By Joe DeMonte
ASNT/PdM Thermal Infrared Level 3
Senior Thermography Course Instructor
Infrared Training Center

Here is an article that I put together to show the untrained user of “spot radiometers” why there can be significant errors in measurements. Using infrared devices for non-contact temperature measurement may seem like an easy task. Just squeeze the trigger on the “laser pyrometer” and point it at the target for accurate temperatures, right? Wrong!! Different materials have different efficiencies at radiating. I will discuss briefly the important measures that must be taken to accurately measure temperatures with these devices.

Take a look at an aluminum block heated up on a hot plate. I am viewing this hot plate with an infrared camera that detects the same radiation as a typical spot radiometer such as a Raytek or 3M “laser Pyrometer”. It produces an infrared picture of the heat and allows me to obtain temperatures from thousands of points across the thermal map.

                         
Al block heated on a hot plate                      Temperature of the Tape on the Al block

In the next image, I have placed a simple piece of 3M Super 88 black electrical tape on the surface of the aluminum block.

It is not possible for the tape to actually be hotter than the block. The source of heat is at the bottom of the block and needs to conduct upwards through the aluminum and then outward through the tape. What we are seeing is the difference in the efficiency of both the aluminum and tape to emit IR radiation. The actual value of this efficiency may range from 0.0 to 1.0 and is termed emissivity. The tape has an average emissivity of 0.95 for the wavelengths of my infrared camera. Take a look at the next image for another temperature measurement of the block with the tape still attached.

As you can see, the temperature of the block as read by an infrared device is nearly 100°F lower than that read on the tape! We would have the same results with a spot radiometer. Check out these pictures of the same block with a spot radiometer:

         
Temperature on the tape!                  Temperature on the block!

Next, I will correct for emissivity using my infrared camera by setting it to 0.95 and take the same measurement of the tape.

 
Temperature with Emissivity Correction

Proper compensation for emissivity results in another correct temperature rise. We can now adjust the infrared camera to give us a better understanding of the aluminum temperature now that we know the actual temperature is 203°F, not 191°F or 103°F as previously thought.

There is much more to this than meets the eye, and the basic course that I teach on infrared science/certification lasts for a full four days. We just have to remember that accurate temperatures on clean, unpainted, and uncoated metals are not easy with infrared devices. Take your temperature measurements from highly corroded metals, or from other higher emissivity targets and you will have less error in your reading. If you want accuracy from a chromed piece or other clean metal, just place a piece of electrical tape on it and you will be much better off than without. But remember that this kind of tape will melt at around 200°F!

IF YOU DON'T HAVE AN ACCURATE TEMPERATURE ON ONE OBJECT, YOU CANNOT GET AN ACCURATE DIFFERENCE IN TEMPERATURE BETWEEN TWO OBJECTS EVEN WHEN THE EMISSIVITY IS EQUAL BETWEEN THE TWO!!

• Space Shuttle Processing Status Report: S04-029
  NASA, DC - Aug 27, 2004
  ... Thermography was also performed at KSC to check for internal flaws. ... light to heat areas that are immediately scanned with an infrared camera for temperature ...

• One Star's Life Ends With A Ring
  PhysOrg.com, (subscription) United States - Aug 19, 2004
  ... Spitzer's infrared camera, which captured the new picture of NGC 246, was built by the Goddard Space Flight center, directed by the Smithsonian Astrophysical ...

• The hunt for Fort Louis
  AL.com, AL - Aug 16, 2004
  ... A couple of years ago, Waselkov tried to use some advanced methods, including a radar system and a thermal imaging system, to locate the remains of buildings. ...

• Raising bars beyond reach
  Press-Enterprise (subscription), CA - Aug 15, 2004
  ... In some cases, sports scientists are helping the coaches. "CT scans, X-rays, high-speed video, thermal imaging can be used to help coaches see better," said ...

• Reproductive Efforts for Zoo Atlanta's Giant Panda Lun Lun Were ...
  Business Wire (press release), CA - Aug 9, 2004
  ... awaited conclusive signs of the pregnancy, physiological data were collected which included hormonal and behavioral tracking, ultrasound and thermography. ...

• Options exist in breast cancer screening
  Canton Repository (subscription), OH - Aug 9, 2004
  ... The issue of using screening exams to detect breast cancer early has become even more complex with the introduction of breast thermography. ...

• Surveillance of Illegal Aliens Tested
  Grand Forks Herald, ND - Aug 6, 2004
  ... The initiative already uses remote-controlled aerial drones and infrared thermal imaging cameras to search for migrants and smugglers. ...

