1. Infrared Thermal Testing Reading VII My ASNT Level III, Pre-Exam Preparatory Self Study Notes 12 June 2015 Charlie Chong/ Fion Zhang 2. Military Applications Charlie Chong/ Fion Zhang 3. Military Applications Charlie Chong/ Fion Zhang 4. Military Applications Charlie Chong/ Fion Zhang 5. Military Applications Charlie Chong/ Fion Zhang 6. The Magical Book of Infrared Thermography Charlie Chong/ Fion Zhang 7. Charlie Chong/ Fion Zhang 8. Charlie Chong/ Fion Zhang ASNT Certification Guide NDT Level III / PdM Level III IR - Thermal/Infrared Testing Length: 4 hours Questions: 135 1. Principles/Theory Conduction Convection Radiation The nature of heat and heat flow Temperature measurement principles Proper selection of Thermal/Infrared testing 2. Equipment/Materials Temperature measurement equipment Heat flux indicators Performance parameters of non-contact devices 9. Charlie Chong/ Fion Zhang 3. Techniques Contact temperature indicators Non-contact pyrometers Infrared line scanners Thermal/Infrared imaging Heat flux indicators Exothermic or endothermic investigations Friction investigations Fluid Flow investigations Thermal resistance (steady state heat flow) Thermal capacitance investigations 4. Interpretation/Evaluation Exothermic or endothermic investigation Friction investigations Fluid flow investigations Differences in thermal resistance Thermal capacitance investigations 10. Charlie Chong/ Fion Zhang 5. Procedures Existing codes and standards Job procedure development 6. Safety and health Safety responsibility and authority Safety for personnel Safety for client and facilities Safety for testing equipment Reference Catalog Number NDT Handbook, Third Edition: Volume 3, Infrared and Thermal Testing 143 Fundamentals of Heat and Mass Transfer 952 ASNT Level III Study Guide: Infrared and Thermal Testing 2265 11. Charlie Chong/ Fion Zhang 12. Fion Zhang at Shanghai 12th June 2015 http://meilishouxihu.blog.163.com/ Charlie Chong/ Fion Zhang 13. Charlie Chong/ Fion Zhang 14. Charlie Chong/ Fion Zhang http://greekhouseoffonts.com/ 15. Charlie Chong/ Fion Zhang 16. Charlie Chong/ Fion Zhang Notation: h = Planks constant = Stephen-Boltzmann constant = absorptivity = emissivity = reflectivity = transmissivity 17. Charlie Chong/ Fion Zhang Infrared Spectrum 18. Charlie Chong/ Fion Zhang IVONA TTS Capable. http://www.naturalreaders.com/ 19. Charlie Chong/ Fion Zhang Assorted Reading Subject matters approaches 20. Charlie Chong/ Fion Zhang Reading VII Content Reading One: Thermocouples: The Operating Principle Reading Two: Facilities Instructions, Standards, & Techniques Vol.4~11+2 Thermal Analysis Reading Three: Infrared Thermography Guide-R3 Reading Four: Emissivity: Understand the difference between apparent and actual IR temperatures 21. Charlie Chong/ Fion Zhang Reading: One Thermocouples: The Operating Principle http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html 22. Charlie Chong/ Fion Zhang THERMOCOUPLES: THE OPERATING PRINCIPLE A thermocouple is a device made by two different wires joined at one end, called junction end or measuring end. The two wires are called thermo elements or legs of the thermocouple: the two thermo elements are distinguished as positive and negative ones. The other end of the thermocouple is called tail end or reference end (Figure 1). The junction end is immersed in the environment whose temperature T2 has to be measured, which can be for instance the temperature of a furnace at about 500C, while the tail end is held at a different temperature T1, e.g. at ambient temperature. Figure 1: Schematic drawing of a thermocouple http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html 23. Charlie Chong/ Fion Zhang Because of the temperature difference between junction end and tail end a voltage difference can be measured between the two thermo elements at the tail end: so the thermocouple is a temperature-voltage transducer. The temperature versus voltage relationship is given by: where Emf is the Electro-Motive Force or Voltage produced by the thermocople at the tail end, T1 and T2 are the temperatures of reference and measuring end respectively, S1,2 is called Seebeck coefficient of the thermocouple and S1 and S2 are the Seebeck coefficient of the two thermoelements; the Seebeck coefficient depends on the material the thermoelement is made of. http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html 24. Charlie Chong/ Fion Zhang Looking at Equation1 it can be noticed that: 1. a null voltage is measured if the two thermoelements are made of the same materials: different materials are needed to make a temperature sensing device, 2. a null voltage is measured if no temperature difference exists between the tail end and the junction end: a temperature difference is needed to operate the thermocouple, 3. the Seebeck coefficient is temperature dependent. In order to clarify the first point let us consider the following example (Figure 2): when a temperature difference is applied between the two ends of a single Ni wire a voltage drop is developed across the wire itself. The end of the wire at the highest temperature, T2, is called hot end, while the end at the lowest temperature, T1, is called cold end. http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html 25. Charlie Chong/ Fion Zhang Figure 2: Emf produced by a single wire http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html 26. Charlie Chong/ Fion Zhang When a voltmeter, with Cu connection wires, is used to measure the voltage drop across the Ni wire, two junctions need to be made at the hot and cold ends between the Cu wire and the Ni wire; assuming that the voltmeter is at room temperature T1, one of the Cu wires of the voltmeter will experience along it the same temperature drop from T2 to T1 the Ni wire is experiencing. In the attempt to measure the voltage drop on the Ni wire a Ni-Cu thermocouple has been made and so the measured voltage is in reality the voltage drop along the Ni wire plus the voltage drop along the Cu wire. The Emf along a single thermoelement cannot be measured: the Emf measured at the tail end in Figure1 is the sum of the voltage drop along each of the thermoelements. As two thermoelements are needed, the temperature measurement with thermocuoples is a differential measurement. Note: if the wire in Figure 2 was a Cu wire a null voltage would have been measured at the voltmeter. http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html 27. Charlie Chong/ Fion Zhang The temperature measurement with thermocouples is also a differential measurement because two different temperatures, T1 and T2, are involved. The desired temperature is the one at the junction end, T2. In order to have a useful transducer for measurement, a monotonic Emf versus junction end temperature T2 relationship is needed, so that for each temperature at the junction end a unique voltage is produced at the tail end. However, from the integral in Equation1 it can be understood that the Emf depends on both T1 and T2: as T1 and T2 can change independently, a monotonic Emf versus T2 relationship cannot be defined if the tail end temperature is not constant. For this reason the tail end is maintained in an ice bath made by crushed ice and water in a Dewar flask: this produces a reference temperature of 0C. All the voltage versus temperature relationships for thermocouples are referenced to 0C. The resulting measuring system required for a thermocople is shown in Figure 3. http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html 28. Charlie Chong/ Fion Zhang Figure 3: A measuring system for thermocouples http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html 29. Charlie Chong/ Fion Zhang In order to measure the voltage at the tail end, two copper wires are connected between the thermoelements and the voltmeter: both the Cu wires experience the same temperature difference and as a result the voltage drops along each of them are equal to each other and cancel out in the measurement at the voltmeter. The ice bath is usually replaced in industrial application with an integrated circuit called cold junction compensator: in this case the tail end is at ambient temperature and the temperature fluctuations at the tail end are tolerated; in fact the cold junction compensator produces a voltage equal to the thermocouple voltage between 0C and ambient temperature, which can be added to the voltage of the thermocouple at the tail end to reproduce the voltage versus temperature relationship of the thermocouple. A sketch of a thermocouple with cold junction compensation is reported in Figure 4. http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html 30. Charlie Chong/ Fion Zhang Figure 4: An example of Cold Junction Compensation http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html 31. Charlie Chong/ Fion Zhang It should be underlined that the cold junction compensation cannot reproduce exactly the voltage versus temperature relationship of the thermocouple, but can only approximate it: for this reason the cold junction compensation introduces an error in the temperature measurement. Figure4 shows also the filtering and amplification of the thermocouple. Being the thermocouple voltage a DC signal, removal of AC noise through filtering is beneficial; furthermore the thermocouples produce voltage of few tens of mV and for this reason amplification is required. The small voltage range for some of the most common thermocouples (letter designated thermocouples) is shown in Figure5, where their voltage versus temperature relationship is reported. Type R, S and B thermocouples use Pt-base thermoelements and they can operate at temperatures up to 1700C; however they are more expensive and their voltage output is lower than type K and type N thermocouples, which use Ni-base thermoelements. However, Ni base thermocouples can operate at lower temperatures than the Pt-base ones. Table1 reports the approximate compositions for positive and negative thermoelements of the letter designated thermocouples. http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html 32. Charlie Chong/ Fion Zhang Figure 5: Voltage vs Temperature relationship for letter-designated thermocouples http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html 33. Charlie Chong/ Fion Zhang Table 1: Approximate composition for thermoelements of letter-designated thermocouples http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html 34. Charlie Chong/ Fion Zhang All the voltage-temperature relationships of the letter designated thermocouples are monotonic, but not linear. For instance the type N thermocouple voltage output is defined by the following 10 degree polynomials, where t is the temperature in degree Celsius: The coefficients Ci are reported in Table2. In order to have a linear voltage-temperature relationship the Seebeck coefficient should be constant with temperature (see Equation1); however the Seebeck coefficient is temperature dependent, as shown for instance for type K thermocouple in Figure6. Additional