Re: [time-nuts] Visiting Greenwich

[Peter Monta]

Hi Dave,

The Harrisons are indeed at the observatory; also look for a regulator
pendulum clock in the octagon room.  I'm not quite sure whether it was
running when I was there some years back.

Could it hurt to petition the observatory's powers-that-be for a little hut
or something at the ITRF meridian?  :-)

If you do get to Bletchley Park, give the National Museum of Computing a
look-see as well (it's just a short walk).  I believe both facilities have
benefited from recent infusions of money and support, which is great.

Cheers,
Peter
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Re: [time-nuts] Visiting Greenwich

[Tom Van Baak]

Hi Dave,

Last year a more up to-date and highly-technical version of the meridian 
mystery was published:

"Why the Greenwich meridian moved"
http://link.springer.com/article/10.1007/s00190-015-0844-y

See especially figure 3. The PDF is here:
http://link.springer.com/content/pdf/10.1007%2Fs00190-015-0844-y.pdf

When I was in Greenwich last year I made these plots to show the old/tourist 
meridian (red x) and the true meridian (green x):
http://leapsecond.com/pages/meridian/map-100.gif
http://leapsecond.com/pages/meridian/map-101.gif

I also brought a laptop and 3 GPS receivers with me and collected 3 x 20 
minutes of NMEA data while sitting on the old/tourist line. Sure enough, the 
mean error approached 102 meters:
http://leapsecond.com/pages/meridian/simul-5.gif

/tvb

- Original Message - 
From: "Dave Martindale" 
To: "Discussion of precise time and frequency measurement" 
Sent: Monday, July 04, 2016 8:14 PM
Subject: Re: [time-nuts] Visiting Greenwich


> Wouldn't that be "un pied dans chaque hemisphere" in France?
> 
> I visited the Greenwich observatory a number of years ago, but it was after
> 5 PM and all of the exhibits were closed for the day.  So we only saw the
> repeater clock and the meridian line.  One interesting fact:  A GPS
> receiver will not agree with the line set into the concrete about where
> zero degrees of longitude is located.  The GPS prime meridian is somewhere
> nearby, within the park, but not at the marked line.
> 
> An explanation for this (that I found at the time) is that the line in the
> ground at the observatory is defined as zero longitude in whatever geodetic
> ellipsoid and datum the British were using at the time.  The GPS zero
> longitude line is at zero in WGS84.  Apparently WGS84 is defined to agree
> with the older British datum in longitude *at the equator*, but the two
> ellipsoids use different models of the earth's axis and so the two
> zero-longitude meridians do not agree at Greenwich's latitude of ~50 N.
> 
> Google found this more recent article:
> http://www.thegreenwichmeridian.org/tgm/articles.php?article=7 that has
> more interesting (and more detailed) information about the difference in
> the prime meridian definitions.
> 
> Dave
> 
> On Tuesday, 5 July 2016, jimlux  wrote:
> 
>>
>> One must, of course, take a picture with one foot in each hemisphere.
>> (Unless, you would follow the French, in which case, the Paris meridian is
>> the only true meridian, and then you'd have one meter in each
>> hemisphere...
>>

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Re: [time-nuts] Visiting Greenwich

[Dave Martindale]

Wouldn't that be "un pied dans chaque hemisphere" in France?

I visited the Greenwich observatory a number of years ago, but it was after
5 PM and all of the exhibits were closed for the day.  So we only saw the
repeater clock and the meridian line.  One interesting fact:  A GPS
receiver will not agree with the line set into the concrete about where
zero degrees of longitude is located.  The GPS prime meridian is somewhere
nearby, within the park, but not at the marked line.

An explanation for this (that I found at the time) is that the line in the
ground at the observatory is defined as zero longitude in whatever geodetic
ellipsoid and datum the British were using at the time.  The GPS zero
longitude line is at zero in WGS84.  Apparently WGS84 is defined to agree
with the older British datum in longitude *at the equator*, but the two
ellipsoids use different models of the earth's axis and so the two
zero-longitude meridians do not agree at Greenwich's latitude of ~50 N.

Google found this more recent article:
http://www.thegreenwichmeridian.org/tgm/articles.php?article=7 that has
more interesting (and more detailed) information about the difference in
the prime meridian definitions.

