Cor, A voltage reference is excellent, you can't argue with that (is is calibrated?).
Here is a message that was rejected for to much quoted stuff: Cor, Like I said, it is fine as long as there is not a lot of money riding on it. That accuracy in the spec sheets is "readings no more accurate than..." Something to consider. If I was choosing a battery technology for the next 3 years production, or something like that, I would pay close attention to the accuracy and get the data acquisition tools calibrated. If you are comfortable with your measurements being as far off as they may be, then I am too. It is simply a good idea to know this when you are taking absolute measurements. As you note relative measurements will be better at least between small swings, you can't assume linear. When it comes time to make a decision based on this meter, be sure to ask your self what it it wasn't correct? I just got back a rotameter from calibration. These are as simple an instrument as you could want, a tapered channel and a weight that gets lifted by the flow. It has marks you look at to gauge the weight. How hard could that be to get good readings? The accuracy is rated at ±2% of the reading. At 2 GPM, it is off by 17% of the allowable error, by the time it reaches full scale of 10 GPM it is almost out of tolerance 98.7% of the 2% is used up. Last time it was calibrated only 26% of the tolerance was used up at 10 GPM. There is no good explanation for it. This true for all measurements, there is always a certain amount of, "no good explanation for it." DMMs are no different. If they stayed right then no one would ever calibrate them. When you look at the cute curves the Chinese shows us on cell performance, you really have to wonder. There is no information at all on how or with what the readings are taken. No standard for the testing is produced if you ask for it. They graph out voltage over SOC and we have no idea if the can even measure ±10mV accurately. On Thu, Dec 19, 2013 at 7:43 PM, Cor van de Water <[email protected]> wrote: > Hi Mike, > This is an old meter and it has been sitting for a long time in the same > environment (my garage) meaning that the day after day readings will be > orders of magnitude more accurate in *relative* accuracy (between the days) > than the *absolute* accuracy that you are calculating for this meter. > In addition, I am using the same meter to follow the charging cells and > the discharging cells. And I am plotting both graphs. > If there was more than 1mV of drift at a particular day of measurement, it > would show up as a bump or valley in *all* graphs and so I would > immediately spot it. I stand by my claims that I can see the cells > self-discharge, especially since I have been measuring them since about 2 > months and most of them have dropped more than 0.1V in that time - some > much more, some less, discharge has about a 1:2 variation between cells. > > BTW, the 77 cannot be overvolted since it is auto-ranging, so the 3.2xx > range will automatically switch to 03.2x range at around 3.25V, which means > that up to that voltage I can see a 1mV resolution (not accuracy, but in > relative measurements it pretty much *is* mV accurate) while at higher > voltages I can only see 10mV steps. > > Charging current is simply determined from the difference between supply > voltage and the actual cell voltage, divided by the resistance of the pair > of resistors that I wired between them. Current is not so critical - it is > a lower current than I wanted, but it confirms that the self-discharge is > pretty low. However, I see a curious effect when a cell hits 3.225V that > the voltage increase suddenly flattens, apparently hitting the flat range > of the SoC curve. > > Regards, > > Cor van de Water > Chief Scientist > Proxim Wireless Corporation http://www.proxim.com > Email: [email protected] Private: http://www.cvandewater.info > Skype: cor_van_de_water Tel: +1 408 383 7626 > > -- > Put this question to yourself: should I use everyone else to attain > happiness, or should I help others gain happiness? > *Dalai Lama * > > Tell me what it is you plan to do > With your one wild and precious life? > Mary Oliver, "The summer day." > > To invent, you need a good imagination and a pile of junk. > Thomas A. Edison< > http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html> > > A public-opinion poll is no substitute for thought. > *Warren Buffet* > > Michael E. Ross > (919) 550-2430 Land > (919) 576-0824 <https://www.google.com/voice/b/0?pli=1#phones> Google > Phone > (919) 631-1451 Cell > (919) 513-0418 Desk > > [email protected] > <[email protected]> > -------------- next part -------------- > An HTML attachment was scrubbed... > URL: < > http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20131219/0df1aeeb/attachment.htm > > > _______________________________________________ > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > http://lists.evdl.org/listinfo.cgi/ev-evdl.org > For EV drag racing discussion, please use NEDRA ( > http://groups.yahoo.com/group/NEDRA) > > _______________________________________________ > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > http://lists.evdl.org/listinfo.cgi/ev-evdl.org > For EV drag racing discussion, please use NEDRA ( > http://groups.yahoo.com/group/NEDRA) > > -- Put this question to yourself: should I use everyone else to attain happiness, or should I help others gain happiness? *Dalai Lama * Tell me what it is you plan to do With your one wild and precious life? Mary Oliver, "The summer day." To invent, you need a good imagination and a pile of junk. Thomas A. Edison<http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html> A public-opinion poll is no substitute for thought. *Warren Buffet* Michael E. Ross (919) 550-2430 Land (919) 576-0824 <https://www.google.com/voice/b/0?pli=1#phones> Google Phone (919) 631-1451 Cell (919) 513-0418 Desk [email protected] <[email protected]> -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20131220/411f2125/attachment.htm> _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