details on the voltage-temperature relationships for letter designated thermocouple can be found at: http://srdata.nist.gov/its90/main/ http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html 35. Charlie Chong/ Fion Zhang Table 2: Type N thermocouple coefficients http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html 36. Charlie Chong/ Fion Zhang Figure 6: Type K Seebeck coefficient versus Temperature http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html 37. Charlie Chong/ Fion Zhang Thermocouple Basics Let's start with T. J. Seebeck, who in 1821 discovered what is now termed the thermoelectric effect. He noted that when two lengths of dissimilar metal wires (such as iron and Constantan) are connected at both ends to form a complete electric circuit, an emf is developed when one junction of the two wires is at a different temperature than the other junction. Basically, the developed emf (actually a small millivoltage) is dependent upon two conditions: (1) the difference in temperature between the hot junction T2 and the cold junctionT1, T. Note that any change in either junction temperature can affect the emf value and V (2) the metallurgical composition of the two wires. S1, S2, Seebeck coefficient of the two thermoelements 38. Charlie Chong/ Fion Zhang Although a thermocouple is often pictured as two wires joined at one end, with the other ends not connected, it is important to remember that it is not a true thermocouple unless the other end is also connected! It is well for the user to remember this axiom : 'Where there is a hot junction there is always a cold or reference junction ' (even though it may seem hidden inside an instrument 1,000 feet away from the hot junction). Still in Seebeck's century, two other scientists delved deeper into how the emf is developed in a thermoelectric circuit. Attached to their names are two phenomena they observed: The Peltier effect (for Jean Peltier in 1834) and The Thompson effect (for Sir William Thompson a.k.a Lord Kelvin in 1851). 39. Charlie Chong/ Fion Zhang Without getting into the theories involved, we can state that: the Peltier effect is the emf resulting solely from the contact of the two dissimilar wires. Its magnitude varies with the temperature at the juncture. Similarly, the Thompson effect can be summarized as having to do with emf's produced by a temperature gradient along a metal conductor. Since there are two points of contact and two different metals or alloys in any thermocouple, there are two Peltier and two Thompson emfs. The net emf acting in the circuit is the result of all the above named effects. Read more on Peltier and Thompson effects http://www.me.uprm.edu/laboratories/inme4031/pdf_Documents/Classes/Microsoft%20Word%20- %20Class%206_Temperature%20Measurements%20using%20Thermocouples.pdf 40. Charlie Chong/ Fion Zhang Polarity of the net emf is determined by: (a) the particular metal or alloy pair that is used (such as iron/ constantan) and (b) the relationship of the temperatures at the two junctions. The value of the emf can be measured by a potentiometer, connected into the circuit at any point. In summary, the net emf is a function primarily of the temperature difference between the two junctions and the kinds of materials used. If the temperature of the cold junction is maintained constant, or variations in that temperature are compensated for, then the net emf is a function of the hot junction temperature. (cold junction either at constant known temperature of compensated) In most installations, it is not practical to maintain the cold junction at a constant temperature. The usual standard temperature for the junction (referred to as the 'reference junction') is 32 F (0 C). This is the basis for published tables of emf versus temperature for the various types of thermocouples. 41. Charlie Chong/ Fion Zhang The Law of Intermediate Temperatures provides a means of relating the emf generated under ordinary conditions to what it should be for the standardized constant temperature (e.g., 32 F). Referring to Figure 4-1, which shows thermocouples 1 and 2 made of the same two dissimilar metals; this diagram will provide an example of how the law works. 42. Charlie Chong/ Fion Zhang Figure 4-1: Thermocouple Operation 200 400 600 8000 0 2 4 6 8mV F Thermocouple 2 Thermocouple 1 Thermocouple 3 43. Charlie Chong/ Fion Zhang Thermocouple 1 has its cold junction at the standard reference temperature of 32 F and its hot junction at some arbitrary intermediate reference temperature (in this case, 300 F). It generates 2.68 mv. Thermocouple 2 has its cold junction at the intermediate reference point of 300 F and its hot junction at the temperature being measured (700 F). It generates 4.00 mv. The Law of Intermediate Temperatures states the sum of the emfs generated by thermocouples 1 and 2 will equal the emf that would be generated by a single thermocouple (3, shown dotted) with its cold junction at 32 F and its hot junction at 700 F, the measured temperature. That is, it would hypothetically read 6.68 mv and represent the 'true' emf according to the thermocouple's emf vs. temperature calibration curve. 44. Charlie Chong/ Fion Zhang Based upon this law, the manufacturer of an infrared thermocouple need only provide some means of substituting for the function of thermocouple 1 to provide readings referenced to the standard 32 F cold junction. Many instruments accomplish this with a temperature-sensitive resistor which measures the variations in temperature at the cold unction (usually caused by ambient conditions) and automatically develops the proper voltage correction. Another use of this law shows that extension wires having the same thermoelectric characteristics as those of the thermocouple can be introduced into the thermocouple circuit without affecting the net emf of the thermocouple. In practice, additional metals are usually introduced into the thermocouple circuit. The measuring instrument, for example, may have junctures that are soldered or welded. Such metals as copper, manganin, lead, tin, and nickel may be introduced. 45. Charlie Chong/ Fion Zhang Would not additional metals like this modify the thermocouple's emf? Not so, according to the Law of Intermediate Metals. It states that the introduction of additional metals will have no effect upon the emf generated so long as the junctions of these metals with the two thermocouple wires are at the same temperature. This effect is illustrated in Figure 4-2, with A and B representing the thermocouple wires. A practical example of this law is found in the basic thermoelectric system shown in Figure 4-3. The instrument can be located at some distance from the point of measurement where the thermocouple is located. Several very basic and practical points are illustrated in this elementary circuit diagram: Quite often the most convenient place to provide the cold junction compensation is in the instrument, remote from the process. With the compensation means located in the instrument, in effect, the thermoelectric circuit is extended from the thermocouple hot junction to the reference (cold) junction in the instrument. The actual thermocouple wires normally terminate relatively near the hot junction. 46. Charlie Chong/ Fion Zhang Conventional couples have what is called a 'terminal head' at which point interconnecting wires, known as 'extension wires' are required as shown. Since these wires are in the thermoelectric circuit, they must essentially match the emf vs. temperature characteristics of the thermocouple. With the cold junction located inside the instrument, internal extension wires of the proper materials must be used between the instrument terminals and the cold junction. With this set-up, there are in effect three added thermocouples in the circuit: one in the thermocouple assembly, one in the external extension wire, and in the internal extension wire. However, according to the Law of Intermediate Temperatures, the actual temperatures at the terminal head and at the instrument terminals is of no consequence: the net effect of the three thermocouples is as if one thermocouple ran from the hot junction to the cold junction. 47. Charlie Chong/ Fion Zhang Figure 4-2: Equivalent Thermocouple Circuits 48. Charlie Chong/ Fion Zhang Figure 4-3: Typical Thermocouple Installation 49. Charlie Chong/ Fion Zhang The Law of Intermediate temperatures The law of intermediate temperatures indicates that the electromotive forces are additive for temperature intervals The sum of two electromotive forces, generated by two thermocouples: E1 with its junctions between T1 and T2 E2 with its junctions between T2 and T3 Eequivalent to emf generated by one thermocouple with its junctions between T1 and T3 http://www.energy.kth.se/compedu/webcompedu/WebHelp/S3_Measuring_Techniques/B7_Temperature_Me asurements/C2_Practical_Thermometers/S3B7C2_files/Intermediate_temperatures.htm 50. Charlie Chong/ Fion Zhang Law of Homogeneous Materials A thermoelectric current cannot be sustained in a circuit of a single homogeneous material by the application of heat alone, regardless of how it might vary in cross section. Law of Intermediate Materials The algebraic sum of the thermoelectric forces in a circuit composed of any number of dissimilar materials is zero if all of the circuit is at a uniform temperature. Law of Successive or Intermediate Temperatures If two dissimilar homogeneous materials produce thermal emf1 when the junctions are at T1 and T2 and produce thermal emf2 when the junctions are at T2 and T3, the emf generated when the junctions are at T1 and T3 will be emf1 + emf 2. Could somebody talk about intermediate connecting 3rd material? 