Hi Steve, I suspect the problem is surface area of the Hanna sensing electrodes are quite small and you're using 1 sq. cm electrodes spaced 1 cm apart as the reference in your calculations. If you look into the arch at the bottom of the meter you will see two small circles near the top of the arch. If one could measure the diameter and determine area I think this could be worked out but it's difficult to measure because it's so hard to get at. It seems they are about .2 inches in diameter and .2 inches apart.
I leave further calculations to you. I'm just happy using calibration solution. And disassembling the meter and reassembling it has its own problems. It's not worth taking the chance of ruining the meter to save a little money. Regards, Trem ----- Original Message ----- From: "S & J Young" <[email protected]> To: "Silver List" <[email protected]> Sent: Friday, June 13, 2003 7:46 PM Subject: CS>Calibrating your PWT > Greetings, > > Recently there have been postings regarding PWT calibration. On a CS > website is a table showing the mg of salt in a liter of water to produce > various readings: > > "The following table shows a typical conversion of the PWT readings: > > µS/cm Reading Resistivity mg/L of NaCl > 99.9 10 Kohms 48 > 10 100 Kohms 4.3 > 1 1 Mohms 0.4 > 0.1 10 Mohms 0.04" > > (sorry if the columns don't line up) > > The 10 uS one is of most interest to us. So, how could one make their own > calibration solution without access to a precision scale? For example, > knowing the distilled water temperature, could one saturate the solution > with NaCl and have it be a predictable mg/L strength - then dilute it down > to 4.3 mg/L? Chemists - what say ye? > > Scheme #2: The PWT meter comes apart fairly, easily exposing the two > connections to the electrodes. So it is easy to bridge those connections > with a precision resistor and note the digital display reading. I tried > that using the resistor values above and did not get the readings shown > above. So I am wondering if the sampling volume is not one cubic cm and > Hanna scales the reading to make it as though it was exactly one cubic cm? > If that is the case, then does anyone know the correct test resistance > (actually reciprocal resistance, mhos)-to-display factor? > > Thanks, > --Steve Y. > > > > > > > > -- > 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]> > > > >
