> >From the archives, on Tue, 18 Apr 2000 06:51:16, M. G. Devour wrote > (Re: the TDS-1 meter) > > > My experience has been that the circuit is stable over time and, if > you calibrate it at, say, 50 ppm or so, it will deliver reasonably > accurate and repeatable measurements in the range in which we are > interested.
Erwin asks: > Sounds like a winner. And just how do I go about calibrating it at, > say, 50 ppm or so? Or better yet, at say 10 ppm? > > What do I use as a standard? My dear wife measured out table salt on an analytical balance at work. We dissolved it in a measured volume of water at room temperature. Thus I have a 250 ml bottle with 12.5 milligrams of salt in it, or 50 mg/liter, which is by definition the same as ppm. > After it is calibrated, is it in a 1:1k relationship from zero up to > 50ppm? I don't know if there is a zero offset, but good distilled water reads zero and I can easily see it climb gradually to 10 or whatever... The TDS-1 is good for repeatability between runs, but it is *NOT* a primary instrument. It can be calibrated to other measurements, but any number of things might affect the reading if you start changing your process. > Does temperature affect the calibration? One of the nice things about the Hanna conductivity based meters is they are temperature compensated over a fairly wide range. A better choice is the Hanna PWT (Pure Water Tester). It's more expensive (~40 to 50 bucks), but has about 10 times the sensitivity of the TDS-1. So instead of trying to read in the bottom 1 percent of the instrument's range, you're at least in the bottom 10-20 percent. But again, either of these devices only measure conductivity, which is indirectly related to concentration with a lot of other possible variables thrown in. Useful for process control, but not all that valuable if you're already monitoring process current. Hope that helps. Be well, Mike D. [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]>
