Isolator or Hard Mount?
Isolator or Hard Mount?
(OP)
Hello all,
I am designing an electronics enclosure which will hold a few circuit card assemblies as well as some other components. The enclosure itself has a first mode of ~300 Hz in the vertical, and the circuit card assemblies have a first vertical mode of ~700 Hz. The enclosure weight it approx. 60 lbs.
The enlocusre is being mounted on a frame which will have the attached vertical PSD input, 5-500 Hz, 3.84 Grms. Colleagues feel I need to mount these enclosures on isolators, although looking at the spectrum I am having difficulty deciding where I would place the isolator mode. Isolator modes from 10-60 Hz seem to do more harm than good. I can see that a stiff isolator (~70 Hz) wouldn't amplify the frame modes at 10 and 40 Hz, but the vibration is already starting to become attenuated by the frame at this point. Placing the isolator mode below 10 Hz will be a challenge due to sway space limitations.
The question is: Is there a need for isolators here? My preliminary model shows are higher output Grms on the isolated enclosure as opposed the the hard mounted enclosure.
Thank you.
I am designing an electronics enclosure which will hold a few circuit card assemblies as well as some other components. The enclosure itself has a first mode of ~300 Hz in the vertical, and the circuit card assemblies have a first vertical mode of ~700 Hz. The enclosure weight it approx. 60 lbs.
The enlocusre is being mounted on a frame which will have the attached vertical PSD input, 5-500 Hz, 3.84 Grms. Colleagues feel I need to mount these enclosures on isolators, although looking at the spectrum I am having difficulty deciding where I would place the isolator mode. Isolator modes from 10-60 Hz seem to do more harm than good. I can see that a stiff isolator (~70 Hz) wouldn't amplify the frame modes at 10 and 40 Hz, but the vibration is already starting to become attenuated by the frame at this point. Placing the isolator mode below 10 Hz will be a challenge due to sway space limitations.
The question is: Is there a need for isolators here? My preliminary model shows are higher output Grms on the isolated enclosure as opposed the the hard mounted enclosure.
Thank you.





RE: Isolator or Hard Mount?
Cheers
Greg Locock
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RE: Isolator or Hard Mount?
TTFN

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RE: Isolator or Hard Mount?
RE: Isolator or Hard Mount?
For pumps and stuff in potentially seismic areas it seems like snubbers are simply added to the mounts that will work ok 99% of the time. http://ecx.images-amazon.com/images/I/51Tjv6cKWIL....
RE: Isolator or Hard Mount?
I've seen PCB's dance away at ~ 25 Hz in a random vib environment and crack early on.
For isolation the comments on sway space are important for the reasons cited. Some isolators have built in snubbing which interestingly adds dynamic response complexity by a stiffening spring effect at the higher amplitudes. Consideration should also be given to durability of the isolator as it must flex to provide the "low" stiffness. I've seen rubber isolators get beat pretty badly for low fn situations in random vib. If this is a road situation there's also the "pot hole" and "speed bump" events that can impact isolator durability.
I've attached a sprdsht of a quick look see for an isolated enclosure to see it's response to the PSD for different isolation frequencies.
Good Luck.
james pike
RE: Isolator or Hard Mount?
Have Fun!
James A. Pike
www.xl4sim.com
www.erieztechnologies.com