Subject: C-Spring Sensor - 5/6 Second Period Has anyone tried this one? A vertical with a 5 to 6 second period using two= hacksaw blades. Would like to hear opinions as to whether this is a worth-= while build. =20 http://www.fairpoint.net/~sparksite/CSpring%20Printer.html =20 Hi Richard, =20 This is an old design. Never use oil damping. It is non linear both wit= h period and with amplitude. It is hideously temperature sensitive and it i= s not easy to adjust.. =20 There is a design for a magnetic damper for a vertical seismometer at w= ww.jclahr.com/science/psn/chapman/as1%20damping/index.html Mount the 1/16" = thick copper damping blade on the arm and put the quad damping magnet block= on the base. You can use soft Aluminum sheet for the blade - if you can bu= y it - NOT hard or alloy sheet - but copper is better, since it is not sign= ificantly diamagnetic. =20 Buy fully hardened hacksaw blades.The ordinary ones have a hardened edg= e, but with a softer blade. Grind off both the teeth and the wavy bends on = the base, otherwise you get cracks developing quite rapidly when the blade = is stressed. DON'T mount a magnet on a seismometer arm. It picks up noise from the = Earth's magnetic field, current surges in the house wiring, the movement o= f large vehicles, etc. Mount the pickup coil on the arm and use a shielded = quad NdFeB magnet block, or use an optical position detector. The response can easily be extended to over 20 seconds using Robert's c= ircuit for extending the period of geophones. You can get a x10 period exte= nsion before running into sensor / amplifier noise, but it does mean that y= ou have to build your own specialised amplifier - not too difficult to do u= sing stripboard? See www.jclahr.com/science/psn/epics/roberts/index.html=20 Do look through the articles on the jclahr website. Regards, Chris Chapman
= Subject: C-Spring Sensor - 5/6 Second Period
Has anyone tried this one? A vertical with a 5 to 6 second period usin= g two hacksaw blades. Would like to hear opinions as to whether this is a w= orth-while build.Hi Richard,This is an old design. Never use oil damping. It is= non linear both with period and with amplitude. It is hideously temperatur= e sensitive and it is not easy to adjust..There is a design for a magnetic damper for a verti= cal seismometer at www.jclahr.com/science/psn/chapman/as1%20damping/ind= ex.html Mount the 1/16" thick copper damping blade on the arm and put t= he quad damping magnet block on the base. You can use soft Aluminum sheet f= or the blade - if you can buy it - NOT hard or alloy sheet - but copper is = better, since it is not significantly diamagnetic.Buy fully hardened hacksaw blades.The ordinary ones= have a hardened edge, but with a softer blade. Grind off both the tee= th and the wavy bends on the base, otherwise you get cracks devel= oping quite rapidly when the blade is stressed.DON'T mount a magnet on a seismometer ar= m. It picks up noise from the Earth's magnetic field, current surges = in the house wiring, the movement of large vehicles, etc. Mount the pickup = coil on the arm and use a shielded quad NdFeB magnet block, or use an optic= al position detector.The response can easily be extended to over 20 seco= nds using Robert's circuit for extending the period of geophones. You can g= et a x10 period extension before running into sensor / amplifier noise, but= it does mean that you have to build your own specialised amplifier - not t= oo difficult to do using stripboard? See www.jclahr.com/science/psn/epics/= roberts/index.htmlDo look through the articles on the jclahr website.=Regards,Chris Chapman