Hello All, Much easier to use the linear CCD array-all the Rube Goldberg fixes are not needed! DL twleiper@........ wrote: > I have no calculations. About ten years ago I erected a very > efficient solar collector to pre-heat my well water. Among > other things, it tracked the Sun in order to maximize the > yield. I built a photo-cell / optical system to do so with > much experimentation, but ran into the challenge of the > diffusion caused by overcast days, non-linear cell response > and so forth. So then I added a "jog" cycle that would just > reset the collector to due east every morning and then drive > it westward for a few seconds every so-many minutes, and > that would keep the dual photo-cell detector close to target. > This worked fairly well until a thunderstorm took out the > photo-cell amplifier that was located up on the collector, > at which point I realized that the jog-cycle method alone > was equally good and far less trouble. That's the last > time I used photo-cells to detect anything. > > The method I speculated earlier today was off the top of > my head. But it does make sense to see if the numbers > agree with my instinct. A modest attempt follows: > > It seems reasonable that the "angular amplifier" I > described using two opposed mirrors that move slightly > off parallel should work and, if you were spinning the slit > at around 30 revs per second any noise and instability would > be effectively averaged out for any but the shortest period > instruments. And, depending upon how many times you > bounce the path between the mirrors it seems reasonable > that you should get a amplification of angular displacement > of the boom by at least an order of magnitude, meaning that > the .01 arc/sec requirement becomes .1 arc/sec. This could > also be expressed as about 1/200,000 of a revolution and > would occur in about 160 nanoseconds in the 30 RPS example. > Detecting phase shifts in 160 ns chunks is a piece of cake, > in fact you could probably go down another order of magnitude. > > All I know is that I can track a radial on a VOR to the degree, and > that thing also uses an antenna that's spinning at 1800 RPM ... > AND you have all sorts of variables like RF propagation. It seems > that with light, good design and controlled conditions (all of which > you can provide) one should be able to do at least a thousand > times better. > > On the other hand, I have a cat that always seems to sleeping > on the sunroom sofa whenever a major quake occurs around > the world. Maybe I can put that to good use... > > Tom > > On Tue, 29 May 2001 17:04:18 EDT ChrisAtUpw@....... writes: > > In a message dated 29/05/01, twleiper@........ writes: > > > > > All this talk about precision matching and ambient light, > > > spectral response, etc., seems crazy. If you really must use > > > a photographic system (without film on a drum) why take > > > > > > > Dear Tom, > > > > Was anyone talking about photographic techniques? We were > > considering > > the precautions / choices necessary to get optical detection methods > > to work > > OK for very small movements. How would your method cope with > > movements from 1 > > sec of arc down to maybe 1/100 sec of arc? I would be very > > interested to read > > your calculations. > > > > Regards, > > > > Chris Chapman > > > > > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-REQUEST@.............. with > the body of the message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information. __________________________________________________________ Public Seismic Network Mailing List (PSN-L)
Larry Cochrane <cochrane@..............>