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01-25-2018
01:49 AM

01-25-2018
01:49 AM

Re: Curve fitting units

I do sometimes so

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01-25-2018
08:05 AM

01-25-2018
08:05 AM

Re: Curve fitting units

There are a couple mistakes (I believe) in your note. MJG is right, this is fatigue (I recognize the MIL-HNDBK-5 equation). So we need to be careful about how we treat this, and about what the definition of cycles is. Please look at the attached Prime 3.0 sheet.

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01-29-2018
07:54 AM

01-29-2018
07:54 AM

Re: Curve fitting units

Borrowing on Fred's idea how about

cycles=1*Hz*sec

Math/label/unit

seems to work fine. Does anybody see a problem with this?

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01-29-2018
08:37 AM

01-29-2018
08:37 AM

Re: Curve fitting units

wrote:

Borrowing on Fred's idea how about

cycles=1*Hz*sec

Math/label/unit

seems to work fine. Does anybody see a problem with this?

Well, Hz = 1/sec

so Hz sec is unitless.

Because (for fft's) I need Hz for frequency of vibration due to a rotating shaft, I set "RPM = Hz/60" (note the caps!) Then I get the correct numerical value for the fft resolved frequency. I like this answer:

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01-29-2018
09:03 AM

01-29-2018
09:03 AM

Re: Curve fitting units

Great. This is the new "DesKohlhepp Equation/Theory"

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01-30-2018
04:58 AM

01-30-2018
04:58 AM

Re: Curve fitting units

Hi Fred.

I prefer 1 RPM = 2 Pi / 60 Hz and 1 rev = 2 Pi.

Best regards.

Alvaro.

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01-30-2018
07:24 AM

01-30-2018
07:24 AM

Re: Curve fitting units

wrote:

Hi Fred.

I prefer 1 RPM = 2 Pi / 60 Hz and 1 rev = 2 Pi.

Best regards.

Alvaro.

Hmmm

so RPM = rpm (already built-in)

And rev is a built-in and equals 2 pi.

Okay!

And cycle?

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01-30-2018
07:12 PM

01-30-2018
07:12 PM

Re: Curve fitting units

For cycle I guess that cycle = 1. Because then for the electrical alternating current you have that 60 cycles/seg = 60 Hz which agrees with the usual frequency.

Best regards.

Alvaro.

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01-31-2018
01:32 AM

01-31-2018
01:32 AM

Re: Curve fitting units

cycle = 1

cycle + % = 2 but must be an error

PS

In Mathcad 11

rad + sr = error (!!!)

In Mathcad 15 and Prime

rad + sr = 2 (???)

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01-31-2018
07:42 AM

01-31-2018
07:42 AM

Re: Curve fitting units

in Prime % is a function, not a unit, so