[time-nuts] Temperature stability for Thunderbolt: results

Mark Sims holrum at hotmail.com
Wed Jan 26 15:33:47 UTC 2011

The KA4 fast autotune has a lot of limitations that make it unsuitable for general purpose use.  It bypasses a lot of the initialization and work of the full (KA) autotune.  It depends upon a stable temperature environment and the proper initial state of the hardware.  Most people should just use the standard KA command to autotune the PID.  

There are also KA1, KA2, and KA3 commands that bypass successively more and more of the autotune cycle.  There are also the KW and KM commands that select a canned fast and slow set of PID parameters.  

Here are Warren's notes on KA4:

> There a couple of things one should be aware of when using the KA4
> quick autoTune.
> When starting the KA4 cycle:
> 1) make sure the temperature error is positive, Otherwise the first
> cycle is sometimes in error
> 2) make sure the Fan PWM speed is at its Average reading, Otherwise the
> cycles will not be symmetrical
> 3) At the completion of the Autotune cycle make sure the recovery
> looks correct. This provide a good check to see if it got the correct
> PID values. If not repeat.
> The Positive recovery peak should be about the same height or just a
> bit higher than the previous positive tune cycle peak and the next
> negative recovery cycle should be a 1/4 or so the size and the
> finial return to the set temperature should be near right on within
> .010 deg or so.


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