Chris,

Thanks for your comments!

I only suggested silicon because of Randall's observations about =
imperfect materials (dislocations, etc.)  Silicon is good from that =
point of view.  It is not an ideal material for mechanical construction =
- diamond machining and chemical etching are not usual home shop =
techniques.  That said, I have seen silicon wafers etched thin enough =
that they could be rolled up like cigarette paper - perhaps silicon in =
that form could be used as a flexure.  Yes, metal construction is the =
norm, but it seems to be in the spirit of this list to consider =
alternative methods and materials.

The book by R. V. Jones - "Instruments and Experiences" is an organized =
collection of many of his articles on instrumentation.  Each section has =
overview material that I have not seen published elsewhere.  =
Unfortunately it is not easy to find considering that it was published =
in 1988.  bookfinder.com has a few copies available from $170 to $850.  =
Worldcat.com shows 12 libraries in the UK that hold a copy.  A similar =
number of libraries have Bob Matthys' book.

I mentioned Aluminum Silicon Bronze because Bob's experiments seem to =
show that it comes back to the same size after temperature cycling than =
most other materials suitable for pendulum bobs.  Thermal expansion of a =
pendulum bob is not a big problem if it supported at the "correct" =
location - note I put correct in quotations because theory and =
experiment seem to give different locations for the support point as per =
Bob's experiments.

Invar is not a panacea as a pendulum rod material.  It requires =
elaborate thermal/shock treatment to achieve good performance, and if =
mechanically shocked or machined, needs to be retreated.  Invar is also =
infamous for unpredictable micro jumps in dimension.  See Dieter =
Riefler's book for details.  Zerodur does not come in thin rod form of =
sufficient length for 1 second pendulums.  Carbon rods have very good =
thermal performance and machine ability, but the binder epoxy is =
humidity sensitive (e.g. the rod gains and losses weight which effects =
the pendulum period) - attempts to slow the process by coating the rod =
with something just slows down the process - no coating is perfect.  =
Fused quartz is a very good material, note tubing is far stronger than =
rod, but end fittings must be attached with adhesive, or with pins in =
cross drilled holes.   All of the above are extensively document in the =
Horological Science Newsletter (HSN).

Yes, I am very familiar with the Littlemore clock.  The reference you =
give is my web site.  I believe that Teddy Hall's first published =
presentation on the clock was at a NAWCC Symposium in Cleveland, USA.  =
Several articles about the clock are in HSN.  The clock is currently in =
storage at the NAWCC Museum - it arrived in not very good shape.  Mice =
had moved in to the computer and had made a real mess.  Documentation of =
the software that controlled the clock seems missing.  If anyone knows =
someone that worked on the project for Teddy - I would love to get the =
contact information.  The hard drive from the computer is currently in =
the process of trying to extract any information that may still be on =
it.  Slow process, because of the components that made up the computer.  =
There is some controversy about the performance of the clock.  Teddy =
used a quartz controlled oscillator to measure the amplitude of the =
pendulum and adjusted the drive force to compensate.  Some people are =
concerned that the quartz oscillator drove the performance of the clock. =
 It is not a simple issue - Tom Van Baak covers the problem very well in =
his article > http://leapsecond.com/hsn2006/hybrid-pendulum-1.pdf

I agree that other forms of suspension are worth investigating.  As you =
have said, clocks and seismometers have different requirements.  A 1 =
second pendulum back and forth more than 31 million times per year over =
much larger amplitudes than a seismometer (correct?)  Wear, =
particulates, variations in spring constant due to temperature, etc are =
all problems to be solved.  The spring I measued was a standard =
Syncronome spring - it is not unusually thick.  The measurement I made =
is more sensitive than that most people make.

The Short and Fedchenko suspensions have a feature that might be worth =
exploring for seismometers. The springs are not flat stock clamped =
between "cheeks" as are most pendulum suspensions instead the springs =
are ground from thicker stock - i.e. they have thick ends.  Stuart =
Smith's book on Flexures has as section on the issues that arise at the =
clamping points.  The Fedchenko clock is the only production, if 30+ =
units is production, that incorporates a working circular error =
compensation mechanism.  Most other attempts have failed because the =
extra mechanism is very difficult to temperature compensate.

