by Bob Rogers
ITC Senior Thermography Instructor
ASNT NDT Level III TIR

Are you close enough to your targets? We can try and obtain a more accurate temperature reading by getting closer, but many times it is not possible. Working around or in the proximity of high voltages we have “safe” minimum approach distances that MUST be adhered to. Other instances, including obstacles, may prove too dangerous to get closer. Of course, entering the correct temperature parameters such as background, emissivity, relative humidity and distance are very important and aid in obtaining the correct value of temperature.

For those of us who are thermographically scanning electrical substations, it is very important to obtain the correct temperature. There are severity criteria that assists us in determining the course of action to be taken based on a temperature. If the measured temperature is not obtained correctly, it could have a disastrous effect on the course of action to be taken on electrical equipment. The electrical anomaly may be interpreted as just a deficiency and not be acted upon as an immediate problem. If the elevated temperature is measured low by “accident” by not being in focus, being on an incorrect range or by not being close enough, it will have a similar situation. This application note deals with not being close enough physically to the thermal anomaly.

The following is an example of a temperature obtained at a substation while I was on a recent trip. The following is a thermal image of a connection in the substation.

  
Click any image to see a larger one

The connection is at a distance much further than you would like to be. The temperature measured on the hot electrical connection was 49.9ºC(121.8ºF). The ambient, air temperature was 25ºC(77ºF). This calculates out to be a temperature increase of 24.9ºC(76.8ºF) over the ambient air temperature and 23.9ºC(75ºF) over a similar adjacent electrical connection. Based on a severity criteria from NETA, the “International Electrical Testing Association”, this would be classified as a Deficiency and would be scheduled to be repaired as-soon-as possible.

Examining this from another viewing angle at the same distance as the first thermal image, I attached a 12ºFOV(Field of View) Lens to the camera. This made the camera appear to be now one-half the distance optically to the object.

Now examining the displayed temperature, the thermal image shows a temperature on the hot connection of 67.3ºC(153.1ºF) which is 42.3ºC(108.1ºF) over the ambient air temperature. The temperature of an adjacent similar electrical connection was made and it calculated out to be an increase of 41.3ºC(106.3ºF) over that similar electrical connection. Based on the severity criteria from NETA again, the repositioning of the camera and the use of a narrow field of view (telescopic) lens, brought the camera optically closer and the resulting temperature would now correctly be classified as a Major Deficiency! This electrical connection must be repaired immediately.

So get closer if you can. Take the temperature measurements from different viewpoints. But best of all, use a telescopic lens that will get you optically closer to the thermal anomaly.

• No more counting sheep
  Charlottesville Daily Progress, VA - Jul 31, 2004
  ... The center, located on Lexington Avenue, has four bedrooms each equipped with an infrared camera, so even when the room is dark staff can see the patients. ...

• Infrared cameras to count UK car passengers
  The Inquirer, UK - Jul 28, 2004
  ... The infrared camera will apparently be able to distinguish between false passengers such as cardboard cut outs, dogs and dummies of the non-human persuasion. ...

• Duke Study Could Lead To Earlier Diagnosis, Treatment Of ...
  WRAL.com, NC - Jul 26, 2004
  ... joints. Scientists have tried to measure that heat before, but thermal imaging machines could not deliver reliable results until now. ...

• NASA Refitting Shuttles For Safety
  Tampa Tribune, FL - Jul 23, 2004
  ... shields the shuttle from 3,000- degree temperatures, penetrating dyes to expose pockets of oxidation, and a heating method called flash thermography to reveal ...

• NASA Infrared Camera Helps Surgeons Map Brain Tumors
  Science Daily (press release) - Jul 19, 2004
  ... cells use different biochemical pathways from normal cells, and when researchers use the infrared camera, they can ... An advantage of thermal imaging is that ...

• Research into hay fever and temperature of the nose rises helps ...
  News-Medical.net, World - Jul 8, 2004
  ... We register this using an infrared camera.” A software ... can be observed non-invasively and very sensitively for hours on end by means of thermography. ...

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.

• Arc Ratings
  What type of clothing should I purchase, how high should my rating be?

• IR window for vaccum chamber
  I have an application which need to inspect a target placed in a vaccum chamber. I need a longwave I.R. window which can resist 1atm pressure difference and the operating temperature is around 45 degC. The diameter of window should be larger than 50mm. Please recommend one if possible. Thanks.

• Detection of false coloration of ornaments and gold coins
  I am new to the field of IR Thermography, the problem I am trying to address requires me to be able to detect "false coloration" of ornaments, and gold coins.
  
  To be more precise, several precious metals are frequently acid washed, or chemically treated to make them have a different color/luster.
  
  Furthermore, is it possible to determine "the degree of corrosion of a metallic surface" or "whether the surface is corroding"?
  
  I am not sure IR Thermography may have the solutions to these problems, any help will be greatly appreciated.

• Induction Heating?
  Based on the picture what do you think could cause the heating around the cable gland. *visually all the grounding cables are burnt rotten. cables from left to right are Neutral, Blue, Yellow & Red respectively.

• Hot Shafts at Couplings
  Where the shaft of an electric motor is coupled to a pump or something similar, the coupling being of uniform temperature, why should one of the shafts be considerably hotter than the other. If this is normal, which one would be expected to be hotter, or, is it an effect of a misalignment, or some other problem.

• Thermography in Strip Mining
  Can someone provide criteria for analysis of hydraulic systems in front end loaders like the 992-G? The joint pin temperatures are between 25°C to 30°C.

• emissivity values of pure water and ice
  Does anybody know emissivity values of pure water and ice.

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.

This is an image of the core component of a hydro generating unit. The spot is a pack (lamination problem), a part of a column that makes up the core.

Congratulations to our winner, James Hilburn from IRZ Consulting in Oregon. Thanks to Gordon Neilson of Bretech Engineering Ltd in New Brunswick, Canada. Both James and Gordon receive a special low emissivity traveling coffee mug.

And this month, we have a special award for most creative explanation from Maurice Lee at MIRA Component Engineering in the UK. His explanation follows:

"At first glance, it looks like a very dangerous but also very small creature in a wire cage that is strapped to the back of something, a sherpa perhaps. If the carrier is indeed a sherpa this might suggest the creature to be Tibetan. Compared to the size of the crate the object is small and the only heat source within the crate. The Yeti, well known Tibetan creature and relative of your Bigfoot would in fact be very well thermally insulated to cope with its Himalayan habitat. Eyes tend to not have any insulation so the warm object must therefore be the eye of a Yeti. So what you have is the first recorded infra-red image of a Yeti in captivity. Well done chaps."

Privacy Statement: We're happy to have you on our list, and since we want to keep you all to ourselves, we never share your e-mail address with anyone. Period.

To unsubscribe or update your user profile, click here.

P.S. Did a friend send you this? Sign up to get your own here - it's award-winning, useful, and complimentary.

P.P.S. Got questions, comments, or ideas for us? Email us - thanks!