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Fitting a thermocouple to a motor

  1. Nov 10, 2016 #1
    Hi. It's my first post

    I work in a manufacturing plant where a hydraulic pump motor has failed. The cause was bearing failure and the motor locked up. The motor still insulation tested ok, but is being sent out for rewind and new bearings I am looking at ways to predict early failure?

    I want to fit a thermocouple to the motor so I can record the temperature weekly. I already have k type cable and display. Where would be the best location for the thermocouple? Ideally I want it inside the terminal box and through to the windings. I am hoping that as the bearing starts to fail the entire motor temp will start to increase so measuring the temp here will be ok.

    Will there be a danger of shorting the windings to earth if I don't install it correctly.

    Thanks
     
  2. jcsd
  3. Nov 10, 2016 #2

    Bystander

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    Can you put the TC directly on the bearing cap?
     
  4. Nov 10, 2016 #3

    dlgoff

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    Anywhere external to the windings; on the frame. All you are getting from the log is a trend. And that's all you really need to predict a failure, IMO.
     
  5. Nov 11, 2016 #4

    CWatters

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    I think it's unlikely that a thermocouple on the winding will give you much warning of a bearing failure.

    However Google found this which might be of interest..

    http://www.machinerylubrication.com/Read/1041/detecting-bearing-failure

    So perhaps put thermocouples on two bearings and look for differences between them?
     
  6. Nov 11, 2016 #5

    CWatters

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    On the other hand...
    http://www.maintenancetechnology.com/2013/10/methods-for-monitoring-bearing-performance/



     
  7. Nov 11, 2016 #6

    jim hardy

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    Yes. We had a 3500 horsepower motor blow up during just such an experiment.

    In my opinion:

    Vibration analysis is your most powerful bearing diagnostic. Fast Fourier Transform(FFT) tells you the frequencies present. It's applying high-tech to the old mechanic's stethoscope.
    In 1974 a FFT analyzer ran on a PDP11 computer and with its signal conditioning equipment weighed a couple hundred pounds.
    Small hand held FFT analyzers came about in late 1970's and seemed like something out of science fiction . Bentley Nevada was a pioneer but there are scores of companies in that business now so try a search. The early ones i knew of started around Knoxville Tennessee.

    meantime here's a paper by an old line bearing manufacturer.
    http://www.skf.com/binary/tcm:12-113997/CM5118/index.html
    see 'bearing defect' spectra starting on page 20.

    FFTbearing.jpg

    I saw my industry learn to use this technology in early 1980's. It's the way to go and is no longer expensive.

    See if you can find a copy of Bentley's classic textbook "Practical Vibration Primer" .

    old jim
     
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