[time-nuts] HP5065A digital clock info
eb at telight.com
Wed Sep 28 19:04:32 UTC 2011
Yes Bert, the "three-board" type uses the counting scheme that you
described, but the other type is as I described. On the "two-board"
version the "set" mode is permanent, and there is no external counter
or logic. The 555 is a normally a one-shot for stretching the narrow
1 PPS pulses from the Rb system, but oscillates at around 60 or 600
Hz (precision not important) during setting, accomplishing the same
result. I think this design is the later one - someone at HP may have
had a "eureka" moment and realized that this simpler approach could
eliminate a board full of logic.
In a message dated 9/27/2011 9:10:25 P.M. Eastern Standard Time,
Sorry Ed you are wrong. Hp generates a 65 Hz signal that advances the
internal prescaler 49 counts and uses the 1 pps output to stop the 65 Hz
output at count 49 and waits for the internal 1 pps to go to 50 and
second digit one count. Sounds crazy but it works, makes the clock advance
in perfect sync with the internal second generator.
In a message dated 9/27/2011 8:16:43 P.M. Eastern Standard Time,
After looking at the manual, I realized that I did look at this
series of parts way back, but didn't get the connection because I
thought it would have to be a type that takes 1 Hz input rather than
50/60 Hz. I see now that they were used in the "set" mode, bypassing
the internal divide by 50/60.
The clock module I have is the type with a 555 used as a one-shot for
normal operation, or as an oscillator for fast setting. I think this
is probably the newer of the designs, since it is simpler.
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