Hi I believe we are talking about material impedances here rather than electrical impedance. One of the weird things about this is that frequency (as in frequency accuracy) *can* be a contributor to the resultant error. Thus my original question about just what the concern actually is…..
Bob > On Apr 8, 2018, at 4:52 PM, Brooke Clarke <bro...@pacific.net> wrote: > > Hi Daniel: > > If you're concerned with accuracy of impedance measurements you might want to > spent a lot of time studying "The Impedance Measurement Handbook", it's the > bible for this. The way the measurement is made has a huge impact on the > accuracy. For example using a vector network analyzer to measure an > impedance that's not near 50 Ohms causes poor results. > http://prc68.com/I/Z.shtml#KeyDocs > For frequencies low enough to use 4 Terminal Pair, that's the way to go. > http://www.prc68.com/I/HP4274_4275_LCR.shtml#MeasMtd > > -- > Have Fun, > > Brooke Clarke > http://www.PRC68.com > http://www.end2partygovernment.com/2012Issues.html > > -------- Original Message -------- >> I´m a long time time-nuts lurker (I posted here just a dozen times). I make >> a few impedance measurement systems for material analysis (i´m a single man >> shop doing custom hardware for clients). Usually they´re based around a >> STM32F4 / F7 microprocessor: DAC generates sine signal (1-400KHz), ADCs >> measure them back, a few calculations later we have modulus / phase. I >> always used internal ADCs and DACs (12 bits each). >> >> I now want to use external ADCs and DACs with more bits to push the limits, >> but i´m afraid that the poor performance of the STM32 PLL that drives the >> clock will get in the way, so I plan to drive the "load" of both DAC and >> ADCs from an external signal derived from a TCXO using a clock divider. >> >> To get some sense of how much things are improving (or not) I need to >> somehow measure these clocks and get a meaningfull measurement about how >> good (or bad) they are. >> >> The tools I have are a Hameg HM8123 with a 10MHz OCXO I shoehorned inside >> and a Picotest U6200A with original OCXO. I can log period information from >> both using serial/USB port. I can make a histogram of the data. I don´t >> have any better idea about what to do and would like to hear from you :) >> >> Daniel >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.