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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