• FLIR Infra Red Camera is a Highlight for UK Company
  Process & Control Today, UK - Aug 2, 2004
  ... explains, “Many companies invest in thermal imaging with preventive ... And he concludes, “the ThermaCAM® E Series ... brought the benefits of thermography to a ...

• Port protection becomes high-tech
  Baltimore Sun, MD - Aug 1, 2004
  ... An alarm is sounded and closed-circuit television cameras equipped with thermal imaging for nighttime can locate and track the potential threat and send the ...

Here is a selection of recent new threads by IR Community members. Feel free to click the links, see how people have responded, and post your own response if you like.

• Clarify for Level One Qualifications
  I note in a document I received that a level one is "qualified to start a 9 Step infrared Program". I am sure I could do it - if I knew what it was!! I assume in a factory setting a predictive maintenance program might be it. Please clarify. Thanks!

• Veterinary Thermal Imaging Seminar, Oct 14-17th, 2004
  Join us at Vetel Diagnostics in San Luis Obispo, California for an informative 3 1/2 day seminar on Veterinary Thermal Imaging, Oct 14-17th, 2004 at the Sands Motel and Conference Center. 1930 Monterey St. San Luis Obispo, CA. 93401, Contact Kelly Martin 800-458-8890
  Our speakers include Tracy Turner, DVM, Jim Waldsmith, DVM, and Mike Walsh, DVM.
  
  The tuition is $350.00 per participant and CE credits are offered. You can find a complete course outline at http://www.veteldiagnostics.com/Training%20Sessions.htm .
  
  Please contact Kelly Martin at Vetel Diagnostics for any additional information you require;
  1-800-458-8890, 805-781-7691 or Veteldiagnostics@aol.com

• Veterinary IR Courses
  There will be a hands on Basic Veterinary IR Course in Roswell, New Mexico on December 4-8, 2004. This session will focus on how to choose and operate an appropriate infrared
  camera from one of several manufacturers; safety, applicable anatomy and physiology, how to prepare the patient and the environment for an infrared examination, proper patient positioning,
  artifact avoidance, etc. Both small and large animal models will be imaged by participants.
  
  A more advanced course will be held in Waterbury, Connecticut on October 1-5, 2004. This session will be a continuation of Session 1, however it will focus primarily on helping experienced veterinary thermographers improve their ability to produce high quality thermal images that are suitable for diagnostic use. Additionally, this session will incorporate opportunities to present and discuss clinical cases, review critical principles such as artifact detection, and take several field trips including a working fieldtrip to a racetrack such as Belmont Park, or other equine facility.
  
  Please see details on : http://www.vet-therm.com

• Infrared market
  I am new to this board. Need your help to understand the Infrared market. I am trying get a sense of what is the potential for the Infrared market. Market size, market share etc.
  
  For a starter, in the automotive industry, for the night vision application, how big is the market for IR camera? How much potential is there. etc.

• Electrical Inspections & Flash Suits
  I recently attended and presented at the EPRI Infrared Users Group Meeting (IRUG) on this subject. There is a lot of concern in regards to safety. There are NO specific guidelines and/or procedures that specifically addresses what the thermographers should or should not wear in regards to additional PPE, etc. A committee is being formed t look at this. Any information, suggestions and/or comments in regards to this subject would be greatly appreciated.

• Pitching PdM to utility power plant managers
  I have an opportunity to make a pitch to a local power plant manager next week. They currently use IR once a year only for a very limited application evidently required by federal law (involving storage of nuclear fuel though it's no longer a nuke plant).
  
  The balance of the plant (now NG, sometimes backup fuel oil) uses no IR whatsoever (outside of occasional switchyard/substation scans). The maintenance supervisor's feeling of course is that they run as tight a ship as they can using preventive maintenance techniques, thus IR is unnecessary. He has agreed to give me some time to try to convince him that regular IR scans throughout his entire facility would definitely be more cost effective if they shift away from schedule based toward condition based maintenance.
  
  I've been to InfraMation once and read what I can to keep up on this stuff, but here is the first chance I've had to go head to head running a large facility who really understands the distinction between PM and PdM, and understands how IR would fit into it, but is convinced he doesn't need it.
  
  I need to find a concise, coherent way to walk in there and sell him IR in 15 minutes or less, on the basis of the cost effectiveness. I need hard data to do so. In the ocean of information out there, I'm looking for one single wave I can paddle into and ride to the shore. :-)
  
  Any advice would be greatly appreciated. Specific examples of power plants who've made the switch from PM to PdM along with some kind of metric gauging the cost effectiveness of the IR program would be invaluable to me right now.

