8.5 DMMs 3458A vs Keithley 2002 Theoretical - Page 1
Forum section: electronics / general

author: itsbiodiversity
author_rank: Regular Contributor
timestamp: November 15, 2019, 09:47:22 pm
content: Say you were choosing between an older, less beautiful HP3458a with options 1 and 2 and a Keithley 2002 in better condition. Already own Fluke 8846a, and one would need to be a significant improvement over the 8846a. Which do you choose, and why? Looking forward to your replies.

author: MiDi
author_rank: Frequent Contributor
timestamp: November 15, 2019, 10:46:52 pm
content: Older 3458A could have U180 desease, this is a high risk.On the other hand it is the standard 8.5 DMM.Ifnoiseflooris an argument:

author: niner_007
author_rank: Frequent Contributor
timestamp: November 16, 2019, 12:39:52 am
content: Quote from: itsbiodiversity on November 15, 2019, 09:47:22 pmhow would you use it, or what do you need it for? depending on the answer, the 2002 might not be in the same class and really not a viable choiceand I don't know what you mean, the 3458A is quite beautiful, some 30 years laterI made quite a few 3458A purchases from eBay, and I would say not all eBay units suffer from the ADC drift problem, but really depends on luck, you have to be prepared to shove an additional $2000-$3000 on top, for me, it will always be worth it, so I don't really care either way

author: ScoobyDoo
author_rank: Regular Contributor
timestamp: November 16, 2019, 10:02:40 am
content: I would opt for an Agilent/KS 3458A in good condition or a Fluke 8558A/8588A/8508A ... and disregard the other options you have as 2002 or Transmille 8000 series if linearity / accuracy / stability is what you are looking for and ask vendor 90 days return warranty - be prepared to invest 4000 ... 5000$ for unit and some reserve to swap A3 board - make sure unit has recent boards.You can also ask 3458A users/owners to transfer knowledge how you determine that your U180 is not drifting (?) - however it requires some flexibility from seller. The flawness of U180 is overstated - and there have been A3 boards sold as refurbished that were actually "new from factory" for 700 USD.The new KS 3458A BE is a RoHS compliant unit with SMD boards and work is in progress to improve all "3458A BE"boards and keep those backwards compatible - but it remains a challenge for their team to reverse engineer the firmware and add extra IF functionality - It is hard to tell whether they will succeed doing so but 3458A community is embracing their vision so that current owners will be able to upgrade in small steps.Herzliche Grüße/Meilleures salutations/Best regardsScoobyDoo

author: niner_007
author_rank: Frequent Contributor
timestamp: November 17, 2019, 12:14:30 am
content: why do they have to reverse engineer anything? don’t they have the original software?

author: dr.diesel
author_rank: Super Contributor
timestamp: November 17, 2019, 12:25:54 am
content: Quote from: niner_007 on November 17, 2019, 12:14:30 amI suspect they do, but I've worked at fortune 100 companies with no version control or software vaults of any kind.

author: niner_007
author_rank: Frequent Contributor
timestamp: November 17, 2019, 12:34:00 am
content: Quote from: dr.diesel on November 17, 2019, 12:25:54 ameven if they did have SCC, I imagine a lot of it is in assembly, typical of the 80s, and even if it wasn’t, there’s probably enough complexity and not designed to port easily between different architectures or microcontrollers, if it were written today it would be different; maybe they could use FPGAs to implement soft cores

