disciplines, and nations often without regard for or knowledge of other similar standards or requirements. Agencies include but are not limited to the American Society for Test methods; American society for Non-Destructive Testing; Canadian Standards Association; International Standards organization; National Master Specifications of Canada (NMS) National Institute of Standards (NIST); and National Fire Prevention Association.
While standards, guidelines and protocols exist in many disciplines and industries, given the recent proliferation of low cost thermal imagers which are easily accessible to the public, it is important and appropriate that there be a widespread understanding of who, how , when, and where these imagers should properly be applied in order to obtain credible, scientific, and repeatable results. The best place to look for this understanding is through the knowledge and use of professional standards guidelines and protocols.
For more than 40 years thermography has been used for electrical problem detection. In addition, since radiometric infrared cameras can establish apparent surface temperature of the problem, a classification system is often utilized based upon surface temperature, or temperature rise above normal operating temperature or ambient air temperature. This however can be an extremely unreliable classification method for a number of reasons including: emissivity and background energy; a lack of regard for failure modes and stressors; surface temperature variability with load and ambient conditions; temperature gradient from internal source to surface; and the presence of convection, just to name a few. Standards, such as NFPA 70B, try to address some of these issues by having very low threshold temperature limits, but this as well has issues including identifying an over-abundance of non-critical problems for immediate repair. This paper will present a risk assessment process and matrix which classifies electrical problems based upon a variety of factors affecting both probability and consequence of electrical component failure. Inherent in this process will be a discussion of understanding and analysing electrical connection failure modes and failure stressors, as well as consideration of both heat energy flow and stored energy rather than only considering surface temperature as a single point predictor of catastrophic failure.
Water, in its various phases, in any environment other than desert (hot or cold) conditions, is the single most destructive element that causes deterioration of materials and failure of building assemblies. It is the key element present in the formation of mold and fungi that lead to indoor air quality problems. Water is the primary element that needs to be managed in buildings to ensure human comfort, health and safety. Under the right thermodynamic conditions the detection of moisture in its various states is possible through the use of infrared thermography for a large variety of building assemblies and materials. The difficulty is that moisture is transient and mobile from one environment to another via air movement, vapor pressure or phase change. Building materials and enclosures provide both repositories and barriers to this moisture movement. In real life steady state conditions do not exist for moisture within building materials and enclosures. Thus the detection of moisture is in a constant state of transition. Sometimes you will see it and sometimes you will not. Understanding the limitations at the time of inspection will go a long way to mitigating unsatisfied clients or difficult litigation.
Moisture detection can be observed by IRT via three physical mechanisms; latent heat absorption or release during phase change; a change in conductive heat transfer; and a change in thermal capacitance. Complicating the three methodologies is the factor of variable temperature differentials and variable mass air flow on, through and around surfaces being inspected. Building enclosures come in variable assembly types and are designed to perform differently in different environmental regions. Sources for moisture accumulation will vary for different environmental conditions. Detection methodologies will change for each assembly type in different ambient environments.
This paper will look at the issue of the methodologies for detection of the presence of moisture and determination of the various sources from which it accumulates in building assemblies. The end objective for IRT based moisture detection inspections is not to just identify that moisture is present but to determine its extent and source. Accurate assessment of the source(s) and root cause of the moisture is critical to the development of a permanent solution to the problem.
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