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Thread: Emissitivity

  1. #1

    Question Emissitivity

    Hi Brenton,
    We have a lot of aluminium clad surfaces at work which get covered with the product we produce and I have a few issues get the right emissitivty level correct so was wondering is there a tool or instrument that can measure this to give the right level that I can test to.

  2. #2
    Forum Member
    Join Date
    Jul 2013
    Location
    Queensland
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    5
    Hi Craig,
    Do you really need an accurate temperature reading?
    If you are just needing to see if there is a temperature difference over the equipment and it is not vital to know the actual temp then i would set the camera's emissivity to 1.0 and start the inspection.
    If you do need accurate measurements then you can buy tape/stickers that have a rated emissivity (they are usually around 0.95-0.96).
    If it is safe to do so, place a sticker on the equipment you need to get an accurate temp on. Wait for the sticker to reach the same temp as the equipment. set the camera's emissivity to the rating of the sticker and take a reading. Then take a reading of the equipment in question. if the temp is the same the emissivity is the same. if it is different then you need to adjust the camera's emissivity until the temp reading is the same as the original reading from the sticker.

    Another thing to note is if the aluminium cladding is shiny, you will have issues trying to set the emissivity due to reflectance. Also the product that covers the surface of the cladding, can you use that to get a good reading? or can you safety wipe it off to compete the inspection if required?

    If you could post a photo of the equipment in question and give a few more details of the type of inspection required, it may help us all to give you a better evaluation and answer,

    Regards
    Cam Wilson

  3. #3
    Hi Craig,

    Cam's reply is spot on and you may follow his suggestions. There are devices known as Emissometers. They are prohibitively expensive (tens of thousands) but they do accurately measure emissivity. In fact they actually measure reflectance in our wavelength and then provide us with the inverse which is emittance.

    However for just a few dollars you can follow the methods described in the Infrapsection Institute Standard for measuring emittance. http://www.ipi-infrared.com.au/infra...on-standards#6

    You can use the non contact method which Cameron described above, or you can use the contact method which involves using a contact thermometer (thermocouple/RTD) and adjusting your emittance accordingly.

    Things to be aware of...

    You will also need to calculate reflectance, and input this into your camera before you attempt adjusting the emissivity value.
    Calculating reflected Temperature standard is here... http://www.ipi-infrared.com.au/infra...on-standards#5

    As Cam pointed out above, if the surface has a particularly low emittance (ie the clean surfaces) they will be very difficult to measure (maybe practically impossible).

    Also be aware that if your surfaces are not kept clean (and they are covered with your product), the insulating properties of your clad equipment are being undermined. Increasing the emittance of the surface will increase your radiant heat loss... ie you will loose much more energy.
    Brenton Ward
    Level III Infraspection Institute Certified Thermographer
    Level II Airborne Ultrasound

  4. #4

    Emmissitvity

    Hi Guys ,
    Thanks for replying,sorry I have not got back sooner been on holidays and also quite busy at work . Will try the contact thermocouple as we have one of these handy as for the tape don't know how long it will stick due to the temperature being around 350 degrees. The aluminium was originally shiny but due to the product we produce nearly covers everything, the surface looks more like a flat white paint but I will try the tape method on other parts of the plant that are not as hot.
    Cheers Craig


    Quote Originally Posted by camwilson75 View Post
    Hi Craig,
    Do you really need an accurate temperature reading?
    If you are just needing to see if there is a temperature difference over the equipment and it is not vital to know the actual temp then i would set the camera's emissivity to 1.0 and start the inspection.
    If you do need accurate measurements then you can buy tape/stickers that have a rated emissivity (they are usually around 0.95-0.96).
    If it is safe to do so, place a sticker on the equipment you need to get an accurate temp on. Wait for the sticker to reach the same temp as the equipment. set the camera's emissivity to the rating of the sticker and take a reading. Then take a reading of the equipment in question. if the temp is the same the emissivity is the same. if it is different then you need to adjust the camera's emissivity until the temp reading is the same as the original reading from the sticker.

    Another thing to note is if the aluminium cladding is shiny, you will have issues trying to set the emissivity due to reflectance. Also the product that covers the surface of the cladding, can you use that to get a good reading? or can you safety wipe it off to compete the inspection if required?

    If you could post a photo of the equipment in question and give a few more details of the type of inspection required, it may help us all to give you a better evaluation and answer,

    Regards
    Cam Wilson

  5. #5
    Hi Craig,

    Another tip for an emissivity check would be to paint a small coupon of high temp black paint. Just a couple of inches in diameter would help you get a reference. The pot belly black paint we use is rated to over 500C. Emissivity is very high at approx. 0.95 - 0.97 depending on which brand you use.
    Brenton Ward
    Level III Infraspection Institute Certified Thermographer
    Level II Airborne Ultrasound

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