author: TiN
author_rank: Super Contributor
timestamp: November 17, 2019, 01:36:11 am
content: It is quite funny to read comments comparing 3458 ($10k) vs 2002 ($7k) or 8588A/8508A($18k+) units. Also keep hearing that new 3458 Black is improved/enhanced/etc but so far manufacturer suggests that it is not any better than original 1989 vintage 3458A, but RoHS compatible (it's a big move, granted that). So until we actually see independent test results that give any hint of improved performance, all that is just marketing woowoo, sorry. I hope when Keysight does officially launch 3458A Black, it will get some proper coverage and details explaining the new technology used to refresh the legendary design. Refresh your memories reading HP Journal from 1989, that goes into very fine details about 3458A's core design. Even then it took me multiple years of measurements and tests to believe my two 3458As, and I know other owners who also feels same way. But somehow I feel this wish will remain unaswered, because showing tech behind the instrument is expensive and lengthy project on its own.Now back to 3458A vs 2002. 2002 has *110% overrange, (e.g. base range is 21V) instead of only 20% on 3458A. 2002 has better resistance stability, natively supports RTDs, TCs, scanner cards, has better display and half the size/weight (sometimes that matters if you work in field) and cheaper new. But 2002 is not a metrology type unit, has shrouded bananas and no ACAL functionality, so you need 5720A and signal generator to be able keeping 2002 within it's best ability. Noise on 21V DCV range is about 2-2.5 times worse than average 3458A, but still blows any 7.5d meter away in typical cases.3458A is industry metrology standard for DCV and linearity, there is no meter better. It has ACAL, which is essential if you don't have calibrated Fluke 5700A/5720A/5730A/standards maintained and available 24/7.3458A also can be very fast and high-performance as digitizer, but that needs some coding/programmingAlso finding proper golden 3458A may take you thru many many units. I played A3 lottery too, and failed every time. Many of the A3 boards (old or new, does not matter) while still good enough to meet 1989's 3458A specifications, are not good enough to meet more strict specs such as 2ppm/year.Datron 1281s and it's derivatives (8508A) are also great options if you more care about resistance, than voltage measurements. Thanks to internal scanners and electronically-controlled rear ports, you can do really good transfers between standards, without sweating out with manual labor and bridges.In the final answer - best choice is to get both K2002 and 3458A, so you can enjoy both worlds. I used my 2002's to travel internationally, to act as a transfer calibration units, while my 3458A's are lab queen's, running 24/7/365 to make best DCV measurements possible. Any 8.5d meter will kill the 8846A with ease, but you have to be ready for expensive ownership cost and know what you doing, and how to make proper measurement. Even simple things like connection cable to your DUT or temperature stability in your lab WILL introduce errors into your measurements. You could think - these folk on forum, talking about copper only connectors and shielded PTFE-cables for $1000 a piece are just like audiofoolers, but unlike audiofoolery 8.5d meters are often sensitive and low noise enough to show you real difference. But does your application actually have need for such a trouble? That is different question.

author: martinr33
author_rank: Frequent Contributor
timestamp: November 17, 2019, 01:57:45 am
content: The 3458a software is pretty advanced - they built on an HP 68k workstation. Quite likely that they would have used custom compilers and assembly tools to make the package, so the build environment could be very difficult to recreate. Back then, we didn't really have networks, and 8" floppies, mag tapes, and 5.25" hard drives with stepper motors were standard fare.If you look at the HP journal article, it was a very disciplined software develpment process.https://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1989-04.pdfPerhaps the most important thing is a more modern communications interface. Modern microprocesors would not need the accelerator hardware that the original design needed. And you could do a lot in the space in that chassis.

author: niner_007
author_rank: Frequent Contributor
timestamp: November 17, 2019, 03:05:35 am
content: 8588A is $15K according to a Fluke quote I was given, 3458A is close to $12K with the extended warranty, opt 2 and one time calibration against JJwhich makes more sense given very close specs, the Fluke has better resistance, but the 3458A is the DCV king, and the Fluke has premium pricing, because Fluke...

author: ScoobyDoo
author_rank: Regular Contributor
timestamp: November 17, 2019, 05:16:40 am
content: Hello folks - the process of the remake of the 3458A evolved into two steps:Part 1 - 3458A - BE:RoHS compliant version - same specifications as original using mainly SMD components - all boards backwards compatible, expected release early December 2019Part 2 - Upgrade: KS is considering to improve all building blocks and had to reverse engineer firmware - aim is to keep new boards reverse compatible with 3458A BE edition. It is a work in progress that will take time - several years - to complete from start to finish and will come with improved specifications - Only time will tell if they succeed ...K2002: In 2016 the K2002 units were sold at list price of 4000 euros - the moment KS was forced to withdraw the 3458A due to RoHS legislation in January 2017, the price of K2002 went up above +7000 euros ... - these days you even pay more ... - check it out.How does Keithley justify such difference ... ? It is not that the K2002 suddenly came with better specifications rivaling the 3458A or F85xxA - just Keithley marketing spotted a window of opportunity to boost profit.Herzliche Grüße/Meilleures salutations/Best regardsScoobyDoo

author: niner_007
author_rank: Frequent Contributor
timestamp: November 17, 2019, 06:25:12 am
content: Quote from: TiN on November 17, 2019, 01:36:11 amyou can use your own scanner with the 3458A and achieve the same or better results thoughdon’t they both have VFDs? I guess the 2002 has a second row

author: itsbiodiversity
author_rank: Regular Contributor
timestamp: November 17, 2019, 12:50:36 pm
content: TiN brings up a few good points. This specific meter would be used for metrology, but can be at least checked with internally maintained standards throughout the 1 to 2 year cycle. A main function of this unit would be to measure temperature, which the 8846a can only perform at ±0.06°C. If this were buying new, the 3458a would 100% be my choice as I am familiar with the model and the accuracy is legendary. I don't mind using Ω to temp calculations myself either. Rarely if ever do long term logging. Use would be around 3 hours / wk.The theoretical is the 2002 in functional shape or a mystery 3458a in questionable shape. It sounds like both

author: Kleinstein
author_rank: Super Contributor
timestamp: November 17, 2019, 01:24:21 pm
content: Many temperature sensors are resistive and the limiting factor is more like the sensor than a 6 digit or better DMM. So just for an PT100 there is no need for a 3458 or keithley 2002. I would expect the Fluke 8846 also to get better tha 0.06 K resolution with a suitable sensor.

