[volt-nuts] Agilent 3458A Issues

Todd Micallef tmicallef at gmail.com
Sat Nov 18 16:10:11 EST 2017


If you were able to run CAL 0 with the inputs shorted, then security is not
an issue.

After that, try CAL 10.xxxxxx whatever the value is. I think overload means
the expected value is out of range.

On Sat, Nov 18, 2017 at 3:58 PM, Randy Evans <randyevans2688 at gmail.com>
wrote:

> When I try to execute a 10V cal, I get an error code "209 HARDWARE FAILURE
> - - INTERNAL OVERLOAD:31" I suspect that the unit has a different security
> code than 3458.  I can't change it without opening up the unit, which I
> don't want to do unless I decide to keep it.  Do you have any other
> suggestions on how to check the A9 card?
>
> On Sat, Nov 18, 2017 at 11:17 AM, Randy Evans <randyevans2688 at gmail.com>
> wrote:
>
> > Illya,
> >
> > That is a great idea.  I will give it a try.
> >
> > Thanks
> >
> > On Sat, Nov 18, 2017 at 4:47 AM, Illya Tsemenko <illya at xdevs.com> wrote:
> >
> >> Since you have 732A, testing should be easy enough. Calibrate faulty
> >> meter for zero and DCV 10V to 732A, record CAL? 2,1 value. This is your
> LTZ
> >> output. Then leave it running for few days to drift away and calibrate
> >> again to same 732A. Check CAL? 2,1 again. Calculate the difference and
> if
> >> it matches output drift (that 1.1ppm/day you mention) - you can be 80%
> sure
> >> that A9 is a problem. Other 19% go to A1 and A3 circuits, as 7V is not
> used
> >> directly in the meter, and there are still gain parts to get +12 and
> >> -12VREF on A3 and 10Vish bipolar levels on A1. If your CAL? 2,1 stays
> same
> >> (within 0.3ppm) then A9 is fine.
> >>
> >>
> >> On November 18, 2017 12:59:53 PM GMT+08:00, Randy Evans <
> >> randyevans2688 at gmail.com> wrote:
> >>>
> >>> I just received an Agilent 3458A that has a problem with noise and a
> >>> drifting voltage measurements.  I am using two Fluke 732As to compare
> >>> absolute voltage measurements over time against the Agilent and an HP
> >>> 3458A.  The HP unit has a new A3 ADC card and seems to be very stable
> and
> >>> low noise, so is being used for comparison.  I have been doing
> simultaneous
> >>> absolute voltage measurements and DC Cal Constant measurements several
> >>> times a day and then calculating the drift rates of the two units
> using the
> >>> HP Service Note 18 procedure.
> >>>
> >>>
> >>>
> >>> The results indicate the Cal Constant drift rate of both units is very
> >>> similar and within spec per Service Note 18.  However, the absolute
> value
> >>> measurements show the Agilent unit changing 1.1 ppm over a day whereas
> the
> >>> HP unit is within a tenth of a ppm over a day.  In my way of thinking
> the
> >>> Cal Constant procedure assumes the voltage reference board in the
> 3458A is
> >>> stable, hence the absolute value reading should remain essentially
> constant
> >>> after each ACAL DCV, which is the case with the HP unit.  Since the
> Agilent
> >>> unit shows a steady drift in the absolute reading, this would indicate
> to
> >>> me that the voltage reference board is likely the cause of the
> problem, and
> >>> is also likely the cause of the noisy readings.  If so, this is a
> >>> “relatively” easy fix (I have several 3458A voltage reference boards,
> one
> >>> of which has been continuously powered up for several years).
> >>>
> >>>
> >>>
> >>> The issue is that I have to make a decision to keep or return the
> Agilent.
> >>> It has a cal seal on it and if I open the unit up to change the voltage
> >>> reference board, I own it and can’t return it.  I would appreciate an
> >>> opinion from the members of the group as to what they think the odds
> are
> >>> that the voltage reference board is the source of the problems with the
> >>> Agilent 3458A.
> >>>
> >>>
> >>>
> >>> Thanks,
> >>>
> >>>
> >>>
> >>> Randy Evans
> >>>
> >>>
> >
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