Old story about the PM6681 (18 Nov 2015, thread: "PM6681 and Timelab") where a sort of calibration procedure is described: the PUD command is NOT a calibration command. PM6681 programming manual, page 9-127: PUD Protected User Data...This is a data area where the user may write ANY data up to 64 characters... If the user can write any data, how can it be a calibration command or calibration data area? Better watch out those 3V coin cells, we will never get the real calibration commands/procedure. I have tried with the disassembled firmware, no way. The visible strings of GPIB commands are all described in the programming manual, so nothing useful.
On Sat, Nov 7, 2020 at 3:31 AM Magnus Danielson <[email protected]> wrote: > > Hi Rex, > > I need to dig in the archive to refresh my memory. I don't recall > precisely, but I think I recalled that the manual indirectly describes > the calibration data string. > > I have learned a few things from Pendulum, but I did not have the right > tools at hand to set things up. > > There was a more recent setup that could use more modern generators, but > the trick was still the same. You lock the generator and counter to the > same frequency, then you set the generator to a small offset frequency > from 10 MHz, which is 9.999 MHz as I recall it. This slowly sweeps > through all the phase-relationships between the reference oscillator and > the counter input, thus sweeps the interpolator phase. It then chooses > the calibration constant giving the lowest RMS error, as this is the > best compensation for the hardware min-point. All this is free from > memory. Then that value with calibration date is written into memory. If > I recall correctly 2.21 ns is a typical value. > > I have PM6681 in need of calibration, and as I recall it I was able to > program it enough for the calibration error warning did not show up. > This not to say it was actually calibrated. > > At some point I will return to that project. The generator I used did > not support that offset frequency, but I have others that do. Also, my > crapiola GPIB programming needs attention. My intention is to share the > fruits of this project when it comes to that. The lab has been in > shambles for too long, but shaping up slowly and nicely. > > Cheers, > Magnus > > On 2020-11-05 09:30, Rex wrote: > > Hi Magnus, > > > > Just catching up on list messages and saw this one from you. > > > > I have a Fluke PM 6881 counter. I don't think I've ever seen a > > description of a method for reading/restoring these battery backed up > > calibration constants. I looked for a way, as losing them is something > > I've worried about. Not that it has happened and I did replace the > > battery once. > > > > Is doing this described in one of the manuals? Sounds like it is > > through GPIB? I'd greatly appreciate any pointers to info or other > > details you might provide. > > > > I did see, in the service manual, a short description of a method for > > Interpolator calibration that seems to be for making these > > calibrations. Seems if the saved cal values get lost, the counter will > > display "CaL.LOSt". The cal procedure is driven by an old DOS program > > (that I've never found) and requires a: PM5768 Pulse gen, PM5193 LF > > Sig Gen, good 10 MHz, all GPIB controlled from the program. Never saw > > more details but sounds messy. If there is description of GPIB > > commands for reading/setting cal values, I missed them. > > > > thanks for mentioning this and anything more you can provide > > -Rex > > > > On 10/29/2020 5:37 PM, Magnus Danielson wrote: > >> Hi, > >> > >> I second this. You can read the calibration data out of the counter and > >> save. I've done some experiments with that, but nothing conclusive, but > >> I blame my lack of patience and not a proper setup. > >> > >> Do replace the battery, it is cheap and relatively easy to do. > >> > >> Would you loose this calibration, through a little GPIB commands one can > >> write a fake value in. This will however not produce the best resu. The > >> calibration routine actually runs an off beat frequency and then test > >> different values, and look for least RMS value, because it is the > >> calibration point. I've not had time to replicate all that, but I did > >> manage to write the fake value in and at one time get rid of the CAL > >> LOST warning. > >> > >> Cheers, > >> Magnus > >> > >> On 2020-10-29 14:17, Azelio Boriani wrote: > >>> For those who have the PM6681 (aka CNT81): check the 3V memory backup > >>> cell and replace it before the dreaded calibration lost (CAL LOST) > >>> will appear on the LCD. Replace the coin cell with great care (with > >>> the counter powered up), see the service manual for the procedure. > >>> <https://archive.org/details/FLUKE_PM6681_Service_Manual> > >>> > >>> On Fri, Oct 23, 2020 at 6:17 PM Magnus Danielson > >>> <[email protected]> wrote: > >>>> Hi, > >>>> > >>>> On 2020-10-22 19:13, Attila Kinali wrote: > >>>>> On Thu, 22 Oct 2020 11:50:08 +0000 > >>>>> Giorgio Barinetti <[email protected]> wrote: > >>>>> > >>>>>> Choices are many, but I'll try to avoid the "older" machines lile > >>>>>> 5370 or 5335. The 531xx series seems nice ( money apart ) > >>>>>> But again : which one between the 3 ? 