Author Topic: EEVblog #731 - Keithley DMM7510 7.5 Digit Multimeter Teardown  (Read 34778 times)

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Inside the new Keithley DMM7510 7.5 Digit Bench Multimeter
What gives this unit it's superb 16ppm/1year accuracy specification?
What construction techniques have they used?
How and why are Fluke so heavily involved?
What considerations are given to the power supply and isolation aspects?
How does it compare with the cheaper Keysight 34770A meter?

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LTC1050: http://www.linear.com/product/LTC1050
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LSK389 Ultra low noise matched JFET http://www.linearsystems.com/assets/media/file/datasheets/LSK389.pdf
SSM2212 Dual matched transistor: http://www.analog.com/media/en/technical-documentation/data-sheets/SSM2212.pdf
DG411 Precision analog switch: http://www.vishay.com/docs/70050/dg411.pdf
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Freescale MPC5125 Processor: http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=MPC5125

 

Offline Dr. Frank

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Re: EEVblog #731 - Keithley DMM7510 7.5 Digit Multimeter Teardown
« Reply #1 on: April 09, 2015, 07:26:24 am »
Dave,

thank you very much for that great video!!

You can literally feel and see, how much of analogue magic was designed into this instrument..

All these guard rings, isolation slots, and shielding methods, including that really ingenious low noise DC/DC converter..

They put in all of their know how about  Keithley electrometers and Fluke calibrators, obviously..

And one of the former HP3458A engineers works for Keithley since a few years..

So there's really where the brain is inside, not in the Keysight  counterpart.. that's very obvious, if you simply watch both videos.


OK, some remarks about the voltage reference and the thermal shielding..

This LTFLU package is supposed to be the regular one with 4 pins only, (judging from the type designator printing and photos from this device),  so there  is no heater inside the TO99 package, or not used, if there is any heater implemented on the reference chip. (as DiligentMinds always speculates)..

The white (ceramic ?) collar you see around the LTFLU, seems to be the exterior heater, it's named 'H2', obviously.
Its temperature might be controlled by the 2nd OpAmp , maybe.

The plastic or metallic shield around the whole assembly, also the one on the bottom side, also serve as a thermal isolation, so that the whole interior may heat up .. there's a LM35D temperature sensor also, maybe to measure if the whole assembly has been stabilized.

On the bottom side, I assume that there are 4 stable, (leaded?) resistors, which are always needed for the topology of this Reference Amplifier, aka LTFLU / SZA263 / T.I. device from all Fluke calibrators and voltage standards.

Anyhow, very impressive, and maybe, some day, Keithley will replace Keysight as the top notch DMM manufacturer..

Frank
« Last Edit: April 09, 2015, 07:53:13 am by Dr. Frank »
 

Offline HighVoltage

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Re: EEVblog #731 - Keithley DMM7510 7.5 Digit Multimeter Teardown
« Reply #2 on: April 09, 2015, 07:39:20 am »
Really great tear down! Thank you for that.

Nice to see some German made WIMA capacitors on the board as well.
Now it would be nice to have a side by side comparison between this one and the Keysight 34470A 7 1/2 digit meter.
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Offline 3roomlab

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Re: EEVblog #731 - Keithley DMM7510 7.5 Digit Multimeter Teardown
« Reply #3 on: April 09, 2015, 08:58:50 am »
when pointer tip wriggled with the special DC-DC xfmr ... the magnet wire moved ... shouldnt that be glued and not moving? like the capacitor?
spheres of influence, example linustechtips. can you feel the brainwashing? showing off equipment, etc. were you swayed and baited? with immense popularity (and social "titles"), can you afford to disagree?
 

Offline digital

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Re: EEVblog #731 - Keithley DMM7510 7.5 Digit Multimeter Teardown
« Reply #4 on: April 09, 2015, 09:47:14 am »
Dave thank you for the look at something that I will not be able to afford,what a beautiful piece of design engineering.To be able to look at such engineering goodness was a treat,thank's again for the video.Regards to all.
 