51. Charlie Chong/ Fion Zhang What is the law of intermediate metals? According to the Thermocouples Law of Intermediate Metals, illustrated in the figure, inserting any type of wire into a thermocouple circuit has no effect on the output as long as both ends of that wire are the same temperature, or isothermal. Consider the circuit in the next figure. Both circuits are quite similar but a short length of constantan wire has been inserted just before junction J3 and the junctions are assumed to be held at identical temperatures. Assuming that junctions J3 and J4 are the same temperature, the Thermocouple Law of Intermediate Metals indicates that the circuit in the figure on left is electrically equivalent to the circuit of the figure on right. Consequently, any result taken from the circuit in the figure on left also applies to the circuit illustrated in the figure on right. http://www.thermibel.be/documents/thermocouples/thermoocuple-law-metals.xml?lang=en 52. Charlie Chong/ Fion Zhang What is the law of intermediate metals? According to the Thermocouples Law of Intermediate Metals, illustrated in the figure, inserting any type of wire into a thermocouple circuit has no effect on the output as long as both ends of that wire are the same temperature, or isothermal. Mtls-A Mtls-B Mtls-A Mtls-BMtls-C Isothermal Region 53. Charlie Chong/ Fion Zhang The Law of Intermediate temperatures The law of intermediate temperatures indicates that the electromotive forces are additive for temperature intervals The sum of two electromotive forces, generated by two thermocouples: E1 with its junctions between T1 and T2 E2 with its junctions between T2 and T3 Eeqv Equivalent to emf generated by one thermocouple with its junctions between T1 and T3 http://www.energy.kth.se/compedu/webcompedu/WebHelp/S3_Measuring_Techniques/B7_Temperature_ Measurements/C2_Practical_Thermometers/S3B7C2_files/Intermediate_temperatures.htm 54. Charlie Chong/ Fion Zhang Peltier effect The Peltier heat is the quantity of heat in addition to the quantity I2R that must be removed from the junction to maintain the junction at a constant temperature. This amount of energy is proportional to the current flowing through the junction; the proportionality constant is the Peltier coefficient AB , and the heat transfer required to maintain a constant temperature is: Q =ABI http://www.me.uprm.edu/laboratories/inme4031/pdf_Documents/Classes/Microsoft%20Word%20- %20Class%206_Temperature%20Measurements%20using%20Thermocouples.pdf caused by the Peltier effect alone. This behavior was discovered by Jean Charles Athanase Peltier (1785-1845) during experiments with Seebecks thermocouple. He observed that passing a current through a thermocouple circuit having two junctions, as in Figure 4, raised the temperature at one junction, while lowering the temperature at the other junction. 55. Charlie Chong/ Fion Zhang Thomson effect Consider the conductor shown in Figure 5, which is subjected to a longitudinal temperature gradient and also subject to a potential difference, such that there is a flow of current and heat in the conductor. Q = I(T2-T1) where is the Thomson coefficient http://www.me.uprm.edu/laboratories/inme4031/pdf_Documents/Classes/Microsoft%20Word%20- %20Class%206_Temperature%20Measurements%20using%20Thermocouples.pdf 56. Charlie Chong/ Fion Zhang End Of Reading One 57. Charlie Chong/ Fion Zhang Reading: Two(abstract) Facilities Instructions, Standards, & Techniques Vol.4~11+2 Thermal Analysis U.S. Department of the Interior Technical Service Center Bureau of Reclamation Denver, Colorado 58. Charlie Chong/ Fion Zhang 1.1 Infrared Thermogram Image Quality Image quality is affected by many factors, as shown in figure 7: Image quality contributors. 59. Charlie Chong/ Fion Zhang 1.1.1 Spot Size (IFOV) The thermal analysis equipment will record the temperature of a spot in the image and display this temperature. The size of the spot is critical since the temperature recorded is the average of the temperatures of the pixels within the spot. If the spot is too large, the average may water down a hot spot pixel, giving the false impression that the temperature is lower (or higher) than the pixel centered on the hot spot. Ideally, the spot size will be as small as possible, but there are practical limits. The spot size is partially determined by how close the device is to the target; and, in some cases, the approach distance must be relatively large for safety or physical obstructions or because the target is in the air. Using a telephoto lens on IR cameras will reduce the spot size of distant targets. Even though these can be expensive, they should be used where quantitative measurement is needed. 60. Charlie Chong/ Fion Zhang When using hand-held radiation thermometers, it is critical to understand and take into account the spot size for your specific equipment. Hand-held radiation thermometers typically have a spot size ratio ranging from 6:1 to 110:1. For comparison, thermal imaging cameras have a spot size ratio ranging from 63:1 to 889:1 with the typical spot size being approximately 250:1. The spot size of a thermal imaging camera can be changed depending on work to be performed by using different lenses. Figure 8 is an example of how the actual spot size changes based on spot size ratio and the distance from the target. Assuming the employee is 6 feet from the equipment under test, the actual spot size can vary from 0.65 inch to 12 inches. If the actual target size is 0.5 inch, then with a spot size ratio of 110:1, the employee would need to be within 55 inches of the target to only measure the temperature of the target. If the spot size ratio was 12:1, then the employee would need to be within 6 inches of the target to only measure the temperature of the target. 61. Charlie Chong/ Fion Zhang Figure 8. Spot size of hand-held radiation thermometer. 62. Charlie Chong/ Fion Zhang It is important to understand the devices spot size ratio, sometimes called the distance-to-spot ratio or instantaneous measurement field of view (IFOV), which determines the maximum distance the thermographer can be from the target and still get a good reading. For example, a spot size ratio of 250 to 1 means that, at 250 inches (about 21 feet), the spot size to be measured must be a minimum of 1 inch (the projected spot will cover 1 by the individual sensing pixel, should the target of interest is smaller than 1, the reading will be the averaging of the adjacent areas of interest covered by the projected spot?) . If the thermographer cannot get within 21 feet, a telephoto lens should be used. If the spot size or target is less than 1 inch (for example, inch), the device would need to be closer than approximately 10 feet for accurate temperature readings, or a telephoto lens would be required. For inch, the device would need to be closer still. The target should be larger than the spot size to ensure accurate data. 63. Charlie Chong/ Fion Zhang The realtionship between IFOVgeo and IFOVmeas IFOVmeas = 3 x IFOVgeo Where IFOVgeo = is the theoretical spot size base on angle subtended by the pixel in mRad. IFOVmeas is the practical spot size for correct measurement. The area of interest should not be larger than IFOVmeas for meaningful measurement. (to be verified!) 64. Charlie Chong/ Fion Zhang 1.1.2 Distance The physical distance of the IR thermal equipment to the target is one parameter that cannot be corrected after the image is taken and saved. The distance to the target is an important variable in determining apparent temperatures. The distance should be measured or estimated and entered into the camera. Using a laser distance device is an easy way to measure the distances between the thermographer and equipment. Never use a metal tape measure to determine the distance between the thermographer and equipment when working near energized equipment. The discussion above on spot size shows that the correct distance is very important to obtain quality IR images and proper analysis. The distance from the IR thermal equipment to the target needs to be reported on the PM forms. To simplify the process, it is possible to mark the floor in front of the equipment so the thermographer always maintains the same distance from the target, allowing for repeatable measurements. 65. Charlie Chong/ Fion Zhang 1.1.3 Field of View and Instantaneous Field of View The definition of field of view depends on the type of instrument used. For a hand-held radiation thermometer, the field of view (or instantaneous field of view [IFOV]) is the target spot size. (as there is only one sensor FOV=IFOV?) In a scanner, imager, or radiometer, the field of view is the scan angle, picture size, or total field of view. This can be related to a regular 35-millimeter (mm) camera; a 50-mm lens will provide a certain picture size. If the lens size is doubled to 100 mm (a basic telephoto lens), at the same distance, the overall field of view is reduced, but the items in the picture appear closer and clearer in detail. In IR thermography, the lenses are designated using angular notations. As the lens angle increases, so does the field of view. A standard 24-degree lens will have a larger field of view than a 12-degree telephoto lens. IFOV relates directly to spatial resolution of the instrument used. IFOV is the smallest area that can be accurately seen at a given instance. Figure 9 illustrates the field of view and the relation to the instantaneous field of view when using a thermal imaging camera. 66. Charlie Chong/ Fion Zhang Figure 9. Field of view of an IR camera. 67. Charlie Chong/ Fion Zhang 1.1.4 Estimating Emissivity Before inspection of any component, it is essential that the emissivity of that component be estimated and set in the IR thermal inspection equipment. Otherwise, inaccurate temperatures will be recorded. For qualitative inspections, the starting emissivity may be estimated at 0.90.95. It is a good practice for a facility to establish a uniform starting emissivity for consistent results. Hand-held radiation thermometers may or may not allow the user to change the emissivity of the instrument. If the instrument does not allow the user to change the emissivity, then it will only provide accurate results for objects with the preprogrammed emissivity. Coatings may be added to equipment included in the thermal analysis program that will change the emissivity of the object. 68. Charlie Chong/ Fion Zhang Some cameras and the associated analyzing software programs can adjust emissivity after the image is saved. However, if the emissivity is set prior to imaging, quicker analysis may be made in the field as to the severity of any anomalies found. Emissivity tables are provided in many publications and also can be found in appendix F. These tables should be used sparingly and with caution. The best emissivity value for a given target is established in the field using accepted practices for determining the targets emissivity. See appendix E. 69. Charlie Chong/ Fion Zhang 1.1.5 Background Sources Heat energy from sources of radiation other than the target must be estimated and entered into the camera for a more accurate temperature measurement. There are specific procedures for using the camera to determine the background temperature. Once obtained, these values should be inputted into the camera. (The reflectivity ? or Tamb only? without the , the ambient contributions could not be quantified?) 70. Charlie Chong/ Fion Zhang 1.1.6 Pointing, Aiming, and Ambient Reflections Viewing angles can affect the amount of IR radiation gathered by the thermal analysis instrumentation. The optimum angle of the instrument to the target is 90 (perpendicular) to the plane of the target. Effort should be made to ensure the best possible viewing of the target. The optimum angle cannot always be achieved or maintained. Therefore, the temperature recorded from a target on an angle other than 90 may not be as accurate. Generally, shiny surfaces do not emit radiation energy efficiently and can be hot while appearing cool in an IR thermographic image or on the readout of the hand-held radiation thermometer. Likewise, direct reflections of sun rays from shiny surfaces into the camera can be misread as hot spots. One method of determining if the spot observed in a camera is an anomaly or is the result of a reflection is to move around the target when possible. Usually, when conducting outdoor inspections, if the hot spot goes away or diminishes significantly, then the hot spot was probably a reflection. If the hot spot remains, measure it. 71. Charlie Chong/ Fion Zhang Do not rely on this technique for all targets. Targets may be large or shaped so that hot spots on the front side may be completely obscured when viewed from the back side. The technique of moving around then will not accurately locate all anomalies. The thermographer must be aware of unusual conditions that may influence the IR radiation measured by the test instrument. This points out the need for training and experience. It also emphasizes the need to have the thermographer familiar with the workings of the equipment being inspected. 