url: http://escribe.com/health/thesilverlist/m61932.html Re: CS>SilverGen specs. From: Wayne Fugitt Date: Tue, 12 Aug 2003 19:52:44
> Evening Mike, >> I'll probably continue making that mistake forever:) > Real technicians don't worry about that because they make the same > mistakes. > They read "what you meant", not what you said. <grin> > Wayne Morning Wayne, It used to be called "mho". Everyone thought that was a stupid name and nobody used it. Then they changed it to Siemens, which sounds exotic so everyone uses it. They even marked it on the instruments, so I guess we're stuck with it:) Anyway, I guess it has a useful purpose. I just ordered some samples from Analog Devices to make a simple A/D converter to measure the cell voltage during the brew. I figure if I plot the conductance during the first half-hour or so, it should show a straight line until the respective ions reach the opposite electrodes. Then, when they start to combine and make oxide, the slope of the line should change. But that's ok. The initial slope shows the conductivity constant for the electrode configuration. We can use it along with the Faraday equation to tell what the actual ppm is. Here's an attempt to show a diagram: |\ | \ Initial Slope | \ | \ | \ | \ | \ | . Oxide Formation | - -. | - -. | - - -------------------- Now all we have to do is project the initial slope to intercept the X-axis, and draw a horizontal line from the final conductance value over to the Y-Axis. The two lines will intersect. Since we know the current and the cell volume, the intercept point should give us the final ppm of the cs. The circuit is very simple. If you are interested, go to Analog Devices, make a nice-sounding business name such as XYZ Consulting, and register for free samples. Their policy is generous, so you are not cheating. They want to give you free samples. Get two each of the following (The circuit uses one of each, but you always need spares:) AD7791 24-bit A/D, 19 usable bits AD8554 Quad Op Amp. 5nV/C tempco, 20pA input bias current ADR381 2.5V 5ppm/C reference NOTE: the samples link for the AD7791 points to the AD7788. I ordered them by mistake, and now it won't let me order the AD7791 since I have reached the limit. So the first try will only be 16 bits, which is probably good enough. When you go to order the AD7791, you will see a long string in the url that contains "AD7788". Just change it to AD7791 and it will take you to the correct page. The plan is to use a cheap optocoupler like the 4N26 for isolation and several lines off the parallel port for data transfer. A simple 9V wallwart will supply the power and give isolation probably good to 250V or so. I won't bother getting precision resistors for absolute accuracy - probably 1% is all that is needed. All we want is the slope of the line and we can do the rest in software. It will be in Pascal and run under dos, as usual. Time permitting, we should have yet another way to measure the ppm! Best Regards, Mike Monett -- 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>