author: itsbiodiversity
author_rank: Regular Contributor
timestamp: November 17, 2019, 02:29:44 pm
content: The resolution for temperature on the 8846a is 0.01 °C (I believe it shows 3 digits, though); however, the accuracy for a 8846a is ±0.06 °C. When added the 5615A probe an uncertainty at k=2 can be around 0.14 °C. Looking to lower this uncertainty.Otherwise - I have a handheld Jofra Ametek DTI050 that is brand new that was damaged internally in shipping. It has an accuracy of around ±0.03 °C. The damage is not visible, and at times I get it to read mV (TC) correctly like spot on. Resistance floats. Anyone want to take a whack at repairing it? Willing to pay for the expedition / journey / time but it may be something "simple". The user manual is available and has the pinouts for the LEMO connector that is used so it is pretty straightforward for someone with more knowledge than myself.

author: TiN
author_rank: Super Contributor
timestamp: November 17, 2019, 04:05:19 pm
content: If you want temperature measurements (for whichaccuracybetter +/-0.1 °C is already very expensive challenge), perhaps more suitable instrument is thermometry bridge, such as Fluke 1590 (eBay borked unit). Maybe you confused accuracy with resolution? For thermometry K2002 have more functionality built-in, and can do compensated thermocouples when you use optional TC-SCAN2001 card.Alternative is also to use reference thermometer readout such asFluke 1529combined with reference PRT or even standard SPRT. So you would need better probe than 5615, and all the additional toys like TPW cell, precision thermal baths and so on.And beware high calibration costs, even if you just want limited temperature range it could easily go multiple thousands $ for one PRT calibration, and these are very fragile devices. Sadly you can't get away paying those costs, if you needaccuracy. Those who think paying $2600 for 3458A calibration is a lot just didn't look into calibration of standard thermometersTranslation of voltage/resistance from DMM into temperature is also nothing simple, as you must know exact characteristics of your specific probe and math can be quite complex for corrections. Sure, you can order cal lab to provide the measurement and data, but that's even more gold.

author: tggzzz
author_rank: Super Contributor
timestamp: November 17, 2019, 04:59:59 pm
content: Quote from: martinr33 on November 17, 2019, 01:57:45 amThe HP 9000 series 300 "bobcat" computers ran HPUX. HP did indeed write the compilers, and it could well be a challenge to recreate the environment. However, I would hope and expect that the engineering documentation and source code would still be available. A lot could be learned from that, but as always happens when new people come on board, there is a learning curve. Doubly so if the original team isn't availableQuoteThe bobcats had 3.5" floppies, wereverywell networked (as you would expect with any Unix o/s). Hard drives weren't 5.25"; I remember 300MB winchesters that fitted into an under-desk "dalek" cabinet.

author: guenthert
author_rank: Frequent Contributor
timestamp: November 21, 2019, 03:48:50 am
content: Quote from: martinr33 on November 17, 2019, 01:57:45 am28kloc C, 11kloc Assembler? That's much more complex than I would have guessed. The built-in BASIC interpreter (not mentioned in those articles) doesn't explain that either. Wouldn't have thought that auto-cal or GPIB would take that much code.

author: niner_007
author_rank: Frequent Contributor
timestamp: November 21, 2019, 08:37:04 am
content: lines of code is not a good measure for complexity, in fact it is not a good measure for anything, 28k is very little by today's standards as well

author: iMo
author_rank: Super Contributor
timestamp: November 21, 2019, 09:09:58 am
content: Add 12000 lines of 68k assembler (page 34) - that could be the issue for KS guys, though. I would bet in the black edition they run the original binary on an emulated 68k.

