[time-nuts] Temex LPFRS-01

Wed Apr 18 13:30:25 UTC 2012

The disadvantage of the digital adjustment is that it's meant to be 
"permanent", the MPU also modifies it's internal EEPROM cell that stores 
the new value. Too many adjustments bear the risk of the used EEPROM 
cell wearing out, which would be inevitable in a disciplining process, 
and an unknown reaction of the firmware to such an event.
Initially, I thought too it would be more convenient to use the serial 
interface for disciplining (this being one of the criteria favoring the 
LPFRS) but after a detailed reading of the specs it's clearly unusable 
as such.
A dual pronged approach, with the external analog input rerouted to the 
C-Field adjustment circuit (with a narrower control range, equivalent to 
that of a few digital steps), and the digital "fine" adjustment used 
just when the analog range exhausts, should be the right one.

Did your lock output test succeed?

On 4/18/2012 1:25 PM, Azelio Boriani wrote:
> I'm not using the analog input but the serial port, yes, this doesn't
> improve the 1E-11 step but at least I skip the first A/D conversion. The
> direct access to the C-field control seems necessary but I like to have my
> stuff in the original state. My LPFRS is very rusty so I can drop my "keep
> it original" rule.
>
> On Wed, Apr 18, 2012 at 10:29 AM, MailLists<lists at medesign.ro>  wrote:
>
>> That would be the tougher part, as, with highest probability, the external
>> analog adjustment is first AD converted in the MPU (AIN4) summed with the
>> internally stored fine adjustment value, and then applied to the C-Field
>> correction, through an external DAC8800.
>> As both conversions are 8 bit, the obtained resolution of 1E-11 is
>> insufficient to discipline the unit with enough accuracy, it was just meant
>> to adjust the working frequency.
>>
>> In the last day of the easter holidays I opened one up, and now I'm trying
>> to grasp the inner workings... time allowing.
>>
>>
>> On 4/12/2012 7:50 PM, Azelio Boriani wrote:
>>
>>> Interesting... have to check my LPFRS now: only tested for the lock
>>> indicator when received and then put aside to complete first the
>>> "discipliner".
>>>
>>> On Thu, Apr 12, 2012 at 5:00 PM, MailLists<lists at medesign.ro>   wrote:
>>>
>>>   Well, the saga continues...
>>>> A replacement part (for which a thorough check was specifically asked)
>>>> has
>>>> arrived. It boasts a "Checked OK" written with a marker pen on the label.
>>>> Promising...
>>>> With high expectations, the necessary connections were made, power
>>>> applied, and after warming up it locks at precisely 9.999,817,1 MHz...
>>>> bummer.
>>>> Sometimes, for (yet) unknown reasons, it unlocks again, and, if the
>>>> frequency adjustment trend is upwards, it locks again at ~10.000.000 MHz.
>>>> The lock signal is active even at higher temperatures - that's quite
>>>> better
>>>> than the first unit, but after a power cycle the story repeats... mostly
>>>> the wrong frequency comes out, but, on the brighter side, it's locked.
>>>>
>>>>
>>>> On 3/18/2012 10:26 AM, MailLists wrote:
>>>>
>>>>   Yes...
>>>>> Thank you, and the others, for the suggestions for cleaning/reviving the
>>>>> unit, but I can't recommend to my friend to keep a pile of rust (if
>>>>> water damage really is the problem) advertised as an used working item.
>>>>>
>>>>> Regards,
>>>>> bbg
>>>>>
>>>>>
>>>>> On 3/17/2012 4:10 PM, Azelio Boriani wrote:
>>>>>
>>>>>   LPFRS from fluke.l? OK, then open it up and clean it, the LPFRS from
>>>>>> fluke.l suffers from high humidity/water immersion and usually are very
>>>>>> rusty inside. I have received one that was very bad but after cleaning
>>>>>> with
>>>>>> tetrachloroethylene (translated with google) it is working properly,
>>>>>> maybe
>>>>>> it will fail soon but now works. I complained with fluke.l and he
>>>>>> refunded
>>>>>> me without asking to ship back the LPFRS.
>>>>>> TIP: handle with extreme care an opened LPFRS, there is a flexible PCB
>>>>>> that
>>>>>> holds the DB9 connector that can tear in the corners.
>>>>>>
>>>>>> On Sat, Mar 17, 2012 at 10:59 AM, MailLists<lists at medesign.ro>   wrote:
>>>>>>
>>>>>>   Hello all,
>>>>>>
>>>>>>>
>>>>>>> a friend purchased from the bay a<subj.>   in the LPRO configuration.
>>>>>>> After
>>>>>>> some problems encountered during the first power ups, he asked for
>>>>>>> help -
>>>>>>> I'm passing the questions further...
>>>>>>> After about 9 minutes of warm-up from room temperature (22°C) the lock
>>>>>>> signal goes low, but after a short time starts to switch low/high with
>>>>>>> decreasing low periods, until it remains high with short low pulses,
>>>>>>> spaced
>>>>>>> at about 2 seconds. After power-down, and sufficient cooling time, the
>>>>>>> cycle repeats.
>>>>>>> First step was to reapply the thermal interface to the integrated Al
>>>>>>> radiator, which helped a bit, the time during which the unit is locked
>>>>>>> growing slightly.
>>>>>>> Next step was forced cooling, which helped more, so the lock loss
>>>>>>> could be
>>>>>>> attributed with high probability to elevated operating temperatures.
>>>>>>> The
>>>>>>> temperature of the base plate (integrated Al radiator) at which lock
>>>>>>> gets
>>>>>>> lost is about 40°C, so for a reasonable operation it should not pass
>>>>>>> about
>>>>>>> 36°C, at which the power consumption raises to about 17W. That also
>>>>>>> means
>>>>>>> that for a 1°C/W heat sinking - obtainable with a larger passive HS or
>>>>>>> active cooling - operation above 30°C ambient gets practically
>>>>>>> impossible
>>>>>>> (except refrigeration, Peltier, etc.).
>>>>>>>
>>>>>>> Any further help or suggestions are welcome.
>>>>>>>
>>>>>>> Regards,
>>>>>>> bbg
>>>>>>>
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