In a message dated 16/11/02, meredithlamb@............. writes:

> Sean's reluctance sensor sounds like it could be used in a "S-G" also, 
> although one might have a devil of a time especially when any kind of small 
> height S-G feedback system, might influence the sensor. Perhaps a fixed 
> eddy current damping system might be workable, if far enough away from the 
> 

Hi Meredith,

       Sean's system should be fine for a pendulum sensor, if a bit 
elaborate. I would not expect there to be any problem over the physical size 
of the sensor. The miniature transformers are 15 mm (~5/8") across the 
windings and 19 mm (~3/4") across the jaws of the E. The usual method of 
suspending the iron armature on a brass plate should provide quite adequate 
magnetic isolation.
       SG seismometers normally use active damping with a coil and a bar 
magnet.  This can, with advantage, be coupled directly to the seismic mass. 
The 'true' SG systems (as opposed to damped pendulums) get much of their 
sensitivity from damping the otherwise underdamped pendulum.

       On the side issue of magnetic damping, the Wing shaped two face pole 
magnets sold by www.wondermagnet.com are very effective indeed at providing 
magnetic damping and size for size, are much more effective than single pole 
magnets. The smaller damping plate is placed over the joint between the two 
wings, where the field reverses.

> >> The LX1358 Kit price is E 51.65 + Carriage. At today's exchange rate, this 
>> is just US $51.23. There will be a charge on your Credit Card for the 
>> currency conversion and the exchange rate will be lower than the 
>> International Banking Rate quoted. Air Mail packets are reasonably priced 
>> and may take 10 days to arrive. Be warned that International Carriers may 
>> have a minimum charge of near $50 for any packet! They seem to be only 
>> 
> Am missing something here....whats the difference between a "air mail 
> 

       Air Mail goes through the normal Mail system of most countries, but 
there are strict limits on the size and weight for letters, packets and 
parcels and you have to insure seperately over certain values. By 
International Carriers, I am referring to Fedex, Amtrak, DHL, TNT etc. which 
handle heavier, industrial and urgent goods. 
       When the UK part of Measurement Specialities, Schaevitz's 
distributors, folded a while back, Schaevitz offered to supply direct from 
the USA, but mentioned 'carriage charges'. When I enquired, these turned out 
to be over $40 on any item, no matter how small. Schaevitz seemed incapable 
or unwilling to provide near normal distributor service over some months and 
seemed to have the bizarre idea that their customers should happily foot the 
excess bill, as well as suffering a delivery delay and increased currency and 
import charges. You don't either keep or win customers that way, particularly 
when there is strong local competiton.  
   
       Nuova Elettronica are a large Italian organisation producing a very 
wide range of well designed Kits and probably have more product lines than 
Heathkit ever had. They assume that the builder can recognise components and 
can read. They provide adequate constructional documentation, but they do not 
provide 'idiot's construction guides'. 
       The sensor coils used on the LX1358 are obviously new and are similar 
to low wattage 1:1 mains isolation transformer windings. There are two coils 
mounted side by side in a sealed nylon case, which is the usual EEC 
construction for 'double insulated' transformers. The coils look to be well 
wound, but because of the geometry of the system, the output linearity of the 
sensor does not depend on the 'precision' of the winding, like in an LVDT. On 
the cutaway construction photo in the Schaevitz introduction, 
http://www.msiusa.com/schaevitz/pdf/lvdt/LVDT_Intro.pdf  you may notice that 
the fatter sensor windings on their LVDTs are also split up into a series of 
short coil sections, on much the same principle. There is a nice java applet 
demonstrating a LVDT operating at 
http://www.rdpe.com/displacement/lvdt/lvdt-principles.htm 

       Regards,

       Chris Chapman
In a message dated 16/11/02, meredithlamb@............. writes:



Sean's reluctance sensor sounds like it could be used in a "S-G" also, although one might have a devil of a time especially when any kind of small height S-G feedback system, might influence the sensor. Perhaps a fixed eddy current damping system might be workable, if far enough away from the sensor itself. 



Hi Meredith,



       Sean's system should be fine for a pendulum sensor, if a bit elaborate. I would not expect there to be any problem over the physical size of the sensor. The miniature transformers are 15 mm (~5/8") across the windings and 19 mm (~3/4") across the jaws of the E. The usual method of suspending the iron armature on a brass plate should provide quite adequate magnetic isolation.

       SG seismometers normally use active damping with a coil and a bar magnet.  This can, with advantage, be coupled directly to the seismic mass. The 'true' SG systems (as opposed to damped pendulums) get much of their sensitivity from damping the otherwise underdamped pendulum.



       On the side issue of magnetic damping, the Wing shaped two face pole magnets sold by www.wondermagnet.com are very effective indeed at providing magnetic damping and size for size, are much more effective than single pole magnets. The smaller damping plate is placed over the joint between the two wings, where the field reverses.



The LX1358 Kit price is E 51.65 + Carriage. At today's exchange rate, this is just US $51.23. There will be a charge on your Credit Card for the currency conversion and the exchange rate will be lower than the International Banking Rate quoted. Air Mail packets are reasonably priced and may take 10 days to arrive. Be warned that International Carriers may have a minimum charge of near $50 for any packet! They seem to be only relatively reasonably priced within the USA.

Am missing something here....whats the difference between a "air mail packet", and a, "International Carriers"? 



       Air Mail goes through the normal Mail system of most countries, but there are strict limits on the size and weight for letters, packets and parcels and you have to insure seperately over certain values. By International Carriers, I am referring to Fedex, Amtrak, DHL, TNT etc. which handle heavier, industrial and urgent goods. 

       When the UK part of Measurement Specialities, Schaevitz's distributors, folded a while back, Schaevitz offered to supply direct from the USA, but mentioned 'carriage charges'. When I enquired, these turned out to be over $40 on any item, no matter how small. Schaevitz seemed incapable or unwilling to provide near normal distributor service over some months and seemed to have the bizarre idea that their customers should happily foot the excess bill, as well as suffering a delivery delay and increased currency and import charges. You don't either keep or win customers that way, particularly when there is strong local competiton.  

   

       Nuova Elettronica are a large Italian organisation producing a very wide range of well designed Kits and probably have more product lines than Heathkit ever had. They assume that the builder can recognise components and can read. They provide adequate constructional documentation, but they do not provide 'idiot's construction guides'. 

       The sensor coils used on the LX1358 are obviously new and are similar to low wattage 1:1 mains isolation transformer windings. There are two coils mounted side by side in a sealed nylon case, which is the usual EEC construction for 'double insulated' transformers. The coils look to be well wound, but because of the geometry of the system, the output linearity of the sensor does not depend on the 'precision' of the winding, like in an LVDT. On the cutaway construction photo in the Schaevitz introduction, http://www.msiusa.com/schaevitz/pdf/lvdt/LVDT_Intro.pdf  you may notice that the fatter sensor windings on their LVDTs are also split up into a series of short coil sections, on much the same principle. There is a nice java applet demonstrating a LVDT operating at http://www.rdpe.com/displacement/lvdt/lvdt-principles.htm 



       Regards,



       Chris Chapman