> -----Original Message----- > From: Ode Coyote [mailto:[email protected]] > Sent: Sunday, 27 October 2002 3:55 a.m. > To: *Silver-List* > Subject: RE: CS>TDS/PWT meters > > > > Both TDS meters and the PWT do the same thing the same way. Unless > colloidal particles are actually touching, or perhaps very > very close > together, they won't register at all with either meter. > The best you can do is guesstimate the particulate content > with a laser > pointer and add a fudge factor to the reading. > Further, the Hanna people have seen fit to mix metaphors > with their specs > for the PWT. > 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.
Ken, Hanna's spec reporting is industry standard. Full scale and range are two different things. The range is a description of an interval of numbers in which the unit will perform within spec. Full scale (reading) is largest number within the range. Error in transducer output is normally minimised by processing the 'least squares best fit straight line' (normally greatest in the middle of the range) and is reported as percentage full scale (this is because some meters have more than one range and thus the full scale reading and error is altered accordingly). So the FUD is unfounded. The fact that the meter can read outside the range is of no consequence. More expensive meters would report an out of range reading in this event. > That said, at least the meters are repeatable within > themselves, but don't > expect any two to read the same thing any more than two different > laboratories have a tendency to tell you the same thing > within +/- 10 PPM. > If any two PWTs get within 10 microsiemens of each other, > that would be > very very good and at least somewhat accidental. > I guess that "state of the art" means just that....Art > "Looks like" an > object. > > I asked my researcher friend about the discrepencies [He > has a huge muliti > million megabuck lab at his disposal including mass > spectrometers, TEMs and > such]. Basically, he says that to get any sort of > 'accurate' measurement > in the lower parts per million ranges, it takes huge samples and the > averaging of several tests. > ..and the term 'accurate' is STILL subject to definition. The absolute determination of ppm as silver ions etc. may be difficult, but the measurement of conductivity is not. Discrepancies between different meters can be overcome by multi-point calibration within the expected range. > It's best not to use any those 'standards' to flesh out an > arguement. > [everyone will be wrong or if someone is right, no one will > know who that is.] > > In our case, where there are no dosing standards at all and > elimination/adsorption rates vary minute to minute, +/- 2% > of 999.9 is OK. Well, you may be happy with +/- 20uS (+/- ~25ppm silver) as a reading but I certainly would not be, but your argument is false anyway as shown above. > Your taste buds, a laser pointer and a 'strong...not so > strong' resolution > might do just as well. > It's Not very objectively informative but well within the > 'one glug or > three' range of practical application. > > No matter how tall a mountain actually is, no matter if > it's measured from > sea level or it's lowest accompanying valley in millimeters > or feet..... > the top is still the top and it still looks like a mountain. A mountain to an ant is what to an elephant? Ivan. > > Ken -- 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: [email protected] Silver-list archive: http://escribe.com/health/thesilverlist/index.html List maintainer: Mike Devour <[email protected]>
