EEVblog #723 - Keysight 34470A 7.5 Digit Multimeter Teardown - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: March 13, 2015, 02:38:59 am
content: What's inside Keysight's new 34470A 7 1/2 digit Truevolt bench multimeter?What are the PCB changes from the 34461A?What voltage reference does it use to get 16ppm nominal accuracy?34470A Datasheet:http://literature.cdn.keysight.com/litweb/pdf/5991-1983EN.pdf34470A Operating & Service Manual:http://literature.cdn.keysight.com/litweb/pdf/34460-90901.pdfLTZ1000 Voltage Reference:http://cds.linear.com/docs/en/datasheet/1000afd.pdfAD8638 Chopper Amplifier:http://www.analog.com/media/en/technical-documentation/data-sheets/AD8638_8639.pdf

author: BravoV
author_rank: Super Contributor
timestamp: March 13, 2015, 03:28:43 am
content: For vref board, curious why using thru hole type of the jelly bean transistor 2N3904 ?I'm guessing its not just for saving few cents, right ?Any particular reason why using thru hole instead of using smd like SOT type ? Does it has anything to do with temp compensation thingie ?

author: EEVblog
author_rank: Unknown
timestamp: March 13, 2015, 03:33:50 am
content: Quote from: BravoV on March 13, 2015, 03:28:43 amI explained a possibility in the video.

author: Vgkid
author_rank: Super Contributor
timestamp: March 13, 2015, 03:42:00 am
content: Thanks for the teardown, now to wait for a review.I believe you are correct about the 2n3904, it is even in the datasheet, though I'm curious about the lack of remaining precision resistors in the vref circuit. Though I'm not familliar with smd's.

author: gslick
author_rank: Frequent Contributor
timestamp: March 13, 2015, 03:59:17 am
content: In case anyone is curious, the listed replacement part price for the 34470-66303 voltage reference PCB is $344.http://www.keysight.com/my/faces/partDetail.jspx?partNumber=34470-66303

author: EEVblog
author_rank: Unknown
timestamp: March 13, 2015, 04:04:22 am
content: Quote from: Vgkid on March 13, 2015, 03:42:00 amThey mention that detail? Where?

author: EEVblog
author_rank: Unknown
timestamp: March 13, 2015, 04:11:56 am
content: Quote from: gslick on March 13, 2015, 03:59:17 amHang on...The only physical difference between the 34470A and the 34465A seems to be this $344 retail board. But the price difference is $1500.So they are charging $1156 retail for turning on the extra digit in the software and (technically) calibrating it to a higher standard? (but likely the same production cal jig)I suspect Keysight have a lot of margin here to price crush any competition that might come along. I don't see why they couldn't potentially sell the 34470A for $1600 retail...

author: Vgkid
author_rank: Super Contributor
timestamp: March 13, 2015, 05:38:07 am
content: Quote from: EEVblog on March 13, 2015, 04:04:22 amnot mentioned, but in the schematic

author: EEVblog
author_rank: Unknown
timestamp: March 13, 2015, 06:17:28 am
content: Quote from: Vgkid on March 13, 2015, 05:38:07 amI thought you meant my guess about it being a TO-92 package to enable dissipation though system airflow?That's not mentioned on the schematic.

