Happy Metrology Day 2020! - Page 1
Forum section: electronics / general

author: TiN
author_rank: Super Contributor
timestamp: May 21, 2020, 03:29:38 am
content: IntroHappy Metrology Dayto everyone! This article was in the works since December 2019, and I apologize to everyone for such long delay for this publication. I know many people are interested in newest Keysight 3458A RoHS refresh.Original Hewlett-Packard project "SENTRY" was developed and introduced in late 1988. This project better known as model 3458A 8½-digit DMM designed for best performance money can buy. It was evolution of already successful 3456A and 3457A system DMMs and very first 8½-digit for HP. 3458A came out so good, that it remained in production all these years until today. Obsoleted parts, closed fabs and new ecology and industry regulations implemented to reduce harmful heavy metals waste dictated design update to continue production of this great instrument after year 2019. Back then environment and safety regulations were not as strict as we have now. This mean that original instrument components and design had trouble to meet currentRoHS(Restriction of Hazardous Substances Directive)compliance requirements, latest version of which came into effect last year.High-speed and high accuracy applications that need DMM like 3458A continued to be in demand, so just killing off 3458A was not an option. There are very few manufacturers remain today who actually build and sell long scale 8½-digit multimeters. Most known are Keysight, Keithley and Fluke. Past years Keysight had used few workarounds to sell existing stock of older non-RoHS 3458A, but that couldn't last forever. Market forced DMM group to modify and facelift well proven HP3458A design to meet all latest regulations and RoHS compliance, while keeping same decades-long proven performance levels of traditional design.It is still amazing to see fresh 2020 production of same design ideas from original 1988 release. Yes, there are small updates here and there due to components obsolescence (hello, hermetic can components), but at core it is still the same design. If we step back same 32 years from the oscilloscope market perspective, difference is amazing. We went fromfirst digital(ish) 4-channel 100 MHz HP 54500 seriesscopes still with CRO tubes to something insane likeKeysight UXRwith 110 GHz real-time bandwidth.Image 1: HP 54501A oscilloscope released same 1989 year as HP 3458A DMMIf we extrapolate same progress from oscilloscope industry and personal computer market to multimeters we should surely have 12½-digit DMM available by now, right?Nope, even today we still stuck at 8½-digits and have the same 3458A and it still holds a gold standard for multimeter applications, especially in voltage domain. Why all the progress in modern ASIC design, amplifiers, digital processing, memory capacity and computational performance cannot help us to get much better DMM? New opamps, computer CAD software and analytical methods should enable at least one more digit?Image 2: Keysight UXR 110GHz real-time oscilloscope released in 2019. Photo courtesy ofKeysight web-siteReason is simple - limitations for long-scale DMMs are not in lack of post-processing but in physical abilities and analog circuit limits of the front-end and ADCs. Adding smarts in digital domain can help a bit to squeeze an little extra resolution, but does not recreate missing information buried under noise floor.Of course, there are technicalpossibilitiesto get higher than 8½-digit resolution for voltage measurements but these devices continue to remain only niche scientific and metrology lab domain with cryogenic agent requirements, and not something that we can get on a bench for some reasonable price (below $20k USD that is). To be fair, above mentioned Keysight UXR oscilloscope is out of reach for traditional engineering lab too.I would say even more, we may not see a magical "9½-digit" voltmeter for at least decade or two from now, as this require some new breakthroughs on new lower-noise and better stability voltage references and precision component designs. That is why in 2020 we still do not have "model 3459A" , just like flying time-travel capable DeLoreans. As result we may need to enjoy current and legacy Keysight 3458A DMM yet many years to come.Lot of today's automated setups and applications still rely on 3458A use. Very rare find of the high-precision ADC or DAC product that was not tested against this DMM at some point in time during development or production. As result to preserve investments in current 3458A infrastructure existing and new customers need new 3458A availability and 100 compatibility with original 3458A operation and firmware/software. This dictated Keysight to apply very conservative approach for RoHS design update