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>
