On Tue, 06 Nov 2012 02:14:04 +0100, Magnus Danielson <[email protected]> wrote:
>Hi Bob, > >On 11/05/2012 01:30 PM, Bob Camp wrote: >> Hi >> >> As a practical example - a SR620 will look much better reading it's own >> reference than it will looking at almost anything else. That said, it's >> still a good idea to make sure the counter looks good reading it's own >> reference. If it doesn't look good, then you need to fix something. > >I agree that this is a good self-test strategy, it usually gives a good >clue if something is really bad or not, but as I pointed out, it doesn't >give a fair idea of the measurement noise floor. > >Cheers, >Magnus A lot of counters support a self check mode which counts the internal reference. I tracked down an interesting problem in a Tektronix DC505 by wiring the internal channel A input to measure the internal reference. Noise from the display multiplexing was getting into the level shifter located before the last 4 integrated counter stages and causing spurious counts. Based on the documentation and how it did not match the actual circuit, I suspect Tektronix fiddled with the values in production until it seemed to work but never figured out the real problem or back annotated the documentation. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