72. Charlie Chong/ Fion Zhang 1.1.7 Calibration Have the thermal analysis instrumentation calibrated periodically, according to the manufacturers recommendations. This will help ensure the instruments are working properly and recording accurate thermograms and/or temperatures. 73. Charlie Chong/ Fion Zhang 2.1.8 Reference Photos It is very helpful when analyzing thermograms to have a visual reference photo taken with a standard camera of the equipment at the same time and point of view as the thermogram. The reference photo will make it easier to identify components that might not be obvious in the thermogram. When using hand-held radiation thermometers, reference photos are critical to identify locations of hot spots. Since hand-held radiation thermometers do not capture data, extensive notes and reference photos are the only way to document the location of temperature data for future reference. 74. Charlie Chong/ Fion Zhang 1.2 Methods of Determining or Enhancing the Emittance of a Target Thermographers calculate or determine the emissivity of different targets in a number of ways. Accurate emissivity values are needed if quantitative temperature measurements are required. If possible, emissivity enhancement coatings can be applied to target areas. Coatings, usually in the form of paint, have known emissivities. These coatings are usually applied to shiny or reflective surfaces to provide a higher known emissivity and to provide accurate temperature measurements. Most of the coatings today have emissivities at or near 0.95. Black electrical tape (3M Scotch 33) can be used to determine the emissivity of targets. This tape has been measured and is used as a reference by many thermographers. Emissivity of the tape is 0.95. This technique requires the tape to be placed on the target material prior to energizing, loading, or heating the equipment to be monitored. For the following technique to work properly, the measured target or component temperature must be raised 20 degrees Fahrenheit (F) or higher above ambient temperature. This technique will not work if the target is at ambient temperature. 75. Charlie Chong/ Fion Zhang Place a - to 1-inch square of the electrical tape on the target. Measure the background temperature by setting the emissivity to 1.0 in the infrared (IR) camera and pointing the camera away from the target. In most cases, defusing the focus will give an average background temperature. The background temperature also can be measured by using a piece of cardboard with an aluminum foil cover set next to the target. Again, set the camera emissivity to 1.0 and the camera slightly out of focus. Measure the temperature at the center of the cardboard/aluminum foil. The background temperature should be entered into the camera if the camera being used allows this. The correct distance to the target should be added to the camera settings. The thermographer needs to recognize the spot size and ensure that the target size is adequate and is in focus. (the target should be 3x the instrument spot size) Set the camera to an emissivity of 0.95. Once the target is at temperature, measure the temperature of the taped (or emissivity enhanced) area. 76. Charlie Chong/ Fion Zhang Note the temperature. Move the measuring spot just off of the tape and on to the surface for which emissivity is to be determined. Adjust the emissivity in the camera, until the temperature of this spot matches the temperature measured on the tape. Once the temperatures match, read and record the emissivity. This emissivity now can be used in the future for this particular equipment and perhaps similar equipment. Other techniques for increasing emissivity of targets include using the geometry of the components. For instance, the intersection where a lug or nut meets the connection surface will form a small cavity that, when viewed in the IR camera, will have an increased emissivity. ( if the depth to width ration is 7, the emissivity could be assume to be 0.98?) All types of cavities will tend to have higher emissivities and should be used whenever possible. Other techniques or formulas for calculating emissivity can be found in numerous publications and are usually included in most training classes. Cavity radiatorA hole, crack, scratch, or cavity that will have a higher emissivity that the surrounding surface because reflectivity is reduced. A cavity seven times deeper than wide will have an emissivity approaching 0.98. 77. Charlie Chong/ Fion Zhang Thermograms Figure 1. Transformer bushing with incorrect washer that does not allow correct connection. Connection spot 1 (52.4 degrees Celsius [C]), is greater than (>) 30 C hotter than spot 2 (22.2 C) on similar bushing under same load. 78. Charlie Chong/ Fion Zhang Thermograms Figure 2. High-side connection from transformer, illustrating a barber pole effect where only part of the cable strands carry the current. This qualitative image prompted immediate remedial action. 79. Charlie Chong/ Fion Zhang Thermograms 80. Charlie Chong/ Fion Zhang Thermograms 81. Charlie Chong/ Fion Zhang End Of Reading Two 82. Charlie Chong/ Fion Zhang Reading: Three Infrared Thermography Guide-R3 Electric Power Research Institute 83. Charlie Chong/ Fion Zhang 84. Charlie Chong/ Fion Zhang ABSTRACT This guide is a valuable reference for the development of infrared thermography (IR) capabilities as part of a plant predictive maintenance program. The guide includes IR theory, a summary of IR inspection applications, and the technical information necessary to develop an effective in-house program. The body of the guide is structured for the general user of IR, and the appendices provide a more in-depth look at this technology for the advanced user. This third revision of Infrared Thermography Guide contains updated information on IR equipment technology, IR inspection applications, and training and certification criteria. 85. Charlie Chong/ Fion Zhang INTRODUCTION Many electric generating stations and utilities have integrated the non-contact, nondestructive capabilities of infrared thermography (IR) for condition monitoring and diagnostics in their predictive maintenance program. The purpose of this guide is to assist the nuclear industry in its efforts to factor IR into its predictive maintenance program. This guide provides the theory of IR, a summary of existing and potential applications, and the technical information necessary to develop an effective in-house program. Also included is a matrix that lists all of the known manufacturers of IR instruments for a broad range of applications. 86. Charlie Chong/ Fion Zhang IR has been used in commercial applications since the early 1970s. In the early 1990s, at the time this guide was first completed, the most frequent applications centered on building energy losses, roof moisture detection, and inspections of major electric equipment. Applications have since expanded to almost all areas of plant predictive maintenance (PdM), product and process control, and nondestructive testing of materials. The wide and growing selection of thermal imagers and viewers available for these applications provides both qualitative and quantitative displays of temperature distribution patterns. 87. Charlie Chong/ Fion Zhang The manufacturers of modern thermal imagers and viewers have kept pace as detector and microprocessor technologies have advanced. The capabilities of today.s IR thermal imagers and viewers have yet to be fully explored and developed for commercial applications. In addition, computer software programs are now available to store, retrieve, analyze and compare infrared images. Much of the information presented in the original guide was developed as a result of a demonstration project at a U.S. nuclear utility. In addition to information gathered through this demonstration project, all Nuclear Maintenance Applications Center (NMAC) members were surveyed to provide data on the implementation status of IR technology at their facilities. This latest revision of the guide (Revision 3) was undertaken to correct text errors, to update the information on IR products vendors, certification, training, and techniques, and to restructure the guide so that it can become a living document, able to be readily updated to reflect technology changes. The body of the guide is structured for the general user of IR, and the appendices provide an in-depth look at this technology designed for the more advanced user. 88. Charlie Chong/ Fion Zhang Basic IR Concepts A target at any temperature above absolute zero will emit infrared radiation in proportion to its temperature. Thermal imagers develop an electronic image by converting the invisible heat radiation emitted by that target into electrical signals that can be displayed on a monitor and/or recorded on a variety of electronic storage media. By monitoring these targets with thermal imaging equipment, a visual image of their temperature differentials can be displayed. The variations in intensities of the blacks, grays, and whites (or color variations) provide an indication of the temperature differences. Areas of higher temperatures will appear brighter and the areas at lower temperatures will appear darker (or appear as different colors). The quantity and wavelength distribution of the energy that is radiated depends upon the temperature and spectral characteristics of the material, and on that materials radiation efficiency (emissivity). Thermal imagers convert the invisible heat radiation (thermal detector?) into visible images while spot radiometers convert the heat radiation from a single spot into a number indication on a meter. (the photon detector not addressed?) 89. Charlie Chong/ Fion Zhang The thermographer views the target through an IR instrument, while looking for unexpected or unusual temperature patterns. A qualitative examination compares the apparent temperature pattern of one component to that of an identical or similar component under the same or similar operating conditions. Temperature differences can be measured quantitatively as well. The achievement of accurate temperature indications, however, is dependent upon many factors and extreme care must be taken in the selection of variables used in temperature calculations. The thermal images obtained can be stored on memory sticks, PCMCIA cards, computer hard drives, floppy disks, CDs, ZIP disks, or video tape. An advantage of infrared monitoring or testing is that it can be performed with the equipment in service at normal operating conditions (that is, it will not interfere with normal plant operations). 