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shaft rotation detector

Discussion in 'General Electronics Discussion' started by stormin norman, Nov 6, 2013.

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  1. stormin norman

    stormin norman

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    Dec 1, 2011
    Is there some 'simple' device I can put together that will detect a shaft once it starts turning? I need it to trigger an indicator light that lets me know a conveyor belt is running.
     
  2. duke37

    duke37

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    Jan 9, 2011
    Combine harvesters used a magnet on the shaft which closed a reed relay. Newer systems which I do not know about would use a Hall effect detector.

    It all depends on the size of the shaft, the speed, the space available and the balance required.

    The output would be a square wave, a voltage goung up and down. Passing this through a capacitor would only give a signal when the shaft is rotating.
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    If you place a magnet or similar on the shaft where it can be detected by a hall effect sensor (or similar) then AC couple it to something you will see a signal only when the shaft is turning. This signal could trigger a monostable so the output remains turned on whenever the rotational speed exceeds some limit (say one turn every second).
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    *SNAP*!
     
  5. stormin norman

    stormin norman

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    Dec 1, 2011
    Duke & Steve...ok. So you both have 'answers' for me here....but point me to a plan for constructing this device. This is a conveyor belt that carries aggregate. I have access to the tail pulley shaft which I am guessing sitting here at home is about 2" dia. Plenty of room to glue a magnet to. Rotation speed is something I need to look at tomorrow... maybe 140 per minute...that's just a guess on my part. If I can get this to trigger and hold a relay said relay will switch on for the light I want to be able to see when the belt is running.
     
  6. duke37

    duke37

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    Jan 9, 2011
    It is rare that anyone can beat Steve to the draw !

    I have used a reed switch on a 10 inch shaft up to 1000rpm. It worked for two years.

    I attach a simple circuit using a 4093 quad two input Schmitt trigger, one gate is not used and the spare inputs should be earthed. Steve will have guessed the reason for my 'solution'.

    The time constant of R*C will determine the hold time, this will need to be a compromise between the minimum shaft speed detected and the rapidity of action.
     

    Attached Files:

  7. duke37

    duke37

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    Jan 9, 2011
    It is rare that anyone can beat Steve to the draw !

    I have used a reed switch on a 10 inch shaft up to 1000rpm. It worked for two years.

    I attach a simple circuit using a 4093 quad two input Schmitt NAND, one gate is not used and the spare inputs should be earthed. Steve will have guessed the reason for my 'solution'.

    The time constant of R*C will determine the hold time, this will need to be a compromise between the minimum shaft speed detected and the rapidity of action.
     
  8. stormin norman

    stormin norman

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    Dec 1, 2011
    It is a 2 1/4" shaft turning somewhere close to 96 RPM. I have ample room to locate the pickup at the shaft end or along the length of it.Since it has a keyway cut into the shaft I could mount the magnet in that, providing I find one that fits inside of it... Duke...if you PM me I'd like more details regarding the schematic you posted here.
     
  9. duke37

    duke37

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    Jan 9, 2011
    I have had a look at the availability of Hall effect devices, the A3144 is common and cheap.

    The Hall effect device will go in as a direct substitute to the reed switch but would need a 12V supply. It will be easier to fit than the delicate reed switch.
    When we fitted up our ten inch shaft holding a 25 ton flywheel we found that we could not drill or shape the modern magnets, they just shattered.

    Will send you a PM but it is better to put things on the open forum so I can be castigated when I get things wrong !
     
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