Dave

On Tuesday, 5 July 2016, jimlux  wrote:

>
> One must, of course, take a picture with one foot in each hemisphere.
> (Unless, you would follow the French, in which case, the Paris meridian is
> the only true meridian, and then you'd have one meter in each
> hemisphere...
>
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Re: [time-nuts] Z3815A Unofficial Docs

[Brad Stockdale]

Hello all,

   After some time and some twists and turns in life, I've found time
to work with my GPSDO's again. I've added two Z3815A's to my
collection, after wanting to do so for a number of years. After
reading through the listserv's historical posts to re-acquaint myself
with the units (and the hobby in general), I've found references to an
unofficial documentation CD, from Kit S. I've tried emailing Kit, but
have received bounces. Was wondering if anyone knows of a new email
address. Seems like bytecan may have had some issues and is no longer
providing services. Just trying to track down whatever information I
can on the Z3815A's, above and beyond the basic connections (which I
found by sorting through a half dozen other posts on the list; thank
goodness for the archives). I understand that the command set is very
similar to the SCPI command set used with the Z3801A's. Just more
curious about what other information is out there on these.

Thanks!

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Re: [time-nuts] Visiting Greenwich

[Bob]

Hi Dave,

Yes, as many mentioned all the clocks are up the hill at the Observatory, and 
very much worth the trip.  As you mention you are with your family, I would 
like to add that yes I did cajole my family to the NMM and the Observatory, but 
also to Bletchley Park (just a short train ride outside London) and Bletchley 
Park was easily the most memorable.  There are wonderful volunteer guides, and 
many interesting devices that you can get up close to.  Bletchley was more like 
visiting a working lab than a museum.  I think every time nut would enjoy 
Bletchley quite a bit.

https://www.bletchleypark.org.uk/ 

Cheers,

Bob

> On Jul 4, 2016, at 6:31 PM, Dave Martindale  wrote:
> 
> I am in London England at the moment, playing tourist with the rest of my
> family.  I want one day to be a visit to the National Maritime Museum at
> Greenwich, which includes the Royal Observatory Greenwich.  I am
> particularly interested in seeing Harrison's H1 through H4, plus other
> high-precision mechanical timekeepers (pendulum clocks, etc).
> 
> I know they are at the NMM - their web site shows some of them.  But where
> are they located on the site?  The NMM has a large main building down near
> the Thames, while the Royal Observatory and related buildings are on the
> top of a hill further inland in Greenwich Park.  Are the chronometers and
> other precision timekeepers on display somewhere in the Royal Observatory,
> or down in the main NMM building?  I've spent an hour or two browsing web
> sites without finding this particular bit of information.
> 
> I figure there must be list members who have visited the NMM, and know
> where the precision timekeepers are actually displayed.
> 
> Thanks,
> Dave
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Re: [time-nuts] Visiting Greenwich

[Tom Van Baak]

Do visit the main maritime museum down by the river. But the Harrison clocks 
are at the observatory, where the ball drops, about a 10 minute walk up the 
hill. Map here:

http://leapsecond.com/pages/meridian/

Besides H1-H4 see if you can get a peek at Clock B:

http://leapsecond.com/pend/clockb/

/tvb

- Original Message - 
From: "Dave Martindale" 
To: "Discussion of precise time and frequency measurement" 
Sent: Monday, July 04, 2016 3:31 PM
Subject: [time-nuts] Visiting Greenwich


>I am in London England at the moment, playing tourist with the rest of my
> family.  I want one day to be a visit to the National Maritime Museum at
> Greenwich, which includes the Royal Observatory Greenwich.  I am
> particularly interested in seeing Harrison's H1 through H4, plus other
> high-precision mechanical timekeepers (pendulum clocks, etc).
> 
> I know they are at the NMM - their web site shows some of them.  But where
> are they located on the site?  The NMM has a large main building down near
> the Thames, while the Royal Observatory and related buildings are on the
> top of a hill further inland in Greenwich Park.  Are the chronometers and
> other precision timekeepers on display somewhere in the Royal Observatory,
> or down in the main NMM building?  I've spent an hour or two browsing web
> sites without finding this particular bit of information.
> 
> I figure there must be list members who have visited the NMM, and know
> where the precision timekeepers are actually displayed.
> 
> Thanks,
> Dave
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Re: [time-nuts] Visiting Greenwich

[jimlux]

On 7/4/16 3:31 PM, Dave Martindale wrote:

I am in London England at the moment, playing tourist with the rest of my
family.  I want one day to be a visit to the National Maritime Museum at
Greenwich, which includes the Royal Observatory Greenwich.  I am
particularly interested in seeing Harrison's H1 through H4, plus other
high-precision mechanical timekeepers (pendulum clocks, etc).