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 13, 2015, 06:49:42 am
content: The 34470A is not the first 7 1/2 digit instrument (from HP / agilent).Before that, the 34420A, nV/ µOhm meter already had 7 1/2 digit.It is based on the elder Multislope III A/D, similar to the 34401A, and had slightly better linearity than this new DMM.The 34420A features DCV and Ohm only, and has an LM399H built inside.The LTZ1000A reference is even stable to 8ppm/yr, as the 10V DCV range has 8ppm 24h uncertainty, and after one year 16ppm, therefore 8ppm drift.It's a pity, that they did not improve that stability above the 3458A, by also running the LTZ1000A on 95°C. (15k/1k divider for oven)They could have reduced that temperature to 75°, so that the elaborate selection process would have been easier, as that lower temperature would give stabilities of 2..4ppm/year very easily.About the monitoring process, see HP journal 4 / 1989, for the 3458A.http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1989-04.pdfAlthough the circuit is very similar to the one in the 3458A, it only features 1ppm/°C temperature stability, whereas the 3458A has 0.15ppm/°C. Maybe that's due to the usage of all SMD resistors for the oven and reference circuitry, (instead of leaded metal foil ones), which mainly influence the T.C.The reason, why the 10V DCV range is the most stable on mostly all bench DMMs, is the fact, that this range relies on the stability of the reference plus one or two resistive amplifiers for the A/D conversion reference voltages of about +/-10 or +/- 12V. These two amplifier circuit will also be Autocal'ed for T.C.All other DCV ranges have additional resistor dividers implied, which create these 5ppm/°C.That is the 100:1 high voltage divider for 100, 1000V, and a x10, x100 amplifier for 1V, 100mV.Latter one is also used on DCI, so creating an even higher T.C. as the current shunt resistors add up here.The 10k VH102Z resistor is used as a real reference resistor, max. 0.8ppm/°C T.C. and (per datasheet) 2ppm/6 year stability.The Autocal function transfers its uncertainty and stability to all other Ohm ranges, to some degree.The datasheet of the 34470A therefore is very conservative regarding Ohm 1 year stability, although this reference resistor may probably be much better than the one in the 3458A!Frank

author: EEVblog
author_rank: Unknown
timestamp: March 13, 2015, 07:34:36 am
content: Quote from: Dr. Frank on March 13, 2015, 06:49:42 amYes, but it's not a general purpose multimeter.QuoteWhy would they?The 34470A is not aimed at the same metrology market as the 3458A. It is not a replacement for the 3458A.

author: hikariuk
author_rank: Unknown
timestamp: March 13, 2015, 08:08:19 am
content: It looks like they were even thinking of using that pin header on the old model, if those holes you can see just to the right of the old voltage reference are anything to go by (they look a bit too big for vias and they seem to line up with the header).

author: bundy
author_rank: Newbie
timestamp: March 13, 2015, 08:45:07 am
content: Funny how they build their reference. All refdesses are equal to the typ. application schematic. They put a '9' in the 'extra' parts, so e.g. R95 is in parallel to R5.Once I've designed such LTZ1000 reference. Since the datasheet is very conservative I've asked LT for more info and they said just use a 1:1 copy of the original Jim Williams's design and layout and it will work. I got even some hand written notes about this reference... They could not tell me some specific tolerances of the LTZ (for worst-case designing) or if the 1013 dual opamp could be replaced with a more common type nowadays, etc.So it is like Keystone got the same advice from LT as I did:)

author: HighVoltage
author_rank: Super Contributor
timestamp: March 13, 2015, 10:12:50 am
content: Thanks for the great teardown. We have ordered one of these meters today.As to removing the case, if you bring the handle upwards, you can remove the handle by pulling it out and the the case will slide off easily.

author: Tothwolf
author_rank: Regular Contributor
timestamp: March 13, 2015, 12:05:40 pm
content: 'I_BOOT' is still present, they just moved the sinkscreen down next to the relay. Part of the second "O" is missing due to the guard groove.The 2N3904 on that particular voltage reference board is a Fairchild part (the -C43 batch code gives it away, I've been using a lot of these recently).One glaring question I have is why did they use one of Nichicon's cheapest series for the two large filter capacitors? VR series are general purpose 85C parts which aren't long life, low ESR, or anything. Couldn't they have at least gone with some 105C rated VZ series parts since those would last longer? (Capacitor life doubles for every 10C below its rated temperature.) Better still, a PM or PW series 105C long life part? For $3000 I would certainly not expect to see VR series capacitors in the thing. Heck, if Nichicon was still making VX series radials (which they only make in axial now) I guess Keysight probably would have probably would have even used those...

author: funkyant
author_rank: Unknown
timestamp: March 13, 2015, 12:38:32 pm
content: This might be a really stupid commentOn the 24 hour specs, which you mention is pretty much useless unless you are using it in the factory, doesn't it say ACAL, which you can perform yourself?

author: 6thimage
author_rank: Regular Contributor
timestamp: March 13, 2015, 02:26:54 pm
content: Quote from: funkyant on March 13, 2015, 12:38:32 pmACAL compensates for temperature not time - it is so you can take a multimeter calibrated at 23 deg C and run it in a 50 deg C environment (i.e. in a rack) without having to deal with large temperature-based errors or getting the cal lab to calibrate it at a higher temperature.