Offline TiN

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Re: EEVblog #731 - Keithley DMM7510 7.5 Digit Multimeter Teardown
« Reply #5 on: April 09, 2015, 11:36:25 am »
Money video!

I bet it will put some heavy thinking into voltnut minds who wanted to buy 3458A before.

Few notes I think worth mentioning.

Reason for wonky optoisolation board shape was probably due using same digital processing board between different instruments, not just DMM7510. Not checked, maybe 2450/2460 uses same digital board? Would be expected to unify that piece of design and carry over with different instruments, since it's lot of man-hours spent on doing that bad boy. EDIT: Dooh..yes, video at 44min:09 sec says that :D

Keithley are good on low-signal magic. During tracing and reversing my Model 2001 units I had a lot of time scratching my head, thinking what are hell is this circuit is doing :) Even now since we have full schematics for 2001, lots of areas in it are rather cryptic.

Dave mention it's 18-bit ADC, but I remember Keithley marketing materials says 32-bit? Can find source yet, but somehow that stick into my mind.

Given options and free space on board, unpopulated FPGA, empty spot likely for VPG foil near LTFLU reference, wonder if there is something like DMM8510 in works with 8.5 digit somewhere in Keithley.

Interesting that they did not use Z-foil VHP resistor, but rather normal VHP203

R250,R499,R252,R500,R83,R81 around VREF are 99% surely VPG resistors, I have very similar looking VPG foil SMD resistor with same marking style as well :)

NFP version of Keithley gear usually more expensive than usual ones, btw :D

Also taking usual Keithley's numbering scheme on PCB boards, I bet million dollars that DMM7510 originally had Model 2040 name, as on analog board labels :D
« Last Edit: April 09, 2015, 12:06:32 pm by TiN »
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Offline HKJ

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Re: EEVblog #731 - Keithley DMM7510 7.5 Digit Multimeter Teardown
« Reply #6 on: April 09, 2015, 11:39:04 am »
Dave mention it's 18-bit ADC, but I remember Keithley marketing materials says 32-bit? Can find source yet, but somehow that stick into my mind.

It has two ADC, one for high resolution and one for fast sampling.
 


Offline HighVoltage

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Re: EEVblog #731 - Keithley DMM7510 7.5 Digit Multimeter Teardown
« Reply #8 on: April 09, 2015, 12:03:45 pm »
Money video!
I bet it will put some heavy thinking into voltnut minds who wanted to buy 3458A before.

You know, that is exactly what I was thinking.
I have been looking at the 3458A for a long time, just have not made a decision to buy.
Who knows, this one might be a good alternative.
May be Dave will also give us a review video.

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Offline TiN

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Re: EEVblog #731 - Keithley DMM7510 7.5 Digit Multimeter Teardown
« Reply #9 on: April 09, 2015, 12:09:02 pm »
If that would be me, I would not think a second chance, and get Keithley beast. Yes, 3458A is great and proven, but something bends me in Keithley way.
I wish my hobby funds could allow getting 7510. Trade 2002 to 7510 anyone?  ;D
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Offline Dr. Frank

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Re: EEVblog #731 - Keithley DMM7510 7.5 Digit Multimeter Teardown
« Reply #10 on: April 09, 2015, 12:17:18 pm »
No way, guys!

Even though Wayne C. Goeke, designer of the HP3458As ADC, is the person to join Keithley, the 7510s ADC by no means comes near the 3458A!
Lay their specs side by side, and you will promptly see a big quality difference, yet.

Its linearity is mediocre 1..2ppm, again, like most all other 6 1/2 ... 7 1/2 DMMs, and still no other DMM has got this unique , true AUTOCAL function...
Obviously, the true value of this function (i.e., a complete cal lab built inside) is still not clear to everyone...

Frank

« Last Edit: April 09, 2015, 12:26:11 pm by Dr. Frank »
 

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Re: EEVblog #731 - Keithley DMM7510 7.5 Digit Multimeter Teardown
« Reply #11 on: April 09, 2015, 12:34:10 pm »
I have been looking at the 3458A for a long time, just have not made a decision to buy.
Who knows, this one might be a good alternative.
May be Dave will also give us a review video.

