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bsr201283

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Reply with quote  #1 
Dear Friends ........


This is regarding single vs tri-axial accelerometer reading on Motor. If I take vibration readings X, Y and Z  axis with single accelerometer and same readings with Tri-axial accelerometer , will it be same ???


John from PA

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Reply with quote  #2 
Maybe.

Consider a horizontal single axis accelerometer; it should be and likely will be mounted at 90° (reference 0° at TDC) so the axis would pass through the center line of the motor.  If mounted at the top as part of a tri-axial accelerometer, it could see rotational motion of the motor on its base.
OLi

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Reply with quote  #3 
Normally if you use the data for route collection and trend data and yes it is not the same. Here even 3-axis data are basically accepted when doing startup and warranty checking.
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GaryVibe

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Well.... it depends. How is the sensor mounted? screwed down, quick-lock, 2 leg magnet on a painted housing, flat magnet on an adhesive mounted target? 
At my facility we do not use triax sensors for route work. I have adhesive mounted targets on 95% of my equipment and  also take Emerson PeakVue data in my route. My experience with magnet mounted triax on route data is that I lose the high frequency peakvue data on the 2 off axis points. I sometimes do not even see any relative data above 500Hz on some of my pumps. 
The small amount of time (we think we save) with a triax is not worth the loss of some of the data that I monitor. Most of the equipment is process critical. If you are collecting general site support equipment, then maybe a triax would be sufficient. 

An example was a horizontal motor and direct coupled fan- process critical. We had been monitoring for a few years with a single axis accel with a 2 leg magnet. We changed to a triaxial accel with a 2 leg magnet placed on the outboard and inboard bearing point horizontal. We immediately observed dramatically elevated  motor vertical values that put is in an Alert condition. When evaluating the data we saw the 1x peak in the vertical was in alert and there was a lot of raised floor energy around 1x. When we recollected the data with the single axis accel- the data repeated with the trended data. 
We suspect that the 2 leg magnet mounted to a painted motor housing was "sliding" giving us the elevated data. Along with that the high frequency Peakvue values dropped as well. 

For the cost of the triax and related cable, I would recommend adhesive mounted targets (make sure that the paint is removed under the target) provides good repeatable points that can be taken by most techs and yields more clear data for analysis and alarming. 

Just my personal experience and opinion. 
Thanks,
Gary Kaiser
Exelon  Nuclear
OLi

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Reply with quote  #5 
I rarely or never use 2 rail magnets, we use wireless sensor. Top of the sensor that seems to be a consumable cost €90.- so there is always something.
We do 2 paper machines in the time that we used to do 1 and so far it kept the competition away and since we last year only collected 2 times it is nearly impossible,
3-4 times is possible but less is useless.

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MarkL

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Reply with quote  #6 
Olov
,
Are you using washers or targets with the Falcon(I presumed you are on about) sensor? I know they do a keyed quick fit target but I bet they ain't cheap.
I use 2 inch diameter washers which we adhesives on to machine after removing paint, which I take with a 2 rail magnet and get decent enough results, (hard to get customers to pay for dedicated targets from some of the sensor makers)
OLi

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Reply with quote  #7 
Yes it is the Falcon we still use.No we do as we always done, in this case the flat magnet that is OEM and direct on the bearings paint or no paint as is but scraping off the pulp and fluff :-).
I never got any customer to pay for targets, some sensors at difficult places as some pope designs but no more.
I have once sold a bag of targets with a vibrometer on customer request :-) I also advice the washers when someone want a solution.

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Shoveldr

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Reply with quote  #8 

We actually did some testing before switching to the Triax.  I had been doing dual channel collection with two sensors for years, so I didn't expect a big time savings.  We didn't see much difference in side to side comparisons, but as already mentioned, be aware that the secondary and tertiary sensors may have a lower frequency range.  

When I started doing data collection with the triax the time savings was very noticeable, at the time I was doing service work, so 6 - 8 hours of data collection was the norm, I definitely noticed the extra time when I was done with the days work.  The key thing is that the data is repeatable.

JasonTranter

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Reply with quote  #9 
In a past life, we used triax accelerometers. As noted, they should be fixed to a permanently mounted pad that is firmly attached to the machine (no paint, super-strong adhesive). In the axis in line with the pad you will achieve an excellent transmission path and thus the desired high-frequency response (better than with a two-pole magnet in our experience). In the other two axes, you will see late-stage bearing failures and "all" other fault conditions with the complete picture that three axes provides.

We gained a time saving, and the triaxial view of the data helped with the diagnosis.

Jason
MarkL

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Reply with quote  #10 
I think along the lines of what Jason said if we are getting velocity on all 3 axes for general machine condition and one axis for high-frequency bearing and gear defects surely is good enough?
MarkL

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Reply with quote  #11 
Sorry for this double post,  (edited with Better grammar)
Rusty, I presume this was you who left the 'Wrong wrong wrong' comment in response to the video?
;-) 
 The particular guy making the video I have heard on a few webinars for Fluke and I reckon he's a complete charlatan, just curious what he said exactly you were commenting on ;-)
RustyCas

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Reply with quote  #12 
(Nope, not me Mark)  I watched 30 secs of the Fluke video and this guy is an idiot. Motor stator is one of the worst places to mount a sensor.  Keep in mind that most vendors (especially those like Fluke who are new to vibration) want to make the process sound "very simple" as he said in the video.  Nothing about it is simple.  Everything done improperly will impact the usefulness of the data and program, and errors will stack up quickly.

I use the CSI triaxial sensor where it's appropriate, and where it makes sense.  But I don't see any way to use triax sensors exclusively.  There are just too many situations where it's too far from the bearing, with no good transmission path. Sometimes the "primary" sensor will be located OK, but the other sensors will not provide the data that's readily available at other positions using a single-axis sensor.

The triax has a place, but it's not every place.

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MarkL

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Reply with quote  #13 
No, Rusty, I think you misunderstood my question, 
I know it was not you talking on the Video, The guy speaking is an ex DLI guy working with Fluke now, and yes a complete moron in my eyes. 
I was asking was it you who left the comment below on the video!

( look at whom commented on the video.)

Wrong, wrong, wrong!
 

Curran919

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Reply with quote  #14 
Quote:
Originally Posted by RustyCas
Motor stator is one of the worst places to mount a sensor.


Um, what?

I like least when he is talking about vibration transmitting through the bearings. Forces are transmitted through the bearings. Vibration is steady state, so how does that transmit? He says that if you have a close coupled driven machine that you won't measure any 1x component if you measure on the "machine with no bearings". That's the biggest joke to me.
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