[time-nuts] My Racal-Dana 1992

[Don Latham]

This is typical for an underdamped second order servo. The oscillation
is the penalty for a shorter settling time. A critically damped system
would not oscillate, but approach the final value smoothly in a slightly
longer time. It may have been designed for a slight overshoot...
Don

Ed Palmer
> Charles,
>
> My restart followed the same pattern as yours.  Start high, go higher,
> drift down, undershoot, recover.  The start was 10 MHz +51 counts, rise
> to +60 counts after 5 minutes, drift down to a minimum of +8 counts
> after 90 minutes and recover to +11 counts after 10 more minutes for a
> total shift of -40 counts (peak error of 4e-9).  I'm going to redo all
> these tests, but I think I'll be sticking to the external standard.
>
> Ed
>
> On 12/19/2011 12:33 PM, Charles P. Steinmetz wrote:
>> I wrote:
>>
>>> I put one of mine in standby earlier this afternoon.  I'll turn it
>>> back on tomorrow afternoon and report the results.
>>
>> (All results using 10 second gate):  Yesterday, the 1992 had been
>> reading "000.000000 E-3" stably for several days, and I switched it to
>> standby.  After 16 hours in standby, it came on 4 counts (4 mHz) high,
>> rose to 9 counts high in 5 minutes, hung there for about 15 minutes,
>> then slowly came down to 0 over the next hour.  It undershot 0 by the
>> tiniest bit (several minutes of occasionally reading "999.999999
>> E-3".  It has been reading 0 stably for over 3 hours now.
>>
>> So, mine also has an error with a long time constant when it comes out
>> of standby, but of lesser magnitude than Ed's (peak error 9x10 E-10).
>> I presume the magnitude of the error may change with ambient
>> temperature (in my case, 74.1 F throughout).
>>
>> Chuck speculated several days ago that the 9462 fine adjustment may be
>> an oven parameter (temperature?) adjustment.  The long, oscillatory
>> nature of the settling when the fine adjustment is changed does
>> suggest the action of a somewhat underdamped control loop.  Both the
>> ringing and the long time constant tend to support the oven
>> temperature hypothesis (but I am still reluctant to believe they would
>> design a frequency adjustment this way).
>>
>> Best regards,
>>
>> Charles
>>
>>
>
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-- 
"Neither the voice of authority nor the weight of reason and argument
are as significant as experiment, for thence comes quiet to the mind."
R. Bacon
"If you don't know what it is, don't poke it."
Ghost in the Shell


Dr. Don Latham AJ7LL
Six Mile Systems LLP
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