Hi Chris, and all,

ChrisAtUpw@....... wrote:

> 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.

Your statement of "a bit elaborate" for the Sean circuit is quite true
to me (ha), by comparison, a general LVDT circuit indeed looks
alot simplier.  I see they've been around for over a hundred years
(in esscense).  Perhaps in general, they could be the better more
sensitive and cheaper future for amateur seismology.  Most U.S.,
companies truely want a "mint" for their LVDT coil items, which
seems to be the main current problem overall in that commercial
part approach.

> 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.

Very true on the "wing" or 4 pole magnets.  I'am rather
surprised more amateurs are not using this cheaper and more
effective damping (and even coil sensor pickup) route.  Perhaps
(?), to be fair in that regard, its usually the larger the neodymium
magnet/s, the better the results.  Most neodymium magnets are
rather small, whereas alot of the Alnico magnets are larger poled
but with alot less "potential" maximum gauss interaction.  On the
other hand, two, "wing" magnets facing (attracting to each
other), can enhance results moreso.

>> > 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.
>>
Most interesting on the cost.  I'd guess the actual cost could be
~ double with the shipping charges added just for the LVDT and
circuit alone.  Getting the mechanical S-G part added would
likely make it prohibitively alot more expensive.... ~ 2-4 times.

>> 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.

Thanks for the info.  Have shipped out to other countries before,
and sometimes the actual cost can even far exceed the value of the
item actually shipped.  Its always quite expensive it seems.

> 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.

True; alot of U.S. companies seem to go the same "self defeating"
route.

> 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'.

Too bad they don't promote more of their items information via
the internet; but I think it might be related to a less hectic "way of
life" approach.

> 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

Thanks for the info!  Take care, Meredith Lamb




Hi Chris, and all,
ChrisAtUpw@....... wrote:
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.
Your statement of "a bit elaborate" for the Sean circuit is quite true

to me (ha), by comparison, a general LVDT circuit indeed looks

alot simplier.  I see they've been around for over a hundred years

(in esscense).  Perhaps in general, they could be the better more

sensitive and cheaper future for amateur seismology.  Most U.S.,

companies truely want a "mint" for their LVDT coil items, which

seems to be the main current problem overall in that commercial

part approach.
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.
Very true on the "wing" or 4 pole magnets.  I'am rather

surprised more amateurs are not using this cheaper and more

effective damping (and even coil sensor pickup) route.  Perhaps

(?), to be fair in that regard, its usually the larger the neodymium

magnet/s, the better the results.  Most neodymium magnets are

rather small, whereas alot of the Alnico magnets are larger poled

but with alot less "potential" maximum gauss interaction.  On
the

other hand, two, "wing" magnets facing (attracting to each

other), can enhance results moreso.


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.


Most interesting on the cost.  I'd guess the actual cost could be

~ double with the shipping charges added just for the LVDT and

circuit alone.  Getting the mechanical S-G part added would

likely make it prohibitively alot more expensive.... ~ 2-4 times.

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.
Thanks for the info.  Have shipped out to other countries before,

and sometimes the actual cost can even far exceed the value of the

item actually shipped.  Its always quite expensive it seems.
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.
True; alot of U.S. companies seem to go the same "self defeating"

route.
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'.
Too bad they don't promote more of their items information via

the internet; but I think it might be related to a less hectic "way
of

life" approach.
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
Thanks for the info!  Take care, Meredith Lamb