[time-nuts] Time Interval Measurement Hint

Brooke Clarke brooke at pacific.net
Tue Mar 8 16:19:13 EST 2005


Hi Tom:

The SR620 start is raw GPS 1 PPS.  The SR620 stop is the rising zero 
crossing of the FTS4060/S24 1 MHz output.
Set for averaging 1,000 readings (a little over 16 minutes). 

Just before and after the power cycle I'm using the PRS10 10 MHz as the 
SR620 reference frequency because I was concerned that the FTS4060 was 
acting strange.

There's no way to say what the offset was prior to the power cycle since 
the SDEV was up to 400 ns.  Too soon to tell about after the power 
cycle, but it's looking extremely good.  See the plot at:
http://www.pacificsites.com/~brooke/pdf/sn1227_CF565.pdf

Have Fun,

Brooke

Tom Van Baak wrote:

>Brooke,
>
>Interesting clues.
>
>What input triggering were you using for the SR 620
>channels before and after the power cycle?
>
>Do recall the approximate 4060 frequency offset
>before and after power cycle?
>
>/tvb
>
>----- Original Message -----
>From: "Brooke Clarke" <brooke at pacific.net>
>To: "Discussion of precise time and frequency measurement"
><time-nuts at febo.com>
>Sent: Tuesday, March 08, 2005 10:51
>Subject: [time-nuts] Time Interval Measurement Hint
>
>
>  
>
>>Hi:
>>
>>For a number of months I've been trying to get the C field set on a Cesium
>>    
>>
>standard.  This is a continuing learning experience.  In order to help in
>setting the GPS elevation mask angle (now at 50 degrees) I started
>monitoring a number of parameters, but now have stopped most of them except
>for the standard deviation of the time interval.  I'm taking 1,000 readings
>of the 1 PPS to Cesium standard 1 MHz zero crossing and the SR620 counter
>provides not only the mean value but also the standard deviation.
>  
>
>>It turns out the the standard deviation is a great indicator that
>>    
>>
>everything is working correctly.  If this value gets to 40 nano seconds or
>higher there's a problem.  Recently I tweaked the beam current on the
>FTS4060 (open loop, center beam current, close loop) the green lock LED
>turned on in a number of seconds, BUT the SDEV value was many hundreds of
>ns!  Even after giving the FTS4060 overnight in the morning the SDEV was
>still way high.  But unplugging the mains AC power for 15 seconds fixed the
>problem, probably be resetting the micro computer.
>  
>
>>I highly recommend watching the SDEV value when making precision
>>    
>>
>measurements.
>  
>
>>Have Fun,
>>
>>Brooke
>>
>>--
>>w/Java http://www.PRC68.com
>>w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml
>>http://www.precisionclock.com
>>
>>
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>>time-nuts mailing list
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>>
>>
>>    
>>
>
>
>
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>  
>

-- 
w/Java http://www.PRC68.com
w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml
http://www.precisionclock.com




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