On Mon, 20 Feb 2017 19:29:55 +0000, you wrote: >... > >The A/D in a 6½ digit instrument by definition must have at least >22 bits (2^21 = 2097152 + sign bit) and if we scale things so the >least significant bit is 5 microvolts, we have a full scale voltage >of 2^21 * 5e-6V = 10.48576V. > >QED: Uncertainty on your 6½ digit meter on a 10V signal will always >be at least ± 5 microvolts. > >If you do the same math for a true 8½ digit DVM, you need a 29 bit >A/D converter (2^28 = 268435456 + sign) which means you can use 40 >nV as stepsize yielding 10.73V range, and thus in teory get ± 40nV >measurements.
I just have a minor quibble with the above which does not alter your point. There is no requirement for an ADC output to be a power of 2. Slope integration and voltage-to-frequency designs commonly use or used BCD counters to produce a power of 10 output. I remember when supressing negative zero was a new feature. _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