Again - the goal here is cross fertilization - perhaps something from =
the world of horology might be of use to seismologists.  I know I have =
learned about a lot of other kinds of suspensions from the discussion =
here on this list.

Bob

On Oct 3, 2012, at 12:00 AMOctober3, =
psnlist-digest-request@.............. wrote:

>=20
> ------ ------ ------ ------ ------ ------ ------ ------ ------ ------.
> | Message 1                                                           =
|
> '------ ------ ------ ------ ------ ------ ------ ------ ------ =
------'
> Subject: Re: Something old with something new
> From:    chrisatupw@.......
> Date:    Tue, 2 Oct 2012 19:13:07 -0400 (EDT)
>=20
>=20
> rom: Bob Holmstrom 
>=20
> To: psnlist 
> Sent: Sat, 29 Sep 2012 23:56
> Subject: re Something old with something new
>=20
> Hi Bob,=3D20
>=20
>    Thanks for your Email. I always find the differing points of view =
of ot=3D
> her people building similar types of equipment quite interesting !=3D20
>    Sorry, but I doubt if either silicon or diamond could be of use to =
us. =3D
> Seismometers need to be very stable, robust and shock resistant, so we =
tend=3D
> to use metal construction. They also have to be very sensitive, =
typically =3D
> measuring movements down to 10, or even 1 nano metre.=3D20
>=20
> Assembling a "stable structure" is an impossible task, but it is =
possible t=3D
> o do better with good design.  A good overview of the required design =
and a=3D
> ssembly techniques is covered in R. V. Jones "Instruments and =
Experiences" =3D
> - fasteners though holes in one object attaching it to another object =
is no=3D
> t stable.  Tutorial sessions at precision mechanism symposiums provide =
addi=3D
> tional material. A Google search for "design guidelines for thermal =
stabili=3D
> ty" yields a bit of useful information. Most if not all materials =
undergoin=3D
> g a temperature cycle do not return to their initial dimensions!  Some =
mate=3D
> rials do better than others.  Bob Matthys, in his book "Accurate Clock =
Pend=3D
> ulums" (Oxford University Press) evaluated many materials using the =
period =3D
> of a pendulum as the measurement means (useful to better than .01ppm) =
- The=3D
> best material he found was "aluminium silicon bronze" - e.g. it came =
back =3D
> to its initial dimensions better than other materials.  Clearly a =
limited e=3D
> xperiment, but a place where "amateurs" can contribute.
>   =3D20
>    Do you have the reference for R V Jones' paper, please ?=3D20
>    Aluminium silicon Bronze has too high an expansion coefficient at =
18 pp=3D
> m / C Deg, for it to be easily thermally compensated, but it could be =
used =3D
> as a component in a 'grid iron' type pendulum. I don't, at the moment, =
have=3D
> access to Bob Matthys's book to be able to comment further. $140 for =
276 p=3D
> ages is very expensive.
>    Some suitable materials for very high precision clock pendulums are =
Inv=3D
> ar, Super Invar (when stabilised), Zerodur glass, fused silica and =
carbon f=3D
> ilament rod / tube. Two part Acrylic glue can be used for sticking =
glass, q=3D
> uartz and carbon eg Holdtite ST3295. We don't need such accurate =
periods in=3D
> seismometers, but we do need very low loss / low error precision =
suspensio=3D
> ns
>    Check out the Littlemore Clock made by E T Hall =
http://www.hsn161.com/H=3D
> SN/hsn_article.php It used a 2 second Invar pendulum and mass, a =
triangular=3D
> Agate bearing / Agate Flat suspension and it was enclosed in a high =
vacuum=3D
> chamber which was mounted on a 12 ton concrete base ! The mean total =
varia=3D
> tion over 50 days was +/-10 milli seconds =3D3D 2.3 10^-9 error. He =
did have =3D
> some problems in strong winds with a large nearby Walnut tree. Someone =
in t=3D
> he USA bought it when Teddy Hall died. You might try to track it down =
?
>=20
> Much of the concern in seismometers seems to be the about the =
non-perfect n=3D
> ature of springs (or other mass suspension pivots, etc.).  I have =
attempted=3D
> to suspend a pendulum so that it has the period vs amplitude predicted =
by =3D
> theory.  It will not surprise you that springs, knife edges, rollers, =
etc g=3D
> ive less than perfect results.  The best I have done is to use porous =
graph=3D
> ite air bearings.  http://www.newwayairbearings.com/  By best, I mean =
that =3D
> the period vs amplitude error ("circular error" in clock vernacular) =
was th=3D
> e best.  An image of the pendulum and a bit of the results are at =
http://ww=3D
> w.hsn161.com/HSN/airclock2.html  It is not clear that this form of =
suspensi=3D
> on is of any use for a seismometer, but perhaps one of the long period =
pend=3D
> ulum configurations could be implemented with air bearings.
>=20
>    The suspension springs on vertical seismometers are very highly =
stresse=3D
> d and the lever system makes the position of the mass extremely =
sensitive t=3D
> o any small changes in the tension. The springs are composed of small =
hard =3D
> metal crystals, in a semi random orientation and the displacement =
signal is=3D
> greatly amplified, so you are likely to observe signals if any slips =
occur=3D
> in individual crystals.    =3D20
>    I can't think why you might have had any problems with crossed =
roller b=3D
> earings. These and spherical bearings rolling on flats, crossed foils =
and m=3D
> ore especially figure of 8 rolling foils, can ALL give excellent =
results. I=3D
> suspect that your suspension spring may have been too thick.
>    The highest precision pendulum clocks  (Riefler, Shortt, Fedchenko, =
Den=3D
> t) all use small, precise, stable angles of swing, to reduce any =
variations=3D
> in the 'circular error'.=3D20
>    The Russian Fedchenko clocks use a three foil suspension layout to =
comp=3D
> ensate for the circular error over small angles. Another method is to =
mount=3D
> two pairs of small magnets on the mass and the frame, so that =
increasing s=3D
> wing amplitudes give increasing repulsion. The bob then needs to be =
magneti=3D
> cally screened to eliminate interactions with the Earth's and other =
magneti=3D
> c fields.=3D20
>=20
>    The NBS found that when two precision pendulums of the same period =
were=3D
> mounted on the same wall (80 tons?), they tended to beat together and =
to i=3D
> nterfere with each others' motion. To get them to beat totally =
independentl=3D
> y, it was necessary to mount the swing axes at right angles. Is the =
high se=3D
> nsitivity of pendulum clocks to the stability of their wall / frame =
mountin=3D
> gs appreciated by your enthusiasts ?
>=20
> Bob Holmstr=3DC3=3DB6m
> Editor Horological Science Newsletter
> www.hsn161.com =3D20
>=20
>    Regards,=3D20
>=20
>    Chris Chapman