90. Charlie Chong/ Fion Zhang CONTENTS 1. Thermography overview 2. A compendium of commercial infrared sensing and imaging instrument 3. The measurement mission 4. Inspection techniques 5. Examples of infrared applications 6. Basic elements of an in-house program 7. Training and certification 91. Charlie Chong/ Fion Zhang 1. THERMOGRAPHY OVERVIEW Temperature and thermal behavior of plant machinery, power generation and distribution equipment, control systems, and related materials are the most critical factors in the maintenance of operations. For this reason, temperature is frequently considered the key to successful plant maintenance and is, by far, the most measured quantity. Although conventional methods of temperature measurement using thermometers and thermocouples are still commonly used for many applications, infrared thermography (IR) sensors have become less expensive, more reliable, and electrically interchangeable with conventional thermistors and thermocouples. Noncontact measurement using infrared sensors has become an increasingly desirable alternative over conventional methods. Now, with the proliferation of innovative computer hardware and software, computer-aided predictive maintenance (PDM?) is feasible and efficient. 92. Charlie Chong/ Fion Zhang 1.1 Advantages of Non-Contact Thermal Measurement The four most commonly stated advantages of non-contact thermal infrared measurement over contact measurement are that it is non-intrusive, remote, much faster than conventional methods, and that it measures the temperature at the surface of the target (test subject) not the surrounding air. Any one, or a combination of the following conditions, warrants the consideration of a noncontact sensor: Target in motion . When the target to be measured is moving, it is usually impractical to have a temperature sensor in contact with its surface. Bouncing, rolling, or friction can cause measurement errors and the sensor might interfere with the process. Target electrically hot . Current-conducting equipment and components present a hazard to personnel and instruments alike. Infrared sensors place both out of harms way. Target fragile . When thin webs or delicate materials are measured, a contacting sensor can often damage the product. Target very small . The mass of a contacting sensor that is large with respect to the target being measured will usually conduct thermal energy away from the target surface, thus reducing the temperature and producing erroneous results. 93. Charlie Chong/ Fion Zhang Target remote . If a target is very far away from, or inaccessible to, contacting sensors, infrared measurement is the only option. Target temperature changing . Infrared sensors are much faster than thermocouples. Infrared radiant energy travels from the target to the sensor at the speed of light. A rapidly changing temperature can be monitored by infrared sensors, with a millisecond response or faster. Target destructive to thermocouples . When the high mortality rate of thermocouples due to jarring, burning, or erosion becomes a serious factor, an infrared sensor is a far more cost effective alternative. Multiple measurements required . When many points on a target need to be measured, it is usually more practical to re-aim an infrared sensor (IR Scanner, Line scanner) than it is to reposition a thermocouple or to deploy a great number of thermocouples. The fast response of the infrared sensor is important. There are, of course, limitations to the non-contact approach conditions that might make it impractical or ineffective. These will be covered as the discussion progresses. 94. Charlie Chong/ Fion Zhang 1.2 Heat Transfer and Infrared Radiation Basics Infrared thermography is based on measuring the distribution of radiant thermal energy (heat) emitted from a target surface and converting this to a surface temperature map or thermogram. The thermographer requires an understanding of heat, temperature, and the various types of heat transfer as an essential prerequisite in preparing to undertake a program of IR thermography. This section is an overview discussion to provide the reader with a basic understanding of how heat transfer phenomena affect non- contact infrared thermal sensing and thermographic measurements. For a more detailed discussion of temperature and heat transfer basics, see Appendix A. Comments: The differences in detecting principle by thermal detectors and photon detector were not addressed Thermal detector heat sensitive? Photon detector spectral sensitive? 95. Charlie Chong/ Fion Zhang 1.2.1 Heat and Temperature Heat is defined as thermal energy in transition, flowing from one place or object to another as a result of temperature difference, with the flow of heat changing the energy levels in the objects. All of the energy must be taken into account because energy can neither be created nor destroyed. What we often refer to as a heat source (like an oil furnace or an electric heater) is really one form or another of energy conversion; the energy stored in one object is converted to heat and flows to another object. Temperature is a property of matter and not a complete measurement of internal energy. It defines the direction of heat flow when another temperature is known. Heat always flows from the object that is at the higher temperature to the 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 steadystate condition, energy needs to be continuously supplied to the hotter object by some means of energy conversion so that the temperatures and, hence, the heat flow, remain constant. 96. Charlie Chong/ Fion Zhang 1.2.2 Instruments for Temperature Measurement (Contact and Non- Contact) Conventional temperature measuring instruments use various contact sensors. A mercury thermometer works on the principle of expansion with heat: the mercury expansion is calibrated based on its known characteristics and the reading is an indication of the temperature at the site of the mercury reservoir. Thermometers using thermocouples, thermopiles, and thermistors are based on the electrical-thermal characteristics of these sensors and produce a reading based on the temperature of the object with which the sensor is in contact. Infrared thermal instruments are non-contact devices and produce readings based on the surface temperature of objects at which the instrument is pointed. 97. Charlie Chong/ Fion Zhang 1.2.3 Converting Temperature Units Temperature is expressed in either absolute or relative terms. There are two absolute scales called Rankine (English system) and Kelvin (metric system). There are two corresponding relative scales called Fahrenheit (English system) and Celsius or Centigrade (metric system). For a detailed discussion of temperature units and formulas for converting from one scale to another, see Appendix A. Table 1-1 is a conversion table to facilitate the rapid conversion of temperature between Fahrenheit and Celsius values. Instructions for the use of the table are shown at the top. For convenience, Table 1-1 is repeated in Appendix A (Table A-1). For quick reference, the conversion factors are summarized in Appendix C, Plate 1. 98. Charlie Chong/ Fion Zhang 99. Charlie Chong/ Fion Zhang 1.2.4 The Three Modes of Heat Transfer There are three modes of heat transfer: (1) conduction, (2) convection, and (3) radiation. All heat transfer processes occur by one or more of these three modes. IR, Infrared thermography is based on the measurement of radiative heat flow and is, therefore, most closely related to the radiation mode of heat transfer. For a detailed discussion of heat transfer modes and the relationship between infrared measurements and radiative heat flow, see Appendix A. 100. Charlie Chong/ Fion Zhang 1.3 Measuring and Mapping Temperature Without Contact All targets radiate energy in the infrared spectrum. The hotter the target, the more energy that is radiated. Very hot targets radiate in the visible spectrum as well as in the infrared. As targets cool, they no longer glow but they continue to radiate. The radiation can be felt on a hand placed near the targets surface, but the glow cant be seen because the energy has shifted from red to infrared. Infrared detectors can sense infrared radiant energy and produce useful electrical signals proportional to the temperature of target surfaces. Instruments using infrared detectors allow a fast and highly sensitive target surface temperature measurement without contact. Instruments that combine this measurement capability with the capability of scanning a target surface area are called infrared thermal imagers. They produce thermal maps, or thermograms, where the brightness intensity or color of any spot on the map is representative of the surface temperature of that spot. In other words, they extend non-contact point temperature measurements to non-contact thermography. 101. Charlie Chong/ Fion Zhang 1.3.1 The Three Elements of a Non-Contact Temperature Measurement In using infrared instruments for making non-contact temperature measurements, three sets of characteristics need to be considered: Target surface Transmitting medium between the target and the instrument Measuring instrument Figure 1-1 shows how the instrument is aimed at the target and makes the measurement through the medium. 102. Charlie Chong/ Fion Zhang Figure 1-1- Categories of Conditions for Infrared Thermal Measurements 103. Charlie Chong/ Fion Zhang 104. Charlie Chong/ Fion Zhang Every target surface above absolute zero radiates energy in the infrared. The hotter the target, the more radiant infrared energy is emitted. The physical laws that define this behavior are discussed in detail in Appendix A, along with a detailed discussion of medium and instrument characteristics. Emissivity is a very important characteristic of a target surface and must be known in order to make accurate non-contact temperature measurements. Methods for estimating and measuring emissivity are discussed throughout this guide, and the emissivity setting that is needed to dial into the instrument can usually be estimated from available tables and charts. The proper setting needed to make the instrument produce the correct temperature reading can be learned experimentally by using samples of the actual target material. This more practical setting value is called effective emissivity. 