Miniature pressure transducer installation

[RaduP]

I'd like to measure TBL pressure fluctuations on the surface of a small tube (~.370" DIA), in water (I know it's different from aerodynamics measurements - air- but nevertheless...). I found a sensor that fits, but what's next? I have some specific questions, but any other comment on related work/expereince is welcomed:
1. should the sensor be flush, or at the bottom of a small cavity?
2. can I use silicone grease or similar to insulate the sensor from the flow, or to make it flush with the surface (as the sensor sensing surface is flat)?
3. Can silicone grease be removed/cleaned without damaging the sensor?
4. The smallest sansor I found was with Entran (.050" diameter). Any other suggestions?

 

[btrueblood]

1. flush is better. A cavity acts as a 1/4-wave tube, and can damp (and sometimes amplify) at certain frequencies, also eddy shedding from the "lip" of the cavity can skew your results.

2. silicone grease in contact (and air vs. water in contact for that matter) with the diaphragm can/will affect the transducer's frequency response. You will want to try and calibrate the dynamic response in the "as installed" configuration if possible, using the test fluid of interest. The response to a step pressure change is one method; also see the PCB and Entran websites.

3. Cleaning silicone grease can be a pain, but we have pretty good luck using either petroleum distillate solvent, and/or products containing orange-oil.

4. 0.05" is pretty tiny. There are some low-pressure fiber-optic based sensors out there, but not sure what their resolution (or co$t) is. You may want to spend some time looking throught the NASA and NACA literature (NACA tech notes are publicly available in .pdf form on the Langley website), and seeing how they "used to do it". Flush-mounted strain gage diaphragms, typically.