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  1. #1
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    Measuring Fan RPM

    I would like to be able to mount a fan tachometer or strobometer while the fan is off, then have our staff stand outside of the fan section while testing during operation to increase safety.

    Is there a tool that allows this?

    Most that I have seen require you to be in the fan section or within view of the rotation shaft/belts/etc.

    Thanks,

    Wes

  2. #2
    Join Date
    Dec 2014
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    Bluetooth tach with a homemade bracket .
    clamp it on close the door take your reading.

    Sent from my SM-G950U using Tapatalk

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  4. #3
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    Icy nailed it . Also, is this unit on a vfd? If so , you can measure the rpm once and calculate the rpm from the hertz of the vfd at different settings.

  5. #4
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    I use brad's method. Backed up with one actual fan RPM reading it is very accurate.
    No man can be both ignorant and free.
    Thomas Jefferson

  6. #5
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    Quote Originally Posted by bradluke0 View Post
    Icy nailed it . Also, is this unit on a vfd? If so , you can measure the rpm once and calculate the rpm from the hertz of the vfd at different settings.
    Ah interesting. Can you explain?
    It's not linear, or is it?
    30hz is rpm of 60?

    Sent from my SM-G950U using Tapatalk

  7. #6
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    Quote Originally Posted by icy78 View Post
    Ah interesting. Can you explain?
    It's not linear, or is it?
    30hz is rpm of 60?

    Sent from my SM-G950U using Tapatalk
    Turns out it's not quite linear. But very close. Using slip percentage of motor. About 2.2% for 1800rpm motor with 1760rpm label.
    40 1800 =2.2%
    30 hz =50% of 60hz =17602=880
    880- 2.2%=861

    So 861rpm

    Sent from my SM-G950U using Tapatalk

  8. #7
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    Good work but just use the linear way . New hertz old hertz x old rpm = new rpm .

  9. #8
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    Maybe a bracket with rare earth magnets. I imagined my dial indicator that has a magnetic base and I can position the dial where I want. I actually could probably use the setup to do this.
    Give me a relay with big enough contacts, and I'll run the world!

    You can be anything you want......As long as you don't suck at it.

    If a person wants to create a machine that will be more likely to fail...Make it complicated.

    USAF 98 Bomb Wing 1960-66 SMW Lu49

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  11. #9
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    Much easier perhaps is to download an app to your cell phone that uses the accelerometers built into the phone. I have used this before and it shows a PSD with very clear peaks so you can pick out once per rev and maybe even blade passing frequency. If the free apps don't work there are others that cost $5 that might do the trick. Some use audio, some use accels some use both.
    Just a thought.

  12. #10
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    Quote Originally Posted by Tom Thermo View Post
    Much easier perhaps is to download an app to your cell phone that uses the accelerometers built into the phone. I have used this before and it shows a PSD with very clear peaks so you can pick out once per rev and maybe even blade passing frequency. If the free apps don't work there are others that cost $5 that might do the trick. Some use audio, some use accels some use both.
    Just a thought.
    Can you reccomend one or two Tom?

    Sent from my SM-G950U using Tapatalk

  13. #11
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    Quote Originally Posted by Tom Thermo View Post
    Much easier perhaps is to download an app to your cell phone that uses the accelerometers built into the phone. I have used this before and it shows a PSD with very clear peaks so you can pick out once per rev and maybe even blade passing frequency. If the free apps don't work there are others that cost $5 that might do the trick. Some use audio, some use accels some use both.
    Just a thought.
    Can reccomend one or two of those apps Tom? Be fun to try it.

    Sent from my SM-G950U using Tapatalk

  14. #12
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    May 2018
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    motor pulley divided by blower pulley times motor rpm. You wont know if the motor is doing the actual rpm on the name plate or slippage. But it will get you close.

  15. #13
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    Feb 2016
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    Buy a tachometer and measure the fan RPM @ 60 Hz. From there if you wish you can calculate the actual RPM pretty close.
    No man can be both ignorant and free.
    Thomas Jefferson

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