Hi Well a few years ago I was very interested in those piezoelectric disks. Radio Shack has them for one. I thought they would make a good sensor without the use of magnets or excitation electronics. To give you the end of the story first, I got confused as to what I was measuring and gave up. The sensor: I'll try to describe the sensor with the dimensions from memory. There is a plastics shop near me that sells acrylic plate and tubing. The sensor exterior was a ~2.5" diameter tube about 5" long. At the ends I made caps of the next size larger tube that telescoped over the main tube about 0.5". To form the end I glued a ~3" square plate at the end of the cap tube. I now had a "sealed" tube. For the sensor(s) I bought two radio shack piezo disks. Each disk was the same diameter as the main tube. I put the disk at the end of the main tube them put the cap over that. I did leave a small spacer inside the cap so the disk wouldn't touch the cap plate. Ok, for the mass I used a ~1" diameter steel round stock. The idea was to position the round stock inside the main tube and have it attached to the disks at both ends. When the mass moved relative to the tube there would be an output from both disks. I wired them so the flex output would sum rather than cancel. I won't go to much into the disk mechanical attachment to the mass at this time. It did give an output when put it on my work bench and applied a tilt to the bench top. The problem: As I understand it, for short period sensors(accelerometers) , the displacement output is a directly proportional to the ground acceleration for periods below the natural period of the sensor & at ~ 0.7 damping. Peizoelectric material seems to output velocity. Therefore was the sensor I described above outputing the differential of acceleration since I was measuring velocity rather than displacement? I'm not sure. I also wasn't sure about how to apply damping to the sensor short of maybe filling the interior with oil or some such material. I would like any feedback as to what I was measuring. Could piezoelectric mat'l be used for hinge material and their output measured? I still think there maybe some possibilities for them in strong motino sensors. Regards Barry ChrisAtUpw@....... wrote: > In a message dated 26/01/00 20:52:58 GMT Standard Time, sean@........... > writes: > --snip--- > Has there been any use of piezo electric accelerometers, either directly > or with the output integrated to give velocity? (I am not talking about > silicon chip devices.) What period would you recommend, please? I can extend > the response out to ~15 sec without problems. > > > Regards Chris _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L)
Larry Cochrane <cochrane@..............>