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In article ,
says...

On Wed, 11 May 2005 03:19:14 -0000, (gudmundur)
wrote:

~~ snippage ~~

As for the silicone RTV glue, you are right on the money
there. I have glued ultrasonic doppler transducers to PVC pipes for many
years, and RTV is at least 90% as conductive to sound energy as any of the
lavishly expensive glues sold specifically for transducer mounting.

I was given to understand that silicone wasn't that transparent to
50Hz transducers. Any truth to that?

Later,

I wish I could be helpful on the 50khz vs. silicone glue, but all
of our doppler 'fluid flow rate' transducers were higher in frequency,
at least 200khz and higher. With a higher frequency transducer, the
doppler shift is also higher for a given flow rate, and therefore, a
more accurate reading can be measured using the very same simple circuits.
In our case the silicone was both the mounting method, and the conductive
medium. When I first went to work for the company I saw this method being
used, and I insisted it was only half-assed at best, but the waveforms
on the scope, and the readings on the analog meters were rock solid!
To some degree, my career is based on "If I don't know it can't possibly
work, then it will probably work".