author: jklasdf
author_rank: Regular Contributor
timestamp: December 05, 2019, 08:59:23 pm
content: The 28K lines of C code for the main outguard processor is not surprising in terms of lines of code, even back then. Sure you can (and people used to) make digital multimeters without a single line of code, but this was the most complex multimeter in terms of firmware when it was released, and lines of code don't tend to scale linearly with software complexity either.The 12K lines of assembly for the main outguard processor is slightly more surprising, but I guess really shouldn't be for the late 80s given it was both more common and more necessary to get the performance needed, even with the relatively powerful (for the era) 68k processor. I can see the assembly code being an issue for Keysight given 12K of assembly is a lot for anyone to comprehend on a new project, even if it's well structured and commented. It's also the part that probably needs changing the most though if they updated to a new processor (with different peripherals). At least 68k's are still being produced...I wonder how many (if any) of the people on the original development team are still around. It really doesn't seem that long ago (maybe because the 3458a is still being produced and sold), but even a relatively-young 30-year-old engineer working on the project in the late 80s would be nearing retirement age now. I do remember when Agilent was releasing replacements for the 34401a (similar era, 1992 instead of 1989), they emphasized that some of the original designers worked on the replacements. But those were never that high performance anyways, even compared to the much-older 3456a. There's a lot more that keysight has to get right with the 3458a.If the HP Journal article is to be believed, HP apparently had a very extensive firmware test system back in the day written by both the firmware and hardware engineers. (In my experience though, written praise about test systems is often just fluff, and the fact that two test engineers were added only very late in the development process does usually tend to indicate that testing is somewhat of an afterthought...which it often is. Probably only the original designers working on the system know how good or bad the test system actually was. It was probably not bad though given the extremely-low number of reported issues compared to modern graphing multimeters with fancy displays).It sounds like a hardware-in-the-loop test setup given both hardware and firmware designers helped write the tests, and also given the fact that the tests apparently took 12 hours to run by the end of the project. I'd be extremely surprised if any of this test setup still exists, and it's probably impossible to duplicate today, both because of obsolescence and how little effort/how difficult it is to properly revision/configuration control the test setup (at least they used RCS for the actual firmware development). The production test system is probably completely different than the firmware development test system...can't spend 12 hours on testing for most commercial products, even the 3458a. If they don't have the original firmware test system, it's probably pretty hard to change the overall architecture and measurement side of things if they're mostly using the original code. A lot of the measurement/calibration knowledge is probably more institutional knowledge and not that well-documented in code why things are done a certain way. Changes that are non-intrusive for the actual measuring part, like adding USB or ethernet might be easier.Changes to the measurement side of things probably require much more understanding at the system level, and I can't see keysight making many changes there. The inguard 8051 is likely all assembly given the era and the fact that they're using an 8051. Luckily compatible parts are still available, and 8051 peripherals are much more standardized than most microcontrollers. My guess would be they won't try to change much here at all. The gate array ASICs (used for ADC timing/control, and also the UART between inguard/outguard) are already replaced with an altera CPLD in newer 3458a meters. According to the pi chart on page 34, about 40% of the outguard processor firmware is dedicated to the measuring side of things, and I can't see much changing here either. I wonder how much of it is in assembly (maybe for speed?) vs. C.Quote from: ScoobyDoo on November 17, 2019, 05:16:40 amScoobyDoo, what is your source that there is a part 2 of more upgrades? Do you know what keysight is planning to do?

author: tggzzz
author_rank: Super Contributor
timestamp: December 05, 2019, 10:02:19 pm
content: Quote from: jklasdf on December 05, 2019, 08:59:23 pmYou should believe it.HP had the HPWay running through every body in the company. It was inculcated by numerous "Bill and Dave" anecdotes. One that was relevant to this concerned Paul Ely in the mid 70s.At that time he was the project manager for one of the HP minicomputers. It shipped on time, but there were many customer complaints. Packard investigated, fond the complaints to be valid, and sent Ely a memo "Please do not ship products until they meet the advertised specification". In other words, don't play games with our customers; telling the truth is of paramount importance.That was, in HP terms, regarded as a stinging rebuke, I.e. career limiting material.Ely did the right thing. He framed the memo, and hung it in his office. Ely continued to rise through the ranks and had a distinguished careerThat's an example of how the HP Way shaped HP and was revered by employees.Carly Fiorina, may she rest in California, explicitly abolished the HP Way.

author: eplpwr
author_rank: Regular Contributor
timestamp: December 15, 2019, 03:03:21 pm
content: Quote from: TiN on November 17, 2019, 01:36:11 amIs it correct that the range of K2002 is 10V, with 110% overrange? As I read the specs, I read the range as 20V, with 5% overrange. This would mean that measuring a 10V Vref, the  error is 6 ppm + 0.15 ppm of range (20V) - this is for 1yr spec. This is not a big deal, but the range related error is just a tiny bit worse than 0.15 ppm of a 10V range. I note that the new Fluke 8558/8588's has their range spec'd as 10V, with a very large overrange.Best regards,eplpwr