Grant (and all),
This thread is getting really interesting to me. I'm certainly no
mechanical engineer but I'm beginning to understand how these things
work and can certainly see what the Loos gauge issues are with Kevlar.
So, having looked up S-type load cells and Dillon force gauges, I have a
couple questions. 1: How does one put a gauge inline with the guy, set
the tension and then remove it and restore the same tension? The S-type
load cell is basically a Wheatstone bridge, so what is the 'excitation'
voltage required? Some 'cookbook' style instructions would be very helpful.
I say all this because I'm one of the schmucks that ran his Philly all
the way down to the anchor. This summer I plan to change the HF Yagi at
the top of my 80' 25G to one with much more torque from wind force and
want to make sure the guy wire tensions are correct.
73,
-de John NI0K
Grant Saviers wrote on 7/13/2021 6:46 PM:
Calibrating against the actual fiber is *probably* good enough for ham
tower work, BUT
Be aware that the Kevlar fibers of Phillystran behave very differently
than steel wire. The Kevlar fiber is very strong axially with about
60% the modulus of steel. The fiber also has very complex lower
modulus behavior longitudinally, the fibers are anisotropic.
The Loos gauge is based on the isotropic (equal in all directions)
modulus of steel, approximately the deflection of a beam center loaded
and simply supported at both ends. A simple equation that can be
looked up on the web, that doesn't apply to Phillystran.
If the Kevlar "beam" was isotropic, then the Loos gauge on Kevlar
would deflect 1/0.6 more on the same diameter as EHS (IE the exact
diameter of the actual fiber or wire bundle if all air was removed -
weight per foot is the easiest means to get the value for both). A
0.22" diameter of the PE Phillystran sheath, isn't that value.
So perhaps the best use of a Loos gauge is to get all guy tensions
equal and use a simple force gauge to measure the tension. Sometimes
cheap on ebay ("dillon force gauge") and all mechanical (D shaped
steel ring and dial gauge).
They can be made on a milling machine, google for instructions. Like
these. They work in tension or compression.
https://scienspec.com.tw/userfiles/files/MODEL%20X.PDF
Grant KZ1W
On 7/13/2021 14:43, n0tt1@juno.com wrote:
Kurt,
Perhaps, and I don't know,
does Phillystran require something more complex, and specialized than
any other material under tension that fits in the gauge?
Not really. The guage should be calibrated for whatever cable one
intends
to measure. It's that simple.
73,
Charlie, N0TT
On Tue, 13 Jul 2021 12:27:43 -0700 KD7JYK DM09 <kd7jyk@earthlink.net>
writes:
After searching far and wide to come to the conclusion there is
none
commercially available, I built my own tension gauge
I'm super confused here. I haven't looked for tension gauges since
putting up my own mast in 2013, and haven't looked again until a few
moments ago. I got 22.71 million hits for sites, and enough pics to
choke the internet, with tension gauges ranging from small handheld
models for string, to gauges for suspension bridges, most in the
range
of anything any of us would ever use, wire, rope, cable, you name
it.
If price is a concern, and it's a one-shot deal, look at belt
tension
gauges at an auto parts store. Even the companies that supply bits
and
pieces for our hobby, supply the tools, and gauges to install, test,
and
use them (look up guy wire tension gauge, or cable tension gauge, or
even rigging gauges if you're into boating). Perhaps, and I don't
know,
does Phillystran require something more complex, and specialized
than
any other material under tension that fits in the gauge?
Kurt
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