A limited comparison of four Infrared Thermometers - technical measurements

Discussion in 'Portable and Other Gear Measurements' started by atomicbob, Sep 24, 2021.

  1. atomicbob

    atomicbob dScope Yoda

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    Man with one meter always knows the reading, man with two or more less certain.

    Motivation
    Laboratory work requires well specified, calibrated devices. Fluke 62 max plus is an example for non contact infrared thermometers. However, for DIY and hobbyist use lower cost devices allow those on a budget to make thermal measurements over a qualified operating range. This led to pondering the differences between standards such as Fluke and less expensive, less well known IR thermometers.

    Methods
    Each of the IR thermometers evaluated were compared at the following three temperatures:
    1. 0 °C ice bath
    2. 26 °C ambient heated plate
    3. 35 °C SW51+ transformer cover after thermal equilibrium achieved

    Ice bath calibration
    01 IMG_2916_small.jpg
    List of IR thermometers from left to right:
    Fluke 62 max+
    Raytek MT4
    ThermoPro TP30
    Etekcity LaserGrip 800

    Examples of ice bath setups and standards may be found at these links:
    https://www.thermoworks.com/thermapen101_creating_an_icebath
    https://us.flukecal.com/products/te...ial-application-baths/7911a2-constant-tempera
    https://www.astm.org/Standards/E2488.htm

    Each IR thermometer has a specific D:S ratio (distance to spot size)
    Measuring distance was adjusted accordingly to achieve approximately the same measurement spot size

    High mass, high thermal inertia plate with thermocouples attached:
    02 IMG_2919_small.jpg
    Edmunds Optics 56937 bench plate placed on mouse pad on top of Holo Audio KTE Spring 2
    Plate temperature tracked until thermal equilibrium reached, approximately 2 hours
    Plate has a very high thermal inertia allowing consistent readings over the measurement period

    IR thermometers observed temperature from approximately 20 cm above the center of plate.
    Thermocouples were taped to the center of the plate and allowed several minutes to equilibrate.

    SW51+ transformer cover top surface temperature measurements:
    03 IMG_2906_small.jpg
    More information about this particular setup here

    Example elevated temperature bench plate thermocouple measurements at equilibrium:
    04 20210727  34465A + Fluke K thermocouple on optical bench.png
    This graph is a reminder that all measurements have some noise in them.
    Even though observations include tenths of a degree, better than 0.5 degree is mostly noise.

    Tabulated data:
    05 20210727 temperature sensor calibration data.png

    IR thermometer linearity plot from the tabulated data:
    06 20210727 sensor calibration - psi plot version.png
    Low cost IR thermometers are reasonably accurate when operated at room temperature. They are not typically specified to work over a wide ambient temperature range and are likely not temperature compensated.

    A few observations
    Etekcity deviated the most from the group but still well within mfg specifications
    TP30 was harder to obtain consistent readings during the evaluation

    Typical low cost IR thermometer specificiations:
    07 Etekcity Lasergrip 800 specifications.png

    What does the more costly Fluke 62 max+ offer?
    1. A greater number of operating conditions specified over which accuracy will be maintained.
    2. ISO standard calibration and related documentation available
    3. Known ruggedness and reliability
    4. Two lasers which aid measurement spot visualization

    08 Fluke 62+ specifications 1.png

    09 Fluke 62+ specifications 2.png

    Design to greater levels of performance specifications is more costly.

    Having any ability to quantify relative temperatures such as component at operating temperature vs. cold is a useful addition to the tool box.

    20210925 edit: added two laser feature to Fluke 62 max+ advantages
     
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    Last edited: Sep 25, 2021
  2. Cryptowolf

    Cryptowolf Repping Chi Town - Friend

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    While working on my bar tending skills, I spent several months stirring with a Thermopop instant read. you’re right, even with measurement inaccuracies, relative temp can help develop consistency and aid in comparisons. thank you for this post.
     
  3. purr1n

    purr1n Super Friend

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    Curious of their performance when at higher temperatures, e.g. flaming hot output devices on amps by users who abuse their Loki EQs into sub 20-ohm impedance planar headphones, folks who use Magni as speaker amps, etc.
     
  4. atomicbob

    atomicbob dScope Yoda

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    Higher temperature comparison.
    Subject: Studio B left channel, Genalex 300B power tube

    tabulated data:
    21 20210924 temperature sensor comparison data.png

    IR thermometers integrate over the spot size given by the D:S ratio.
    The FLIR has greater resolution and ability to measure smaller areas with greater precision.

    An average for the left channel 300B
    22 FLIR0318_111_C.jpg

    With slight repositioning a range of ± 7 °C is observed
    23 FLIR0316_104_C.jpg 24 FLIR0315_118_C.jpg
    FLIR E4 is approximately 10x cost of the Fluke 62 max plus
     
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    Last edited: Sep 25, 2021
  5. Melvillian

    Melvillian Friend

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    I own a General IRT205 that I bought from Home Depot for around $30 a couple of years ago and it's consistently around 6 degrees Celsius off.
     
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  6. atomicbob

    atomicbob dScope Yoda

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    @Melvillian: I was expecting one or two of the inexpensive devices tested to have some offset as you describe along with more linearity deviation. My samples were obtained very recently.
     
  7. Pancakes

    Pancakes Friend

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    @atomicbob what emissivity do you use on amp heatsinks and other iron and do you set it to something else when hitting tubes? Thanks dude.
     
  8. atomicbob

    atomicbob dScope Yoda

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    Often I just use 0.95 unless looking for greater precision or the material emissivity diverges greatly.

    Anodized aluminum heat sinks typical emissivity is 0.83 ~ 0.86
    Bare aluminum typical emissivity is 0.04 to 0.06

    For anodized aluminum heat sinks difference using 0.84 might be 2 °C higher at 35 °C.
    Bare aluminum requires changing the setting.

    I have attached a pdf from Fluke on emissivity for many common materials.
     

    Attached Files:

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  9. Tube crazy

    Tube crazy Rando

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    Contactless IR is good to do comparative measurements and not so good in determining absolute temperatures. The background temperature is also reflected of the to be measured object. Metals with a matt finish can be an almost perfect mirror for IR. This influences the measured value. In professional FLIR equipement you can enter this background temperature.
     
  10. atomicbob

    atomicbob dScope Yoda

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    IR thermometers are deceivingly easy to use. Spot size, considerations for reflections from other heat sources, emissivity, thermal air currents etc. can impact absolute temperature. Relative measurements as temperature changes are easier to obtain reasonably accurate information as mentioned. The Fluke 62 series has a very useful visual manual which is a great tutorial for proper use.
     
  11. atomicbob

    atomicbob dScope Yoda

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    Looking at post #4 above the FLIR image shows Studio B right channel 300B with a lower thermal profile and no hot spot. I should have investigated this as that tube's filament failed 14 days later.
     
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  12. Armaegis

    Armaegis Friend

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    Does the tube still glow? if it does, I'd be curious to see how the temperature profile has changed post-failure.
     
  13. atomicbob

    atomicbob dScope Yoda

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    No, filament failed completely, open circuit. Temperature profile is now room ambient.
     

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