bookfinder.com has a few copies =
available from $170 to $850.  Worldcat.com shows 12 libraries in the =
UK that hold a copy.  A similar number of libraries have Bob =
Matthys' book.

I mentioned Aluminum Silicon =
Bronze because Bob's experiments seem to show that it comes back to the =
same size after temperature cycling than most other materials suitable =
for pendulum bobs.  Thermal expansion of a pendulum bob is not a =
big problem if it supported at the "correct" location - note I put =
correct in quotations because theory and experiment seem to give =
different locations for the support point as per Bob's =
experiments.

Invar is not a panacea as a =
pendulum rod material.  It requires elaborate thermal/shock =
treatment to achieve good performance, and if mechanically shocked or =
machined, needs to be retreated.  Invar is also infamous for =
unpredictable micro jumps in dimension.  See Dieter Riefler's book =
for details.  Zerodur does not come in thin rod form of sufficient =
length for 1 second pendulums.  Carbon rods have very good thermal =
performance and machine ability, but the binder epoxy is humidity =
sensitive (e.g. the rod gains and losses weight which effects the =
pendulum period) - attempts to slow the process by coating the rod with =
something just slows down the process - no coating is perfect. =
 Fused quartz is a very good material, note tubing is far stronger =
than rod, but end fittings must be attached with adhesive, or with pins =
in cross drilled holes.   All of the above are extensively document =
in the Horological Science Newsletter =
(HSN).

