[time-nuts] (no subject)

Poul-Henning Kamp phk at phk.freebsd.dk
Sun Jan 25 12:28:14 EST 2015

In message <B260783A-8A00-4053-B2E5-E2462746D446 at gmail.com>, Didier Juges write
>Without a D term, PI loops can be unstable when the gain (P) is
>increased. If you will, with a large error, the correction will
>itself be large and as the system corrects itself, it may overshoot
>the target value, going into a low (or high if you really blew it)
>level oscillation around the target value. The D term slows it
>down just enough and minimizes that overshoot while maintaining a
>high gain (low steady state error) and a fast response.

Before anybody gets any ideas that causes them to waste a lot of time:

D terms are themselves very temperamental because they, by definition,
amplify measurement jitter noise.

In the precision time/frequency domain, D-terms are almost never

Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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