Re: CS>Hanna Meter Model Number From: Dan Nave Date: Sun, 17 Oct 2004 19:56:48
> Ode and Mike, > As you indicate, the range that we would use the PWT is at the > lower end of the meter's range. The accuracy, when calibrated at > full scale, along with the linearity of the response, makes the > error large when compared to the smaller readings at the low end > of the scale. > I would suggest, then, that we increase the accuracy of the > readings in the range that we will be using them. The way to do > this is to calibrate the meter at the maximum uS reading that we > are likely to encounter, say, between 25 to 30 uS. This will throw > off the accuracy at readings substantially above this level, but > will increase the accuracy between 0 and 30 uS. So, unless the > linearity of the meter's response between 0 and 30 uS is > particularly bad, we would approach an accuracy of near +/- 2% of > full scale, with full scale being 20 or 30 uS (our new "full > scale" value). If the linearity between 0 and 30 uS is > particularly bad, then we will not achieve this accuracy, and the > accuracy of the meter with normal calibration will also be bad; in > short the meter would be useless for our purposes... > Dan Hi Dan, Good suggestions - but the standard Hanna calibration solution is 84uS. It could be diluted two or three times, and then you have the problem of maintaining better than 2% accuracy. That may be difficult to do. NIST-traceable calibration solutions are available that may be in our ppm range, but they are very expensive. I think the real issue is making sure the process is working properly and getting good repeatability. In my case, I have a good constant current source and I use the Faraday equations to predict when it will hit 22 ppm, which is when the gray whiskers start to form on the cathode. A typical brew takes 6 hrs or so, and I may be a bit late returning from shopping or some other distraction may occur. So I don't always stop it exactly on time, but that really doesn't matter much. Then I reverse the polarity and let it run another hour or so. I am confident the resulting cs is above 20 ppm, but I don't know by how much. One way to tell is the reaction on your teeth after holding the cs in your mouth for ten minutes. I get a raspy feeling when I move my tongue along the teeth, and any plaque falls off sometime later. So I know it's getting in there and killing bacteria. So I'd suggest calibrating a Hanna at several points using the Faraday equations and plot the results. If you use low current density, the results should be reasonably accurate up to 22 ppm or so. Of course, Ken's suggestions on temperature control should be followed. Also, I'd probably stick with using only one Hanna. Like they say, a man with one watch always knows what time it is. A man with two watches is never certain:) Best Wishes, Mike Monett -- The Silver List is a moderated forum for discussing Colloidal Silver. Instructions for unsubscribing are posted at: http://silverlist.org To post, address your message to: silver-list@eskimo.com Silver List archive: http://escribe.com/health/thesilverlist/index.html Address Off-Topic messages to: silver-off-topic-l...@eskimo.com OT Archive: http://escribe.com/health/silverofftopiclist/index.html List maintainer: Mike Devour <mdev...@eskimo.com>
