[volt-nuts] 3458A Questions - The Sequel

Charles Black cblack at centurytel.net
Sat Oct 29 19:12:38 UTC 2011

Hi Joe,

Your noise and drift on your 731B is more than I see on my Datron 4910. 
I have no experience with the 731B but my 4910 is very similar in 
specifications to a 732B. My major drift with my 3458a measuring a 4910 
cell is the room temperature. It is about 10 microvolt per degree C. My 
peak to peak noise is dependent on NPLC settings up to 200 where it 
becomes very usable with only a minor improvement at NPLC = 1000. NPLC 
1000 is useful to get the ultimate accuracy on my system since it 
integrates out some of the lowest frequency noise in the 4910. I use 
shielded #24 cable with no connectors.  The wire is tin plated Tefzel 
STP but that seems to only cause 0 to 10 nv errors and reaches thermal 
stability much faster than my otherwise identical #22 STP. I have 
included two recent plots of one of my Datron 4910 Cells (it has four 
cells which perform similarly) to illustrate NPLC settings. Notice the 
downward drift in both plots that is caused by changes in room 
temperature and the peak ti peak noise which I assume is 4910 noise. The 
4910 noise spec is 0.04 PPM RMS and my cells are well within that.

I tried using connectors but only the gold plated spade lugs were af any 
use to me. Most of my issues had to to do with thermal mass. To use 
banana plugs I had to wait and wait. Dual gold plated banana plugs  
(about 1mv thermal offset at first) never stabilize on my 3458A. I have 
too many air currents I guess. Fortunately no connectors works perfectly 
here and is the cheapest too.

Enjoy your new (to you) 3458A.


On 10/28/2011 8:41 PM, J. L. Trantham wrote:
> Considering all the info this group supplied, I wound up with a new (to me)
> 3458A that was offered on theBay as a BIN or Best Offer.  We negotiated back
> and forth and I wound up with SN 2823A18533, no options, delivered for less
> than $3800.  Perhaps more than the $2500 suggested by other list members but
> I am happy.
> It has been on for about a month now and reads my two Fluke 731B's about 15
> uV apart and it drifts up and down about 10 uV, P-P, at 10V, but with a
> relatively stable 15 uV difference between the 731B's.  It has ver 8.2
> firmware and all the date codes on the chips along with the dates stamped on
> the various covers and boards are all around Aug 1997.  The bottom cover has
> 'Aug 20 1997' and the top cover has 'AUG 22 1997' stamped on.  IIRC, Agilent
> was born around 1999.  Later, in the early 2000's, manufacturing was moved
> from the US to Malaysia.
> I talked to the folks at Agilent regarding 'new vs. a fine vintage' and they
> suggested, similar to others on the list, that a 'fine vintage' at the right
> price coupled with their 'Repair Per Incident' at $2363.56 would be the
> preferred approach.  They basically disassemble the unit, check everything,
> including the 'crimps' on the cables, repair or replace whatever is needed,
> test it 'to new standards', do a 'Gold Cal' (IIRC), and return it basically
> as a 'new unit' including the option to purchase a 3 year extended warranty
> on the meter.
> The 'drift' issue of the reference is not tested for a non Option 002 unit
> but when the next 'Gold Cal' is done, the drift would be provided as
> compared to the first 'Gold Cal'.
> List members suggested that I back up 'CALRAM' ASAP.  I would agree.  How do
> I do it?  The Dallas chips are soldered in place.  By HPIB I presume?  That
> means that I am finally going to have to solve the 'HPIB issue'.  Or is it
> available from the front panel?
> Of course, if I send it back to Agilent, backing up 'CALRAM' is less
> important, at this time at least.
> My A5 board is 03458-66505 Rev C.  I note that the Option 001 board is
> 03458-66515.  Other than the installation of the four HM66256LP-12 chips,
> which would appear to be about a $30 investment, is there any difference
> between the boards?  Does the firmware need to be changed to acknowledge the
> presence of Option 001?  Is there a way to tell if the chips are installed
> using front panel controls?  Using HPIB?  I notice that there are two
> 'jumpers' in the vicinity, JM600 and JM132.  Are these involved?  On my
> board, both jumpers connect the center pin and the pin to the left, as
> viewed from the front, and as shown on the labeling on the board.
> I also note that on my A5 board, there is a single ST M27C4002-12F1 chip,
> soldered in place, instead of the six TM27C512's shown in the CLIP and the
> ALRM.  Unless there is a way to read the chip, installed, erase it,
> installed, and reprogram it, installed, to upgrade the firmware to ver 9
> would require the removal of the chip, installation of a socket, then
> installing a new chip with the latest data programmed in.  I don't know if
> this is done or not.  When I spoke with the folks at Agilent, I was given
> the impression that part of the 'repair' was to upgrade everything to the
> latest version by replacing the appropriate components rather than replacing
> the various boards, citing the desire not to change the 'character' of the
> meter by virtue of keeping all the 'aged' components possible.
> Therefore, the question arises as to how practical is it to remove the three
> Dallas chips (perhaps it is only one that needs to be archived) and the
> single EPROM with a hot air rework station, install sockets, archive the
> data, then reinstall the chips in the newly installed sockets?  Is the board
> just a dual level board or multiple layers?  If I am going to send it back
> to Agilent for their 'repair', would it be desirable to make the attempt
> now?
> Again, thanks to everyone on the list for their input and I look forward to
> more input.
> Joe
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