Hi all, A few points to recap the issue of meters for measuring CS concentration...
The Hanna Instruments TDS-1 and PWT meters are both conductivity meters, period. The differences between them are in the way they are calibrated and their sensitivity. If you are going to be fairly serious about your CS making or if you just don't mind spending the extra $35, the PWT is by far the better choice: 1) It is calibrated in microSiemens, a unit of electrical conductivity, not ppm. This helps to remind you that you're *not* making a direct measurement of ppm. Properly calibrated, its readings are independent of which of the various chemical salts is used in the calibration solution... 2) It is 10 times more sensitive than the 0-1000 ppm reading TDS-1. So, instead of trying to make readings at 1/2% of full scale, you're attempting to read at 5% of full scale. Still not ideal, but much better matched to the measurements we're trying to make. The reason so many of us have the TDS-1 is that it was the first one we found out about. It is cheaper -- about $15 vs. $50. As has been pointed out, neither meter is sensitive enough for really accurate measurements. No meter costing $50 or less will be. However, experience shows that *both* units are quite usable as long as you understand their limitations. The *only* thing you can really use these meters for is to: 1) Measure the relative quality of your distilled water. 2) Cross check the concentration of your product from batch to batch ***PROVIDED*** that you keep things the same as much as you can. If you standardize your CS making procedures and send some samples off for testing using other analysis methods, you can then roughly correlate your conductivity readings with ppm for your process -- as long as you don't change anything! Apparently some folks processes don't lend themselves to using conductivity based measurements. They will tell you not to waste your money on either meter. Others of us have found it useful enough as a cross-check and for testing our water. It is also very useful to meter the current flowing through your cell. This is more difficult to compare with other people's results, but gives you very good consistency from run to run. It's also cheap, with perfectly serviceable multimeters available for $20 at Radio Shack or similar stores. Lastly, as for Stephen's remarks about Trem's "marketing" efforts, I'm sure Trem won't mind at all if we remind folks that they can also get their PWT or TDS-1 meters at the Hanna Instruments site: http://www.hannainst.com/products/testers/pwt.htm http://www.hannainst.com/products/promo/tdspromo.htm Really, if things get out of hand I'll try to step in. If something on the list offends you, please tell me in private e-mail. Be well, Mike Devour silver-list owner [Mike Devour, Citizen, Patriot, Libertarian] [[email protected] ] [Speaking only for myself... ] -- The silver-list is a moderated forum for discussion of colloidal silver. To join or quit silver-list or silver-digest send an e-mail message to: [email protected] -or- [email protected] with the word subscribe or unsubscribe in the SUBJECT line. To post, address your message to: [email protected] Silver-list archive: http://escribe.com/health/thesilverlist/index.html List maintainer: Mike Devour <[email protected]>
