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PT50- Slight Mods
(06-13-2018, 10:00 AM)EOU Wrote: This design offers many possibilities with regard to rerunning test media including leaving the fixture in place on the instrument while test media is rerun.

The point above may give us the ability to measure our pull tension on the media.  I don't know how differing tensions affect the cut pressure, but I'm all about trying to reduce/eliminate variables when testing.

Ed K.
 I don't know how differing tensions affect the cut pressure, but I'm all about trying to reduce/eliminate variables when testing.

I experimented with this tension thing at first Ed. If you really bear down on the test media  maybe 10 or 15 grams lower on a fairly sharp edge. Sometimes you might think that you're seeing more than that but you might just have hit a little sharper part of the edge too. Could be more than 10 or 15, I don't know with duller edges. I just got in the habit of doing it like the instruction manual says and pull the slack out then tighten the screw. So now I don't worry about it and my numbers are just fine. Seems to me like someone said a 100 grams of tension. That's maybe 3 ounces and that's next to nothing. I think that's what pulling the slack out is, next to nothing.To me its like taking my blood pressure at home. If I hold my arm too high I get a low number and if it's too low low I get a high number. So I hold it right where the doctor told me and I'm all good. My blood pressure isn't all good but my doctor seems happy and that's the important thing.
Thanks to Ed for asking the question and it's far from the first time it's been asked. I think the question must be based in what we have learned about cutting things our entire lives. If you want to cut a piece of rope, string, twine etc. it really helps to tension it out to make it cut easier so there is just something inside us that screams "you must really stretch this test media out if you're going to cut it". While the severing action of test media is much different than string or twine, it is still subject, to a much smaller degree, to the effects of tensioning. This is why questions/comments like Ed's are always welcome because we generate new users around here everyday and they simply haven't heard the news yet. 

There are a few people running around here with BP issues as well Bud and the author of this post is one of them. Your analogy with regard to taking accurate blood pressure readings is just pretty much to the point. Correct tensioning of test media may be even simpler than gauging arm position when taking blood pressure. As you say, apply only enough tension to remove the slack and then tighten the tensioning screw. You may like the sharpness number you get better if you over tension just as you like your bathroom scale number better if you rest one hand on the wall while weighing but if you want accurate numbers, don't over tension test media and don't lean against the wall when you're weighing yourself. 

You're right on the 100 grams Bud and you're right that it is "practically nothing". 100 grams is enough to remove the slack from the test media across the ATF measuring slot. So the short answer to "how much tension should I place on the test media?" is "none" or perhaps more accurately and as Bud would put it "practically none".
In case you missed it, they recently lowered blood pressure target numbers. Now 1/2 (was 1/3) of the US population has high BP.   Whaasup

I learned something interesting about BP a while back. My heart is incredibly finicky about oxygen saturation. If my blood oxygen saturation is 96-97% (normal, resting, for me), my BP is at least 10% higher than it is when I take two deep breaths, which instantly raises my oxygen saturation to 99-100%. If I continue slow, deep breathing (not hyperventilating), my BP goes down dramatically.

The friendly nurse who taught me about it said a person should always take two deep breaths before they get the cuff on you, but that was the first time I'd ever heard such thing.

It's almost like there might be many people who make a lot of money off your "high" BP...
Somehow I typed up a reply but it got lost in space.

The gist of my reply was that the test clip media was ~20% lower due to too much tension - slightly bend the clip to reduce tension and the measured force would be closer to the ATF.

That sent me down the rabbit hole that ATF tension had a fairly large effect on measured cut force.

If I lose this one I'm going to bed as I also have elevated BP.  Thanks for all the replies to my previous post.

Ed K.
Good observation concerning test clips Ed. Here's the difference between clips and ATFs. Clips are purposely over tensioned. Over tensioning yields tighter relative (relative as opposed to absolute) test groupings when measuring sub-35 BESS edges. The combination of over tensioning and a very short run length (with clips) creates more error compared to ATFs which all have much longer run lengths.  As an aside, the 20% deviation rate for test clips is a testament to the engineering factors that drive Test Media Run Lengths/Test Media Tension and BESS Test Media calculations. The deviation remains nailed at 20% throughout the BESS score range 10 - 500 when comparing ATF scores to clip scores. 

Mark - you're preaching to the choir. Had a physical two years ago and the doctor told me the number to shoot for was 150/90. Since that's just about where I sat at the time, life was good. I went in with the same numbers two months ago and find out that I now have "hypertension". Now I take blood pressure medicine and I'm about 120/75 and the doctor says that's "just right". I'd give her some guff about all that but she's just too good looking to argue with.

It's not all bad though Mark. When my wife starts to give me a hard time now I tell her "Now Joan, haven't you heard that the doctor diagnosed me with HYPERTENSION? Surely you wouldn't want to upset me." I may have about run my string out with that one though. She told me last night that she'd just about had it with that line. I told her that I was sorry but that this was a disease that I had to live with and that because she was married to me, she had to live with it as well. Her reply was "Well I might have to do something about that last part." Take care of your BP fellas, apparently hypertension is hard on marriages.
Like I said before, the BESS forum is always a good place to pick up at least one good chuckle. I've always had low blood pressure. It's never caused any problems other than being asked the same questions every time I see a new doctor. Do I feel faint after standing? Do I feel unusually tired? I think now that I would like to switch. I need some good ammunition to use at my house and it seems that hypertension just might be a good bet. How do you catch it?

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