On Wed, 12 Jan 2000 22:22:23 +0000 n0cwr@......... writes: >Our Lehman is in a room off the garage. >Two cars in the garage great... >Fine with one car in the garage but, >if I attain too high of a period (16 sec plus) with both cars >out of the garage the boom rolls over to the side - flatline till >ones back! 12 - 16 second period = no problems. My daughter's Lehman is on a pier cast atop what is either an immovable huge bolder or exposed bedrock in the root / wine cellar. It is a very stable environment with natural temperature control and the seismo is made from thermally stable materials, such as a granite tool and die makers slab for a base. With a natural period of 50 seconds it only needs seasonal centering adjustment for what I theorize is increased weight of the frame house (the foundation rests on said bolder about 15 feet away) due to higher relative humidity in the summer, or the presence of leaves on a rather large beach tree about 30 feet away. My wife will not let us cut the tree down to see... With this level of sensitivity I can not only tell when the oil truck backs into the driveway (about 75 ft away), but I can also tell whether I am at the beginning or the end of his run based on the weight of the truck. When the truck is empty I have to know he is there to pick out the offset in the six second noise level, but full is a clear LP tilt event of about 8 times the background amplitude. He is a friend of mine and I have verified it. So is the insanity worth it? Not really. Only in the case of the most distant surface waves have we been able to see higher performance than with her original unit (http://www.seismicnet.com/leiper/seismograph.html) running end to end, and in no case did it detect anything that was not discernable on the "science fair unit". That first unit is no slouch and can be adjusted to about a 40 second period, but dimensional instability and perhaps magnetometry effects of the suspended magnet design limit the "seasonally adjusted" period to about 15 to 18 seconds. It can only see the oil truck when it is full. So here is the challenge question: Assuming identical detector,gain and filtration (they are) and only the difference in period, can you calculate the capacity of the oil truck? (ST, Give everybody else a day before posting the correct answer, please...) _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L)
Larry Cochrane <cochrane@..............>