which affected only minimal and necessary amount of components. New DMM keep same model number, same calibration procedures, same specifications and same level of Keysight support. No new interfaces, no USB, no LCD and minimal internal changes.Some people with desires for shiny touchscreens and fancy graphical UIs and snappy LXI port communications may argue with this way, but why introduce new unknowns and complications? It is wise to preserve decades of existing experience and proven gold standard design in voltage measurement for more than 32 years with all data trace, history, stability and knowledge around that? Granted, very few instruments on the test equipment market need such special approach. HP 3458A multimeters survived rebranding three times already, first from HP to Agilent transition, and then later from Agilent to Keysight. High value of these instruments is obvious, even if we browse eBay, where old and broken 3458A's are still fetching hefty penny, despite their age and need of repair. Good used 3458A with long stability history is like rare wine, can be also quite expensive.Also special ability of 3458A to perform very fast sampling with high absolute accuracy or very high accuracy with moderate speeds make it as go to instrument for many semiconductor characterization rigs, automated test setups, scientific equipment, metrology bridges and calibration systems. It is as close to golden standard in multimeter field, as one could ever be.In this article we will look in detail onnew RoHS-complaint Keysight 3458A 8½-digit multimeter. It is exact match to original instrument in size, UI, core firmware, performance and specifications. New instrument fully RoHS compliant, has modern Keysight dark-grey exterior color theme, updated PCB assemblies with obsolete components replaced and fitted with extended memory (Option 001) standard by default out of the box. More on this later in the article.Image 3: Keysight 3458A RoHS refreshed 8½-digit multimeterOther than color theme update exterior design is unchanged. Instrument have bright single-line dot matrix VFD with excellent view angles and contrast, quick function change keypad section to select DCV, ACV, 2-wire Ohm, 4-wire Ohm, DCI, ACI, frequency measurement and sampling measurement modes.Keysight 3458A does not have functionality to measure direct capacitance, inductance, or diode functions with audible signals like typical benchtop DMM. It main purpose is high-accuracy or high-speed measurements.Function selection is intuitive and does not require owner to read instruction manual to get instrument up and running. User manual have good details about more advanced topics, such as triggering, data handling and additional setups for high-sleep sampling or programming of the instrument. In fact 3458A front panel controls are much easier than many modern touch-screeny DMMs and benchtop instruments, thanks to very flexible hot-key customization and simple layout. There are no multi-level depth menus inside system menus or fuzzy controls with 25 different functions dependency.Image 4: Keysight 3458A RoHS refreshed 8½-digit multimeterAll Keysight 3458A RoHS ship with latest REV 9,2 firmware version, same as recent year production of legacy 3458A's. All internal menu structures, commands and functions are exactly the same.Two keypad blocks allow advanced settings and controls for things like Auto calibration, NPLC sampling setting, offset compensation function for improved resistance measurements, triggering modes and autozero. Numeric keypad allows entering values, writing simple programs and scripts on meter directly or use as hotkeys Fn.Image 5-6: Keysight 3458A RoHS input low-thermal binding posts and hidden fuse for current jack protectionNew 3458A equipped with same custom 5-way binding post block that can accept *unshrouded* 4mm banana cables, bare wires or spade lug terminations. All connectors except current input are made from special copper-tellurium alloy to ensure low thermal EMF errors when used with proper copper metrology grade cables. Vertical spacing between posts is 19 mm, so standard dual-banana jacks can be accepted without problems vertically. Horizontal spacing is bit wider - 22mm. Thus shorting plugs designed to uniform 19 x 19 mm spacing like on most 6½-digit and 7½-digit DMMs will not work easily with 3458A. But with binding posts it’s not a problem, as one can always use piece of clean copper wire between all four posts to perform zero offset calibration or relative null function.Protection fuse rated for 1 A current is hidden inside nickel plated current jack. It is removable without tools to allow easy replacement in case of current overload event and fuse damage. Just press the jack in and twist it clock-wise half a turn to release the lock and