[time-nuts] no 23:59:60 in TAC32

Bill Beam wbeam at gci.net
Sun Jan 1 16:20:54 EST 2006


On Sun, 01 Jan 2006 08:55:19 -0500, John Ackermann N8UR wrote:

>Bill Beam said the following on 12/31/2005 11:45 PM:
>> I have since compared UT+ raw data with TAC32 display
>> as follows:
>> 
>> UT+ raw data             TAC32 display
>> 
>> 12/31/05 23:59:59     same
>> 12/31/05 23:59:60     1/1/06 00:00:00
>> 12/31/05 23:59:60     1/1/06 00:00:01
>> 1/1/2006 00:00:00     1/1/06 00:00:01
>> 1/1/2006 00:00:01     same
>
>Isn't there an extra extra second there?  The UT+ is showing two :60s;
>shouldn't there  be only one?
>

No.  Each line of data above is not one line per second but is obtained
from sequential D70 camera photos of the computer screen.  Here the D70
takes about three photos per second.  The D70 'phase' and UTC is random.
Each line of data is from a snapshot of the computer screen.  To draw a
conclusion about reality from each snapshot requires knowledge of the
UT+, TAC32, computer display and D70 behaviour.

>Another thing I haven't dug into, but if the GPS is outputting the time
>at the *next* PPS signal, the sentence will appear to be ahead compared
>to a display that's attempting to show the *current* time.  Not sure if
>that's the case with TAC32.

The UT+ does output a time sentence for each second.  It also can (and does)
accept comands from TAC32 and respond at other times.  I don't
know how and exactly when the computer displays occurs.  The 1 PPS is also
sent on the RS232 port.

I can say for certain:  During the 12/31/05 23:59:60 and 1/1/2006 00:00:00
seconds the TAC32 was never correct.  At all other times (before and after) it was
correct.  The UT+ appeared to properly transition thru the leap second event.

>
>[ snip ]
[snip]


Bill Beam
NL7F
wbeam at gci.net or NL7F at amsat.org





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