Bryan, You are at the fun part. I have two Lehman's and I use the older PSN amp design. I set my gain to 2000 and then adjust it up or down as needed. The operation you describe sounds correct for the stage you are at. I have a 12-bit A/D and can induce a count of -/+ 40-50 by walking next to the device. The amount of gain is governed by two factors. The gain of the amplifiers and the sensitivity of the device. I was looking at your pictures, nice work, so let me suggest the following, it should be doable when setting initial device sensitivity. Your boom looks like it is about 36-inches. With a 36-inch boom and .25 degrees of forward tilt of the base plate, a level boom will have a natural period of 18.2 seconds. If I were setting up the device, I would first set the gain to around 2000 and then set the undampened period of the device to 10-seconds making sure that the boom returns to center whenever after it is excited. Next, I would slowly lengthen the period to 20-seconds undampened and then adjust the damping magnets to stop the boom from swinging in 3 1/2 cycles. This will bring the dampened period to about 17-18 seconds. At that point you are ready to record and see what you get. Increase / decrease the amp gain based on urban noise thresholds. For the first 30 days or so the boom may drift off center overnight. This is due to the nature of the metal frame and the floor under it settling. At that point you are ready to wait and see... Another point, I can't emphasize how important an airtight cover is. I use a full sheet of 1/2-inch plywood to make a box 2X2X4 and then put 2" insulation foam board inside it which thermally protects the device from sudden temperature changes and tape the seams in the plywood and floor. Look'en good- Regards, Steve Hammond PSN Aptos, California -----Original Message----- From: Bryan & Regina Goss [SMTP:bgoss@................... Sent: Thursday, November 30, 2000 9:24 PM To: psn-l@.............. Cc: Larry Cochrane Subject: HELP << File: ATT00001.html >> 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@..............>