remove jack with fuse. Fuse size is standard 5 x 20 mm; type is slow-blow.Overall this is same design as original 3458A, but on our review sample connector nuts felt a bit wobbly, with excessive freedom. It's no functional problem, cables and connectors are still fixed very tightly once locked in place, but left a mixed feeling compared to original 3458A . Perhaps just due the early case of first production unit with updated plastic color/style and could be easily improved as the instrument manufacturing is mature.Image 7: Keysight 3458A RoHS refreshed 8½-digit multimeterLeft and right sides of the instrument don't have any special features, just some vent slots towards the rear to allow air exhaust. Steel strap in soft rubber envelope allow easy transport of the instrument if needed. Fan noise is noticeable, but not annoying. It is more like a low background hum. There is no fanspeed control, fan always runs on maximum speed to avoid changing thermal gradients and thermal problems around precision circuits inside.Image 8-9: Keysight 3458A RoHS refreshed 8½-digit multimeterTop of the front panel plastic bezel have recessed slot to allow stacking of the 3458A's. Bottom side have matching configuration on four feet and steel clips on front feet to allow tilted setup on the bench. These feet are very common for HP/Agilent/Keysight equipment of the last 30 years.Image 10: Keysight 3458A RoHS refreshed 8½-digit multimeterRear side of the instrument has intake fan opening with dust filter and protection metal grill. There are same 5-way terminals for rear input, with same spacing and layout but rotated 90-degree CCW. Serial number sticker reveals Malaysia as country of manufacture and lists options for this particular meter. All RoHS black edition 3458A have extended memory option 001 installed as factory standard, so this option is taped out with black mylar patch.There is external isolated trigger in and trigger output BNC ports and single type of communications interface - GPIB IEEE-488. New 3458A does not understand today's commonSCPI language. Sending typical *IDN? would only trigger "command not understood" error from 3458A. Own Keysight's software such as BenchVue promoted to work with SCPI lab instruments also does not know how to talk to 3458A properly.Instead of SCPI both old and new 3458A talks own language, very similar to BASIC. It also has simplified state machine and programming capabilities that provide powerful customization capabilities for integration. It is non-issue for us, since all remote programming and control at xDevs.com is done via simple open-source Python applications, running on various platforms, such as PC, Raspberry Pi Linux SBC, DE1-SoC FPGA boards, etc. We will cover some programming example later in this article as well.DMM is powered by linear custom transformer, which is configured for 110 VAC or 220 VAC operation by switches at the back.Pay attention to mains voltage selection switches, located near mains IEC connector. Using incorrect voltage setting (e.g. set 120 VAC with 220 VAC mains applied) will can destroy transformer because it is directly wired to mains. New transformer cost around US$420 + tax + shipping, will be rather pricey mistake to make.Image 11: Keysight 3458A RoHS refreshed 8½-digit multimeterFront or rear terminals selection is done via mechanical multi-pole switch just like in old 3458A. There is no way to switch selected input from remote program, which complicates use of 3458A for comparison or ratio measurements. This is one aspect where some competitor 8½-digit DMMs still offer better functionality.Keysight is already manufacturing updated instruments, available for purchase worldwide since December 2019. Black RoHS edition instrument serial numbers start from *MY59350000*. Unit that xDevs.com got for testing has serial number *MY59350622*. Jumping ahead, this particular instrument was manufactured around 38th week of 2019, so at the time of this review it was just 16 weeks old. Essentially fresh out of press, still in the infancy. This also means that calibration verification can be done against 30 day specifications, and not 1 year.There are also special versions of 3458A with options, such as:Table 1: Keysight 3458A options and versionsReference stability optionsHere are details how to determine installed options in each specific unit (besides looking at option labels/stickers). Option 001 (extended memory) units will return a *1,0* when queried with an OPT? command, either from front panel or GPIB. All new meters come with this option as standard (always enabled). Option 002 (high stability 4ppm/year reference - this option can be bought by ordering kit 03458-80003, around $1400 USD extra) can be checked by checked box on rear panel or verified by label on A9 PCBA under top inguard shield. The RoHS 002 A9 assembly is labeled 03458-66549 (the A9 assembly in a standard unit is labeled 03458-66539). Even better HFL 2ppm/year stability reference option, standard option for rare Fluke/HP 3458A-HFL version is not available and obsoleted for RoHS meters.Option H01 (1000 Volt ACV measurement capability - Standard units are limited to 700 Volt RMS for ACV) - $1500 extra.On old units’ part-numbers used for this option are:* The A1 assembly is labeled 03458-91002 (the A1 assembly in a standard unit is labeled 03458-66501 or 03458-69501).