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Danny Harvey

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Reply with quote  #1 
Has anyone been brave enough to buy one of these?

http://www.ebay.com/itm/VMC-606-Vibration-Calibrator-Handheld-Shaker-Check-ing-of-Accelerometer-Vibratio-/262351954675?epid=1341683213&hash=item3d156522f3:g:FHIAAOSwdU1W9PH5

The price is right but what do you get?
John from PA

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Reply with quote  #2 
I've never tried the Chinese knock off but have used the PCB variety for some sea trials.  See http://www.pcb.com/Products/model/394C06.  I think there is also a newer version called a 699A02 that can shake a sensor up to 250 gm weight.  Price is about $2000 unfortunately but you can rent either from the Modal Shop (see http://www.modalshop.com/rental/Calibration-Products?ID=392).



pcb.jpg

ivibr8

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Reply with quote  #3 
Danny

I have an old B&K shaker (model 4294) that would only turn on for a few seconds and then turn off (and even then it would not start every once in a while). New batteries did not fix the problem. I did an initial contact for repair and there was no guarantee it could be fixed, so it still sits in my drawer.

With some trepidation I bought the referenced shaker and have been very pleased so far. Firstly, the body of the shaker is HEAVY and well constructed. Access to the 9 volt battery is from the bottom which has a threaded bottom cap. It comes in a nice aluminum case along with a battery charger (which I really don't use - I just keep the 9 volt out until needed).

The circuit board is attached to the top shaker head....there is not much to it (as I suspect most shaker's circuit boards are). The board has a foam pad holding it against the inside diameter.

It has worked just fine since I bought it over a year and half ago.
I you like, I can send pictures and other information.

Regards
Jim Powers

p.s.  Does anyone want to offer a small token $$ for the B&K shaker?


Shoveldr

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Reply with quote  #4 

I have a CSI branded IMI shaker that is probably over 20 years old and still working fine.

I think it would really depend on what you are using if for, we normally just use the small shaker to validate sensors, specifically permanently installed ones.  As long as it is giving consistent values it should be fine.

It will also work in a pinch when you need to validate some displacement probe readings to test out a system and the equipment you really need is in another office.

2016-09-01 08.38.51.jpg 


Danny Harvey

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Reply with quote  #5 
John,

I wasn't aware that you could rent them.

There are a few differences. The output is 10 m/s/s instead of 1 g but I could get used to that.

The IMI will shake a 250 gram accel and the cheap one will only do 150 but the heaviest accel I normally use is 145 g.  I'm not sure about the 500 mv/g accels but I don't use them for much of anything anyway.  Our 50 and 10 mv/g accels are tiny.

I'm going to compare the other specs more closely but for a $1500 savings, it looks worth the risk.

Thanks
ivibr8

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Reply with quote  #6 
The Modal Shop (good people to deal with) quoted me $171.00 to rent the shaker for a week.  This seemed a bit high to me but it may be an affordable alternative to those who use the shaker to validate their sensors and equipment on a yearly or bi-annual basis.

For me, I needed to have one always available for confidence in my setups; hence, the reason I decided to buy the VMC-606 shown below

JP 20171011_102428.jpg 

Danny Harvey

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Reply with quote  #7 
Jim,

Thanks for the information. I'm glad to hear of at least one person with direct, positive experience.

I don't see anywhere that is states that the output is traceable to some standard.  Are you aware of a traceable source?

Shoveldoc,

I suspect that the IMI is a much better made unit that in real test lab situations would show much better durability, but my needs are only occasional. Like, Jim though, when the need arises it is immediate and we would not want to have to wait for a rental unit.

Thanks to all.  I'll let you know what happens.


John from PA

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Reply with quote  #8 
Quote:
Originally Posted by Danny Harvey
I don't see anywhere that is states that the output is traceable to some standard.  Are you aware of a traceable source?


The datasheet for the PCB 699A02 states "Meets NIST traceability requirements", whatever that means.
ivibr8

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Reply with quote  #9 
Quote: I don't see anywhere that is states that the output is traceable to some standard.  Are you aware of a traceable source?

Danny- There was no documentation of calibration. I was lucky in that a local PCB rep had a NIST shaker (the very same model John shows) that he let me borrow for a few days so that I could sit at my bench and go thru all of my transducers. A few weeks later when I got my VMC-606, I was able to re-perform the tests and feel comfortable the new shaker "shook as expected".[smile]

Interestingly - I purchased this same shaker for $382.00    You might want to Google to see if you can get it for that amount; assuming the non-traceable calibration is not an issue.   My paperwork indicates an email contact @ lucia@tereninstruments.com

JP


Danny Harvey

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Reply with quote  #10 
Jim,

That was my plan too.  I've got one accel that was last measured at 100.1 mv/g. I'll send it back to CTC for calibration and then put it on the shelf as a standard.

At least this way I'll have a more constant signal than my bench grinder.

I made an offer on one.  We'll see what I get it for.
John from PA

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Reply with quote  #11 
Keeping the goal of "calibration" in mind, one has to use some care with these portable devices.  The PCB 699A02 for instance only outputs mechanical motion at a single frequency, that being 159.2 Hz and at a single amplitude equivalent to 1 g rms (switchable to peak).  These singular values can be is can be limiting.  Generally speaking, the goal again being "calibration", you want to calibrate at three frequencies and three amplitudes.  You might want to check an accelerometer at 100 Hz, 1000 Hz and 10000 Hz.  If the full scale output of the device was 50 g's, then you might also do each of those frequencies at 1 g, 10 g's and 50 g's. 
Danny Harvey

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Reply with quote  #12 
John,

Correct. It's not for calibration it's for verification of function. If we see a large-scale variation in amplitudes, especially in our portable stuff, we want to be able to verify that it is not our instrumentation.  It just happened at one location.  We are no longer concerned about our stuff, but they are concerned about the crew that did the recent PM's etc on those gearboxes.

The cheap one puts out the same frequency by 10 m/s/s instead of 9.81. I don't really care that it's not 1 g but it will take some getting used to.  It's not switchable from RMS as far as I can tell (thanks for mentioning it). I normally use peak velocity but for verification purposes I don't think it really matters. Or does it?

Thanks again
OLi

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Reply with quote  #13 
I know 100Hz is used a lot in 60Hz countries but it is not always that good in 50Hz places as it is 2xLF and sometimes some noise happen to be there so I like the 159.2Hz as it lock Amp, Vel and Acc at the same time.
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Danny Harvey

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Reply with quote  #14 
I guess you could call 159.2 hz the center of equilibrium of the vibration analysis universe.
John from PA

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Reply with quote  #15 
Quote:
Originally Posted by Danny Harvey
I guess you could call 159.2 hz the center of equilibrium of the vibration analysis universe.


100 Hz or 159.2 Hz is quite common, the 100 Hz being used in the States and 159.2 Hz the rest of the world.  Although not an issue with a handheld battery powered device, Europe wanted to avoid the 100 Hz standard to avoid any issue with 50 Hz line frequency.  

With the frequency of 159.2 Hz, the angular frequency of 2pwhere f is frequency in Hz, is 1000 rad/sec.  This means the conversion from displacement > velocity or velocity > acceleration is accomplished by multiplying each successive step by 1000.

I'll let you do the math.  [kiss] 

159.jpg 

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