105. Charlie Chong/ Fion Zhang Although the transmitting medium is usually air, non-contact temperature measurements can be made through a vacuum, gas, or certain solid materials. The characteristics of the medium need consideration and a detailed explanation of this is included in Appendix A. Figure 1-2 shows the necessary components of an infrared radiation thermometer that makes a single point non-contact temperature measurement on the target surface. Collecting optics (that is, infrared lenses, etc.) is necessary in order to focus the energy radiated from the target onto the sensitive surface of an infrared detector. The detector converts this energy into an electrical signal that is representative of the temperature of a spot on the target. Adding scanning elements between the target and the detector (also shown in Figure 1-2) allows the instrument to scan the target surface and to produce a thermogram. Most currently available infrared thermal imagers incorporate multi-detector focal plane array (FPA) sensors that are electronically scanned and that eliminate the requirement for an opto-mechanical scanning mechanism (single sensor type?) . 106. Charlie Chong/ Fion Zhang When an infrared radiation thermometer (point-sensing instrument) is aimed at a target, it collects energy within a collecting beam, the shape of which is determined by the configuration of the optics and the detector. The cross- section of this collecting beam is called the field of view (FOV) of the instrument and it determines the size of the area (spot size) on the target surface that is measured by the instrument. On scanning and imaging instruments this is called the instantaneous field of view (IFOV) and becomes one picture element on the thermogram. 107. Charlie Chong/ Fion Zhang Figure 1-2 Components of an Infrared Sensing Instrument (non FPA?) 108. Charlie Chong/ Fion Zhang 1.4 Performance Parameters of Thermal Sensing Instruments This section previews the performance parameters of point-sensing instruments and scanning and imaging instruments. For a detailed discussion of these parameters and how to specify and test the performance of instruments, please refer to Appendix A. 1.4.1 Point-Sensing Instruments Point-sensing instruments are defined by the following performance parameters: Temperature range . The high and low limits over which the target temperature might vary Absolute accuracy . As related to the NIST (National Institute of Standards and Technology) standard Repeatability . How faithfully a reading is repeated for the same target 109. Charlie Chong/ Fion Zhang Temperature sensitivity . The smallest target temperature change that the instrument needs to detect Speed of response . How fast the instrument responds to a temperature change at the target surface Target spot size and working distance . The size of the spot on the target to be measured and its distance from the instrument Output requirements . How the output signal is to be utilized Spectral range . The portion of the infrared spectrum over which the instrument will operate Sensor environment . The ambient conditions under which the instrument will operate 110. Charlie Chong/ Fion Zhang 1.4.2 Line Scanners and Imagers - Qualitative and Quantitative The parameters used for assessing the performance of infrared thermal line scanners and imagers are more complex because a thermal line-scan or image is made up of a great number of discrete point measurements. Many of the performance parameters of infrared thermal line-scanners and imagers, such as accuracy, repeatability, and spectral range, however, are the same as those of radiation thermometers. Others are derived from, or are extensions of, radiation thermometer performance parameters. Some types of thermal imagers show comparative temperatures and not actual temperature measurements. For users of these thermal viewers (see section 3), parameters dealing with accuracy and repeatability do not apply. Parameters exclusive to thermal line-scanners and imagers are as follows: 111. Charlie Chong/ Fion Zhang 1. Total field of view (TFOV) . The thermogram image size, in terms of scanning angle. (example: TFOV=20 Vertical x 30 Horizontal) The TFOV of a line scanner is considered to be the TFOV of one scan line. 2. field of view (IFOV) . The spot size represented by one detector element at the target plane: Imaging spatial resolution. (example: IFOV= 2 milliradians) (1 = 35 milliradians) 3. Measurement spatial resolution: (IFOVmeas) . The spatial resolution that describes the minimum target spot size on which an accurate temperature measurement can be made. (example: IFOVmeas = 5 milliradians) 4. Frame (or line) repetition rate . The number of times every point on the target is scanned in one second. (example: Frame rate = 30/second or 30 Hz; Scan rate = 60 lines/second) 5. Minimum resolvable temperature (MRT) . The smallest blackbody equivalent target temperature difference that can be observed: Temperature sensitivity. (example: MRT=0.1C @ 30C target temperature) 6. Other parameters such as spectral ranges, target temperature ranges, accuracy and repeatability, and focusing distances are essentially the same as those for point-measuring instruments. 112. Charlie Chong/ Fion Zhang 1.4.3 Thermal Imaging Software In order to optimize the effectiveness of thermographic measurement programs, the thermographer needs a basic understanding of the thermal image processing techniques. The following is a list of broad categories of thermal image processing and diagnostics currently available. A discussion of each of these categories is included in Appendix A. A detailed description of currently available thermal imaging and diagnostic software is provided in section 2. Thermal imaging software can be categorized into the following groups: Quantitative thermal measurements of targets Detailed processing and image diagnostics Image recording, storage, and recovery Image comparison Archiving and database* *Although data and image database development is not an exclusive characteristic of thermal imaging software, it should be considered an important part of the thermographers tool kit. 113. Charlie Chong/ Fion Zhang 2. A compendium of commercial infrared sensing and imaging instruments This chapter begins with a classification of infrared sensing and imaging instruments by type and application. The list includes commercially available instruments, from single- point thermal probes to on-line control sensors, to high-speed, high- resolution thermal imaging (thermography) systems. A detailed overview of performance characteristics and features follows, along with a discussion of the typical thermographic display approaches that are used by various imager manufacturers. This is followed by a discussion of currently available thermographic image processing software and image hard-copy recording accessories. Finally, a tabulation of currently available instruments by category and manufacturer is appended, including a digest of performance characteristics and features. A current index of manufacturers addresses, phone numbers, Web sites (where available), and/or e-mail addresses is also included. 114. Charlie Chong/ Fion Zhang 2.1 Classification of Instruments Infrared sensing instruments are traditionally classified into three groups: point-sensing, linescanning, and thermographic (two-dimensional scanning). Point-sensing devices (commonly called Infrared Radiation Thermometers) collect radiant energy from a spot or area on the surface of an object to be measured (the target) and provide an output indication, usually in terms of target temperature. Line-scanning instruments provide an output, generally an analog trace, of the radiant energy (or, in ideal cases, temperature) distribution along a single straightline projection from the target surface. Thermographic instruments (imagers) provide an image of the energy distribution over a scanned area on the target surface. This is presented in the form of an intensity-modulated black and white picture or a synthesized color display called a thermogram. 115. Charlie Chong/ Fion Zhang Point sensors, line scanners, and imagers can be further divided into sub- groups. This section will review commercially available instruments along the lines of this breakdown: Point-Sensing Probes and IR thermocouples Portable (hand-held) On-line monitoring and control Specials Line-Scanning Opto-mechanically scanned Focal plane array (FPA), electronically scanned Thermographic Opto-mechanically scanned imagers (single element, mechanical manipulated) Electronically scanned pyrovidicon imagers (?) Electronically scanned FPA focal plane array imagers (multi-elements array) 116. Charlie Chong/ Fion Zhang 2.2 Instrument Manufacturers Particularly in the point-sensing category, there are many companies offering the same instrument under different private label arrangements. In order to avoid duplication, the original manufacturer or prime (U.S.) distributor will be listed in the material that follows. At the end of Section 2, a comprehensive list of instruments is included (Table 2-1), for which descriptive literature was available at the time of the preparation of this text. The performance characteristics are summarized rather than presented in detail. The listed manufacturer should be contacted for detailed performance information. A listing of current addresses, phone numbers, Web sites, and/or e-mail addresses, for the listed equipment manufacturers, is included in a separate table (Table 2-2) at the end of Section 2. In addition, a third table is included, which summarizes proven industrial applications for thermal imaging instruments (Table 2-3). The information that follows will highlight the applications for which each instrument category and group is particularly suited, based on configuration or performance characteristics. 117. Charlie Chong/ Fion Zhang 2.3 Discussion of Instruments 2.3.1 Point Sensors (Radiation Thermometers) 2.3.1.1 Probes Temperature probes are characterized by low price (from less than $100 to about $1,000), pocket-portability, and wide-collecting angle. They are battery- powered and are generally optically pre-adjusted for minimum spot size at a short working distance (a 1/4" (6.35 mm) spot at a 3/4" (19.05 mm) working distance is typical). Some models are designed to operate into a conventional multi-meter and some incorporate their own readout box with a liquid crystal diode (LCD) display. They usually feature disposable batteries and some models have ac adapters. Temperature ranges are from about 0F, or slightly below, to 600F, and a sensitivity of +/- 1F is easily achieved. Emissivity adjustments are available on some models. Probes are ideal for close-up measurements and are used in circuit board analysis, troubleshooting of electrical connections, the inspection of plumbing systems, and in application to biological and medical studies. 