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 <[email protected]> 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. >> _______________________________________________ >> volt-nuts mailing list -- [email protected] >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts >> and follow the instructions there. >> > > > > _______________________________________________ > volt-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. > -- *John Phillips* _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
