What is the motor speed?

One thing that can make the phase difference close to 0 degrees (or 180) is rsonance. The force driving a resonance can be at 1X.

If one is looking for a solution by balancing, the question to ask is whether the response to balance weights will work, i.e. do you get enough response, the right response--the right response in some systems has to do with whether you have sufficent balance planes and planes in a good place.

In a resonant system balance weights can respond with a 0 degree difference between vertical and horizonal. In fact 0 or 180 degrees might be expected.

Where are you with respect to the natural frequency.

Hi William,

Thank so much for your response,

The motor speed is 2986 rpm.

If resonance to be suspected in 1xrpm, that means the natural frequencies should have 1 frequency close to 1xrpm right? I'm not sure about the current state of resonance identify for this case (as it's not in my company). But should I be concern about resonance if there are significantly highly directional vibration? (i.e much higher horizontal vibration than vertical vibration or vice versa).

Many people only look at cross phase, but I like bubble charts with amplitud and phase... Sometimes makes me wonder if I'm wrong or is the people teaching are, end of the rant.

Hi fburgos,

Well I guess maybe it is because of the convenient for using cross channel measurement compare to the use of phototach (which might require the machine to be stop to set up the reflective tape, and a lot of facility want to avoid stop machine for checking). From your experience, do you think that bubble charts will be more precise than cross phase? I would like to know more about it.

Even with cross channel it always give your the amplitude, and yes bubble charts are best and can be used with cross channel, just don't move the reference and write down the other sensor your are moving, I rarely use tach reference.

For me it's best others might disagree but I could be totally wrong

Thanks for your sharing, fburgos. I haven't thought of using cross channel for bubble charts. I will definitely try it next time. For this particular case, do you have any comment about this phase behavior?

Directional vibration does not have to be higher in either the horizontal or vertical direction..

What is directinal vibration? Loosely, vibration mostly in one direction. From a measurement view, vibration at a natural frequency should be close to a modeshape (pedantic examples excepted). For many modes of which people speak, normal modes, modeshapes the measurements are either inphase or out of phase. Complex modes would have other phase relations.

Not much to add, as William said, looks like resonance, just because the many harmonics at axial if the alignment was not done with laser, do it with laser and keep an eye on the axial gap of the coupling, I won't trust anyones using dials if I'm not there.

Good old 4*2 wood is very handy with a trigger level, rectangular window and averages

So the possibilities is Resonance and Misalignment (Parallel?). Do we also rule out unbalance since the H-V differencies is not 90 (+-30)? And even though the horizontal phase difference (H1H2) and the vertical phase difference (V1V2) is similar, we cannot rule out misalignment?

Do I understand your point correctly?

One more thing I want to add, when solo run the motor, all the overall amplitude is below 1.5 mm/s (highest is 1.23mm/s), so I think we could rule out unbalance of motor right?

Solo run in same base?

The solo was not in the same base

Here is an early post along the lines of your questions. Looks like it might be from 2010 (12 years ago)

It has a few more members responding. But appears to say, more or less what the current replies say.

In my opinion, in most cases, phase is not an absolute, "fix-all"  tool. Just another tool used with an open-mind when in the search for the real problem.

https://www.maintenance.org/to...about-phase-behavior

Thanks,

Ralph

BTW: The balance might be from the driven machine and not from the motor, if you have it coupled up, and based on the "misalignment" statements, it sounds as thought you do have it coupled up. Being a screw compressor, I would lean toward alignment or mounting base problems.

@Registered Member posted:

The solo was not in the same base

Probably the balance of the motor is good.

I just was curious if the same base and lower vibration was due to uncoupled or different base.

Anyway, I had experience with a screw compressor, improving alignment improved the axial vibration, I could not find a solution, I think the problem was in the screws itself, but the motor had lot higher vibration than the compressor side