[volt-nuts] What's the probability of a random used 3458A passing a Keysight calibration?

[Dr. David Kirkby]

But the seller told me he had been quoted 2100 Euros for repair, so I
assume Keysight thought it needs repair, not just adjustment. Also, as far
as I know, all Keysight calibration do include adjustments.

I'd like one, but don't really have the money, but I thought the price
excessive.

Dave

Dr David Kirkby Ph.D C.Eng MIET
Kirkby Microwave Ltd
Registered office: Stokes Hall Lodge, Burnham Rd, Chelmsford, Essex, CM3
6DT, United Kingdom
Registered in England and Wales as company number 08914892
http://www.kirkbymicrowave.co.uk/
Tel 01621'680100 / +44 1621-680100


On 16 January 2018 at 16:46, Dr. Frank <frank.stellmach at freenet.de> wrote:

> David,
>
> that instrument on ebay is definitely from the agilent area, i.e. built
> after 2000.
>
> It is really ok, and does not need any repair.
>
> Obviously, this AC range is a bit outside calibration @ 3V, 4MHz, but that
> is normal after some years w/o adjustment, and not a defect at all.
> Probably you know the different kinds of calibration at HPAK, obviously
> they chose the cal w/o adjustment option.
>
> Currently, the KS server is down, otherwise one could download the full
> calibration document, and check that, also the date of manufacturing .
>
> If you'd ever need these high frequency measurements, it's possible to do
> that by means of an appropriate signal generator and a thermocouple.
>
> The internal LTZ1000A circuit might stabilize with age, also the internal
> 40k VHP100 reference resistor might get better.
>
> The annual drift of the LTZ circuit is nominally 8ppm, but that is not
> fully specified.
> In theory, that applies only if the instrument is powered on continuosly.
> If it's switched off most of the time, the LTZ chip should not age at all,
> but it may show hysteresis (see AN-18, first item)
>
> So to my opinion, in this case it makes no difference, if you have an
> older or a younger instrument.
>
> The rest of the circuit is either (short term) stable, or not, also mostly
> independant from vintage.
> Due to the regular AutoCal process, this is of no real concern, as all
> these other drifts will be cancelled by the machine.
>
> The only component which determines the short term stability, is the ADC
> ASIC.
>
> It might have a good T.C., from zero to max. 0.5ppm/°C, and it might have
> a low timely drift in its calibration parameter CAL? 72.
>
> If latter is not the case, as described in AN-18, 2nd item, you really
> have a monetary problem.
>
> But in any case, this stability risk is the same for every vintage of
> instruments.
>
> Anyhow, I would prefer a newer unit like this one, as some other
> components degenerate over time, like the un-obtainium fast comparators.
>
> In the end, this instrument is not cheap, especially w/o proper
> adjustment. 3000$/€ would be a more reasonable price.
>
> Frank
>
>
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