author: funkyant
author_rank: Unknown
timestamp: March 13, 2015, 02:30:52 pm
content: Ok, so that 24 hour spec is drift in the first day from factory cal?

author: Tek_TDS220
author_rank: Regular Contributor
timestamp: March 13, 2015, 02:52:14 pm
content: Regarding the cutouts surrounding the LTZ1000 reference, you mentioned that the board might be a FR4 or a special low coefficient of thermal expansion material. It is likely that the board is made from conventional epoxy. In glass fiber boards (as these are), the CTE in the XY axes (in the plane) are dominated by the glass fibers that are oriented in the XY plane. The use of low CTE thermosets in such boards has a significant reduction only in the Z-axis CTE.Another important specification for PCB's is water absorption, which causes changes in AC and DC dielectric properties. That might be a factor in a high accuracy meter like this one.

author: 6thimage
author_rank: Regular Contributor
timestamp: March 13, 2015, 03:15:54 pm
content: Quote from: funkyant on March 13, 2015, 02:30:52 pmYes, that's correct.

author: drago
author_rank: Contributor
timestamp: March 13, 2015, 04:08:31 pm
content: Would be interesting to see what Agilent competitor have put into Keithley DMM7510.DMM7510 atNewarksells for $3,990.00 which is almost 1k more than 34470A.Looking at the 10V specs it could be LTZ1000.Datasheet

author: schopi68
author_rank: Regular Contributor
timestamp: March 13, 2015, 04:44:27 pm
content: I am sure the cutouts on the boards are thermal "moats" for a thermal decoupling of the voltage reference. Otherwise every temperature change produced by airflow and the other parts on the board would change the temperature/temperature gradient on the the LTZ1000. So putting the 2N3904 behind a third thermal moat and outside of the air shielding case (and using a non smd device) makes sense too.

author: saturation
author_rank: Super Contributor
timestamp: March 13, 2015, 04:45:46 pm
content: Yes, I would too. There was a supposed to be a tear down in eevblog mid-Feb of one other Keithley model that has not yet been followed through. There are not many DMMs [ or manufacturers, for that matter] that do >= 7.5 digit. Given the long term history of reliability of Agilent, and this tear down, good as always by Dave, it made me favor the Keysight model, not to mention its more attractive list price.Quote from: drago on March 13, 2015, 04:08:31 pm

author: tszaboo
author_rank: Super Contributor
timestamp: March 13, 2015, 07:30:37 pm
content: The 24H is useful if you have your own calibration equipment inhouse, just to know how often do you need to cal.I was kinda disappointed looking at the refernce board. The old 3458A had proper vihay foil resistors, these look like (probably still very good) thin film. Also the capacitors...Anyone noticed how the diode from the reference was also missing the diode in series with the heater? Or how Dave was showing the wrong page schematic for the negative reference?

author: 6thimage
author_rank: Regular Contributor
timestamp: March 13, 2015, 09:59:22 pm
content: Well I finally got around to watching the end of the video (it's great as always) - so this is aimed towards Dave.The chip with the thermal pad and exposed copper (U606) is a TMP75 - an I2C temperature sensor from TI (Burr Brown)http://www.ti.com/lit/ds/symlink/tmp75.pdf. This is used by the multimeter to report its temperature (in the calibration settings).With the Vishay resistor (R324 - in the metal can) having a very low temp co, it makes sense for them to be using it for the ACAL functionality - hence why it isn't present in the 34461A.From what I've heard, they have also added a temperature sensor near the front panel connectors for cold point compensation (for thermocouples). As there isn't one on the measurement board, my guess is that it is on the front panel next to the connectors. I don't suppose there is any chance you fancy taking the front panel off, is there?

author: EEVblog
author_rank: Unknown
timestamp: March 13, 2015, 11:00:17 pm
content: Quote from: drago on March 13, 2015, 04:08:31 pmI'm supposed to have one of those on the way as well.

author: EEVblog
author_rank: Unknown
timestamp: March 13, 2015, 11:01:55 pm
content: Quote from: 6thimage on March 13, 2015, 09:59:22 pmI had a quick look for that but didn't see it. I can only presume it is buried away under the plastic connector housing.