* The A2 assembly is labeled 03458-91000 (the A2 assembly in a standard unit is labeled 03458-66502 or 03458-69502).* The A10 assembly is labeled 03458-91001 (the A10 assembly in a standard unit is labeled 03458-66510).New units most likely to bear updated PCBA part numbers.Manuals referencesManuals for 3458A were updated to reflect cosmetic changes for the new RoHS instrument. There are no new functions or performance metric changes compared to legacy model. One rather funny mistake that caught my eye - in User's Guide BASIC program example listing shown to test instrument response to *ID?* command. Manual lists response from instrument as "Keysight 3458A" but it is not correct. New RoHS DMM is identical to old one, and still responds with classy *HP3458A* when queried with *ID?*.Keysight 3458A Multimeter datasheet3458A Multimeter RoHS User's Guide, Edition 1, January 9, 20203458A Multimeter RoHS User's Guide, Edition 1, December 1, 20193458A Multimeter Legacy User’s Guide, Edition 7A User’s Guide to Keysight 3458A Front Panel Operation (RoHS Compliance), Edition 4, August 2019A User’s Guide to Keysight 3458A Front Panel Operation (Legacy)Assembly Level Repair Manual show some low resolution photos of inner construction. We can see that layout remained the same, with most changes implemented to A1, A3 and A5 boards.Keysight 3458A RoHS Assembly Level Repair Manual, Edition 1, December 2019Keysight 3458A RoHS Assembly Level Repair Manual, Edition 1, March 2020Agilent 3458A : Quick Reference Guide, Edition 2, Dec 20003458A Multimeter Calibration Manual, Edition 73458A Multimeter Calibration Manual, Edition 6There are no public service notes currently issued for new RoHS DMM version.SpecificationsBrief specification for Keysight 3458A Opt 002 (same new and old versions) listed in table below. More detailed specifications can be found in Appendix A of User's Guide.Table 2: Keysight 3458A Opt 002 key specificationsBlack box performance testingThis testing protocol will be used to compare meters, assuming no knowledge about instrument internal design. Just like as black box, that comply with manufacturer specifications. This mimic majority use cases for 3458A customers, including calibration service. During calibration meters are shipped to the lab, get evaluated for functions and performance with "as received" and "as returned" measurement data. Depends on meter meeting manufacturer specifications, it will be tagged in or out of tolerance and returned to customer. If customer request adjustment, then it's possible to obtain additional data set, "as returned after adjustment". Thanks to Artifact Calibration feature and best of the best ADC linearity unique to 3458A all adjustments are done internally by DMM itself.Keysight 3458A RoHS Black unit was received onJanuary 8, 2020in original manufacturer cartoon box, bundled standard accessory. Units passed the initial self-test functional verification and ACAL(Artifact Calibration). Instrument left powered on to warm-up for 24 hours before taking any measurements. Data readout and instrument control was done usingKeysight E5810A GPIB-LAN interface bridgeandTerasic DE1-SoC FPGA board, running Linaro Linux 3.18.0, compiled Mon Aug 8 17:11:41 EDT 2016 for armv7l arch.Image 13: Keysight 3458A RoHS refreshed 8½-digit multimeter reporting CAL? 2,1 valueThis was a standard unit, received it'sfactory calibration in Malaysia fab on December 15th, 2019. It was standard process calibration with Fluke 5720A/5725A and HP3458A as check reference standard.Unfortunately, I was not able to get actual measurement data points and uncertainties for this review DMM, but we can somewhat guesstimate results from 90 day specifications andKeysight Malaysia fab scope of accreditationfor electrical calibrations.People around xDevs.com are not strangers to 3458A. We use these instruments a lot for voltage and resistance calibration workloads, repair of other equipment and troubleshooting of various circuits. We also maintain fleet of our own older units, many of which kept running non-stop for many years to collect history and analyze stability.In this review we will also look at data from older DMM, using my modifiedHP 3458A #1andHP 3458A #2that will be used as