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Thread: Balancing rotors of rotating machinery using Smart yaw sensor to measure vibration

  1. #1
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    Balancing rotors of rotating machinery using Smart yaw sensor to measure vibration

    The yaw or lateral acceleration sensor found in Smart 450s without ESP is perfect for measuring vibration and balancing rotors in rotating machinery.

    In this post I am using above mentioned sensor to single plane balance a very noisy bathroom extractor fan.


    Above photo shows the fan, a very common and noisy axial fan purchased years ago from B&Q. Fan motor removed from fan housing and bolted onto a piece of chipboard. The Smart lateral acceleration sensor is held on to the motor by a Royal Mail rubber band (Note that this rubber band is not red as they used to be. Wonder why they had to change to an off white colour?).


    Required supply voltage for the sensor is 5 Volt so I just powered it from a USB outlet on my laptop. Fed signal to microphone connection on same laptop.

    Then download and install version 1.4 of Christian Zeitnitz' Soundcard Ozcilloscope software.
    http://www.zeitnitz.de/Christian/scope_en


    Above shows initial waveform and unbalance of the fan. The signal has been filtered so only the unbalance is present. The software has a built in frequency analyser and band pass filter so very simple to carry out the measurements especially if one is familiar with oscilloscopes.

    Presently I have no means for measuring phase angle. Need a separate sound card and an optical sensor to measure rotor rotation, something I will acquire later. Balancing can still be done using a four-run method and one can solve the balancing problem graphically.


    Above figure shows the graphical solution to the four-run method.

    Rather than me trying to explain how the four-run method works, I suggest you study page 4 of below document:
    http://www.engdyn.com/images/uploads..._-_peg&tdf.pdf

    Trial weights used: Quick Silver twin thread wood screws size 4 x 1/2 inch acquired from Screwfix. One has to measure the weight or mass of the trial weight. May be difficult unless you are in possession of a high accuracy Lidl electronic scale like me. Alternatively, count up hundreds or thousands of screws and weigh on whatever scale you may have, then calculate the average screw weight.


    Above shows remaining residual unbalance of my fan. Less than 4% of the initial unbalance. And best of all, the fan now runs without any annoying noise or rattle so one can finally enjoy a decent ****.

    Intend to check dynamic balancing of my turbo next using two sensors and a rotation sensor. I will therefore need a second Smart lateral acceleration sensor. Please PM me if you have one that you no longer need. It does not have to be 100% operational on a Smart. The one I used was one that was found faulty on a 2001 Smart 450 and therefore replaced.
    Drives a Smart Cdi - 65 to 85 MPG

  2. #2
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    Some might say you need to get out more Tolsen, but I couldn't possibly comment!

  3. #3
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    Quote Originally Posted by XTEN10 View Post
    Some might say you need to get out more Tolsen, but I couldn't possibly comment!
    You mean I should spend less time on my throne?
    Drives a Smart Cdi - 65 to 85 MPG

  4. #4
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    Could you not remove the need for an optical sensor by adding a known weight in a known place, saving the trace, comparing to the fan without the added weight. That will tell you where the imbalance is with reference to your added weight.

    In theory.

    But the whole job is easier with a gyro off a radio controlled helicopter I think, that will balance in 3 dimensions then which may not be important for such a short axis device but for sure is important on turbochargers..

  5. #5
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    Nope, that won't work. I shall peruse this.

    I think I am as sad as Tolsen is.

  6. #6
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    As already stated in first post, one can do single plane balancing without any rotation sensor for measuring phase angles when the "four-run method" is chosen.

    Dynamic balancing, that is balancing in at least two planes, can also be done without a rotation sensor but there are too many runs and trial weight shifts that keep adding complexity and errors. Two plane balancing is therefore a lot easier to carry out and more accurate when phase angles are measured. A complication with two plane balancing is that computing the compensating weights and their position is rather complicated, in fact too complicated for mere mortals.
    Drives a Smart Cdi - 65 to 85 MPG

  7. #7
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    Tolsen....YOU ARE A PRAT!!!!!

    I have good education, and I DO try to keep up with most of your maths/physics....but this time you've gone too far...for a bl**dy BATHROOM fan!?!??!?!?!

    It's almost as frustrating as the morons who ask stupid questions in some language you have to Google to decipher!!! (OK, at least your posts make sense after 3 hours research, whereas a certain newbies never got interpreted by any know translation program from this world....take the hint Kermi).


    EDIT:

    My mechanical stepson (NO..not a robot, his mind thoughts) just said..."Why not put a timer on it, so when you leave the throne room, THEN the fan comes on"?!?!??!
    Last edited by Or_GazM; 22-11-2012 at 04:17 PM.

  8. #8
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    Good thread TK. Thanks.

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