I read the article on PID on Wikipedia last night. I do not fully
understand it, but I see/learning some of the relationship.
I did a test on the FRS-C rubidium. The average frequency was 10 000
000.0025 hertz at the rubidium 10 turn dial dial setting of 255, and the
control voltage out of the pot was 1.7900 volts. I recorded the
frequency for a while and then changed frequency to see how long it took
to get there. I changed the dial setting to 516 (3.5800V) and it took
8 seconds for the rubidium to change frequency and settle on a average
frequency of 10, 000 000.0131 hertz.
I did another test and the rubidium dial setting was 000 for a control
voltage of 0.068V and the average frequency was 9 999 999.9933 hertz.
The dial setting was changed to 721 for a control voltage of 4.9999V and
the average frequency was 10 000 000.0216 hertz
The measurements were taken with a HP5370B time interval counter
referenced to a HP5065A rubidium oscillator. The data was recorded
using a ProLogix GPIB adapter. The data was recorded in 10 minute
intervals with the data coming in at one measurement a second. When the
frequency was changed, I allowed 20 minutes between the recordings.
Based on the above measurements, Said, can you recommend some starting
point for the DAC Gain, EFC Scale, and the EFC Damping ?
Also from previous measurements, I know this particular rubidium was at
9x10E-11 at 0.1 sec, 1.8x10E-11 at 1 second, 5x10E-12 at 10 seconds,
1.5x10E-12 at 100 seconds, 7x10E-13 for 1000 seconds, and 2.5x10E-13 for
10000 seconds - running on a Shera GPS controller - which the PIC was
modified for this rubidium (it was changed from a 30 second time
interval measurement to 120 seconds, and Shera changed the sensitivity
of the PIC to 1X10-9/volt).
Thanks to Don and Scott for the ops info.
Thanks
Brian KD4FM
On 7/27/2010 2:57 PM, saidj...@aol.com wrote:
Hi guys,
it may help to increase DAC gain to get faster recovery times from "bumps"
etc.
On an OCXO, the frequency recovery from an upset should happen within a
couple of minutes, definitely less than 15 minutes to achieve frequency lock.
The phase recovery (to 0ns offset) may take a couple of hours to do.
If it takes a very long time to recover, then I think increasing the DAC
gain, or alternatively the EFCS and PHASECO together may help.
Wikipedia has some good instructions on how to optimize PID type controller
gains to get the fastest response with minimal noise...
Also, please make sure to disable temperature compensation when using the
external source, unless a thermistor is connected to the board, sensing the
Rb temperature. Otherwise the temperature compensation may add noise due to
it scaling the gain to huge values due to the missing thermistor.
bye,
Said
In a message dated 7/27/2010 09:58:41 Pacific Daylight Time,
true-...@swbell.net writes:
My experience is very similar to Scott's. I ran many hours with both an
LPRO-101
and FE-5680A. The disciplining behavior and Fury settings were the same
for
either Rb. My biggest disappointment was the recovery time due to various
common
or intentional bumps or especially, after power loss. I also had to let
the
"system" settle in for a week before acceptable tracking smoothed out. Any
long
term slope to the EFC trace (gpscon) caused excessive hunting and this
didn't
settle down until the Rb was VERY stable. My gpscon TI and stddev was
virtually
the same as Scott's if I had EFCS set to 1.0 to 1.5 but recovery was
unacceptable (maybe 24-hours) so I usually ran at 2.0 or 3.0 with
slight degrading of stddev to around 3.2. This EFCS setting allowed a much
better settling time around 3-hours.
DACG= 1000
EFCS = 2 to 3
EFCD = 50 (25 allows little better settling time)
PHASECO = 15 (I favor 10 Mhz over PPS)
Regards...
Don
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