118. Charlie Chong/ Fion Zhang 2.3.1.2 Portable Hand-Held With few exceptions, these instruments are pistol-shaped and designed for middle-distance measurements. They are usually optically pre-adjusted for infinity focus. A typical 2 field of view resolves a 7.5-cm (3-inch) spot at a 150-cm (60-inch) working distance, and a 30-cm (1- foot) spot at a 9-m (30- oot) working distance. Prices range from about $100 to more than $3,500. Sighting and aiming methods vary from simple aiming notches to enclosed illuminated reticles. There are instruments with extremely narrow fields of view (0.5) that include a rifle stock and telescopic sight. Most instruments in this group incorporate emissivity adjustments and some include microcomputers with limited memory and data-logging capabilities. Most are available with a recorder output, although this feature is seldom used. A meter is always provided and, with one exception that reads in BTU/ft-h, the readout is always in temperature units. Analog displays are still available, although they are decreasing in popularity. Digital readouts featuring light emitting diodes (LEDs) were introduced first but the LCD display, introduced more recently, is now used almost universally because its tiny power drain extends battery life. 119. Charlie Chong/ Fion Zhang For this reason, the more recent instruments offer replaceable rather than rechargeable batteries and battery life approaches one year. Some instruments in this group have zeroing adjustments, but all of the newer instruments include auto-zeroing features. Temperature ranges are, typically, from 0C to 1500C. Temperature sensitivity and readability are usually 1C (or F) or 1% of scale, although sensitivities on the order of 0.1C (or F) are achievable. This instrument group is particularly suited to applications where spot- checking of target temperatures is sufficient and continuous monitoring is not required. A typical use would be for periodic maintenance checks of rotating machinery to detect whether or not bearings are beginning to overheat. These instruments, over the past few years, have become an important part of many plant energy conservation programs. Although many of these instruments provide extremely accurate readings, accuracy, like the recorder output, is less important to most users than repeatability, ruggedness, portability, reliability, and ease of use. Some newer models incorporate microcomputers with special features such as a data-logger, which has the capability to store as many as 60 readings for future retrieval and printout. 120. Charlie Chong/ Fion Zhang 2.3.1.3 On-Line Monitoring and Control These instruments are primarily used for monitoring and control of manufacturing processes. The one feature that distinguishes this instrument group from the others is dedicated use. The instrument is generally mounted where it can measure the temperature of one specific target, and it remains there for the life of the instrument or the process. With few exceptions, these instruments operate on line power. The output signal of the instrument can be observed on a meter, used to operate a switch or relay, feed a simple or sophisticated process control loop, or it can be used in any combination of these functions. Early on-line instruments consisted of an optical sensing head and an electronics/control readout unit at the other end of an interconnecting cable. This configuration still exists to some extent, but most of the newer units feature sensing heads that are more stable electronically and, hence, more independent of the remote control units. 121. Charlie Chong/ Fion Zhang The trend is for these new sensors to mate with universal indicator/control units that accept input from various types of industrial sensors. This instrument group is selected to perform a specific task, so the manufacturer provides a shopping list ordering format to the customer, enabling them to purchase all required features. Manufacturers offer sensing head features such as variable or fixed focus, sighting tubes, light pipes, water-coolable housings, air purge fittings, air curtain devices, and see-through aiming with target-defining reticles. The shopping list for the indicator/controller unit might include digital readout, binary coded decimal (BCD) output, analog output, single, double, or proportional set point, rate signals, sample and hold, peak or valley sensor, and data-logger interface. Emissivity controls, located in a prominent place on a general-purpose instrument, are more likely to be located behind a bezel on the sensor on these dedicated units, where they are set one time and locked. 122. Charlie Chong/ Fion Zhang Spectral characteristics are worth mentioning separately, although, technically, they are part of the sensing head shopping list. The spectral interval over which the sensing head operates is selected to optimize the signal from the target, to reduce or eliminate the effect of an interfering energy source, or to enable the instrument to measure the surface temperature of thin films of material that are largely transparent to infrared energy. This last application has made these instruments important factors in the manufacture of thin film plastics and also of glass. Exercise: What is the spectral filter need to measure the surface temperature of PU. 123. Charlie Chong/ Fion Zhang 2.3.1.4 Specials There are several special categories of spot-measuring instruments that are worth mentioning, although they might, by strict definition, fit into one or more of the above categories. (1) Two-color or ratio pyrometers are one special case of an on-line instrument. These are particularly useful in high-temperature applications and in measuring small targets. The effective emissivity of the target need not be known, providing that it is constant and that reflections are controlled. The target need not fill the field of view, provided that the background is cool, constant, and uniform. Impurities in the optical path that result in broadband absorption, do not affect the measurement because the measurement is based on the ratio of energy in two spectral bands. Ratio pyrometers are, generally, not applicable to measurements below 500F. 124. Charlie Chong/ Fion Zhang Another special case is the (2) fiber optic-coupled thermometer. With this instrument, inaccessible targets can be measured by replacing the optic with a flexible or rigid fiber optic bundle. This, of course, limits the spectral performance and, hence the temperature range, to the higher values, but it has allowed temperature measurements to be made when none were possible. 125. Charlie Chong/ Fion Zhang Fiber Optic-coupled Thermometer 126. Charlie Chong/ Fion Zhang (3) The infrared microscope is a third special case. This instrument is configured like a conventional microscope. Through the use of reflective microscope objectives and beam splitters, it enables the operator to simultaneously view and measure targets down to 0.0003" (.00762 mm) in diameter with an accuracy and resolution of about 0.5F. Another special case, known as the (4) laser pyrometer, has also become available. This instrument uses the reflected energy of an active laser to measure target reflectance. A built-in microcomputer calculates target effective emissivity and uses this to provide a corrected true temperature reading. The laser pyrometer is useful for high temperature diffuse target surfaces. Prices of instruments in the on-line control instrument group vary from less than $1,000 for an infrared switch, to more than $15,000 for infrared microscopes and on-line instruments equipped with many control features. Generally speaking, the price goes up when sensitivity, small spot size, and speed of response are all required and, of course, when many shopping list items, or additional features, are added. 127. Charlie Chong/ Fion Zhang 2.3.2 Line Scanners The purpose of spatial scanning is to derive information concerning the distribution of radiant energy over a target scene. Quite often, a single straight line scanned on the target is all that is necessary to locate a critical thermal anomaly. In the newer line scanners, the single-element detector is replaced by a multi-element single-line focal plane array (FPA) and the optomechanical scanning element is eliminated. Probably the first approach to line scanning that was adopted commercially was in an aerial-type thermal mapper in which the line scanner was mounted on a moving aircraft and scanned lines normal to the direction of motion. The outputs representing these individual scan lines were intensity-modulated and serially displayed in shades of gray on a strip map. This display represented the thermal map of the surface being overflown by the vehicle. 128. Charlie Chong/ Fion Zhang 2.3.2.1 Opto-Mechanically Scanned Line Scanners The earliest process-monitoring line scanners (many of which are still in use) employed a single element detector and a single scanning element, usually a mirror. The instantaneous position of the scanning element is usually controlled or sensed by an encoder or potentiometer so that the radiometric output signal can be accompanied by a position signal output and be displayed on a chart recorder, an oscilloscope, or some other recording device. One portable, battery-powered line scanner, still used commercially, scans a single line on target, develops a visible temperature trace using light emitting diodes and, by means of optical beamsplitting techniques, superimposes this trace over the visible scene viewed by the operator. The operator selects the line to be scanned by aiming the instruments horizontal centerline. 129. Charlie Chong/ Fion Zhang Photorecording of the composite scene is accomplished by aiming a conventional instant color camera through the eyepiece of the scanner. This instrument has no recorder output and is, therefore, not suited for process control applications. Unlike most thermal viewers, however, absolute temperatures are obtainable with this device. Good applications for this line scanner include electrical switchgear and transmission lines, the troubleshooting of plumbing systems, and webprocess profiling. 130. Charlie Chong/ Fion Zhang 2.3.2.2 Electronically Scanned Focal Plane Array FPA Line Scanners The newest high-speed on-line commercial line scanners employ linear focal plane detector arrays that are electronically scanned. They develop high resolution thermal maps by orienting the linear array along an axis normal to the motion of a moving target such as a paper web, a rotating kiln, or a strip steel process. The output signal information is in real-time computer compatible format and can be used to monitor, control, or predict the behavior of the target. The best applications for this scanner are in on-line real-time process monitoring and control. In significant recent developments, families of line cameras have been made available with a wide selection of linear focal plane array detectors based on the speed, resolution, and spectral sensitivity requirements of the process being monitored. 