I'll be re-tensioning all guys in another week or so and will do another
comparison at that time to see how close they come.
73
Roger (K8RI)
Dick Green WC1M wrote:
> W8JI compared the readings with EHS and fiberglass guy material in series
> and found a large discrepancy. As far as I know, he didn't compare EHS and
> Phillystran. My experiment compared the readings of two gauges on the same
> material, 1/4" EHS.
>
> The "thought experiment" that with increasing tension the material becomes
> more "rod-like", and therefore the differences in tension tend to decrease,
> sounds reasonable. After all, my own empirical experiments showed that the
> percentage difference between the Loos and Dillon gauges decreases with
> increasing tension. Unfortunately, the range of difference was 50%-20%.
>
> But let's try another thought experiment. The PT-2 calibration plate chart
> in the Loos manual says that at a reading of 32, the tension of 7/32"
> stainless wire rope will be 1060 lbs and the tension of 1/4" stainless wire
> rope will be 780 lbs. That's a difference of 36% from a mere 1/32"
> difference in diameter of the same material. Most of the other differences
> in the series are closer to 50% (they're not very linear, which is what I
> found with my Loos gauge.) Given the relatively wide spacing between
> markings on the calibration plate, you would think that a 1/32" difference
> in the movement of the rollers wouldn't result in that much difference in
> the reading. I would conclude that the most of the difference is due to the
> difference in stiffness between 7/32" and 1/4" 1x19 stainless steel wire
> rope.
>
> My bottom line on this is that either the material really does makes a
> difference or my Loos gauge has a bad spring. I'd include the alternative
> that my Dillon dynamometer needs calibration, but that wouldn't explain
> W8JI's results. Maybe his Loos gauge has a bad spring, too, and we need to
> wonder about quality control on these gauges.
>
> Don't get me wrong: the Loos gauge is incredibly useful for setting the
> final tension of all the guys to the same value, which is very important.
> Also, I suspect the difference between 660 lbs (my Dillon reading) and 840
> lbs (my Loos reading) won't have a significant effect on the typical amateur
> tower installation. I'm sure a lot of people out there just eyeball the
> tension and don't get all that close to the 10%-of-breaking-strength target.
>
> 73, Dick WC1M
>
>
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|