author: EEVblog
author_rank: Unknown
timestamp: March 13, 2015, 11:05:07 pm
content: Quote from: NANDBlog on March 13, 2015, 07:30:37 pmWhy are people expecting the 34470A to match the metrology grade 3458A?The 34470A is designed as a cheap-ish good value bench/system 7.5 digit meter in the TrueVolt range. It is not a replacement for the 3458A for metrology applications.

author: blackdog
author_rank: Frequent Contributor
timestamp: March 13, 2015, 11:16:39 pm
content: Hi Dave,Because al lot of people want 3458A specs in a nice box like the 34470A...Kind regarts,Blackdog

author: John Coloccia
author_rank: Super Contributor
timestamp: March 13, 2015, 11:24:54 pm
content: Do we seriously need to call it "Keysight", or can we just keep calling it HP or Agilent?

author: Someone
author_rank: Super Contributor
timestamp: March 13, 2015, 11:49:02 pm
content: Quote from: Tothwolf on March 13, 2015, 12:05:40 pmThese high reliability devices are designed very conservatively, a proven part that has been used in designs with a long field record would be preferred over the modern equivalent even if there were some small theoretical improvement available. Shock testing and thermal cycling can be much more destructive on the tighter built capacitors and these environmental tests are the sorts of characteristics that are built into HP/Agilent/Keysight (and Tektronix) products that dont make it to the spec sheet.

author: tszaboo
author_rank: Super Contributor
timestamp: March 14, 2015, 12:19:35 am
content: Quote from: EEVblog on March 13, 2015, 11:05:07 pmThe SMD Z-Foil resistors cost something like 5-6 dollars each, you need 4-6 of them for the LTZ1000, that could get your stability much further as it is now. And we expect things like this because the price difference between the 65 and the 70 is big, it would have fit into the gap. Also, as you pointed out, it wasn't too expensive for the current sense on the main board, there is that hermetic resistor. Also, there are some not populated part on the reference, that is where the more stable parts will go.I'm guessing there is a 34480A coming, and they save all the possible improvement for that one. I'm actually not blaming the engineers for that, but it looks like the specifications were written by the marketing department.

author: JoeN
author_rank: Frequent Contributor
timestamp: March 14, 2015, 04:26:46 am
content: Since there seem to be a surplus of very knowledgeable people in this thread concerning high stability voltage references and high stability resistors, I wanted to ask this question that is bugging me:What is the difference between the LTZ1000ACH and the LTZ1000CH? The specs seem to give the ACH as lead free and also seem to indicate that the CH should be run hotter, but it gives the performance of both as the same. Is that true or are one of these "better" than the other? The LTZ1000ACH is priced as if it is the better part but I can't figure out why.http://www.linear.com/product/LTZ1000As far as high stability resistors go, you mention that Vishay resistors are expensive. Is there any possibility that LT's quad matched resistor IC could be used instead? Not that it is all that much expensive, but damn, the temperature stability on these resistors seems almost impossibly good (0.2ppm/°C and matched). That's a lot better than what I see from Vishay. What do you know about it?http://www.linear.com/product/LT5400http://cds.linear.com/docs/en/datasheet/5400fc.pdfThanks for any info.

