> Hi Dwayne,
>=20
> As far as I know, truly achieving such accuracy will require periodic re-
> calibration to transfer standards which are themselves kept calibrated to
> primary standards. I don't think there is any way (short of replicating a
> primary standard) to make an instrument which will simply measure true
> 6.5 or more digits of accuracy for years on end with no re-calibration.
> This means that whoever developed this instrument for this customer would
> have to also provide a means of re-calibration, such as instructions for =
cal
> labs. I don't even know if a typical cal lab would be willing to perform
> calibration on a custom instrument.
>=20
> All of this is doable but I don't think it will be less expensive, when y=
ou
> consider all the difficulties, than an off-the-shelf bench multimeter. No=
te
> that the Agilent 34401A is a classic 6.5 digit multimeter of high quality=
 and can
> be purchased new in the $1100 USD range. Price climbs very quickly above
> 6.5 digits, of course ($9300 for the 8.5 digit Agilent 3458A). The majori=
ty of the
> cost comes from the "infrastructure" within the meter for achieving the b=
asic
> voltage accuracy. Most of the measurements besides voltage simply "piggy-
> back" on this basic capability, so I do not think that deleting the addit=
ional
> functions would save very much money.
>=20
> Sean

I would agree with Sean's assessment. It is one thing to achieve good accur=
acy with a 12 bit A/D, but once you start going beyond that the tricks invo=
lved in achieving higher accuracy cause the price to climb significantly. I=
 am surprised they consider something like the Agilent meter mentioned abov=
e, or a Keithley 2700 series DMM, expensive when you consider the accuracy =
you get. I would be surprised if they couldn't get some form of bulk buy di=
scount by approaching  FAEs of companies that supply such instruments. I ge=
t 20% discount on single items as I work in an academic establishment, but =
I would have thought that by playing Agilent off against Keithley, against =
Fluke, ... it would be possible to push for 10 to 15% discount on a multipl=
e instrument bulk purchase, especially if there is also a carrot for regula=
r recalibration, which is really needed to maintain the accuracy, as Sean s=
tates.

And I would agree that limiting the meter to just one function/range would =
not reduce the cost much at all, once you start going to those sorts of acc=
uracies the front end range switching becomes a relatively small part of th=
e overall cost.


--=20
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