• Electric Utility-Distribution Class MOV Arrestors
  Looking for anyone who has established an upper threshold temperature rise on MOV arrestors. We have been finding numerous MOV's with a 20 to 30 degrees rise over reference temperature. Responses will be greatly appreciated.

• Trying to understand IR
  I'm trying to understand why infrared is such a hot technology right now? Seems as though spending on IR is outpacing most other areas of technology right now.
  
  If you are a purchaser of IR equipment, could you help me understand what applications are driving this growth? Also, by how much do you anticipate your purchases of IR equipment will increase next year (is the growth sustainable)?
  
  Thank you much for helping me understand what I'm missing here.

• Help with estimating?
  While of course I'm aware that no two situations are alike and thus there can be no hard and fast rule of thumb for estimating the time it takes to do a competent and thorough IR inspection of any facility, I'm wondering if there exists somewhere out there at least a flow chart or outline guide that allows you to hang your hat on an estimate range before you've actually executed the job.
  
  For instance, I'm going to bid on a creamery that runs 24/5, generally with between 35 and 40 people on the line at any given time. They have peak loads around 2 MW, with baseline a little under half that. They estimate about 5000 hp total motor loads, with a couple of 500 units, two or three 200's, several 100's, a handful of 20 to 50's, and more 5 to 10 hp motors than they can keep track of. Production is variable across several different lines (milk, cheese, ice cream, etc.).
  
  Again, I know it's not like opening up an auto mechanic's guidebook, which tells him he should estimate 3.45 hours for a serpentine timing belt on a particular make and model car -- but does knowing the parameters above, along with perhaps net floor area and a rough layout of MCC locations, allow for at least a ballpark "standard" hour estimate if we make enough assumptions?
  
  I haven't run across anything like it in all my research, but I figure just about every independent thermographer on the street must run into the problem on a daily basis. Do people even share this kind of info in the interest of promoting thermography, or is it all played close to the vest in the interest of competition?

• Portable video recorder for Flir E4 thermacam
  Can anyone recommend a relatively inexpensive portable video recording device that will work with a Flir E4 Thermacam.

• IR Window on HT Switchgear
  Most of the switchgear is manufactured with certain design criteria such as IP 65 or IP55 or etc. What will happen to the IP rating if IR Window is installed on those HT switchgear to facilitate scanning?
  
  What will be the repercussion? Any tests done on the switchboard for "before and after"?

• Stator thermal patterns
  I was wondering how successful anyone has been in attempting to isolate localized heating resulting from crack rotor bars, or shorted end-rings in motors? Thermal differences degree wise that have been identified with above faults. I am trying to utilize this technology to confirm what I identify in my vibration spectral data as faults above. I would also like to hear how aluminum stator cases (covered with at least .9 emissivity media) verse sheet metal/cast steel housings show these localized hot spots.

And of course if YOU have a question or want to start a discussion on a topic, we would love to hear from you. Just post a new thread on a message board.

Brainteaser of the Month  [top]

Here is this month's brainteaser. Readers who email us the correct identification and explanation of the object(s) in the thermograms are entered into a drawing to win a prize from ITC. Please put "Brainteaser" as the subject of the message.

Click here to email your guess

Do you have an interesting image that you think would stump other thermographers? If so please email me your image (preferably in native .img, .jpg, .tif, .tgw, or .tmw format) with an accompanying visible photo and explanation. If your image is used, you receive a gift as well.

Our thanks goes to our Brainteaser contributor last month, Michael O'Neill from PPL Electric Utilities Corp. in Lancaster, PA, who explains what these are below.

"We have had a problem with core-10 steel transmission line poles that require drilling of the poles for attachments. These poles range from 50 to 135 feet tall and support 138 kV or 69 kV lines on our system. If the drilled areas are not properly sealed, water enters and can freeze causing the pole to split at the weld seam. After our first discovery of one of these poles we spoke of various ways to identify how to find and repair them before they failed in service. IR of course was the best alternative. We are presently performing the inspections from the air and on the ground.

The images were taken with direct sunlight striking the pole surface. The emissivity of the surface is 0.96 over all the areas in question. This is due to the nature of the steel (core - 10) used. It is designed to rust with the resulting patina protecting the pole from further rusting."

Congratulations to our winner, Lee Wills from Infrared Technology Services near Houston, TX. Both Lee and Michael receive a special low emissivity traveling coffee mug.

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