I know they are at the NMM - their web site shows some of them.  But where
are they located on the site?  The NMM has a large main building down near
the Thames, while the Royal Observatory and related buildings are on the
top of a hill further inland in Greenwich Park.  Are the chronometers and
other precision timekeepers on display somewhere in the Royal Observatory,
or down in the main NMM building?  I've spent an hour or two browsing web
sites without finding this particular bit of information.

I figure there must be list members who have visited the NMM, and know
where the precision timekeepers are actually displayed.



Royal Observatory...

http://www.rmg.co.uk/see-do/we-recommend/attractions/john-harrisons-marine-timekeepers

http://www.rmg.co.uk/sites/default/files/rmg_map_2015_-_rog.pdf



One must, of course, take a picture with one foot in each hemisphere.
(Unless, you would follow the French, in which case, the Paris meridian 
is the only true meridian, and then you'd have one meter in each 
hemisphere...)



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Re: [time-nuts] Visiting Greenwich

[John Ackermann N8UR]

When I was there (10+ years ago) the timekeeping stuff was at the observatory, 
which is just a few minutes walk up from the NMM.  Both sites are fascinating 
and well worth spending some time.

I took a tour boat to get to Greenwich from central London -- it's the end of 
the line and if you work the times right you can get on another one for the 
return trip.  The boat ride was also well worth it.

Have fun!
John

> On Jul 4, 2016, at 6:31 PM, Dave Martindale  wrote:
> 
> I am in London England at the moment, playing tourist with the rest of my
> family.  I want one day to be a visit to the National Maritime Museum at
> Greenwich, which includes the Royal Observatory Greenwich.  I am
> particularly interested in seeing Harrison's H1 through H4, plus other
> high-precision mechanical timekeepers (pendulum clocks, etc).
> 
> I know they are at the NMM - their web site shows some of them.  But where
> are they located on the site?  The NMM has a large main building down near
> the Thames, while the Royal Observatory and related buildings are on the
> top of a hill further inland in Greenwich Park.  Are the chronometers and
> other precision timekeepers on display somewhere in the Royal Observatory,
> or down in the main NMM building?  I've spent an hour or two browsing web
> sites without finding this particular bit of information.
> 
> I figure there must be list members who have visited the NMM, and know
> where the precision timekeepers are actually displayed.
> 
> Thanks,
> Dave
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Re: [time-nuts] Visiting Greenwich

[Dan Rae]

Dave, it's been a few years since I was there but the Harrison clocks 
are not in the main part of the museum but in the Observatory which is a 
bit to the South and East if I remember right.  Both are well worth a 
look, but the Harrisons are magic of course.


Dan

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[time-nuts] Visiting Greenwich

[Dave Martindale]

I am in London England at the moment, playing tourist with the rest of my
family.  I want one day to be a visit to the National Maritime Museum at
Greenwich, which includes the Royal Observatory Greenwich.  I am
particularly interested in seeing Harrison's H1 through H4, plus other
high-precision mechanical timekeepers (pendulum clocks, etc).

I know they are at the NMM - their web site shows some of them.  But where
are they located on the site?  The NMM has a large main building down near
the Thames, while the Royal Observatory and related buildings are on the
top of a hill further inland in Greenwich Park.  Are the chronometers and
other precision timekeepers on display somewhere in the Royal Observatory,
or down in the main NMM building?  I've spent an hour or two browsing web
sites without finding this particular bit of information.

I figure there must be list members who have visited the NMM, and know
where the precision timekeepers are actually displayed.

Thanks,
Dave
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Re: [time-nuts] python or matlab/octave for Keysight instruments?

[Poul-Henning Kamp]

In message 
, Keenan Tims writes:

>I've had good luck with python-ivi:

I wrote and use this:

https://github.com/bsdphk/pylt

Very basic, works with the Prologix GPIB adapter but general enough to
also use other carriers (USB, TCP/IP etc)

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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Re: [time-nuts] python or matlab/octave for Keysight instruments?

[Keenan Tims]

PyVISA depends on the NI binary VISA libraries, which you then need to
get to work with your instruments. Getting this all working is an
endeavour I quickly gave up on.

