>I have truly enjoyed 'reading the mail' on this group. > > However, I need some help or a 'refresher' on the lingo. > > I am a Clinical Cardiac Electrophysiologist but in a bygone millennium, I > received a BEE and a MSEE from Georgia Tech before I went to Medical School. > > 'tau'? > > Thanks, > > Joe > WB4BPP
> 'tau'? Joe, Short answer: tau is the measurement duration. Long answer: The accuracy, or resolution, of a frequency measurement depends very much on the duration, or "averaging time", of the measurement interval. Also, the stability of an oscillator typically depends on the duration over which the measurement is made. For example, some oscillators are noisy from second to second, but look much more stable when averaged day to day. Others may be very stable minute to minute but drift over the span of hours or days (averaging doesn't help, it makes it worse). So the Greek letter t, or tau, refers to this averaging time. You see if most often in all those log-log Allan deviation plots (tau is the x-axis). You'll also often hear the words "short-term" or "long-term". There's no fixed rule about what's short and what's long. It's mostly a way to acknowledge that clock behavior at small averaging times may be quite different than behavior at large averaging times I bet the same is true for you with EKG's. You might learn one thing by looking at a minute of data (short-term); and learn quite something else by looking at trends in data taken each day for the span of a week, or even once a year over the span of several decades. So it is with oscillators: they have short-term wiggles and long-term trends. See also the Allan deviation of my heart beat, for tau from 10^0 to 10^3 seconds, near the beginning of: http://www.leapsecond.com/ten/clock-powers-of-ten-tvb.pdf http://www.leapsecond.com/ten/ /tvb _______________________________________________ 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.