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 14, 2015, 08:11:07 am
content: Quote from: EEVblog on March 13, 2015, 11:05:07 pmHi Dave,I simply would have expected stability parameters, which are adapted to a (worst case) 6 1/2 digits reading (at e.g. 1.201000V), to really make use of the 10 times higher resolution.That would require 0.1ppm linearity of range. As it is 1 ppm of range instead, this 1.201000V measurement is uncertain to 10 digits already.Further on, a 24h stability of < 1ppm per 24h would be required, 10ppm give additional 10 digits on a 6 1/2 digits reading.A T.C. of 1ppm/°C (instead of 0.1ppm/°C) additionally gives 5 digits at the usual +/- 5°C interval.That sums up to 25 digits for a 1.201000V reading, making the additional digit absolutely useless!Instead, all these 3 crucial parameters should have been 10 times better.That could have been easily and cheaply achieved, if the Keysight engineers would have put a little bit more brain into the analogue design, and more test and validation time into the development.Instead they obviously simply recycled a lot.And the 34470A is not really a cheap instrument.The design of the 3458A is already 27 years old, so a lot of clever improvements of its circuitry elements could have been done in the meantime, at even lower cost, to be incorporated into lower resolution instruments. (The 34401A was a spin-off from the 3458A techniques)Although promoted as a metrology grade instrument, the 3458A in practise was mainly intended for rough industrial / military environment (high Tamb. of 55°C) and not really optimized for metrology (typ. 15...35°C specification)It is in fact designed to 7 1/2 digits performance (at 1/10 of full scale), i.e. 0.02 ppm linearity of range, 0.15ppm / °C T.C. and 1ppm 24h stability.But in the end, 8ppm/yr. for DCV and 10ppm/yr. for OHM are really mediocre for metrology use, but that can easily be improved by proper component selection, as the Fluke 8508A / Wavetek-Datron 1271 / 1281 demonstrate.Such an improved level of stability I would have already expected for the "new" LTZ1000 reference in the 34470A. Both the key elements, i.e. the volt and Ohm references, already have the potential for greatly improved performance ..As a conclusion, the 34470A is really a nice instrument, with additional statistical and graphical features, and some improved characteristics.Without competing against the still top-of-the-notch 3458A, Keysight could have designed it better, more appropriate to 7 1/2 digits, anyhow.Frank

author: HighVoltage
author_rank: Super Contributor
timestamp: March 14, 2015, 08:21:22 am
content: Quote from: DiligentMinds.com on March 14, 2015, 04:39:44 amThanks for your great explanations.What is the "artifact calibration" in the 3458A and why is it better than the Fluke 8508A.Is the "artifact calibration" similar to the ACAL of the 34470A?

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 14, 2015, 08:39:29 am
content: Quote from: HighVoltage on March 14, 2015, 08:21:22 amThe 3458A requires a 10V and a 10k reference only, to traceably calibrate nearly ALL ranges and modes. Its ultra linear (0.02ppm of range) A/D converter is the key element for that feature, unrivaled up-to-date. See hp journal 4/1989.All other instruments, including the 8508A / 1281 require individual Cardinal Points for each range and each mode, instead. That sums up to about 40 different calibration values to be supplied to the instrument by a calibrator (Fluke 5720A) plus appropriate transfer standards, for correct TUR.The 8508A / 1281 makes intensive use of Vishay BMF resistors, giving lower T.C. and higher timely stability than in the 3458A, and also got a more stable voltage reference, an LTZ1000 or an LTFLU at about 50°C , so most of the 90 days / 1 year stability parameters are better to a factor of 2-3 over the 3458A!The 1kV DCV range in the 8508A features the usual power dissipation compensation, which the 3458A is lacking, that leads to mediocre 12ppm uncertainty at 1000V, compared to 2ppm for the 8508A.By simply replacing these crucial components in the 3458A by better and actual ones, it would easily outperform the 8508A by far.Frank

author: JohnnyBerg
author_rank: Frequent Contributor
timestamp: March 14, 2015, 09:23:27 am
content: Quote from: NANDBlog on March 14, 2015, 12:19:35 amIsn't that always so?I remember my time at the Philips lab. Always a huge battle between the commercial and technical guys. The commercial guys wrote the specs and defined the knobs and other trivialities, and we technicians were "forced" to implemented that.People want bits, digits and megapixels. Only a few look at the specs behind that, and realize that more bits, digits, megapixels does not always improve quality. But who cares, we got a 20 megapixel camera and a 24 bit ADC.

author: HighVoltage
author_rank: Super Contributor
timestamp: March 14, 2015, 09:33:55 am
content: Quote from: Dr. Frank on March 14, 2015, 08:39:29 amThanks so much for this detailed information.May be Keysight is working on a successor to the 3458A?