Yes, I am very familiar with the =
Littlemore clock.  The reference you give is my web site.  I =
believe that Teddy Hall's first published presentation on the clock was =
at a NAWCC Symposium in Cleveland, USA.  Several articles about the =
clock are in HSN.  The clock is currently in storage at the NAWCC =
Museum - it arrived in not very good shape.  Mice had moved in to =
the computer and had made a real mess.  Documentation of the =
software that controlled the clock seems missing.  If anyone knows =
someone that worked on the project for Teddy - I would love to get the =
contact information.  The hard drive from the computer is currently =
in the process of trying to extract any information that may still be on =
it.  Slow process, because of the components that made up the =
computer.  There is some controversy about the performance of the =
clock.  Teddy used a quartz controlled oscillator to measure the =
amplitude of the pendulum and adjusted the drive force to compensate. =
 Some people are concerned that the quartz oscillator drove the =
performance of the clock.  It is not a simple issue - Tom Van Baak =
covers the problem very well in his article > http://leapse=
cond.com/hsn2006/hybrid-pendulum-1.pdf

I =
agree that other forms of suspension are worth investigating.  As =
you have said, clocks and seismometers have different requirements. =
 A 1 second pendulum back and forth more than 31 million times per =
year over much larger amplitudes than a seismometer (correct?) =
 Wear, particulates, variations in spring constant due to =
temperature, etc are all problems to be solved.  The spring I =
measued was a standard Syncronome spring - it is not unusually thick. =
 The measurement I made is more sensitive than that most people =
make.

The Short and Fedchenko suspensions have =
a feature that might be worth exploring for seismometers. The springs =
are not flat stock clamped between "cheeks" as are most pendulum =
suspensions instead the springs are ground from thicker stock - i.e. =
they have thick ends.  Stuart Smith's book on Flexures has as =
section on the issues that arise at the clamping points.  The =
Fedchenko clock is the only production, if 30+ units is production, that =
incorporates a working circular error compensation mechanism.  Most =
other attempts have failed because the extra mechanism is very difficult =
to temperature compensate.

Again - the goal =
here is cross fertilization - perhaps something from the world of =
horology might be of use to seismologists.  I know I have learned =
about a lot of other kinds of suspensions from the discussion here on =
this list.

Bob

On Oct =
3, 2012, at 12:00 AMOctober3, psnlist-digest-reque=
st@.............. wrote:


------ ------ ------ ------ ------ ------ ------ =
------ ------ ------.
| Message 1 =
            &n=
bsp;           &nbs=
p;            =
            &n=
bsp;        |
'------ ------ =
------ ------ ------ ------ ------ ------ ------ ------'
Subject: Re: =
Something old with something new
From:    chrisatupw@.......
Date: =
   Tue, 2 Oct 2012 19:13:07 -0400 (EDT)


rom: =
Bob Holmstrom <holmstro@..........>

To:=
 psnlist <psnlist@..............>
S=
ent: Sat, 29 Sep 2012 23:56
Subject: re Something old with something =
new

Hi Bob,=3D20

    Thanks for your Email. =
I always find the differing points of view of ot=3D
her people =
building similar types of equipment quite interesting !=3D20
 =
   Sorry, but I doubt if either silicon or diamond could =
be of use to us. =3D
Seismometers need to be very stable, robust and =
shock resistant, so we tend=3D
 to use metal construction. They also =
have to be very sensitive, typically =3D
measuring movements down to =
10, or even 1 nano metre.=3D20

