They probably do do it that way at the factory before final assembly. Keeping track of a calibration solution with thousands of meters dipping in and out would be a nightmare. Ode
At 09:38 PM 10/10/2003 -0700, you wrote: >Consider that parts of the system are the ratio of electrode surface area >to sample volume (and to mean distance between electrodes as well as >electrode material) and that the solutions are buffered for a reason, so >that interactions between sols and electrode materials are >controlled. Granted the ultimate result will be a voltage expressed on a >scale (LCD); but if a simple resistor would do it all, wouldn't they do it >that way? >For purposes of comparison, check out > >http://www.extech.com/newsite/instrument/categories/water/subcategory/water Meters.html > > >They have a wide array of instruments beyond the water stuff; their catalog >makes me drool!! >Take care, Malcolm > > 07:58 PM 10/10/03 -0400, you wrote: > >>url: http://escribe.com/health/thesilverlist/m63355.html >>CS>Measuring very high ppms >>From: Trem >>Date: Fri, 10 Oct 2003 15:27:45 >> >> > Mike, >> >> > The meter can easily be calibrated if you use the calibration >> > solution from Hanna. I got one box of 16 bottles of solution that >> > was defective and Ken got one of the bottles. It was the only >> > batch I have gotten that was defective in many years. I think you >> > can generally trust the solution to do what it was intended to >> > do....allow calibration of the PWT. >> >> > It will be very difficult to use a standard resistor since the >> > sensing electrodes are not easily accessible and the meter would >> > have to be disassembled to get at the electronics. Not something >> > the average person would want to do. And it's really not a good >> > idea when all one has to do is use the factory solution. >> >> > Trem >> >> Hi Trem, >> >> Thanks for the update. A calibration solution may be accurate, but >> there's no way to know that for sure. A mistake can occur during the >> dilution, it can be contaminated somehow, or perhaps some of the >> water may evaporate over time and change the reading. >> >> Steve Young posted a table of salt concentrations and resistor >> values some time ago. Ivan did also. >> >> The salt dilutions look scary. Any mistake would destroy the >> accuracy. I'm not good enough to tackle that. >> >> The resistor method is probably the most accurate, but it would >> require knowing the cell calibration factor. I don't have a Hanna >> yet, but I understand it uses a special multiple probe arrangement >> (the details escape me at the moment.) >> >> I understand the probes have a small area, so the actual resistor >> value would be larger than the standard table shows. Also the >> calibration constant might be different for each probe due to slight >> mechanical tolerances. >> >> I found a manual for the hi98308 at >> >> https://www705.vwh1.net/hanna4/downloads/instr/hi98308.pdf >> >> It shows how to replace the electrode assembly, HI73308 >> >> I don't know what is inside the electrode assembly, but from the >> pictures there seems to be a temperature sensor and two terminals >> marked (1) in the diagram. >> >> These terminals look quite large and sturdy. I'd have to get my >> Hanna to take a look, but there might be a simple way to gain access >> to them. >> >> If so, I can diddle with external resistors to find the calibration >> constant for the unit for various readings. Once I know the values, >> I can refer to them later if I think there might be a problem. >> >> Since little old ladies are allowed to change the electrode >> assembly, I don't think I would have any problems taking it apart as >> instructed. >> >> The instructions are given in the manual so people can change the >> electrode assembly when it becomes degraded. >> >> As a matter of curiosity, how do you tell the difference between a >> degraded cell and a bad calibration solution? >> >>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: [email protected] >> >>Silver-list archive: http://escribe.com/health/thesilverlist/index.html >> >>List maintainer: Mike Devour <[email protected]> >> >> >> >> >>--- >>Incoming mail is certified Virus Free. >>Checked by AVG anti-virus system (http://www.grisoft.com). >>Version: 6.0.516 / Virus Database: 313 - Release Date: 9/1/03 > >--- >Outgoing mail is certified Virus Free. >Checked by AVG anti-virus system (http://www.grisoft.com). >Version: 6.0.516 / Virus Database: 313 - Release Date: 9/1/03 >
