Vibration of Sensitive Equipment 1

[StructTaco]

I'm trying to analyze some sensitive equipment to be supported on the roof of an old building. There is nearby mechanical equipment that we will support on vibration isolators.

How do I know how much vibration will still be imparted into the building from the mechanical equipment?

How do I know if the sensitive equipment will still be under an accepted threshold of 65 VdB, based on 1 microinch per second?

I'm structural, not mechanical, so I'm familiar with vibration isolator design for equipment, but not limiting the vibration of a machine to some very small velocity...?

Thanks in advance.

 

[GregLocock]

I'd do an experimental modal analysis of the building, in particular measuring the response at the site of the equipment from a force applied to the ground at the machinery's base (all 3 directions if you are cautious).

You'll also need to know how much the machinery is shaking.

You then have the interesting task of designing the vibration isolators for the machinery to achieve your desired response at the roof.



Cheers

Greg Locock


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[IRstuff]

You should probably do a measurement, if possible; there are companies that specialize in that sort of thing.

Analysis is an approximation of the real thing. Given that you probably do not have the actual design documentation on the original construction of the buildings and modifications thereto, there may be large uncertainties in your model.

TTFN

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[izax1]

What is the frequencies generated by the mechanical equipment? Ideally, you would install very soft isolators, unless that will cause large static deflections. The mechanical equipment on isolators should have a natural frequency at least 0,4-0,5 times the frequencies generated by the equipment.

 

[Tmoose]

Has the sensitive equipment mfr provided specs regarding acceptable limits?

Is the "mechanical equipment" on the roof too?
Roofs are typically so flexible the entire system must be considered.

http://www.mason-industries.com/masonind/downloads/spec/complete/ashlec.pdf

 

[drawoh]

StructTaco,

I have never seen vibration specified as a velocity. I have seen displacement and acceleration. If you have the frequency, you can convert everything back and forth by integrating the vibration equation.

You need to be very inqusitive about everything. I have done a job very similar to yours, quite some time ago. I was to isolate an optical system from the building it was sitting in. This was prior to the internet, so I had difficulties getting useful information on the building vibrations. I quickly observed that a subcontractor had designed a telescope structure that would wobble if exposed to any sort of vibration. Then our laser came in, and we discovered it had a vacuum pump. The vibration isolation would have allowed the vacuum pump to shake our non-vibratable telescope.

Rarely have I seen a straightforward vibration problem.

JHG

 

[jeyaselvan]

My suggestion would be to work with inertial masses (prove your roof structure supports that!)to bring down your mounted resonance frequency of your sensitive equipment..or shall approach using dual isolation where degree of isolation is much larger. Alternatively you shall use this to enhance the isolation of your machinery so that the transmitted energy to your location of installation shall be minimized (provided your transfer function from machine to sensitive equipment is not dominated by responses at your excitation frequencies!)

Jeyaselvan