as with this very "noisy" thread about my adventures, (after many weeks of toying around with my used K2015) i am walking around a large unknown building called "calibration and adjustment" of DMM trying to go inside and play. and while looking at some ebay stuff, i stumbled on something familar, this VREF unit called the D105 that claim to have 2ppm stability (some of you know it has a famous thread in this forum). and i came back to re-read some of the stuff in there. edit** i have parts i do not understand, hopefully somebody who knows more can enlghten
having experienced the kind of noise i dislike, i saw the last few posts where blackdog showed his quad REF based on linear VREF vs the D105 comparing stability and noise. and then on closer look i started to notice something about the D105 plot, which now on 2nd pass, i started to understand what all the accuracy and low noise could possibly mean.
i (hijacked 2 plots from that thread) superimposed 3 plots, blackdogs' quad VREF 10v, 1 of my best 10v NPLC100 (plot 15-Dec30-0101_LOG.ods) shorted test run and D105's 10v (in correct order as it appears in the pic, top middle and bottom). but as i didnt want to squeeze more of the K2015 plot into a smaller volt scale, i have to offset it and show it as double the original Y-axis size (the left side still showing the 2000nV Y-axis size). for explaination, i have sized both yellow plots to have similar Y scale size, which is the original 2uV per div, my shorted plot is magnified 1uV per div. the X scale is nearly the same for all 3 plots at 6min per div or 1 hour total.
if the VREF have very high noise, it will add this noise/uncertainty by its high rms noise value? or by its pk-pk ? is my understanding here correct?
so if i imagine (if i want to calibrate or adjust this DMM in this 10v scale) my DMM shorted STDEV uncertainty = 0.3uV, D105 STDEV noise = assume @ 2uV, the instance of measuring this D105 uncertainty = 2.3uV ? and if i use a better VREF source like blackdog's, if the uncertainty is assume @ 0.4uV, then this instance of measuring the uncertainty is 0.7uV ? do i sound right in theory?