[TowerTalk] Phillystran Tension Gage

[Lux, Jim]

On 7/13/21 4:46 PM, Grant Saviers wrote:
> 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



And if you want to get fancy, there's plenty of load cells for sale at 
remarkably low prices.

(I was looking for <200 lbs, so the ones I found are probably not 
suitable, but they were <$50)  You could monitor the tension in your 
guys at all times, and tell when the wind has shifted.  I found some 
ones rated at 2000kg for $42 (they're used in weighing applications, 
among others) - "Load Cell Sensor S type"

And there's also things like "Digital Crane Scales" (which are basically 
tension sensors, with a display, and sometimes, a USB or BT interface.