Hi, I would reiterate the other replies in stating the importance of a well insulated box. All long period sensors are extremely sensitive to air currents and tilting. As a final touch, add a heater, say 10 watts, to the inside of the top of the box. This will stagnate the air in the box and eliminate convection currents. This can be as simple as a resistor powered by a wall-wart. A small lamp running at half its rated voltage (for nearly infinite life) will also work. My rig works exactly like Conklin's--my basement floor bends when there is foot traffic in the bedroom above. This tilts the sensor. Since these signals don't look anything like a 'quake, just ignore them. I think that a good way to set the gain is to adjust it until you get +/- 10-20 counts on the quietest days. Larry's amp has a low-pass filter which has a cutoff frequency which is much too high for good signal/noise performance with a Lehman. I suggest adding a 6 or 8 pole filter with a cutoff of about 0.1Hz. This will reduce the noise due to microseisms which peak at about 0.16 Hz. Filter design is well described in Lancaster's book, see www.tinaja.com Bob Barns > Bryan & Regina Goss wrote: > > Ok I got my seismograph built and I used Larry's A/D card and > filter/amp, My question is how do I know if I have to much gain? > It looked as if I did so I put 15k res at r29 this reduced noise but I > don't know if it was to much. I can walk across my shop floor > 30x 40x concrete slab and going to seismograph I see the trace go up > about an inch then slowly go back to center when I walk away just the > opposite, The trace seems to drift up and down a little guess this is > normal?????? > I really need help > > this is before the damper and cover > http://www.tsixroads.com/~spardue/seismograph/seismograph.htm > __________________________________________________________ Public Seismic Network Mailing List (PSN-L)
Larry Cochrane <cochrane@..............>