[time-nuts] My Racal-Dana 1992
iovane at inwind.it
iovane at inwind.it
Mon Dec 19 16:26:17 EST 2011
Well, the 1992, at least mine, is sensitive to rapid changes of the ambient
temperature, while ignores quite well the slow changes such as those due to the
cycling of the heating system of the house (which is well evident in the
recorded temperature of the LPRO heatsink).
And I see that the passage from standby to operation might be assimilated to a
rapid change of ambient temperature.
I attach an explanatory graph from the same dataset which produced my
yesterday's curve (which was a bit smoothed). This is a one-day un-smoothed
curve (the 3td day).
There is no trace of the house heating system, but there are some short peaks
and dips of 2 or 3 counts (10 sec gate) which were a mystery until I did
specific tests that day. The variations in readings were due to the fan of my
tower PC !!
The PC was located under the workbench, and the counter on top of the PC. The
LPRO and its power supply instead were on the workbench. Turning the PC on
caused a drop of some 3 counts, and the counter takes a few minutes to settle
down to the right count while the PC is running. Turning the PC off caused a
raise of some 2 counts, and the counter again takes some minutes to recover the
The attached graph shows the sequence of the specific test, which is in the
middle of the figure (peaks = PC has been turned on, dips = PC has been turned
off). Beyond the central test sequence, you could also notice that that day I
turned off the PC at about 01:04, and on at about 21:20.
To Ed: the behavior of your counter looks normal.
>>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).
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