Vibrating Element Structures

[jmw]

Can anyone recommend a good reference on the design of vibrating element sensors?
Mostly Google comes up with MEMs sensors/energy harvesting devices (but not with the information I am looking for) and I am looking for something that relates to somewhat larger sensors that use piezo drives.

The problem is to know how to get the bit you want to vibrate to vibrate and everything else to not vibrate, or to vibrate at lower amplitude and in some well removed frequencies.

Some sort of guidance is needed on how to design the structure to achieve that.

Any ideas?

JMW

http://www.ViscoAnalyser.com

 

[drawoh]

jmw,

Getting the one part to vibrate and everything else to not vibrate is easy. Everything else must be a couple of orders of magnitude less flexible (higher natural frequency). A designer will good engineering skills should be able to pull this off fairly easily.

Getting the one part to vibrate exactly the way you want will be more challenging, and figuring out where the heck it is while it is vibrating, more challenging still.

Proximity sensors?

JHG

 

[jmw]

Thanks Drawoh,
I found a paper on mounting accelerometers which gave some useful advice such as the need to fill cavities with potting compound but nothing that otherwise helps me.

Er, no, not proximity sensors, Im afraid I'm not allowed to say what it is just yet.

JMW

http://www.ViscoAnalyser.com

 

[unclesyd]

We used this product on our high speed machinery to prevent catastrophic sympathetic vibration of the frames.

I just had a discussion about one of the machines that I worked on in the 90's. Interest was lost when I mentioned a purchase order or a temp job.

http://www.iotech.com/vibe.html

If the order of magnitude is fairly high there was a show on TV where they were using a small seismometer to record micro quakes

 

[jmw]

Thanks for the link Unclesyd,
by the way, how high is high temperature?
The limit we have begins with the piezos where it depends on the Curie temp but the manufacturers don't seem that enthusiastic about going too high and it looks as if we might comfortably settle at 160-200degC.
Of course, we are not mounting on a circuit board.

JMW

http://www.ViscoAnalyser.com

 

[unclesyd]

High temperature and high pressure have always been a moving target for me. When I started work our 10,000 psig, with hydrogen and ammonia, process was scary and 300C polymer kelp me on my toes. When I left we had 77,000 psig water and testing equipment pieces to 20,000+ psig.

Just made a call and found out the ones we used are limited to 125C. I don't know if this is manufacturers requirement or just by our procedures. I think manufacturers have gotten more conservative on temperature ratings of equipment.

I would checkout the NASA tech site as I know they have done a lot of work in the area of high temperature transducers.

 

[GregLocock]

I vaguely remember that the upper limit on piezo shear type accelerometers is set by the properties of the epoxy they use.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[jmw]

Can be.
In one design I found that they had a 200degC piezo with 100degC (or some such silly value) solder and the wrong wiring insulation.
Weakest link stuff.

JMW

http://www.ViscoAnalyser.com

 

[unclesyd]

GregLocock,
That is probably why we have a low temperature limit based on the current crop of transducers. As you probably remember some Epoxies weren't very good early on, that is the relatively inexpensive ones.