N2NU@aol.com wrote:
> I thought about this one before I bought the gauge from Champion... Here's my
> reasoning on why I believe that the gauge shoud read correctly... Actually I
> would like someone to check my reasoning, so ok, you physicists...
I'm not a physicist, but then I shouldn't take one to understand this. I'm
merely
another engineer/ham trapped in a purely mechanical world (background and
professionally).That's why I get such a kick out of some of this reflectors
threads. (I.E. What happens to energy on a mismatched transmission line), that
one
was a hoot!
> The gauge measures the force necessary to deform (bend) the guy wire between
> the two pins.
Correct!
> How hard this is should be dependent on the tension only (I
> think, since you shouldn't be able to stretch your guys!).
Dependency on tension is correct! The stretch comment is not. Steel guy wires or
Phillystran or Un-Obtanium always stretch when a load is applied to them. The
appropriate question is hw much do they stretch!
> The only other
> variable would be your ability to crush the guy wire, which shouldn't be an
> issue in either case. I believe that Phillystran would give an erroneously
> low reading for this reason because it will crush and appear to be "thinner"
> as you try to bend it around the two pins.
Crush is a poor choice of terms. Think of the the aramid fibers in the cable as
thousands of teeny rods that are not twisted very much. Because they are not
wound
up in a bundle, they will easily move laterally to spread out and "appear to be
thinner." Which is correct.
> Shouldn't be a problem for most of
> us since we normally put some ehs at the bottom of the guys anyway.
Good for the guys (these are people) who install them in the recommended
fashion!
> Of course the absolute accuracy of the device depends on the spring, and the
> nylon spacers on the pins (if they wear, you will read lower than real
> tension).
Correct! Any measuring device depends on the accuracy of its components.If
anyone
wondered why the really good instruments are more expensive than the others, its
in the accuracy of the components and construction.
If the nylon spacers wear the device will indicate a reading that is higher than
the load.
> Steve if you are going to do a test, you might hang a known weight
> on the spring and let us know the reading. Then the rest of us can do the
> same with ours to see what the variation in the springs end up being.
Looks like N3RR has answered the accuracy question from his experience.
> I take no responsibility for this analysis, but it made me feel better anyway!
> Comments?
I'd really like to follow suit, but can't. I haven't offered an analysis yet so
I'm safe there. But, I'll take full responsibility for my comments. They are
simply based on my knowledge base as of 8/4/98. Tomorrow, when I learn some
more,
I'll say something different!
BTW, the Loos device is used in the marine industry, along with a few other
devices, to adjust the rigging tune on small sailing yachts. This type of device
is intended to be the most economical form of line tension measurement. If one
is
really keen on obtaining an absolutely accurate measurement, change to a
completely different class of device.
The Loos gage was designed to be used on wire rope cables over a certain range
of
sizes and cable constructions.
We mostly use solid Nitronic 50 and other high strength stainless steel alloys
to
rig (or guy) our sailboat masts. The reason is is that the stranded
constructions
are not as strong and they stretch way too much! I'll bet everyone can imagine
what the Loos gage would say if put on a solid rod @ zero tension!
Again, N3RR says he's found good correlation with the Loos for cable we would
use.
So, if it fits our budget, we should move on to the next problem!
The next problem is directly related to this topic and concerns the importance
of
wire stretch (or effective stiffness) of any axially loaded structural member.
Comments I've seen about tower guying and tower loads, since subscribing,
obviously ignore wire stretch.
Just because nobody mentions it, and since the manufacturers specs and building
codes have allowed for it, doesn't mean that it isn't important.
Don't want to confuse the Loos thread readers! This is the subject of another
thread.
73, Kurt
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