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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. Bluetooth tach with a homemade bracket .

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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.

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I use brad's method. Backed up with one actual fan RPM reading it is very accurate.

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 ½ rpm of 60?

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6. Originally Posted by icy78
Ah interesting. Can you explain?
It's not linear, or is it?
30hz is ½ rpm of 60?

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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 =1760÷2=880
880- 2.2%=861

So 861rpm

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

8. 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.

9. 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.

10. Originally Posted by Tom Thermo
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?

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11. Originally Posted by Tom Thermo
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.

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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.

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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.

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