Bob:

Yes, that is eddy current testing. I have not yet considered it. I'd
prefer to use mag particles (iron filings) as this does not require
runing a probe along all possible surfaces.

How about sending an acoustic pulse along the rod rigging the same as a time
domain reflectometer works. The pulse speed is a property of material and
tension and the reflectance a function of acoustic impedance. Cracks would
raise the impedance. The cracks could be located along the length of the rod
by simply applying the pulse signal at one point.

http://www.tscm.com/riprcop.html




wrote in message
oups.com...
Bob:

Yes, that is eddy current testing. I have not yet considered it. I'd
prefer to use mag particles (iron filings) as this does not require
runing a probe along all possible surfaces.

Cracks would
raise the impedance. The cracks could be located along the length of
the rod
by simply applying the pulse signal at one point.

Seems to me that for this to work well you'd need to remove the rod
from the boat and tension it is some sort of way, equally. Then you
might read cracks, but be unable to actually locate them, meaning a
small non-dangerous imperfection in the rod might give a false reading.
Seems like a tool that would get abused to sell a lot of uneeded
rigging..
Just about every rig failure I've ever heard of was wire. While I'm
sure rod has failed....I've never heard of it. Anyone know of a rod
rigging failure they can point to online? I'm too sleepy to google
today.

RB
35s5
NY

Rob:

You don't have to remove the rigging at all. On the TDR pulse you can easily
see the where the spreader touches to rod, you can run your hand up and down
the rod and see its location on the TDR. Since sound waves don't propagate
through cracks, the sound energy would be reflected back at the source and
the location of the crack could easily be identified.

All you need is a good piezo transducer that transmits and receives, a pulse
generator (a simple circuit) and some display like an oscilloscope. You can
even make a display on a laptop. With some signal processing you could
really do some great analysis of the rigging.

Think of a sonar with metal instead of water as the medium. One could even
spot cracks and corrosion in the end fittings. Also think of a musical
instrument. If the fret or neck on a guitar is damaged, it is easy to hear.
These same principals apply to the TDR.

Amen!

"Capt. Rob" wrote in message
oups.com...
Cracks would
raise the impedance. The cracks could be located along the length of
the rod
by simply applying the pulse signal at one point.

Seems to me that for this to work well you'd need to remove the rod
from the boat and tension it is some sort of way, equally. Then you
might read cracks, but be unable to actually locate them, meaning a
small non-dangerous imperfection in the rod might give a false reading.
Seems like a tool that would get abused to sell a lot of uneeded
rigging..
Just about every rig failure I've ever heard of was wire. While I'm
sure rod has failed....I've never heard of it. Anyone know of a rod
rigging failure they can point to online? I'm too sleepy to google
today.

RB
35s5
NY

Bob Crantz wrote:

How about sending an acoustic pulse along the rod rigging the same as a time
domain reflectometer works. The pulse speed is a property of material and
tension and the reflectance a function of acoustic impedance. Cracks would
raise the impedance. The cracks could be located along the length of the rod
by simply applying the pulse signal at one point.

Sounds good to me, I don't belive tension (or compression) has anything
to with the speed of transmission in a solid.

Cheers
Marty

Sounds good to me, I don't belive tension (or compression) has anything

to with the speed of transmission in a solid.

But to get the expected measurements in a solid structure that is being
read for resonent feedback variances, wouldn't said feedback be
effected if the the solid had a wide range of motion? Seems like it
would require isolation for relaible readings. Out of my depth on this
one, folks....just guessing based on what I've read from Bob C.

RB
35s5
NY

"Martin Baxter" wrote in message
...

Sounds good to me, I don't belive tension (or compression) has anything
to with the speed of transmission in a solid.


Assume a completely rigid guitar neck. Adjusting the tension of the string
adjusts its resonant frequency. If the length does not change, but the
resonant frequency does, then the velocity in the string must change.

C = tension/linear density

http://www.faqs.org/docs/sp/sp-172.html

Bob Cranz is correct, this would work for cracks in the rod, even when
it was attached at both ends. When rod fails, where does it fail, I'd
bet at the ends where TDR would be harder.
Given identical types of ends and repeatedly stressed, any engineer
would expect that solid rod would fail before cable type. A crack in a
single strand of wire cannot propogate anywhere except in that strand.
A crack in solid can go all the way through and probably will because
the crack itself becomes a stress concentrator.

Given identical types of ends and repeatedly stressed, any engineer
would expect that solid rod would fail before cable type.


This guy is a funny troll. Even the makers of standing rigging admit
that rod is more durable. It's also a supperior system due to lower
weight. Just take care of it. Surveyors who have no market interest in
selling either also say rod is longer lived.
This guy is some engineer.

RB
35s5
NY

Bob Crantz wrote:

"Martin Baxter" wrote in message
...

Sounds good to me, I don't belive tension (or compression) has anything
to with the speed of transmission in a solid.

Assume a completely rigid guitar neck. Adjusting the tension of the string
adjusts its resonant frequency. If the length does not change, but the
resonant frequency does, then the velocity in the string must change.

C = tension/linear density

I don't think so, you are thinking of resonance in a transverse plane,
not propagation of a sound wave through the medium. Your example is for
a transverse wave, the TDR mode you propose to employ is in fact a
compresion/rarefaction, not unlike the P wave in siesmology. The problem
is going to be "injecting" this pulse, if you just tap the side of the
rod you will generate transverse waves rather than the longitudinal wave
you are seeking. I do not think that that transverse waves will be
reflected by a crack in the rod or the connectors between rod sections.

See http://prola.aps.org/abstract/PRD/v7/i6/p1590_1 for the general
equation.


Cheers
Marty