131. Charlie Chong/ Fion Zhang 2.3.3 Thermographic Instruments An important advantage of radiation thermometers over contact thermometers is their speed of response. The measured energy travels from the target to the sensor at the speed of light. The response of the instrument can then be in milliseconds or even microseconds. This important feature has allowed the field of infrared radiation thermometry to expand into real-time thermal scanning and thermal mapping. When problems in temperature monitoring and control cannot be solved by the measurement of one or several discrete points on a target surface, it becomes necessary to spatially scan (that is, to move the collecting beam (instantaneous field of view) of the instrument relative to the target). The detector output is intensity-modulated in proportion to the total exitant radiant energy at each point scanned on the target surface. The image produced is presented in monochrome or color, where the gray shades or color hue are intended to represent a thermal level at the target surface. 132. Charlie Chong/ Fion Zhang These thermal images are called thermograms. The purpose of spatial scanning is to derive information concerning the distribution of infrared radiant energy over a target scene. Scanning can be accomplished either opto- mechanically or electronically. Opto-mechanical scanning can be done by moving the target with the instrument fixed, or by moving (translating or panning) the instrument, but is most practically accomplished by inserting movable optical elements into the collected beam. Although an almost infinite variety of scanning patterns can be generated using two moving elements, the most common pattern is rectilinear. This is most often accomplished by two elements that each scan a line normal to the other. A typical rectilinear scanner employs two rotating prisms behind the primary lens system (refractive scanning). An alternate configuration uses two oscillating mirrors behind the primary lens (reflective scanning). 133. Charlie Chong/ Fion Zhang This is also commonly used in commercially available scanners, as are combinations of reflective and refractive scanning elements. Electronic scanning involves no mechanical scanning elements, the thermal pattern of the surface is scanned electronically. The earliest method of electronically scanned thermal imaging is the pyrovidicon (pyroelectric vidicon) or thermal video system. With this method, charge proportional to target temperature is collected on a single pyroelectric detector surface, within an electronic picture tube. Scanning is accomplished by an electronic scanning beam. Although offering them in favor of instruments based on solid-state focal plane array technology. Most recently, electronically scanned thermal imaging is accomplished by means of an infrared focal plane array (IRFPA), whereby a two-dimensional staring array of detectors collects radiant energy from the target and is digitally scanned to produce the thermogram. All of the above approaches to producing an infrared thermogram will be discussed. 134. Charlie Chong/ Fion Zhang Commercial thermal imaging systems fall into the following categories and sub-categories: Thermal viewers, opto-mechanically scanned Imaging radiometers, opto-mechanically scanned Thermal viewers, electronically scanned (pyrovidicon imagers) Focal plane array (FPA) imagers, qualitative (thermal viewers), and quantitative (imaging radiometers) Keywords: Thermal viewers (thermal detector) - qualitative Imaging radiometer (photon detector) quantitative (radiometric) 135. Charlie Chong/ Fion Zhang A comprehensive list (Table 2-1) of all known, commercially available thermal-imaging instruments, on which descriptive literature was available at the time of the preparation of this document, is included at the end of Section 2. Performance characteristics are also briefly summarized. A listing of current addresses, phone numbers, Web sites, and/or e-mail addresses, of the listed equipment manufacturers, is included in a separate table (Table 2-2) at the end of Section 2. In addition, a third table is included, which summarizes proven industrial applications for thermal imaging instruments (Table 2-3). The information that follows will highlight the applications for which each instrument category and group is particularly suited, based on configuration or performance characteristics. 136. Charlie Chong/ Fion Zhang Infrared (IR) thermography is a well established technique for remotely measuring the temperature of a surface where it is impractical or impossible to do so by a contact means. The term thermography denotes an imaging capability, but the concepts are the same for non-imaging sensors. IR thermography exploits the correlation between the temperature of a surface and the IR energy emitted by the surface. This relationship is described by Stefans Law: where is the Stephan-Boltzmann constant (= 5.6710-8 W/(m2K4)) and T is the temperature of the surface. The spectrum of the IR light is described by Plancks blackbody function. 137. Charlie Chong/ Fion Zhang 2.3.3.1 Thermal Viewers, Opto-Mechanically Scanned Opto-mechanically scanned thermal viewers are inexpensive battery-powered scanning instruments producing a qualitative image of the (thermally associated) radiant exitance distribution over the surface of a target. The battery packs are rechargeable and usually provide 2 ~ 3 hours of continuous operation. These are one-piece, lightweight instruments, designed to be simple to operate. The first viewers required cryogenic cooling of the detector elements, which was accomplished by means of a small tank of compressed argon. These early units, while still in use, are no longer manufactured. Newer units feature thermoelectric detector cooling provided by a battery-powered cooler. (and sterling cooler?) Note: Although they are being replaced gradually by focal plane array imagers (see section 2.3.3.4), at the time of this writing, opto-mechanically scanned thermal viewers are still in wide use commercially. For this reason, the following operational description is provided. 138. Charlie Chong/ Fion Zhang Thermal viewers are not designed for absolute temperature measurements, but they can demonstrably sense temperature differences in tenths of degrees. Some manufacturers have modified these viewers and introduced absolute temperature references so that absolute measurements are possible in certain applications. (discuss this statement, on how this pseudo absolute temperature measurement is accomplished?) This generally requires an additional box, however, and diminishes the portability that defines the instrument group. (It also increases the price.) Thermal viewers operate most effectively with cooler targets (0C.150C) but, through the use of optical attenuators, they can be used for targets of up to 1500C. Typically, the area scanned (field of view) with thermal imagers is from 6 to 8 high and from 12 to 18 wide, with spatial resolution (instantaneous spot size) of 2 mRad (1 cm at 2 m). (? see next page) Although a hard copy of the thermal image can be acquired by through-the- eyepiece recording using either conventional or instant film, currently available units offer direct video recording by means of a conventional VCR output jack and camcorder accessories. 139. Charlie Chong/ Fion Zhang Applications for thermal viewers are found throughout the industrial environment but are generally limited to those in which the temperature measurements are not critical and the recording quality does not need to be optimum. The combination of a thermal viewer (to locate thermal anomalies) and a handheld thermometer (to quantify them) is powerful and cost effective. Thermal viewers are particularly useful industrially in tight spaces or, conversely, when a sizable area must be traversed and user fatigue becomes a factor. Exercise: From text: 2 mRad (1 cm at 2 m). (?) Calculation: D = d, D = 2 x 10-3 x 2 = 4 x10-3 = 4mm# Q? (4mm or 2mm?) 140. Charlie Chong/ Fion Zhang 2.3.3.2 Opto-Mechanically Scanned Imaging Radiometers Opto-mechanically scanned imaging radiometers provide potentially quantitative temperature measuring capability and high-resolution image quality. Detector cooling is almost always required and this is done using any of several means including thermoelectric (Peltier effect) coolers, compressed argon, refillable liquid nitrogen containers, and, most recently, electricpowered Stirling cycle nitrogen coolers. Most commercial imaging radiometers use a single detector, but some manufacturers offer dual- detector or multi-detector (linear array) instruments. All provide a means of measuring target surface temperature. Note: Although they are being replaced gradually by focal plane array imagers (see Section 2.3.3.4), at the time of this writing, opto-mechanically scanned imagers are still in wide use commercially. For this reason, the following operational description is provided. (Could be misleading note, -) 141. Charlie Chong/ Fion Zhang These imagers use refractive, reflective, or hybrid scanning systems and operate in either the 3.5 m (MWIR) or the 8.14 m (LWIR) atmospheric window. In addition to quantitative temperature measuring capability (Radiometers) in idealized circumstances, these instruments feature excellent capabilities for both spatial resolution (about 1 mRad) and minimum resolvable temperature (0.05C to 0.1C). Most manufacturers offer isotherm graphics features, spectral filtering, interchangeable optics for different total fields of view (FOVtotal) , color or monochrome (black and white) displays, flexible video recording capabilities, and computer compatibility. Most general-purpose systems in use today feature compact, field-portable, battery-operable sensing heads and control/display units, some of which are integrated into camcorder configurations. A complete system, including battery and video recorder, can usually be handled by one person, by either mounting the components on a cart or assembling them on a harness. Detector cooling for all newer models that are intended for field operation is accomplished by means of thermoelectric or Stirling-cycle cooler, thus eliminating the inconvenience of liquid nitrogen refills in the field. 142. Charlie Chong/ Fion Zhang Thermoelectric Cooling - Figure below The operating principle of thermoelectric devices is depicted above which demonstrate that it is possible to convert temperature gradients into electrical currents (or vice versa) and that thermoelectric devices can be used for both cooling and recovery of waste heat. http://www.nano.ucf.edu/research/compsim_masunov1.php 143. Charlie Chong/ Fion Zhang Sterling Cooling Electromechanical Cooling http://www.robertstirlingengine.com/cold.php Sterling Cooling 144. Charlie Chong/ Fion Zhang DIY Temperature Chamber Thermoelectric Cooling / Peltier Cooler https://www.youtube.com/embed/XApTATLNEcQ https://www.youtube.com/watch?v=XApTATLNEcQ 145. Charlie Chong/ Fion Zhang Stirling Cycle Engine, Two-Cylinder Alpha Type https://www.youtube.com/embed/aPxRB6JNfCw https://www.youtube.com/watch?v=aPxRB6JNfCw 146. Charlie Chong/ Fion Zhang Stirling Engines - How They Work https://www.youtube.com/embed/gQb2sN6UWkA https://www.youtube.com/watch?v=gQb2sN6UWkA 147. Charlie Chong/ Fion Zhang Ultra-Low Temperature Cooler - A Product of Precision Manufacture https://www.youtube.com/embed/-B2VcNy8dNs https://www.youtube.com/watch?v=-B2Vc