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 14, 2015, 10:25:45 am
content: Quote from: HighVoltage on March 14, 2015, 09:33:55 amYou're welcome!Probably not.. it's a very limited market, and the 3458A still is one of the best performers.Maybe there's a model upgrade only, as many of its components are obsolete since a long time, and the user and bus interfaces are outdated, and these TrueVolt graphical features may be welcome.But Keysight would have to dig deeply into the software and hardware architecture of the 3458A, and I fear, they have got rid of many of the brains back then, so they simply lack Know How to make real improvements.I repeat again: The 34470A is mostly a copy and paste device, no really new inventions here!Frank

author: TiN
author_rank: Super Contributor
timestamp: March 14, 2015, 02:44:44 pm
content: Given all that it leaves freedom to voltnuts use own more stable LTZ1000 ref's in 34470A or even 34465A'sJust design proper adapter connection and recalibrate unit.

author: schopi68
author_rank: Regular Contributor
timestamp: March 14, 2015, 03:06:52 pm
content: Quote from: Dr. Frank on March 14, 2015, 10:25:45 amTerrible to see, there is a large possibility that you're right. Following the HW-Journal article authors (instrument developers) for the 3458A i could see that:Wayne C. Goeke is working for Keithley in the meanwhile (latest Patent 2014).Ronald L. Swerleinhttp://www.keysight.com/upload/cmc_upload/All/Swerleins_Algorithm.pdfhad his latest Agilent patent 2005.Stephen B. Venzke had its latest Agilent Patent 2007.David E. Smith seems to be working for HP (latest Patent issued 2011)Almost every one of them is aged over 55 in the meanwhile (or even retired).

author: funkyant
author_rank: Unknown
timestamp: March 14, 2015, 09:37:43 pm
content: I learn so much from reading you guys discuss this stuff, both in this thread and all over this forum. These multimeters are well outside the scope (pardon the pun) of my profession, but it's all very interesting none the less

author: Len
author_rank: Frequent Contributor
timestamp: March 15, 2015, 03:55:17 pm
content: Quote from: John Coloccia on March 13, 2015, 11:24:54 pmCall it "that company that makes the E3631A bench supply". That covers all their names, and will probably still be right the next time they re-brand.

author: nixfu
author_rank: Unknown
timestamp: March 15, 2015, 05:44:22 pm
content: Why couldn't they have just spun off a company called "Agilent Instruments" or something.

author: Tothwolf
author_rank: Regular Contributor
timestamp: March 16, 2015, 03:28:00 pm
content: Quote from: Someone on March 13, 2015, 11:49:02 pmTherein lies the rub... Nichicon does offer some high reliability series parts, but Keysight didn't even go with ageneral purpose105C rated product such as the VZ series and instead used went with the cheapergeneral purpose85C VR series. Will those parts last 5 years, 10 years? Sure... 20-30 years? Probably not.I just replaced the aluminum electrolytic capacitors in one of my Tektronix 2213 (not 'A' version) scopes and even back in 1982 Tektronix used some 105C rated parts. It contained a mixture of 85C and 105C, with most of the large can parts being 105C rated.

author: tszaboo
author_rank: Super Contributor
timestamp: March 16, 2015, 04:10:32 pm
content: Quote from: NANDBlog on March 13, 2015, 07:30:37 pmBTW I just noticed they merged the two diodes into CR1.

author: schopi68
author_rank: Regular Contributor
timestamp: March 16, 2015, 04:44:32 pm
content: Quote from: NANDBlog on March 16, 2015, 04:10:32 pm

author: 3roomlab
author_rank: Frequent Contributor
timestamp: March 18, 2015, 04:35:20 am
content: Quote from: TiN on March 14, 2015, 02:44:44 pmi always hear that the units are not user caliberate-able ... or that is not true? ...*waiting for continuation of video part 2?*

author: 6thimage
author_rank: Regular Contributor
timestamp: March 18, 2015, 01:28:11 pm
content: Quote from: 3roomlab on March 18, 2015, 04:35:20 amIt depends on the user, but normally no. They are not difficult to calibrate (the calibration procedure is in the back of the manual and only takes around half an hour), but they require you have specialist equipment - such as a Fluke 5720A calibrator (around $40-50k used) that has been calibrated against a higher standard. Some users will have access to the required equipment, but for the rest of us, it is easier, cheaper and more reliable to send it into a cal lab.

author: Marco
author_rank: Super Contributor
timestamp: April 04, 2015, 02:55:43 am
content: Are the front ends in these new meters still partly discrete? (ie. discrete matched FETs as inputs on the initial differential amplifier.)

