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SNORMAN

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Reply with quote  #16 
Quote:
Originally Posted by Walt Strong
Is the compressor a rotary vane or rotary lobe type?

Is it a compressor or perhaps a blower?

Is it direct drive or by belt or gearbox speed reduction?

Why the odd frequency scale in Orders?

What is the number of vanes or lobes?

Walt

Its a rotary vane compressor (fls) for pneumatic transport it does around 20 Psi 

direct drive

8 vanes 
Walt Strong

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Reply with quote  #17 
The second spectrum has different vibration levels for the vane pass frequency fundamental and the two harmonics shown. This would indicate that the load is different from the first spectrum, even though both spectra show that the load is 100%. If the low-frequency vibration levels, mostly below 1X shaft speed are real, then it should be felt. I still believe it is an instrumentation problem like John does.

If the same vibration spectrum is repeatable when changing the accelerometer and cable, then I would suspect the analyzer or the input adapter as a problem. One test would be to do a low-frequency acceleration spectrum with F-max no more than 50 Hz. Use the cursor to get the amplitude at 1X shaft speed and acceleration units. Then calculate the 1X shaft speed amplitude and velocity units and compared to the amplitude in the velocity spectrum. You could repeat this for 0.5 X shaft speed, since that's where the velocity spectrum starts to go very high. You might also take a look at the analyzer integration setting for analog or digital that may have changed since the previous survey.

There is some indication in the second spectrum that the entire noise floor is raised up compared to the first spectrum. This could indicate that the amplitude range (auto-ranging) of the analyzer is affected by high frequency noise/vibration that is beyond the frequency range of the spectrum. A high frequency acceleration spectrum to at least F-Max of 20,000 Hz or more could detect this.

Walt
Curran919

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Reply with quote  #18 
No way this is physical, but that doesn't necessarily mean there is a problem with the sensor/DAQ either.

Quote:
Originally Posted by John from PA


These integration noise issues can be difficult to diagnose.  A loose cable that is flapping around can sometimes drive the signal nuts.


Yeah true, I forgot triboelectric effect can also cause ski slope.

I have also had ski slope with humidity on my connectors. I imagine corrosion could also have a similar effect.
SNORMAN

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Reply with quote  #19 
I do believe it was a cable issue I had two new ones and they both did it so i threw on an old one and all was better ????? anyone ever had problems with ctc cable?
fburgos

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Reply with quote  #20 
I do have this cable problmes

But in your first post you said that using different, sensor, cords and analyzers had same result, this got me to believe it was a something in the machine driving this, very high noise or impacting overloading the signal, im glad you could find the culprit
Walt Strong

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Reply with quote  #21 
From OP: "I am questioning the 2130 but i used different accels ,cords and even analyzers and had repeat results."

I guess he did use a different analyzer! This supposedly eliminates instrumentation as a source of problem. I previously mentioned that load was different, even though plots showed 100% load.

Walt
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