53131, 53132 or 53181 ? > >>>>> Maybe try to get hold of one of the Philips (later licensed to > >>>>> Fluke) PM6680 or PM6681? These are more common in Europe than > >>>>> in the US, so the big US dominated websites/forums/.. don't > >>>>> mention them that often. Solid devices that can be had as low > >>>>> as 300€ if you are willing to wait, 500-800€ is the usual going > >>>>> price. The SR620 is the workhorse that drives a lot of the > >>>>> time and frequency metrology worldwide and can be had new and > >>>>> used (new on http://thinksrs.com goes for 800-2000€ used). > >>>>> > >>>>> If you go for a new one, I would consider looking at the > >>>>> Pendulum CNT-90 and CNT-91. (Pendulum is the company that > >>>>> took over Philips frequency counter business and the CNT-90 > >>>>> is the continuation of the PM668x line, also sold as PM6690 > >>>>> by Fluke) > >>>> Let me correct on the history and geniology there. > >>>> > >>>> Philips had a instrument making side called Philips Industrier > >>>> Järfälla > >>>> that did a range of measurement instruments. Later they joined forces > >>>> with Fluke. Later Philips felt that the business unit was a bad fit to > >>>> stay in Philips, so they sold it off to become a separate company > >>>> which > >>>> became Pendelum. Pendelum was really the business unit with people etc > >>>> through that process, and the Fluke relation and rebranding continued. > >>>> Naturally Pendelum moved out of the Philips Industrier Järfälla office > >>>> over to Bälstabro (both locations in north of Stockholm) as it was > >>>> sold > >>>> off. Pendelum also managed to rebrand their counters to Tektronix, > >>>> which > >>>> mainly consisted of cosmetic changes to get the look and feel. > >>>> Pendelum > >>>> was operated for many years like this, some of their production in > >>>> Pajala, where as other where done in Bälstabro. Later they reshaped > >>>> the > >>>> production so that it moved to Poland where it remains. Pendulum was > >>>> sold to Spectracom and was operated as a subsidary for a while, until > >>>> they shut operation down. > >>>> > >>>> The CNT-80/81 (PM 6680 and PM6681) production went on as long as they > >>>> had the timing ASIC. The CNT-90 (100 ps) was developed to the > >>>> CNT-91 (50 > >>>> ps), where the later replaced the CNT-81 (50 ps). They aimed to do the > >>>> CNT-92, but could not at that time do it with the same technical > >>>> setup. > >>>> They also had the Wander Meter WM-10 which aided in testing telecom > >>>> sync. After some testing, I suggested they would broaden the > >>>> product to > >>>> handle more signals and that is when they mostly firmware upgraded > >>>> it to > >>>> the WM-11, and first time I tested the WM-11 the second '1' was cut > >>>> out > >>>> from another '10' print and put over the '0'. Also, it was still under > >>>> development. Several years later they where still going back to my > >>>> list > >>>> of feedback. They later did a revamped this into a new instrument with > >>>> even improved capabilities such as interfaces boards. This was later > >>>> sold off to Calnex which sells it as Sentinel, which is a great > >>>> product > >>>> for telecom operators. > >>>> > >>>> I still have contact with some of the Philips/Fluke/Pendelum staff and > >>>> owner. > >>>> > >>>> Cheers, > >>>> Magnus > >>>> > >>>> > >>>> > >>>> _______________________________________________ > >>>> time-nuts mailing list -- [email protected] > >>>> To unsubscribe, go to > >>>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > >>>> and follow the instructions there. > >>> _______________________________________________ > >>> time-nuts mailing list -- [email protected] > >>> To unsubscribe, go to > >>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > >>> and follow the instructions there. > >> > >> _______________________________________________ > >> time-nuts mailing list -- [email protected] > >> To unsubscribe, go to > >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > >> and follow the instructions there. > >> > >> > > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
