But doesn't a CCD have pixels? i would think this would create kind of a stepping data output. Though i have never actualy seen a CCD array so i may be compleatly wrong. By chance have you got a schematic i can study? ~Travis > >Hi Chris, > >You are almost there-forget the photocells and use a CCD >linear array >and a laser beam reflected off the vertical pendulum. The >CCD array >gives you a clean, robust output that is a direct analog of >the POSITION >of the seismic mass. Hence it is not frequency-response >limited. It is >truly an absolute position sensor, rather than the classic >velocity >sensor with all its' attendant problems. I am cobbling up a >system >using the guts from an old HP Laser-Jet printer. Another >similar >method is to monitor the relected laser beam with a simple >optical >interferometer and count the resulting fringe patterns. This >is done in the >USGS gravity observatory instrument here in Boulder. Now you >can >measure displacements down to to wavelength of whatever >color of >light your laser is!! > >Best wishes- >Dave Latsch > > > >ChrisAtUpw@....... wrote: > > > In a message dated 25/05/01, travis5765@........... > > writes: > > > > > >> Although I have not tried it, it seems like it should > >> work. You would have > >> to make sure NO excess light fell onto the sensors > >> though. > >> By the way, I missed the page in scanning that told that > >> the output needs > >> only minimal amplification though it varies with the > >> rated output of the > >> solar panels and the consistency of the light output. > >> My idea for a modification would be to use a laser > >> pointer as a light > >> source. make sure to have a well regulated power supply > >> for it. > > > > The larger area silicon photocells as opposed to > > 'solar cells' tend to > > be better matched as to sensitivity, change with > > temperature and reverse > > leakage. Solid state Lasers are very noisy indeed. LED's > > are also noisy and > > their output is quite temperature dependant. A tungsten > > bulb driven from a > > voltage stabilised source at about 3/4 it's rated voltage > > will give good > > performance. You also benefit from the Infra Red > > sensitivity of the Si cell. > > You can get good performance by butting two cells end to > > end and using a slit > > which exposes about half each cell. > > > > Regards, > > > > Chris Chapman _________________________________________________________________ Get your FREE download of MSN Explorer at http://explorer.msn.com __________________________________________________________ Public Seismic Network Mailing List (PSN-L)
Larry Cochrane <cochrane@..............>