Electronics > Metrology

Agilent 3458A - I joined the club

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TERRA Operative:
I just recently picked up my first 3458A, it's an Agilent unit, with serial US2802xxx

I found it in a test equipment shop in Akihabara, and with a quick email negotiation, managed to get it for 550,000yen, down from the original quote of 600,000yen+tax (for an original total of 660,000yen). Not a bad discount, especially as it has been factory calibrated in 2021 and 2022, so I'm in the process of trying to get my hands on those reports from Keysight.

The only problem with it is apparently a slightly high reading in the -1A range, but it's close enough that a cal might be able to fix it. Unless anyone thinks I should have a poke at it before I sent it to Keysight for calibration and adjustment? (Once my bank account recovers.....  |O )

So far, I have given it a clean, including cleaning and oiling the filthy fan. Ordered a set of HM62256BLP-10 RAM chips from a local seller to upgrade to Option 001, and started making a list of stuff to buy.
I'll also be ordering a few FRAM adapters and parts to ditch the Dallas NVRAM's (I already backed up the calibration constants twice), and I'll socket U110 and update the firmware to v9 (I picked up a 40-pin socket today)

I'm also thinking of replacing the fan with a Papst 612NLE, which seems to be the closest replacement to the original 612L I can find, and replacing the electrolytic and any RIFA capacitors (pending checking for any).


The display is a bit worn as expected for it's age, I may or may not bite the bullet with a new VFD from China... Same with a new front panel plastic from Keysight. The plastic on mine is in pretty good condition, but I did have to apply a little bit of superglue on the corners, so these two parts are on the 'wish list'.

It agrees perfectly with my 3-year-since-last-cal 34461A on 10V and 30K that I tried so far. Until now the Fluke 731B was only adjusted to my 34461A, but now I can really dial it in. :)

So, feel free to educate me on using this instrument and any other things I should be looking at while I'm poking around, and also how to measure drift and performance and stuff, I have no idea but am willing to learn!  ;D

srb1954:
Congratulations on joining the club.

When looking for RIFA capacitors also check the mains inlet filter. If it is a pre-2000 Schaffner unit that may also contain exploding capacitors and it is best to replace it to avoid the risk of the awful stench the filter produces when those internal capacitors explode.

TheDefpom:
Very nice, i'm a bit envious, I would love a 3458A, I currently only have the Advantest R6581T, which is not bad, but not great either.

Kleinstein:
Reading low on the 1 A range is a bit odd. With the ACAL procedure there is no additional calibration factor that is applied. So the error there would be some kind of error in the ACAL procedure, like some thermal effect or not so perfect ground current compensation. Another possible source could be a relatively high TC for the shunt and self heating effect at the shunt.

As a test it may be worth to look at the CAL constants that ACAL calculates for the 1 A range for a few repeated ACAL runs. When done at somewhat variable temperature one could also get an idea on the TC of the shunt.

Before sending the unit in for calibration, I would use and test it for quite some time. It takes some time to recover from longer idle time. A point to test is also the ADC drift according to the SN18 service note. So read the CAL72? constant (and ideally also the temperature) after doing ACAL over a few weeks.

Dr. Frank:
Congratulations!
About 3400 €, that's a very good price, provided that its U180 is good.. but vintage 2000 (like mine, but from HP) should be good in this aspect, anyway.

The 1A range is auto-calibrated  only, it can't be adjusted by an external CAL (which would only adjust/calibrate 10VDC and 10kOhm).
It's strange that it didn't pass the verification, could have been a problem with the calibrator.
Has this cal report been provided by Agilent, or by an external lab?
The limits look odd, as they are not centered, they are asymmetric.. strange.
I have several test reports from other instruments, I'll have a look what's going on.

My instrument still has OK capacitors, and the RIFAs seem so be still fine .. the Schaffner did not blow up yet..
So, before replacing thoughtlessly, check visually and measure capacitance and ESR first. 

Don't you have any possibility to access any precise 10V and 10kOhm from another volt-nuts at your location?
Calibration @ KS is unnecessarily expensive, only because it's a 3458A, and always be aware, that no DMM is regarded as a "standard".
Setting up your own bank of 10V/10kOhm standards would be better, technically and economically.

You need better cables for precise measurements, like PTFE with copper lugs, and you need a lab with constant room temperature, otherwise you can't make any use of the 3458As stability and uncertainty.

Frank

PS: Don't worry about the asymmetry of the 1A range.. that seems to be an offset, which HPAK probably never properly addressed in their calibration/validation routine. I looked into other reports directly from HP, Agilent and Keysight, and this asymmetry is not as prominent as in your case.

Especially the limits of + and - polarity are extremely deviating in your case.

It's not mentioned in the manual, but you always should use a Null before measuring currents, to achieve highest uncertainty.
Same goes for 100mV and 1V ranges; these perform better than specified, if you take care about offsets before mking the real measurement. 

Another hint: The test report you show here, is this status "As received", or "As Completed"?

I have a test report from Keysight, probably Penang, where this 1A range was nOK (i.e. U = Undetermined) before calibration, but good afterwards, although this could only be judged after an ACAL beforehand.

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