Hi Ken,
I've been too busy to follow the PWT accuracy thread with anything more than
casual interest. However, the Hanna technicians assure me the stated range
is what their accuracy is based on.
Today I took 3 PWT meters and put them into distilled water. I then began
to add tap water very slowly and watched the readings rise over 99.9 without
going off scale. However when the reading got to 199.9 it then jumped to
1--.- So, if for sake of argument the accuracy is 2% of full scale, then
the most they would be off is 4 uS. But I think the factory is correct in
saying the accuracy is set by the range they specify rather than the total
reading the meter is capable of indicating. I believe it was Ivan who said
they are just using the most linear portion of the scale to use and the
over-reading capability is not to be considered at the same accuracy.
Unless your meter is different than the three I tried, how can you get a
reading of 999.0 before it goes off scale? Perhaps your meter is not
working properly. Or should I try a few more meters to see if they all act
the same?
I really don't see any problem since we're not trying to measure anything
near the upper limits. We're talking about the range of 5-20 uS in most
cases and an occasional foray into the 30-40 uS area. I think they work
just fine. And the ones I use are always in agreement. I always use 3
meters when calibrating our SG7's to make sure we get them properly
adjusted.
This seems like beating a dead horse to me.
Trem
----- Original Message -----
From: "Ode Coyote" <coyote...@earthlink.net>
To: <silver-list@eskimo.com>
Sent: Thursday, October 31, 2002 10:49 AM
Subject: RE: CS>TDS/PWT meters
> I'm willing, out of curiosity, to 'determine some idea' of how far off
> reality is from various stated views of it. [something within a range in
an
> infinite scale]
> I've got an odd feeling that no one can say anything that's true about
> anything. [Nothing that is, except, perhaps, that statement.]
>
> So, maybe an average standard will do? [along with an illustration that
> that's all we ever had anyway?]
>
>
> The PWT actually has a 4 digit display and pegs out at 999.x uS just
> before it shows a 1 in the far left saying it can't read that high or any
> higher.
> The DIST 1 [much similar to the TDS1 I presume] will read up to 1999 PPM
> before the last 3 places vanish leaving a 1 in the far left place to
> indicate it's beyond capabilities. Range is stated as 1990 PPM
>
> [all regardless of accuracy issues or what or how anything is written,
> these are the actual facts based on doing and seeing it.]
>
> My problem with all this is that accuracy is based on full scale without
> any clear indication of what full scale 'is' even if [especially if] full
> scale is not "as high as it will read". Nor are there any indications
that
> there is more than one scale.
> If they had based accuracy on the intended range within any scale or
> numbers of scales, I'd not even have a question. Who cares what it reads
> beyond it's intended range? But when you base accuracy on scale and then
> don't say what the scale is, leaving you to assume it's something like the
> stated range, but turns out not to be even close and they don't make any
> attempt at all to qualify the possible differences in perceptions and go
on
> to write a specification based on an undefined quantity...I tend to wonder
> what the heck they said or if anything was. It smacks of double speak fit
> for a politician. [or salesman...same motive of persuasion]
>
> Have you seen the negative political ad where the written words say "...
> took $40,000 from sons college fund to buy a new car" [implying that she
> ripped her son off] and the vocals say "..Took $40,000 out of sons
> college fund because 'he' wanted a new car..and slurred the 'he' part just
> a little to sound a little like s-he" ?
> Double speak and misdirection. Manipulation towards a point of view
that's
> not true but done without actually lying.
> The FDA reports on colloidal silver are chock FULL of that sort of thing.
> Why?
> For instance..."not proven safe or effective" does not mean "proven
> unsafe and ineffective", but that's the impression that one gets from the
> reading and phrasing of a collection of studies that have the title
> "Colloidal Silver"...when not one single study within the report even
> mentions colloidal silver.
> One may as well compare a Volvo to rust because they both contain iron,
> then say whatever you want to about Volvos because iron is strong or rust
> is stable. Is it a true statement that rust can't rust, so it's rust
proof?
