[time-nuts] Frequency Counter Choice

Wed Nov 11 14:23:58 UTC 2020

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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