author: EEVblog
author_rank: Unknown
timestamp: April 04, 2015, 04:42:49 am
content: Quote from: Marco on April 04, 2015, 02:55:43 amThe Keithley DMM7510 7.5 digit meter uses a lot of matched paid FET's

author: Marco
author_rank: Super Contributor
timestamp: April 04, 2015, 06:46:22 am
content: The only ones which could be it on Keysight are Q301/302/401/402 ... but there are no guard rails on them, so it seems that Keysight at least have ditched them.The diversity of opamps and multiplexers Keysight uses is almost silly BTW.

author: Marco
author_rank: Super Contributor
timestamp: April 04, 2015, 07:15:38 pm
content: Unless I'm missing something I don't see anything which could be matched (J)FETs in the 34470A, or even non matched individual ones, no metal cans for a start ... but even if they used some in plastic packages (like the ALD ones) there should still be guard rings.

author: Marco
author_rank: Super Contributor
timestamp: April 04, 2015, 08:03:50 pm
content: Quote from: DiligentMinds.com on April 04, 2015, 07:45:38 pmHard to say without doing the math (which I can't, I still don't understand how they even deal with dielectric absorption). In the end if you can keep it steady enough to keep the errors below noise while throwing the occasional cycle of autocal measurements in between the normal ones that's enough.

author: Dr. Frank
author_rank: Super Contributor
timestamp: April 04, 2015, 08:22:13 pm
content: Quote from: DiligentMinds.com on April 04, 2015, 07:45:38 pmI think, i already posted this earlier in this thread..The AUTOCAL of the 34470a is really nothing compared to the 3458a. It also has to be calibrated on each mode and each range, whereas the 3458a only needs 10V and 10kOhm references.Simple reason: The 34470a only is linear to 1ppm, but the 3458a to 0.02 ppm, so precise 10:1 Transfers are possible.The 8508a only lives from its many ultra stable Vishay bulk metal foil resistors.Its linearity is not as good, as the 3458a, so it needs the usual > 34 Cardinal Point referencess from a calibrator, plus additional ratio standards..If you would use better resistors for the 3458A, it would outperform the 8508a, of course.Stable thermal environment is needed in any case for analogue metrology.To my opinion, Keysight is not capable anymore to design such an improved sophisticated instrument..brain drain.. Otherwise the 34470a would've been better.. worth the 7 1/2 digits..Frank

author: plesa
author_rank: Frequent Contributor
timestamp: May 10, 2015, 06:24:16 pm
content: Interesting comparisons Keysight 34470A with Keithley DMM7510http://imgur.com/gallery/Wbx7q

author: saturation
author_rank: Super Contributor
timestamp: May 10, 2015, 06:51:09 pm
content: Very nice, when the Keysight is configured to match the Keithley, you get more with Keithley for your dollar. The test equipment for the evaluation can't be beat.Quote from: plesa on May 10, 2015, 06:24:16 pm

author: HighVoltage
author_rank: Super Contributor
timestamp: May 10, 2015, 09:59:56 pm
content: Quote from: plesa on May 10, 2015, 06:24:16 pmThe results of the 34470A, shown in this comparison, match my own findings of my 34470A.As if the readings are always a little low. (uV and nA)But, who knows, may be the Keithley instrument was just fresh calibrated.Would be nice to see Dave do a comparison between the instruments.

author: Vgkid
author_rank: Super Contributor
timestamp: May 10, 2015, 10:34:39 pm
content: Looks like the Keithley has a fair bit less std dev in the measurement results.

author: twobeseen
author_rank: Newbie
timestamp: May 11, 2015, 10:57:11 pm
content: Hi would somebody be so kind and explain to me why DMMs always have 4.5 or 7.5 displays? What about that half display? why not 4 or 7...Also I don't see a "half" display, the last number always goes from 1 to 0I just don't get it.... Am I just stupid? This must be something so easy to understand that nobody explains it in the data sheets.

author: twobeseen
author_rank: Newbie
timestamp: May 13, 2015, 07:10:34 pm
content: somebody was kind, the half digit seems to be the MSB, that only goes from 0 -> 1, because the whole range is divided into multiple ranges e.g. 100mV, 1V, 10V, 100V