> I've had "dependable" Datsuns that ran till there was nothing left to
> hold the wheels on..in only 10 years. Well, it ran extremely dependably
and
> still does, but you can't drive it. Toyota fixed the rust problems but
> screwed up the motors by replacing a $12 steel part that never fails with
a
> plastic one that tears up the entire front of the motor and contaminates
> the oil which burns up the bearings, rings and cylinder walls when it goes
> out. I drive a 1985 Toyota with a 1978 motor in it. They both died from
> different diseases so I did some grafting. We won't even get into Ford,
> Crysler and GM. {AMC?? Yea, right...no two alike}
>
> Never-the-less, we still use automobiles and they serve us adequately.
The
> ambiguities can often be worked around to make something that's actually
> good in all respects. The manufacturers won't tell you what fits what with
> whatever modification or what's weak. [Just don't asked me what year,
model
> or brand my car is 'cause I'll have to ask you which part?]
>
> My lastest in progress is a Hondumpharly motorcycle. The Triumaha works
> good as did the 1968 thru 1990 510610810620720280240z L/z series
> Subavolksadasun! ;-)
>
> "More doctors recommend this drug over all others combined" OK, what
> doctor would recommend combining all other drugs? The statement is true,
> but does it say what it says? LOL
>
> Maybe, just maybe, we can get doublespeak [our only language] to talk more
> true than false for a change and in one instance.
> Ken
>
> At 01:31 PM 10/29/02 -5, you wrote:
> >Ivan and Ken,
> >
> >You're exploring the issue of accuracy and precision of the Hanna PWT
> >and TDS quite thoroughly! But let's see if I'm misinterpreting you
> >right on a couple of points... <grin>
> >
> >Specs for my Hanna TDS-1:
> >
> >Range: 0 to 999 ppm
> >Resolution: 1 ppm
> >Accuracy: +/- 10 ppm
> >Typical EMC Deviation: +/- 1% of Full Scale
> >
> >If I interpret this right, my TDS meter should read in steps of 1 ppm,
> >with no decimal point or tenths, etc., which indeed it does.
> >
> >That means the smallest increment it can *resolve* is 1 ppm.
> >
> >The display, with 3 digits, will show from 0 to 999.
> >
> >The accuracy of 10 ppm out of a full scale range of 1000 ppm is, indeed
> >1%.
> >
> >I don't know what "Typical EMC deviation" means. What's EMC?
> >
> >It's pretty clear why the TDS-1 isn't the best tool for measuring low
> >ppm CS. I'm attempting to use ruler where a vernier caliper would be
> >better. Still, it's been stable and seems more accurate than spec.
> >
> >So what are the specs for the PWT?
> >
> >From: http://www.hannainst.com/products/testers/pwt.htm
> >
> >Specifications:
> >
> >Range: 0.1 to 99.9 µS/cm
> >Resolution: 0.1 µS/cm
> >Accuracy (@20°C/68°F): ±2% Full Scale
> >
> >This suggests that the smallest step this instrument can resolve is one
> >tenth of a micro-Seimens per centimeter, and it can count up to a
> >thousand of them, or 99.9 µS/cm. So I presume the display should show
> >only 3 digits, one to the right of the decimal place.
> >
> >However, Ken writes:
> >> It says "Range is .01 to 99.9 uS" and "Accuracy is +/- 2% Full
> >> Scale" [but don't mention what full scale is] Now, you'd think that
> >> range and full scale would be the same thing, BUT, stick the PWT in
> >> water and add salt to see where the scale ACTUALLY pegs out. That
> >> would be at 999.9 NOT 99.9. If the meter were accurate to +/- 2% in
> >> its "range" they would have said it that way.
> >
> >It looks like Ken made a small mistake about the low end of the range.
> >That aside, does the PWT actually have a 4-digit display and behave as
> >Ken describes here? It *should* have only a 3-digit display and top out
> >at a reading of 99.9 uS.
> >
> >Whatcha say guys?
> >
> >Be well,
> >
> >Mike D.
> >
> >[Mike Devour, Citizen, Patriot, Libertarian]
> >[mdev...@eskimo.com ]
> >[Speaking only for myself... ]
> >
> >
> >--
> >The silver-list is a moderated forum for discussion of colloidal silver.
> >
> >Instructions for unsubscribing may be found at: http://silverlist.org
> >
> >To post, address your message to: silver-list@eskimo.com
> >
> >Silver-list archive: http://escribe.com/health/thesilverlist/index.html
> >
> >List maintainer: Mike Devour <mdev...@eskimo.com>
> >
> >
>
>
>
