[time-nuts] Frequency Counter Choice

Thu Nov 12 15:41:50 UTC 2020

Hi Rex,

Putting my memory to the test, by opening up the 6681 I conclude my
memory failed me. On the other hand, I also discovered that my 6681 have
failed me, since the power supply fails to boot up. I consider a shorted
tantal to be potential cause, but I felt that smell of burnt electronics
which isn't a good indicator. No obvious electrolyt blown. Will
investigate later. Anyway, I obviously remember wrong, sorry.

Cheers,
Magnus

On 2020-11-12 02:05, Rex wrote:
> Stijn,
>
> Sorry to hear writing the string I read out hasn't worked so far.
>
> Magnus,
>
> Earlier in this thread (date 11/9) you said, "In order to write, you
> need to move the calibration jumper inside."
>
> Do you recall, is there any truth to that? I only saw it mentioned in
> that one message and I thought maybe you were thinking of the
> Unprotect command (:SYST:UNPR;) that must precede the PUD write.
>
> I'm not sure I really understand all the concepts of the process that
> the PC program drives to find the CALPLS parameter. If it actually
> iterates through many values of this parameter to make the tests, then
> there must be a GPIB way to set it without a power cycle. I'm just
> speculating.
>
> -Rex
>
> On 11/11/2020 6:23 AM, Magnus Danielson wrote:
>> Stijn,
>>
>> Have you tried to power-cycle your counter?
>>
>> May seem like a silly question, but just to make sure we are on the same
>> page.
>>
>> I have had similar problems, but did not debug them all. I do remember
>> that after writing the string successfully I had to power-cycle the
>> counter thought, before it got accepted and past Calibration Lost
>> message.
>>
>> When I did this I could not rule out that my programming to control the
>> USB-GPIB infterface was correct, as I bone-headidly wrote my own from
>> ground up. At the time all the stuff with GPIB was flimsy so that's why
>> I just did not use what was available.
>>
>> Cheers,
>> Magnus
>>
>> On 2020-11-11 11:46, Stijn wrote:
>>> Hi All,
>>>
>>> I am one of the lucky persons with a PM6681 that has lost it's
>>> calibration parameters.
>>>
>>> Unfortunatly it seems not as simple as sending: :SYST:UNPR; *PUD #261
>>> CALIBRATED: 2006-11-07, CALPLS: 4.25 ns, TMP: +22 °C
>>> This produces an error.
>>> If I sent: :SYST:UNPR; *PUD #253 CALIBRATED: 2006-11-07, CALPLS: 4.25
>>> ns, TMP: +22 °C
>>> Then the counter accepts the string and stores it.
>>>
>>> BUT, I still get the Calibration Lost message.
>>>
>>> btw. the LF at the end of the string you receive from the counter is
>>> added by the counter itself, so it does not count for the
>>> charactercount.
>>>
>>> I do have a different firmware version: PHILIPS, PM6681, 0, MAIN
>>> V1.05  27 Jan 1997 / GPIB V1.13  27 Jan 1997
>>>
>>> Stijn
>>>
>>> Op 09-11-2020 om 17:47 schreef Rex:
>>>> Magnus and Azelio,
>>>>
>>>> (About Pendulum or Fluke or Philips PM6681 Counter or equivalent
>>>> CNT-81)
>>>>
>>>> Here's a link to the thread where Magnus shared info in 2015.
>>>> https://time-nuts.febo.narkive.com/6WTFfsyN/pm6680-or-53131a-for-timepod
>>>>
>>>>
>>>> Your post is about half way down -- 2015-11-18 22:18:04 UTC
>>>>
>>>> Yesterday I dug out my GPIB-capable PC and sent a couple commands to
>>>> my Fluke PM6681.
>>>>
>>>> First I tried a basic one:
>>>> *IDN?
>>>> and got
>>>> PHILIPS, PM6681, 0, MAIN V1.09  26 JAN 2001 / GPIB V1.13  26 JAN 2001
>>>>
>>>> So connection is good. Interestingly the *IDN command description
>>>> says the PM6681 will return its SN but the SN field here is 0. Oh
>>>> well, not important.
>>>>
>>>> Then I sent *PUD?
>>>> and got
>>>> #261 CALIBRATED: 2006-11-07, CALPLS: 4.25 ns, TMP: +22 °C[LF]
>>>> where the [LF] at the end is not literal, it represents the line feed
>>>> char 0x0a.
>>>>
>>>> So in addition to the CALPLS value, it looks like they also save the
>>>> TMP in centigrade when the test was run. I wonder if the counter uses
>>>> that?
>>>>
>>>> So I hope if my counter ever lost this cal value, I could send it
>>>> this command:
>>>> :SYST:UNPR; *PUD #261 CALIBRATED: 2006-11-07, CALPLS: 4.25 ns, TMP:
>>>> +22 °C
>>>>
>>>> I don't plan to try that now. If it ain't broke don't fix it.
>>>>
>>>> There is one odd thing I see though. The last two of #261 is supposed
>>>> to say the string length is 61. But it isn't. I count it as 53 chars.
>>>> I don't know if this matters but the counter gave that number to me.
>>>> In the Programming Manual description page for *PUD, it gives a
>>>> couple examples and the #2nn values shown do have lengths that match
>>>> their string lengths.
>>>>
>>>> If it is useful to anyone, I made a version of just the *PUD command
>>>> description from the Programming Manual and put it here:
>>>> www.xertech.net/pm6681/PUD_cmd.pdf
>>>>
>>>> I also made a version of the Interpolater calibration process page
>>>> from the Service Manual. It can't really be used since it is obsolete
>>>> and the old DOS program seems unobtanium. It may give a few hints
>>>> what they were up to.
>>>> I put it here:
>>>> www.xertech.net/pm6681/interpolate_cal.pdf
>>>>
>>>> So thanks for pointing out that the *PUD command saved string is what
>>>> you lose if the memory backup battery dies. Reading and saving the
>>>> value is what I hoped for and now I've done it.
>>>>
>>>> If anyone has a PM6681 counter or equivalent with the "Cal.Lost"
>>>> message, sending my string above might be good enough to get it
>>>> working, though maybe not optimum.
>>>>
>>>> On 11/9/2020 1:58 AM, Magnus Danielson wrote:
>>>>> Thanks for the memory refresh.
>>>>>
>>>>> You can read the string using PUD?
>>>>>
>>>>> Do that and keep the result. PUD and PUD? is the magic in the
>>>>> counter,
>>>>> the rest is software and hardware outside of the counter for
>>>>> calibration.
>>>>>
>>>>> In order to write, you need to move the calibration jumper inside.
>>>>>
>>>>> Cheers,
>>>>> Magnus
>>>>>
>>>>> On 2020-11-08 23:01, Azelio Boriani wrote:
>>>>>> 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
>>>>>> <magnus at rubidium.se> 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
>>>>>>>>>> <magnus at rubidium.se> wrote:
>>>>>>>>>>> Hi,
>>>>>>>>>>>
>>>>>>>>>>> On 2020-10-22 19:13, Attila Kinali wrote:
>>>>>>>>>>>> On Thu, 22 Oct 2020 11:50:08 +0000
>>>>>>>>>>>> Giorgio Barinetti <giorgio at barinetti.it> 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
>>>>>>>>>>>
>>>>>>>>>>>
>>>>
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