Hi guys,

What happen to my waveform? I took a peakvue reading from a pump bearing. But the waveform is looking strange.. The pump is operating with severe cavitations.

Waveform.doc (28 Kb, 110 downloads) Peakvue signature

I'm not sure but I'm guessing it might have something to do with accelerometer overload?

electricpete,
if Jenish can show only one revolution number instead 50, to confirm if maybe you are right. In fact from 0 to 40 gs TWF is excesively large and look to be rare, without positive and negative part.

Jenish,

I saw and almost posted the exact same twf last week. I've never seen it before and now twice in a week.

I havn't been able to confirm it yet, but I think I had a bad accelerometer. I should know shortly and I'll let you know what I find.

Danny,
I won the race by posting it before u..Ha ha ha..

Bad accelerometer!! May be... But when i was collecting the data from this pump, i took 3 readings with out moving the accelerometer. The 1st one was a velocity reading and the last one an acceleration reading. Both the signature shows quite normal spectrum and waveform. Also i took lot of readings with the same accelerometer after that!!

About signal overloading, the accelerometer will show the message if it happens and it will not store any data. Thatz what i experienced.. Again i want to ask something about this!! Can we do anything to avoid the signal overload? I had some floating bearings here which sometime shows signal overload. If i change the maximum limit, will it be ok?

Jenish,

The HP-filter is 1000 Hz, and the F-max for waveform is 50-rev = 1490 Hz. Perhaps this PeakView setup is incorrect (F-max greater than HP-filter) and internal processing is displaying incorrect results. Check with Dr Robinson (father of PeakView) about this.

Personally, I would not be happy about winning the race to print bad data!!

Walt

The settings in this case appear to be:

1600 lines, 1000 Hz (60000cpm) Fmax, 1000Hz HP filter.

So the waveform length would be 1.6 seconds, or 47.7 revs (near enough to 50)at 1788 RPM.

I don't think there is an issue with the set-up. More likely, it's just a software glitch that is displaying a nonsensical waveform.

Jenish, how many averages do you take?

If that was the waveform that had been processed by the FFT, wouldn't the spectrum look a liitle weird?

Ian

Hi guys,

Thanks for the comments..

I checked the parameter setup with Robinson. For 1800RPM he recommend a 2000HZ HP Filter with 1600 lines. But it is not recommended to use a 2-pole magnet for HP Filter above 2000Hz..
I am thinking the same like what IanS mentioned. There may not be an issue with the setup. Please feel free to comment if i'm wrong!!

I am using only 1 average for all my Peakvue settings. But i found 1 intersting thing. The "Highest Valid Signal Level" in my point setup is set as 50. I think the problem may be because of that. ryt?

Jenish,

If the "Highest Valid Signal Level" is exceeded, it will just give a Bad Reading message, and unless you have set the program to store the data flagged as "Bad Reading", it will be ignored.

If that waveform was FFT-ed, your spectrum would just be one big ski-slope, wouldn't it?

In an older version of the software, we used to get some really weird looking waveforms. These turned out to just be glitches in the software. When we installed the next release, the problem went away.

Ian

Hi IanS,
I set the program to store the "Bad reading" also!! Anyway i don't know whether it is from that or it is coz of some software gliches.

We will wait for danny to post his findings!

Jenish,
If the highest valid signal level is exceeded, I don't think it has any effect on the data. It only generates a bad reading message. It isn't the cause of the strange looking waveform.

Ian

IanS,
You are ryt!!!

I checked some of my old data and found one having the highest valid signal exceeded. But still i got a normal spectrum and waveform for that.

Normally the spectrum will be generated from the last reading even if you have more than one averages. But here i have only 1 average. So the spectrum should be created from that waveform.

Anyway thanks for your comments..

Have a nice day!