Hmm, I don't buy the lack of suitable calibrators explanation. The use of a multifunction calibrator is a convenience not a requirement - HP could very easily have created their own reference current sources for factory calibration. Presumably they didn't bother because they believed so few customers were sufficiently interested in those current ranges being calibrated, to justify the extra production cost.
Personally it seems a bizarre decision to not even provide wider 'guaranteed by design' limits (due to auto cal), having gone to the expense of providing those ranges. Stating 'typical' means nothing at all without any specified statistical data/confidence levels - the customers are left with the task of calibrating / characterising those ranges themselves by whatever means.
A 10uA reference should be almost trivial with nominal a 10V source and 100k ohm resistor given the 3458A’s 24hr 2.2ppm 1V and 1.8ppm 100k ohm specs, compared to the 17ppm spec for 10uA. The lowest ranges might be a bit more challenging, but then the accuracy specifications get much wider.
I append a document, how HP tried to verify the Artifact Adjustment by themselves.. DCI on page 4.. similar to what you propose.
Maybe that you could really demonstrate the accuracy, but it's probably not sufficient for a
traceable verification / calibration.
To require a 5700A for verification of the other ranges / modes, allows to reproduce this process in any other calibration facility, not only in a very specialized manner in a special hp location.
Mention also, from the hp document, and from more elaborate 3458A calibration certificates, that a 'good' traceable calibration really requires: 'As Found' - Adjustment - 'As left', so the use of a calibrator is a necessity, not only for convenience.
HP may also not have trusted the traceability of these ranges, and Keysight also does not trust the reliability of these ranges, either.
For the 34465A /470A, they also specify 'typical' accuracy only, even for their 100µA range!
A further argument is the observation, that no similar precision instrument on the market has specified traceable DCI ranges of lower than 100µA, like the Fluke 57xxA and Wavetek 4808 calibrators, Datron 1281, Fluke 8508A, KEI 2002, PREMA 6048, and the 3458A.
They mostly have a lowest range of 100 / 200µA, or the uncertainty is undefined.
Your idea of 'simply' using a precise 100k Ohm resistor and 1V measurement also might not do the job, due to additional errors, and again - not really being traceable.
Instead, you might send the 3458A to an NMI for traceable calibration of these ranges, according to the typical specification.
The capabilities can be found here:
https://kcdb.bipm.org/appendixC/search.asp?reset=1&met=EMThat's a complete overview for all countries, just chose UK (NPL) and U.S. (NIST), and open their calibration tables.
They do not even offer DCI calibration at all.
Germany (PTB) and Suisse (METAX) offer that, even low current measurements.
PTB uses a shunt / DCV technique, as proposed.
As of today, they can achieve 3, 20 and 60 ppm for 100µA, 1µA and 100nA .. so that's really very tight, or not that trivial, to verify the claimed typical accuracy of the 3458A .. so probably no chance at all for HP themselves, any other lower grade cal lab, or even the end user to verify / calibrate these ranges precisely.
And don't forget, that the design of the 3458A is dating back 30 years.. as the discussion and verification oft Artifact calibration
I also refer to the discussion about the 5700A II calibrator. Its Artifact Calibration was quickly accepted in the U.S. , but not in the EU.
That's described in the FLUKE document from 1998.
It's referring to a 1996 verification study by PTB, SP and NMi, which gives a good idea, how Artifact Calibration works, what the problem is, and how it is verified..
Just search for: "Artifact Calibration: An Evaluation of the Fluke 5700A Series II Calibrator", it's hosted on the FLUKE site (91 pages).
So, noise and leakage currents might prevent these low current ranges to be easily adjusted by Artifact Calibration.
Frank