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Shoveldr

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Reply with quote  #1 

I have done some questionable data collection in my time, but I can honestly say I have never carried a stinger for normal data collection.

I recently got an RFQ where the customer stated that while their preferred sensor mounting is magnetic, there are some assets where a stinger is required due to access/safety, even though it reduces data quality at higher frequencies.  I was really surprised to see this.  These are primarily air handlers, and I know you can see imbalance and belt issues with a stinger and if I was testing it monthly I might be willing to sacrifice the high frequency, but these are to be tested on an annual basis.

We are essentially saying we do not use stingers and we will collect the data at the closest safe location on the assets or base.  What is your opinion of stingers in this day and age?

On I side note I was surprised that they put in writing that they want us to stick thing through machine guards, I'm not saying I haven't done it, just that I've never seen it in writing to do it.

 

Vibe-Rater

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Reply with quote  #2 
After more than 20 years I finally bought a stinger.  A CTC one. Over the years safety guarding has constantly increased. The 1 inch grid style or smaller. Not large enough to fit a normal accelerometer through.  I don't have conclusive evidence but still think a stinger has its place. Better to get onto that bearing housing than measure it from a distance away.  Bearing faults will transmit so the reduction of of high frequencies is not so important in my opinion.  Maybe not so good for Peaksvue etc.

Poking long extension poles through safety guarding may (questionable?) have made things safer but has increased data collection time which if you have fixed price surveys eats into profit margin. rgds
spciesla

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Reply with quote  #3 
I agree with Vibe-Rater that stingers have their place.  Are they ideal? No.  Do they have limitations?  Yes.  We make a lot of compromises when monitoring equipment with portable instrumentation.  Understanding those compromises and their effects on our measurements and analysis are crucial.

Taking a step-back, we should be thinking about this from a FMEA perspective.  Why do we measure vibration on these machines?  Because they have failure modes that can be detected by vibration monitoring and performing this monitoring is cost effective relative to the other options (PMs, run to failure, something else?).  So, can you detect these failure modes using a stinger?  I'm guessing yes, just that the failure (such as bearing degradation) may be more progressed when you detect it because of the decreased frequency response of the instrument.

Just my 2 cents.
Big Al

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Reply with quote  #4 
I've managed to reduce use of the stinger down to just 2 bearings at my plant. It's not the greatest way of monitoring I know, but I believe it's the best option that I've got on these two measurement points. I believe that potentially limited data is better than no data at all.

Wasn't there someone on the other forum who used a stinger on everything and claimed good results?
JohnJ

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Reply with quote  #5 
Stingers have received a bad name because they were introduce in mass by IRD many years ago as a 9 inch aluminum "probe."  Data beyond about 35,000 cpm wasn't much good. I us a 2-inch steel stinger from IMI for most data collection.  The 2-inch stinger has the same frequency response as the 1 1/2" two-rail magnet -- around 150,000 cpm.  I believe the stinger will produce data that is more consistent than the two-rail magnet unless the magnet is set on a very smooth, dirt-free surface, which is very hard to find in industry.  One speck of dirt under a rail and the frequency response changes.  We dimple the data collection point with a drill and mark a circle around it with a paint marker.  All you have to do is brush the dimple clean to get consistent data.  I use 4 and 8-inch steel stingers due to access problems in a very few locations.  That has to be better than taking magnet data somewhere on the base or frame, though. A stinger also provides faster access to the collection point if you bother to clean the target area. I once saw a guy collecting data with a magnet and he just walked up to the machine and placed the magnet at each location with cleaning the target area (this was a dirty plant).  I guarantee we get more consistent data that he does.  Three of us collect data and you cannot tell the difference in data from one person to the other. The data is consistent from month to month on stable machines. Of course, a cavitating pump will produce inconsistent data no matter what you use.

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John J
RGf

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Reply with quote  #6 
I carry a stinger when doing data collection so I can get to motor inboard bearings. I take route data from any good (?) spot on the motor inboard and if something peaks my interest I take a data point using the stinger on the bearing. Often it is a tight fit between the motor end bell and the coupling guard but I would rather get the data there if I suspect a bearing or grease issue. I'm not sure who expanded the guarding requirements but I would wager that the never tried to collect data on a rotating machine or tried to shoot a coupling with IR.
RustyCas

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Reply with quote  #7 
"Wasn't there someone on the other forum who used a stinger on everything and claimed good results?"

