[volt-nuts] Keysight 3458A vs Keithley 2002 8.5 digit multimeters.

[John Phillips]

Most labs never turn 3458As off. The longer they are on the lower the drift
rate. I would rather have an 20 year old meter with new batteries than a
new meter.

On Mon, Jul 18, 2016 at 4:11 AM, Illya Tsemenko <illya at xdevs.com> wrote:

> Well, it's the topic many can go on and on about.
> As with everything there are specific cons and pros of both units, but
> here are my 5c:
> + K2002 is smaller, lighter (4kg vs 10kg), less powerhungry (sometimes
> it's important if you send unit for cal overseas, or take to remote site).
> + K2002 can support scan cards (standard, or low-EMF ones) via expansion
> slot
> + K2002 DCI/ACI goes up to 2Amps
> + K2002 goes bit higher on ACV frequency (15MHz, but performance there is
> so-so)
> + K2002 natively supports thermocouples, RTDs, SPRT thermal sensors and
> custom settings
> + K2002 supports rare rainbow unicorn nanovolt preamplifier Keithley 1801
> (substitute can be bodged up but that's not beginner's project)
> - Old K2002's require capacitor replacements (units with S/N 06xxxxx and
> 05xxxxx). Mandatory! Meters from 2005+ year have S/N starting with 11xxxxx
> - Readings noisier than 3458A
> I have two units in use, and have worklogs for both :
> https://xdevs.com/review/kei2002/ - newer K2002 from year 2007
> https://xdevs.com/fix/kei2002_u2/ - older K2002 from 1994 which was
> repaired after capacitor leak damage.
> Service of these Keithley meters (and 2001, which are very similar design)
> is not complicated, but require attention and knowledge what you doing.
> There only few custom parts used.
>
> Now regarding industry standard 3458A. Reason why you saw only 3458A in
> metrology lab is simple:
> Superior ADC (many rightfully think it's best on market, ever), amazing
> linearity (JJA was required to test linearity with good confidence), very
> easy calibration (just need 10V reference and 10KOhm standard resistor to
> get 3458A calibrated to uncertainty of used standards), Artifact
> calibration (ACAL) to significantly remove impact of temperature variation
> on accuracy, proven performance. Many labs use 3458A as main transfer
> standard due to it's ADC performance.
>
> It comes at cost though, as key components of meter's A/D are custom
> hybrids. Meaning if you got sour pill, and A/D drifting, you will have to
> replace expensive A/D board. Newer Agilent/Keysight branded 3458A's are
> essentially same boxes, just with newer hardware and likely with new
> FPGA-based digital brains. Performance is same though, unless you really
> getting early 1990's meter. Many design issues and items I got covered in
> my repair worklog: https://xdevs.com/fix/hp3458a/
>
> Brief 10V comparison : https://xdevs.com/datalog_tcomp/ - sampling 10V
> connected to 2001+2002+3458A
> Some of the A/D noise comparisons (meter input shorted) -
> https://xdevs.com/article/dmm_noise/
>
> So decide what fit best your needs. 3458A is overall higher performance
> instrument, but in lot of applications outside of metrology it's
> performance benefits may not cover up for higher price and size. Both 3458A
> and 2002 are still supported and sold new by manufacturers. Regular
> calibration of these is likely be over 1000$USD, and lab-grade calibration
> for 3458A is usually in range of 2600$USD.
>
> P.S. there are also few other 8.5d meters, but much less information
> available on those, as less people have them. Only "modern" 8.5d meter is
> 8508A, which cost even more than 3458A without much performance improvement.
>
> 18/07/16 17:54, Dr. David Kirkby (Kirkby Microwave Ltd) пишет:
>
> I am interested to hear people's view on the relative merits  of the
>> HP/Agilent/ Keysight 3458A vs the Keithley 2002.
>>
>> I noticed that when I recently visit the standard lab for voltage at NPL,
>> the place was littered with Agilent 3458As, but I did not notice a single
>> Keithley 2002. But maybe NPL get better discounts from HP/Agilent Keysight
>> than Keithley/Tektronix.
>>
>> I notice that the used prices of 3458A is higher than 2002s.
>>
>> Also, are there any things ons should be looking out for when buying a
>> 3458A or 2002? I have in the past thought an Agilent front panel was a
>> better than an HP one, as it would not be as old, but this is not always
>> true - see my comment later.
>>
>> What S/N are best avoided? Does anyone have a record of S/Ns of Keighley
>> meters with time?
>>
>> Very recently I had a somewhat scruffy HP 6674A PSU with a damaged LCD. It
>> cost me $50 or so to pick up a clean Agilent front panel with a new
>> display.  The display actually turned out to be unsuitable,  yet my
>> Agilent
>> badged 6674A is actually a fairly old HP unit.  So white my intention was
>> not to rebadge the PSU, that happened as a result of a legitimate reason
>> to
>> get it working. So this really indicates how an old HP 3457A could be made
>> to look a newer Agilent one.
>>
>> Dave.
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>
>
>
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-- 

*John Phillips*