Bob,
To illustrate your point.
The original PM6681 calibration setup includes a PC, an ancient Philips
ISA-bus GPIB interface and an ancient Philips driver and a DOS program.
Collecting these and put them together to work will be an interesting
challenge.
A more modern variant of the calibration routines run can run on more
modern HW and LabView software. Philips PM5781 and Agilent 81112A pulse
generators is supported by those routines.
By now the production of the counter has stopped, as the counter core
ASIC ran out of stock.
The folks who designed and maintained them does not work there anymore.
Turns out the core setup requires a generator that creates a skewed
frequency such that you sweep over the interpolation phases. You tweak
the calibration value (3.86-4.50 ns in 0.02 ns steps) that you set over
GPIB using the *PUD command. You can check it yourself using *PUD?.
It sweeps over this range and checks for the value giving lowest RMS
value (SDEV result) and then sets this as the final value.
You can set the value using the command :SYST:UNPR;*PUD %s where %s is
the string, looking somewhat like this:
FACTORY CALIBRATED: %s%s, CALPLS 3.98 ns
The two %s in there is for some string and date, I just don't bother to
dig up a correct example.
Anyway, you can actually read-out the data and write it back without the
software. It should be possible to do something with the existing pieces
and it might be possible to actually get the calibration software
operational again.
I just don't have a CNT81 anymore to try this out on.
Cheers,
Magnus
On 11/18/2015 01:35 PM, Bob Camp wrote:
Hi
The coin cell / backup battery swap out is something we probably will become
more familiar
with on a *lot* of gear. The battery backed up RAM idea is now old enough that
there is a large
population of test gear / radios / telecom gear out there with this “feature”.
In some cases the
loss of the battery is a temporary issue. In a lot of others it’s a significant
problem.
If you are buying a piece of gear that has important stuff in RAM, the big
question is — has the
data been lost already? I have bought gear that had a good battery in it, but
bad data. If the gear
comes up with “data lost” on the screen, that’s easy to spot. In most cases
…not so easy at all.
Some gear might be configurable by normal means. Almost everything I’ve seen
needs a “factory
only” shoot from a test set that probably no longer exists. Yes, there’s
nothing magic in that test
set. The RAM just has bits in it. Figuring out what all the bits need to be
without any documentation
is not easy.
One might hope that as the gear becomes obsolete, the information about what’s
what would be
released to the public. Based on … errr …. on the job experience - not so
likely. The data rarely
is documented in a “public compatible” fashion. One guy’s notes tell you what
the test setup looks like.
Another set of notes go into the code. Both are buried in log books from who
knows when. Beyond
this, someone actively has to agree to release “corporate IP”. The complex part
of that is the fact
that the calibration techniques probably live on in a modern piece of gear. Not
at all easy ….
Bob
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