I've had good luck with python-ivi:
https://github.com/python-ivi/python-ivi which should work well with
modern instruments that support USBTMC or VXI11 (SCPI-over-IP), and I
wrote an adapter for the Keithley 2000 serial interface that was also
pretty easy. It can also use PyVISA as a backend if you've got some
'real' GPIB gear you need to deal with. The only real gotcha is that
if your instrument is not supported 'natively' you will need to write
the object-oriented driver code yourself. This is not particularly
difficult, and most of the standard device classes need very little
modification, but it might be a turn off if you just want to throw a
few commands at the devices.

This same python-ivi project also contains lower-level VXI11 and
USBTMC drivers you can use if you prefer.

On 2 July 2016 at 09:09, jimlux  wrote:
> I'm looking for a *simple* *portable* software library to do some
> control/data acquisition from either python or octave for Agilent/Keysight
> gear, specifically over the USB or Ethernet interfaces.
>
> the "Keysight IO Libraries Suite CD " is, I think, Windows only
>
> I'm fine with writing the SCPI commands and parsing the output, I'm just
> looking for the "glue" between "send_message_to_instrument" or
> "read_message_from_instrument" and the instrument itself.
>
>
> Sort of like the python interfaces to the Prologix Ethernet/GPIB
> controllers.
>
> I've got the whole numpy/scipy infrastructure already installed, if that's
> relevant.
>
> Is PyVISA reasonably easy to work with, or is it one of those "once you've
> spent 6 weeks recompiling the kernel and finding all the libraries from 4
> different sources, it works great"..
>
> There's also the Agilent Command Expert which seems to provide a matlab and
> python interface, but, looks like "windows only" and I'm in a cross platform
> environment (OS X, Ubuntu, Windows) (Hmm, KCE isn't as nice an acronym as
> ACE)
>
>
>
>
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[time-nuts] Looking for Sulzer 2.5 Manual

[Richard Mogford]

Does anyone have a Sulzer Frequency Standard Model 2.5 manual?

I have the schematic, but not the manual.

I also have the Model 5.0 manual.

Thanks.

Richard
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Re: [time-nuts] How to properly characterize 32kHz oscillators manually and with a microcontroller?

[Pete Stephenson]

I ended up doing just this and it worked out nicely. Using the timer
hardware as a counter freed up the CPU for other tasks and could run
in the background so I wouldn't miss any ticks. It turns out that
using the built-in timer hardware was a lot easier than using external
"jellybean" logic to accomplish the same thing, even if it took a bit
of reading to better understand it.

I whipped up a quick-and-dirty Arduino sketch that I've made available
at https://github.com/heypete/Frequency_Counter_32kHz/ for anyone
who's interested.

I make no claims to its quality, but I've tested it with runs from 10
seconds to 20,000 seconds and it seems to produce the expected results
on both a standard Arduino Uno and a bare 16MHz ATmega328P. Any
suggestions or improvements would be welcome.

Also, thanks to everyone for your assistance. It was a fun learning
experience and excursion outside the standard Arduino commands into
the mysterious depths of the datasheet and hardware registers.

Cheers!
-Pete

On Wed, Jun 29, 2016 at 6:49 AM, Scott Stobbe  wrote:
> For pulse counting, the timer hardware is the way to go. Setup a 16-bit
> timer clocked off your DUT. Then input capture on your PPS edge. This
> leaves you plenty of processor time for string formatting and other tasks
> you may wish to perform.
>
> If you do the decimation as post-processing on your PC (i.e. log cycle
> count every PPS), you can use a zero-phase moving average filter, which may
> provide more visual insight over just a single data point every 1000s.
>
> On Tue, Jun 28, 2016 at 3:48 PM, Hal Murray  wrote:
>
>>
>> p...@heypete.com said:
>> > I have seen those, but I have little experience with PICs and the Wife
>> > Acceptance Factor of buying more stuff for a one-off measurement is low.
>>
>> The PIC family is very similar to AVRs.  The picPET and friends are 8 pin
>> DIPs so the Wife is unlikely to notice the additional clutter.
>>
>>
>> >> The PPS input on a PC may be be useful.
>> > Indeed. I normally use it for NTP.
>>
>> Than you want a second serial port for things like this.
>>
>> Or maybe you can use the parallel port if your system is old enough to have
>> one.  I haven't tried it, but I think Linux has a module that supports it.

-- 
Pete Stephenson
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