[volt-nuts] RE "new" 3458A

Sun Aug 17 14:22:19 EDT 2014

Bill,

I installed the U-short and executed the BLUE-C-0 front panel command and I
get an ERR on the display.  I assume this is not good.  Did I do this
correctly?

Thanks,

Randy

On Sun, Aug 17, 2014 at 10:49 AM, Bill Gold <wpgold3637 at att.net> wrote:

> Randy:
>
>     Look at page #23 of the 3458A Calibration Manual.  Make yourself a "4
> Terminal Short" as shown and put it in as shown.
>
>     Before I did an ACAL I had around -000.00025 mVDC.  After ACAL I now
> read +000.00002 mVDC.  I did the "CAL 0" myself so I would expect that the
> meter should return to a low value, and it does.  I do get a variation of
> +/- 30 nVDC using 100 PLC and just observing the variations.  As I remember
> I have never seen a spec on the ZERO stability over temperature.
>
>     If I turn on the MATH function and then do 40 measurements with 100 PLC
> the statistics show:
>
> Low reading        -70 nVDC
> Mean reading       -28 nVDC
> High reading        +3.5 nVDC
> Total Variation    73 nVDC
>
>     So that correlates with my visual observation of 60 nVDC.  After an
> hour
> the room had gone up around 1 degree C.  Then I observed -000.00023 mVDC.
> After another ACAL the reading was again +000.00002 mVDC.  This particular
> meter has a negative tempco as the room temp goes up.
>
>     Obviously do an ACAL before any precision measurements requiring low
> nanovolts.
>
>     Go to the Keysight website and go to "Technical Support" and choose
> "Parts".  Then enter in the "Part Number"  "03458-66517" which is the
> replacement "03458-66507" assembly and you will see the replacement part
> number on the right hand side.  Click on that and you will get the
> information about the exchange program and so on.  Looks like you can just
> order this part online and pay for it with a credit card, but you have to
> create or use an existing login account.
>
>     I needed a new display a few years ago.  At that time you could order
> just the display for around $80.  Being extremely good at removing and then
> inserting and soldering I ordered the part.  The problem was that the
> spacing from top to bottom of the pins had changed.  It went from around
> 1.3
> inches to around 1.5 inches.  So I had to bend the pins to fit my display
> board and then get something like 72 pins into the holes on the PC Board.
> It took hours.  This change is probably why HP/Agilent/Keysight doesn't let
> you just get the display anymore but wants you to get the whole PC Board
> assembly.  It did work just fine once installed.
>
>     Hope this helps your decision to keep or not.
>
> Bill
>
>
>
> ----- Original Message -----
> From: "Randy Evans" <randyevans2688 at gmail.com>
> To: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
> Sent: Saturday, August 16, 2014 10:36 PM
> Subject: Re: [volt-nuts] RE "new" 3458A
>
>
> > Interesting note.  After the room cooled down from about 79F to 73F, and
> > another ACAL, the meter now reads +000.00035 mVDC, a more reasonable
> value,
> > although it does bounce around a couple of tenths of a uV.
> >
> > Maybe that is OK?  If so, then the only issue would seem to be the
> display
> > has some faint pixels, which a new display should fix.
> >
> > Randy
> >
> >
> > On Sat, Aug 16, 2014 at 9:59 PM, Randy Evans <randyevans2688 at gmail.com>
> > wrote:
> >
> > >
> > > The unit seems to be working so far except for one issue.  After doing
> an
> > > ACAL, and making sure the Auto Zero is ON,  I short the input leads
> with
> a
> > > copper wire shunt across the inputs and the reading is approximately
> > >  -000.0023 mVDC.  That seems rather high.  I would expect the unit to
> short
> > > the input leads internally and force a zero reading during the ACAL.
> > > Anyone have any comments on this reading?
> > >
> > > Thanks,
> > >
> > > Randy
> > >
> > >
> > > On Sat, Aug 16, 2014 at 3:37 PM, Richard Moore <richiem5683 at gmail.com>
> > > wrote:
> > >
> > >> Hi Randy -- sounds like your unit is in cal, based on your
> measurements
> > >> of DCV and precision 10k resistor.
> > >>
> > >> Using autocal all is recommended before doing precision measurements,
> and
> > >> I do that if it's been more than a day or two since last use. The
> autocal
> > >> uses the internal Vref and an internal 10K resistor to do cal on
> everything
> > >> else, so that tells you what the basic cal procedure is. I just got my
> 3458
> > >> back from Loveland, and that's what they did for me -- warmed it up,
> then
> > >> ran autocal, then measured everything against a Fluke 5700, aided by
> an
> HP
> > >> 3325, and another 3458.
> > >>
> > >> It has been 5 years since I replaced the display board (no "exchange"
> > >> deal was available then AFAIK, so I don't know what's changed) and
> also
> the
> > >> NVRAM board, which was dead, with one with the Snap-cap RAM chips. I
> did
> > >> those replacements, then sent it home for cal, which was complete,
> since
> > >> all the RAM was new. Now after 5 years, the unit passed all incoming
> > >> performance tests and was sent back to me without a cal process of any
> > >> kind. This tells me that an old, well-aged Vref module is a good
> thing.
> The
> > >> 10VDC test had changed by a bit under 5ppm, or roughly 1ppm/year.
> > >>
> > >> They have a cal deal -- use code 1.090 -- press them for it -- and
> that
> > >> saved me 30% off the normal price. I think this deal lasts until
> > >> mid-September, so my recent "cal" ended up at just under $400
> including
> > >> shipping. I'm not sure the deal is available on new or first-time
> cals;
> my
> > >> unit was in their data bank.
> > >>
> > >> But this is a long way of saying I don't think you need to send it for
> > >> cal -- just push Auto Cal and Enter and wait about 10 minutes and you
> > >> should be good to go.
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> > >
> > >
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