In a message dated 14/05/2009, geopresp@......... writes:

Anyone here know if any of the old 60's sensors, Long or short  period, 
existing at the World-Wide Standard Seismographic Network  (WWSSN) can be 
adapted to work today with new data acquisition  systems? They were Benioff 
sensors with variable reluctance for the  short-period instruments and Ewing 
Press sensors for the long period.
Regards
Rui 



Hi Rui,
 
    Several Sprengnethers, both V and H, have been  adapted successfully. 
If you add a capacitative position sensor, you  may use the original sensor 
coils + magnets for feedback to get an  excellent broadband response. New 
amplifiers and ADCs should not be a  problem.
    Randall Peters has modified some Sprengnethers. See  
_http://physics.mercer.edu/hpage/peters.html_ (http://physics.mercer.edu/hpage/peters.html) 
    I do not know enough about the larger Benioff  machines, but if the 
springs and suspensions are OK, I can see no reason in  principle why not. You 
might need to look carefully before buying one. They are  likely to have 
been out of use and not maintained for more than 25  years. Some of them used 
photographic recording using light reflected from  sensitive galvanometers to 
give gain with an 'optical lever'. These galvos had  delicate suspension 
systems, so you may need a replacement sensor. Incidentally,  you can get 
resolutions down to <15 nano metres using pairs of large  area silicon 
photocells, a simple moving shutter, a lens and a  tungsten filament bulb, but the 
operating range is restricted by the size of the  photocells and any drift in 
the instrument. You may be able to remove drift  problems with a long period 
integrator and force feedback, while retaining  the original response. 
    I remember some mini Lehmans being  offered on psn about 5 years ago. 
Seismic sensors occasionally  appear on Ebay, but I have not seen anything 
there that I would want to  own, due to very poor condition / parts missing / 
huge prices being demanded for  what appeared to be scrap. Older type 
seismometers tend to be both large and  very heavy = costly to transport. The USGS 
disposed of several of their early  borehole electronic triaxial KS-36000 
units some years back. Check with psn  archives? 
    For a Press-Ewing photo see 
_http://sismordia.blogspot.com/2008/08/sunday-seismometer-10.html_ (http://sismor
dia.blogspot.com/2008/08/sunday-seismometer-10.html) 
    
_http://www.blogcatalog.com/blogs/sismordia-seismology-at-concordia/posts/tag/sunday+seismometer/_ 
(http://www.blogcatalog.com/blogs/sismordia-seismology-at-concordia/posts/tag/sunday+seismometer/) 
    Some very early seismometers used mechanical levers  to amplify the 
ground motion and weighed up to several tons. Later seismometers  used a magnet 
+ coil to drive a sensitive galvanometer fitted with a mirror. A  beam of 
light was reflected from the mirror and focussed onto  photographic film / 
paper, so you had to chemically develop the image  before you could read it. 
You could probably replace the photographic film  with a pair of differential 
silicon photocells. The WWSSN network started  in ~1959, peaked in the 
1970s with about 115 stations world wide and was  replaced after 1983. They used 
paper recordings. 
    I suspect that the answer to your question very  much depends on what 
you are capable of designing / repairing / making /  adapting. Broken / 
missing low Tc springs could be a problem to replace. They  were made specially 
for the particular seismometers. Rewinding coils definitely  requires skill, 
care, time, good eyesight and preferably a coil winding  machine. 
    Where are you based? Are you considering any  particular instrument 
types? 
 
    Regards,
 
    Chris Chapman






In a message dated 14/05/2009, geopresp@......... writes:

  
Anyone here know if any of the old 60's sensors, Long or short 
  period, existing at the World-Wide Standard Seismographic=
 Network 
  (WWSSN) can be adapted to work today with new data acquisition=
 
  systems? They were Benioff sensors with variable reluctance for the 
  short-period instruments and Ewing Press sensors for the long period.
  
Regards
  
Rui 

Hi Rui,
 
    Several Sprengnethers, both V and H, hav=
e been 
adapted successfully. If you add a capacitative position sensor, you 
may use the original sensor coils + magnets for feedback to get an 
excellent broadband response. New amplifiers and ADCs should not=
 be a 
problem.
    Randall Peters has modified some Sprengnether=
s. See 
 http://physics.mercer=
..edu/hpage/peters.html
    I do not know enough about the larger Be=
nioff 
machines, but if the springs and suspensions are OK, I can see no reason=
 in 
principle why not. You might need to look carefully before buying one. The=
y are 
likely to have been out of use and not maintained for more than 25 
years. Some of them used photographic recording using light reflected=
 from 
sensitive galvanometers to give gain with an 'optical lever'. These galvos=
 had 
delicate suspension systems, so you may need a replacement sensor. Inciden=
tally, 
you can get resolutions down to <15 nano metres using pairs of lar=
ge 
area silicon photocells, a simple moving shutter, a lens and a=
 
tungsten filament bulb, but the operating range is restricted by the size=
 of the 
photocells and any drift in the instrument. You may be able to remove=
 drift 
problems with a long period integrator and force feedback, while reta=
ining 
the original response. 
    I remember some mini Lehmans being 
offered on psn about 5 years ago. Seismic sensors occasiona=
lly 
appear on Ebay, but I have not seen anything there that I would want=
 to 
own, due to very poor condition / parts missing / huge prices being demand=
ed for 
what appeared to be scrap. Older type seismometers tend to be both large=
 and 
very heavy =3D costly to transport. The USGS disposed of several of their=
 early 
borehole electronic triaxial KS-36000 units some years back. Check with ps=
n 
archives? 
    For a Press-Ewing photo see =
http://sismordia.blogspot.com/2008/08/sunday-seismometer-10.html
    http://www.blogcatalog.com/blogs/sismordia=
-seismology-at-concordia/posts/tag/sunday+seismometer/
    Some very early seismometers used mechanical=
 levers 
to amplify the ground motion and weighed up to several tons. Later seismom=
eters 
used a magnet + coil to drive a sensitive galvanometer fitted with a mirro=
r. A 
beam of light was reflected from the mirror and focussed onto 
photographic film / paper, so you had to chemically develop the image=
 
before you could read it. You could probably replace the photographic film=
 
with a pair of differential silicon photocells. The WWSSN network sta=
rted 
in ~1959, peaked in the 1970s with about 115 stations world wide and was=
 
replaced after 1983. They used paper recordings. 
    I suspect that the answer to your question ve=
ry 
much depends on what you are capable of designing / repairing / making /=
 
adapting. Broken / missing low Tc springs could be a problem to replace.=
 They 
were made specially for the particular seismometers. Rewinding coils defin=
itely 
requires skill, care, time, good eyesight and preferably a coil windi=
ng 
machine. 
    Where are you based? Are you considering any=
 
particular instrument types? 
 
    Regards,
 
    Chris Chapman