In a message dated 17/02/00 05:57:02 GMT Standard Time, shammon1@............. writes: >> I keep coming up with more questions as I think more about the problem. For example, where is the end of the boom? In my case, the boom is 38 1/4-in long tip to tip. I use a 1/4-copper plate for damping and it hangs on a L-bracket at the at the end. At the 32-inch point, the upper wire intersects the boom. The coil and magnet are mounted at the 24 3/4-inch point. So in your equation, L=which point? The end of the boom or the intersection point where the guide wire is mounted? Regards, Steve Hammond PSN Aptos, California >> In a Lehman 'garden gate' system, the distance 'L' is measured from the HINGE LINE to the 'CENTRE OF GRAVITY' of the whole weight + boom system. If you have a heavy weight and a very light boom and the boom is mounted at right angles to the hinge line, it will be roughly the distance from the hinge line to the CENTER of the weight. With a more complicated system having a heavy boom, a magnet and a weight, you need to take the boom off and holding it horizontal, find the point where it just BALANCES over a horizontal knife edge. You can usually get a rough estimate by balancing it over your finger. L is then the horizontal distance from the balance point to the hinge line at the end of the beam. So long as the beam makes and angle of 90 +/- 8 Degrees with the hinge line, the error is < 1%. [Otherwise you have to calculate the length of the perpendicular from the actual hinge line to the centre or mass.] I hope that this makes it clear. Chris _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L)
Larry Cochrane <cochrane@..............>