[time-nuts] How to measure Allan Deviation?
Dr Bruce Griffiths
bruce.griffiths at xtra.co.nz
Tue Oct 24 01:03:26 EDT 2006
Didier Juges wrote:
> Hi Bruce,
>
> Dr Bruce Griffiths wrote:
>
>> Didier Juges wrote:
>>
>>
>>> Dr Bruce Griffiths wrote:
>>>
>>>
>>>
>>>> Didier Juges wrote:
>>>>
>>>>
>>>>
>>>>
>>>>> I do not understand the signal on the rear trigger outputs. At the
>>>>> moment, I have a single 10 MHz sine signal fed to the START channel, and
>>>>> the 5370 is set to TI, MEAN, SAMPLE SIZE 1, + TI ONLY, START channel
>>>>> triggers on rise and STOP channel triggers on fall, and START COM is
>>>>> selected. The instrument displays about 60 nS (fairly stable, 150 ps
>>>>> jitter) or so at the moment. The rear START trigger shows a negative
>>>>> going pulse (400uS wide, at 62 mS rep rate), with the rising edge
>>>>> (positive going) synchronous with the 10 MHz signal and the phase is
>>>>> adjustable using the *STOP* trigger level! When I trigger the scope on
>>>>> the falling edge of the START trigger output, the 10 MHz signal seems to
>>>>> drift, and the trigger setting has no effect, except that if adjusted
>>>>> too far, the instrument stops updating the display.
>>>>>
>>>>> Apparently, the START trigger adjustment has no effect on the timing of
>>>>> the rear START trigger output, but will cause the display to freeze if
>>>>> the START trigger is set to either extreme, even though the START
>>>>> trigger output on the rear does not change.
>>>>>
>>>>> The STOP trigger output works the opposite: it responds to the START
>>>>> trigger level. Could it be that the outputs are reversed on my instrument?
>>>>>
>>>>> I am not sure this is a complete description, and maybe there is an
>>>>> obvious answer that I am missing, but I am perplexed.
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>> Didier
>>>>
>>>> The 5370A processor can swap the front panel START and STOP inputs over
>>>> via an ECL multiplexer on bord A22.
>>>> The rear panel outputs reflect the actual selected START and STOP events
>>>> not necessarily the signals connected to the front panel START and STOP
>>>> connectors.
>>>>
>>>> Bruce
>>>>
>>>>
>>>>
>>>>
>>> Good catch, but I thought that only came to play when +/-TI was
>>> selected, and I have selected +TI ONLY?
>>>
>>> Didier
>>>
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>>>
>>>
>>>
>> Didier
>>
>> That's not the way I interpret the manual or the article on the 5370 in
>> the HP journal.
>>
>> +TI ignores all STOP inputs until after the START event.
>> +-TI START before STOP is a positive time interval STOP before START is
>> a negative time interval. Internal logic implements a precedence detctor
>> so that the relative order of accepted start and stop events can be
>> determined.
>>
>> Bruce
>>
>>
>>
> You are correct of course, I *assumed* the counter would automatically
> swap the START and STOP rear trigger outputs as needed when the +/-TI
> mode was selected, but that in +TI ONLY mode, there should be no need to
> swap START and STOP, therefore the rear trig outputs would be fixed.
>
> I have a lot more reading to do, it's a big manual. I have a pdf of it
> on my web site and I printed all this week end, big job!
>
> Can you send me the pdf of the HP journal about the 5370?
> If it's too big to attach, can you upload it to my web site?
> dns: ftp.ko4bb.com
> login: manuals
> password: manuals
>
> Thanks
>
> Didier
>
>
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>
Didier
Will do as soon as I find the particular issue again.
May take a little while as I haven't looked at it for a year or so.
Bruce
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