[volt-nuts] Two 4338B high resistance meters fail on the same range - Keysight can't adjust EEPROM of either.

[Dr. David Kirkby]

On Wed, 2 May 2018, 18:28 Charles Steinmetz, <csteinmetz at yandex.com> wrote:

> Dave wrote:
>
> > This has certainty got me thinking about what might be happening,
> although
> > the fact Keysight have said they can't update the EEPROM, suggests they
> > have the software to do it.
>
> Or does it mean they have lost the software to do it?  Does the cal
> certificate have "as received" and "as adjusted" error readings for
> other ranges?  If not, perhaps they adjusted nothing, which would leave
> open the possibility that they simply cannot adjust these meters anymore
> due to lack of software.
>
> Best regards,
>
> Charles


I spoke to someone at Keysight (UK) yesterday who confirmed they do have
the software to update the EEPROM.  I have asked Keysight if they can
confirm they have the latest software as it crossed my mind that the latest
firmware, which both instruments have, may require later software than what
Keysight UK have.

They believe the fault is the CPU board, but if they fit another CPU board,
and it does not fix the problem, I still would need to pay for the CPU
board. Then they would suspect the ammeter board - which is very expensive.

Apparently Keysight UK have asked the USA for advice, but have not received
anything - or at least not anything useful.  Maybe I should suggest they
try Malaysia, as I believe that's where the last ones were made.

I seem to be between a rock and a hard place.

1) I am not confident Keysight UK can calibrate this properly, despite them
saying they have calibrated two others recently.

Several things, such as the inability to give me the uncertainties, does
not inspire confidence.

2) I don't believe that the CPU board is faulty, given two instruments are
displaying the same problem. Whilst I would not paying for a new CPU board
if it fixed the problem, I am not keen to pay if does not resolve the
issue.

3) The user can save settings to the EEPROM. That works.

4) The service manual I have does not go to component level. So changing
the sensitivity of the current to voltage converter in hardware, rather
than software is not practical.

5) Sending these instruments for calibration only to have them fail each
time, gets expensive.

Currently this instrument is supported by Keysight, but from the end of the
year it will become obsolete.

The only good thing is I have a couple of 4349Bs which are different models
if Hugh resistance meters, which use the same CPU board. One of the
instruments has a new (Agilent, not HP branded CPU), which means it would
be newer than either of the others.

If anyone has any ideas how to proceed, pleasure suggest them.

PS I am looking to find a suitable resistor to allow me to produce the 10
nA the same way as Keysight do (10 V and 100 M ohm). The best resistor I
have found to date is 0.1% which is not really good enough to test a meter
which should have an uncertainty close 0.6% (I think 0.603% from memory). I
don't have the 3458A the 4339Bs service manual calls for, but I have a
3457A which should be adequate to measure 10V sufficiently accurately for
this purpose. I am going to send the 3457A to Keysight for calibration as
soon as Keysight can do it.

Dave.