Probably me. John J, I'm right there with you. The key is how you hold them. I use a heavy duty mil spec connector, so that I can put pressure on it with the palm of my hand. And I've usually got my elbow braced on my hip or thigh. You can't just hold it in your hand, with light pressure, like they did when they produced the famous "chart" 30 yrs ago.

How do you know you don't get good, repeatable data using a stinger if you've never earnestly tried it?

Here's an example where a stinger is obviously best: many pumps have a bearing "cartridge" that is held in place in a housing by a "clamp" (essentially). No way to mount a magnet on the cartridge, and what might you miss using a magnet on the clamp? But on the cartridge there is a flat "shoulder" that I assume is used to 'bump' the cartridge into the correct position. It's perfect for using a stinger to get bearing data and not have to wonder about the data lost in the "gap" between the cartridge and clamp. Same situation with "split" bearings on overhung fans.

But if I have a good spot for a magnet, I use it. I carry a 2-rail and a flat magnet. I have pads on critical machines if there is no flat, clean surface. I do what makes sense.

I will wager that on 90% of the machines that folks "will only use a magnet" on that I will get as good or better data using a stinger, that is repeatedable, dependable, and reliable for making accurate assessments.

But, as I've always said, this works because I work alone, and collect my own data. If you have multiple data collectors (folks) this won't work as well. But how consistent are your people using the 2-rail magnet? Is the data "good" because they are so consistent, or because it just doesn't matter how consistent they are?

And a question: for standard run-of-the-mill equipment, what is the max frequency that you need to capture "accurate" data at? What are you looking for at that frequency?

Also, stingers don't typically miss high frequency data... it's usually "amplified." That can be useful in convincing a reluctant client to take action. If it's repeatable, isn't it good data, even if it's amplified?

Not convinced? Motion amplification... what's up with that? One of the benefits is that the amplified motion (even though we know it's "manipulated") has such a strong visual impact. Think that's not useful?

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Ron Brook

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Reply with quote  #8 
To all,
The IRD stinger was at the end of a seismic transducer, which already had the high, and low freq issues.
I have used a short stinger on an accel when 'any data is better than no data' and had good success.
The only place it doesn't work is if there is an argument over meeting an overall vibration specification.
JohnJ

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Reply with quote  #9 
Ron,
I think you and I have been doing thins stuff for so long that, when we started, the Dead Sea was only sick at the time.  IRD continued to send out the 9-inch aluminum probe when they started sending out instruments that use accelerometers, which I think was a big mistake.

Regards,
John J
Curran919

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Reply with quote  #10 
Quote:
Originally Posted by RustyCas
Also, stingers don't typically miss high frequency data... it's usually "amplified." That can be useful in convincing a reluctant client to take action. If it's repeatable, isn't it good data, even if it's amplified? Not convinced? Motion amplification... what's up with that? One of the benefits is that the amplified motion (even though we know it's "manipulated") has such a strong visual impact. Think that's not useful?


Ah man Rusty, I was right with ya til the end here. If you want to make the high frequency end of a spectrum look bad, why not just differentiate it again and represent it in units of jerk? That'll show the customer. Sure, you can do whatever you want with a motion amplification camera, but the intention of those is to expose the data, not to pull one over on the client. If you are knowingly letting a bunch of amplified noise inflate the overall values to over the limit, that's just making up data.
RustyCas

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Reply with quote  #11 
Quote:
why not just differentiate it again and represent it in units of jerk?


Because I don't have that option available.  Keep in mind that I only use a stinger where "it makes sense" and that is not on critical machines.  Also, I don't make recommendations based on "limits" but rather on machine condition which takes into account a number of things.  You are likely thinking in terms of shutting a machine down when it reaches 10 - 15 g's peak acceleration, whereas I am talking 40 - 80 g's "indicated" (using the stinger).  If you "know" the machines you are evaluating, you can be less conservative in making calls, that is, let them run longer without fear of failure.  Some of my customers are reluctant to replace/repair machines, so they need a little 'nudge' sometimes.

I do what I have to do to keep that machine from failing, which makes us ALL look bad.  I'll post some examples later.

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