reference. Both of these multimeters are adjusted and calibrated with our in-house 10V DC reference and 10 KΩ standards and running 24/7/365 without power downs.The modification involves reduced oven temperature for primary reference A9 module to improve long-term stability. Stability of both meters verified by number of external calibrations with DC Voltage standards over the period till April 2020. Both instruments demonstrated annual drift under 2 ppm per year. First unit (GPIB address 3) was repaired and put in service since January 2016. The second unit (GPIB address 2) was repaired and put in service since February 2017. Both instruments are running powered up constantly 24/7 and used as system voltmeters to perform calibration tasks and act as DCV linearity standards.Image 14: Two modified Keysight 3458A 8½-digit DMMsTo transfer cardinal voltage, resistance and current points into arbitrary values with high stability and excellent linearity we use restored and fully optioned up multi-function high-end Fluke 5720A/03 calibrator. Few additional sources and second 5720A are also sometimes used as auxiliary units for complex experiment setups, where more than one high-stability source could be needed.Image 15: High-performance calibration station with Fluke 5720A and Fluke 5725AAmplifier Fluke 5725A used to generate expanded AC Voltage capability for high-voltage range verification. Calibrator rig was also adjusted and verified against our lab standards. For most demanding DC voltage and resistance stability verifications DUT Keysight 3458A RoHS was tested directly against reference standards. These standards are our own 10V project in Fluke 792A power pack or Fluke 732B DC Voltage reference. For resistance tests we use Fluke SL935 or ESI SR104.Image 16: US Lab primary DC reference bank set, 8 x Fluke 732Fluke 732B - 10 VDC and 1.018 VDC output reference. Industry-proven DC voltage standard, widely used by many calibration and metrology labs all around the world. Usually able to deliver stability better than ±2 ppm a year with predictable linear drift. Multiple stable calibration sources are often used at metrology labs for redundancy and cross-verification. If an ensemble of four references is holding accurate value, according to statistics, it is less likely that all four would drift same way. If any single reference in bank start showing unexpected behavior due to electrical or physical damage/stress this can be detected by comparing to other references, even before the next calibration cycle to SI Volt transfer.Image 17: Fluke 732B and prototype Fluke SL935 standardsPrototypeFluke SL935 ovenized resistance standardwith 1 Ω and 10 KΩ output. This prototype device build by secret Fluke lab, using hermetic thin-film laser trimmed resistor networks from no less than ten (!) Fluke 5720A calibrators to obtain ultra-low temperature coefficient and stability for both output values. Unit is built around 732B reference chassis, replacing original DC Voltage reference electronics with custom resistance module. Oven operating at reduced temperature, fixed around 40 &deg;C to reduce annual drift.Image 18: DC Voltage reference 792X based off modified Fluke 792A Power PackOver last few years here at xDevs.com lot of experiments were completed with our own custom designs in search of the ultimate stability DC voltage reference. Most of these utilize best reference on the market - Analog Device (former Linear Technology) LTZ1000 and LTZ1000A Super-Zener. Some publications about these designs availablehere,hereandhere. PrototypexDevs.com 792X FX LTZ1000A reference, assembled in Fluke 792A Power Pack. This standard provides +10 VDC nominal, with tested annual drift less than -3 ppm. Key feature is high output drive capability with minimal loading errors, due to use of true 4-wire Kelvin connection output with active output stage. Unlike Fluke 732B, this unit is able to sink or source currents up to 25 mADC with minimal error to the output voltage.ESI SR104- resistance standard with the ultra-stable resistive element, temperature sensor, all enclosed in a sealed oil-filled metal can. Everything is embedded in nice wooden box (there is an option from IET without wooden enclosure as well). ESI, being one of the industry original experts in resistance field, invented and designed legendary SR104 10000 Ω resistance standard in 1967, considered as metrology primary level grade product by many labs. This standard is still unrivaled on the market, 52 years since. Perhaps that shows how hard it is to make improvements on high-end metrology instrumentation. For fun comparison - Intel 4004 processor (released to market 4 years after ESI SR104!) evolved into modern 64-core monsters on 7 nm semiconductor process.Next post for test results and benchmarks.

