Hi Jan From your recordings, your environmental noise looks like cultural noise from your local community. Notice how it winds up early in the morning when people get up and stays constant through to about bedtime. The intensity of this type of noise will depend on where you live: urban or rural, party zone or non-party zone (just kidding). Try everybody else's suggestions, but if you still have too much noise, you might consider turning down the amplification on the preamp. Another thought that just occurred to me ... do you have a temperature controlled housing over the seismograph? Slight air motions due to thermal gradients, etc. in the house will create noise. I think most people have put a housing over their seismograph and use some arrangement to heat the interior air near the top of the housing by a few degress. This creates stagnant layers of air that do not circulate, because the top is hotter than the bottom. If it were the reverse, you would get convective air motion that would be picked up by the seismograph. If you ask an appropriate question of the list, I am sure that you will get more advice than you could ever possibly use on various ways to build such a housing.It sounds like you have solved your 4 - 5 Hz oscillation, but in case it reappears or your current solution has to be revisited ... As Chris has pointed out, your oscillation is almost surely a mechanical vibration/motion in the seismograph itself. I am not a materials expert, but vibration seems to be strongly correlated to stiffness. Your post, base, and supporting I-beams look solid as rock. The boom also looks relatively stiff. I would be suspicious however of the two diagonal boom support rods. With their round and relatively thin cross-section, they are individually prone to vibration and you will get interesting beat frequencies from the combination of two of them vibrating. It takes very little vibration in these rods to affect the recording. Hope this was useful, Ron Westfall -----Original Message----- From: psn-l-request@.............. [mailto:psn-l-request@................. Behalf Of Jan D. Marshall Sent: Sunday, September 29, 2002 12:18 PM To: Sesmic List Server Subject: New Lehman on line (almost) After about 12 months of thinking, planning and working (and procrastinating) I finally have my seismograph up and working. I now need your expert input on what I did wrong or adjustment that I need to make to get things fine tuned (or maybe coarsely tuned). Please visit my web site www.cableone.net/jandmarshall and choose the Seismic Page to view my project. Problems I note right off 1 - I have a 4-5 hz oscillation in the pendulum. 2 - I seem to have a lot of environmental noise -- I can not correlate it with actions in the house 3 - Am I damped enough?? I am open to all comments and suggestions -- just remember this is my first attempt at building a seismograph! Jan Marshall jandmarshall@............ www.cableone.net/jandmarshall Nampa, ID Hi JanFrom your recordings, your environmental noise looks like cultural noise from your local community. Notice how it winds up early in the morning when people get up and stays constant through to about bedtime. The intensity of this type of noise will depend on where you live: urban or rural, party zone or non-party zone (just kidding). Try everybody else's suggestions, but if you still have too much noise, you might consider turning down the amplification on the preamp.Another thought that just occurred to me ... do you have a temperature controlled housing over the seismograph? Slight air motions due to thermal gradients, etc. in the house will create noise. I think most people have put a housing over their seismograph and use some arrangement to heat the interior air near the top of the housing by a few degress. This creates stagnant layers of air that do not circulate, because the top is hotter than the bottom. If it were the reverse, you would get convective air motion that would be picked up by the seismograph. If you ask an appropriate question of the list, I am sure that you will get more advice than you could ever possibly use on various ways to build such a housing. <smile>It sounds like you have solved your 4 - 5 Hz oscillation, but in case it reappears or your current solution has to be revisited ... As Chris has pointed out, your oscillation is almost surely a mechanical vibration/motion in the seismograph itself. I am not a materials expert, but vibration seems to be strongly correlated to stiffness. Your post, base, and supporting I-beams look solid as rock. The boom also looks relatively stiff. I would be suspicious however of the two diagonal boom support rods. With their round and relatively thin cross-section, they are individually prone to vibration and you will get interesting beat frequencies from the combination of two of them vibrating. It takes very little vibration in these rods to affect the recording.Hope this was useful,Ron Westfall-----Original Message-----
From: psn-l-request@.............. [mailto:psn-l-request@...............On Behalf Of Jan D. Marshall
Sent: Sunday, September 29, 2002 12:18 PM
To: Sesmic List Server
Subject: New Lehman on line (almost)After about 12 months of thinking, planning and working (and procrastinating) I finally have my seismograph up and working. I now need your expert input on what I did wrong or adjustment that I need to make to get things fine tuned (or maybe coarsely tuned).Please visit my web site www.cableone.net/jandmarshall and choose the Seismic Page to view my project.Problems I note right off1 - I have a 4-5 hz oscillation in the pendulum.2 - I seem to have a lot of environmental noise -- I can not correlate it with actions in the house3 - Am I damped enough??I am open to all comments and suggestions -- just remember this is my first attempt at building a seismograph!Jan Marshall
jandmarshall@............
www.cableone.net/jandmarshall
Nampa, ID