Assembling a "stable structure" is =
an impossible task, but it is possible t=3D
o do better with good =
design.  A good overview of the required design and a=3D
ssembly =
techniques is covered in R. V. Jones "Instruments and Experiences" =
=3D
- fasteners though holes in one object attaching it to another =
object is no=3D
t stable.  Tutorial sessions at precision =
mechanism symposiums provide addi=3D
tional material. A Google search =
for "design guidelines for thermal stabili=3D
ty" yields a bit of =
useful information. Most if not all materials undergoin=3D
g a =
temperature cycle do not return to their initial dimensions!  Some =
mate=3D
rials do better than others.  Bob Matthys, in his book =
"Accurate Clock Pend=3D
ulums" (Oxford University Press) evaluated =
many materials using the period =3D
of a pendulum as the measurement =
means (useful to better than .01ppm) - The=3D
 best material he found =
was "aluminium silicon bronze" - e.g. it came back =3D
to its initial =
dimensions better than other materials.  Clearly a limited =
e=3D
xperiment, but a place where "amateurs" can contribute.
 =
  =3D20
    Do you have the reference for R =
V Jones' paper, please ?=3D20
    Aluminium silicon =
Bronze has too high an expansion coefficient at 18 pp=3D
m / C Deg, =
for it to be easily thermally compensated, but it could be used =3D
as =
a component in a 'grid iron' type pendulum. I don't, at the moment, =
have=3D
 access to Bob Matthys's book to be able to comment further. =
$140 for 276 p=3D
ages is very expensive.
    Some =
suitable materials for very high precision clock pendulums are =
Inv=3D
ar, Super Invar (when stabilised), Zerodur glass, fused silica =
and carbon f=3D
ilament rod / tube. Two part Acrylic glue can be used =
for sticking glass, q=3D
uartz and carbon eg Holdtite ST3295. We =
don't need such accurate periods in=3D
 seismometers, but we do need =
very low loss / low error precision suspensio=3D
ns
 =
   Check out the Littlemore Clock made by E T Hall http://www.hsn161.com/H=3D
SN/h=
sn_article.php It used a 2 second Invar pendulum and mass, a =
triangular=3D
 Agate bearing / Agate Flat suspension and it was =
enclosed in a high vacuum=3D
 chamber which was mounted on a 12 ton =
concrete base ! The mean total varia=3D
tion over 50 days was +/-10 =
milli seconds =3D3D 2.3 10^-9 error. He did have =3D
some problems in =
strong winds with a large nearby Walnut tree. Someone in t=3D
he USA =
bought it when Teddy Hall died. You might try to track it down =
?

Much of the concern in seismometers seems to be the about the =
non-perfect n=3D
ature of springs (or other mass suspension pivots, =
etc.).  I have attempted=3D
 to suspend a pendulum so that it =
has the period vs amplitude predicted by =3D
theory.  It will =
not surprise you that springs, knife edges, rollers, etc g=3D
ive =
less than perfect results.  The best I have done is to use porous =
graph=3D
ite air bearings.  http://www.newwayairbearings.co=
m/  By best, I mean that =3D
the period vs amplitude error =
("circular error" in clock vernacular) was th=3D
e best.  An =
image of the pendulum and a bit of the results are at http://ww=3D
w.hsn161.com/HSN/airclock2=
..html  It is not clear that this form of suspensi=3D
on is =
of any use for a seismometer, but perhaps one of the long period =
pend=3D
ulum configurations could be implemented with air =
bearings.

    The suspension springs on vertical =
seismometers are very highly stresse=3D
d and the lever system makes =
the position of the mass extremely sensitive t=3D
o any small changes =
in the tension. The springs are composed of small hard =3D
metal =
crystals, in a semi random orientation and the displacement signal =
is=3D
 greatly amplified, so you are likely to observe signals if any =
slips occur=3D
 in individual crystals.    =3D20
 =
   I can't think why you might have had any problems with =
crossed roller b=3D
earings. These and spherical bearings rolling on =
flats, crossed foils and m=3D
ore especially figure of 8 rolling =
foils, can ALL give excellent results. I=3D
 suspect that your =
suspension spring may have been too thick.
    The =
highest precision pendulum clocks  (Riefler, Shortt, Fedchenko, =
Den=3D
t) all use small, precise, stable angles of swing, to reduce =
any variations=3D
 in the 'circular error'.=3D20
 =
   The Russian Fedchenko clocks use a three foil =
suspension layout to comp=3D
ensate for the circular error over small =
angles. Another method is to mount=3D
 two pairs of small magnets on =
the mass and the frame, so that increasing s=3D
wing amplitudes give =
increasing repulsion. The bob then needs to be magneti=3D
cally =
screened to eliminate interactions with the Earth's and other =
magneti=3D
c fields.=3D20

    The NBS found =
that when two precision pendulums of the same period were=3D
 mounted =
on the same wall (80 tons?), they tended to beat together and to =
i=3D
nterfere with each others' motion. To get them to beat totally =
independentl=3D
y, it was necessary to mount the swing axes at right =
angles. Is the high se=3D
nsitivity of pendulum clocks to the =
stability of their wall / frame mountin=3D
gs appreciated by your =
enthusiasts ?

Bob Holmstr=3DC3=3DB6m
Editor Horological =
Science Newsletter
www.hsn161.com=
 =3D20

    Regards,=3D20

 =
   Chris =
Chapman

=