author: TiN
author_rank: Super Contributor
timestamp: May 21, 2020, 03:40:14 am
content: Part 2 placeholder.

author: TiN
author_rank: Super Contributor
timestamp: May 21, 2020, 03:41:30 am
content: Part 3 bonus placeholder

author: wolfy007
author_rank: Frequent Contributor
timestamp: May 21, 2020, 05:24:29 am
content: Someone has a(nother) new meter...

author: The Soulman
author_rank: Super Contributor
timestamp: May 21, 2020, 09:29:58 am
content: Thanks Tin!That air filter setup looks a bit like an afterthought, probably hadn't have enough clearance for a standard part. lol

author: HighVoltage
author_rank: Super Contributor
timestamp: May 21, 2020, 10:04:09 am
content: What a great summary, TiN, thanks.How about some internal pictures of the new boards?

author: BU508A
author_rank: Super Contributor
timestamp: May 21, 2020, 11:25:24 am
content: Quote from: HighVoltage on May 21, 2020, 10:04:09 amI think, that is the cliffhanger for the part 3 - bonus section.

author: notfaded1
author_rank: Frequent Contributor
timestamp: May 21, 2020, 12:39:37 pm
content: I'm assuming we'll see some actual measurement comparisons to the other 3458A's as well in part 2 or 3... nice introOFC we wanna see pictures of the inside! You really know your 3458's Illya! I was glad to finally own one... geesh we can live vicariously through you though!Bill

author: dr.diesel
author_rank: Super Contributor
timestamp: May 21, 2020, 12:54:45 pm
content: Wow very nice Sir, looking forward to the rest.

author: quarks
author_rank: Frequent Contributor
timestamp: May 22, 2020, 12:26:11 am
content: Bookmark, many thanks for sharing.

author: eplpwr
author_rank: Regular Contributor
timestamp: April 25, 2021, 10:16:46 pm
content: Whatever happened to this thread and the Black Edition 3458A? Is there a continuation somewhere else that I've missed?To say I'm interested in the guts of the new 3458A is an understatement ... like how they handled the discontinuation of the EL2018 comparator, or what the current U180 looks like.Since the new 3458A has been on the market some time, someone ought to have access to a unit for some photos.

author: The Soulman
author_rank: Super Contributor
timestamp: April 27, 2021, 10:02:11 am
content: Another thread with some discussion:https://www.eevblog.com/forum/metrology/3458a-black-edition/

author: eplpwr
author_rank: Regular Contributor
timestamp: April 27, 2021, 03:02:56 pm
content: Quote from: The Soulman on April 27, 2021, 10:02:11 amThanks. I've read it through and it also mysteriously just "stopped i the middle of the discussion". It's very strange.

author: MegaVolt
author_rank: Frequent Contributor
timestamp: April 27, 2021, 03:10:39 pm
content: Tin hides nothinghttps://xdevs.com/doc/HP_Agilent_Keysight/3458B/