They are essentially chalk and cheese.
The 3458A is a metrology grade instrument, used as a transfer standard in cal labs around the world. There is a reason for this.
The 7510 is not. It is a practical 7.5 digit multimeter with a bewildering array of features, orders of magnitude more useful than the 3458A.

IMO, anyone outside of a cal lab or other very specific niche industry requriement who buys the 3458A over the 7510A is (volt)nuts.
I would take the 7510 over the 3458A any day of the week. I'd even take the 34470A over the 3458A. heck, even the 6.5 digit 34461A, there is just no comparison when it comes to practical usage.
 

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Re: EEVblog #731 - Keithley DMM7510 7.5 Digit Multimeter Teardown
« Reply #12 on: April 09, 2015, 12:36:23 pm »
Dave mention it's 18-bit ADC, but I remember Keithley marketing materials says 32-bit? Can find source yet, but somehow that stick into my mind.

Custom 32bit Keithley special for slow measurements, 18bit AD7982 for faster readings.
I actually spy two AD7982's on the board.
 

Offline dr.diesel

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Re: EEVblog #731 - Keithley DMM7510 7.5 Digit Multimeter Teardown
« Reply #13 on: April 09, 2015, 12:45:52 pm »
IMO, anyone outside of a cal lab or other very specific niche industry requriement who buys the 3458A over the 7510A is (volt)nuts.e.

Yup, and like mentioned above I'd bet money a K8510 is in the works, and probably cheaper than the old trusty 3458A.

If you're really dying for that 8th digit to stare at, it might be present via SCPI.

Offline TiN

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Re: EEVblog #731 - Keithley DMM7510 7.5 Digit Multimeter Teardown
« Reply #14 on: April 09, 2015, 01:30:15 pm »
Ok, I'm not voltnutty nut enough then, after rethinking what Dr. Frank said, he have a valid point.

1ppm linearity (1ppm range), somehow I expected better, that missed my attention. They could do better, even 2001 is <2ppm maximum, and 2002 is <0.2 max.

But even then, like Dave says, for bench 7510 is great tool.
Keithley's DS does mention noise is "equivalent to or better than many 8½-digit DMMs.", with 1 NPLC.

Also for fan, i think it was put like that intentionally, to have airflow go around case first, and distribute evently, rather than blow directly on components causing turbulence and all uneven gradients.
« Last Edit: April 09, 2015, 01:58:16 pm by TiN »
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Online Marco

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Re: EEVblog #731 - Keithley DMM7510 7.5 Digit Multimeter Teardown
« Reply #15 on: April 09, 2015, 02:30:26 pm »
Even though Wayne C. Goeke, designer of the HP3458As ADC, is the person to join Keithley, the 7510s ADC by no means comes near the 3458A!
Lay their specs side by side, and you will promptly see a big quality difference, yet.

I'd guess the main problem is the ASIC ... the different channel length FET's for each charge path are a bit excessive/expensive.
 

Offline Lukas

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Re: EEVblog #731 - Keithley DMM7510 7.5 Digit Multimeter Teardown
« Reply #16 on: April 09, 2015, 02:44:49 pm »
A while back, I pulled apart the firmware upgrade for the SMU 2400. Nested zips, then S-Record. IIRC, they used Greenhills Integrity as RTOS. So not your standard Linux / Windows CE job.
 

Offline schopi68

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Re: EEVblog #731 - Keithley DMM7510 7.5 Digit Multimeter Teardown
« Reply #17 on: April 09, 2015, 03:52:03 pm »
i am currently thinking... about that really interesting ingenious solutions in the ke* 7510 and it's high complexity compared to the ke* 34470A with only a quarter of the amount of PCB and parts in it (and it's smaller outside footprint), less cabling stuff and the overall tidy looking construction.  I am not sure if this correlates directly to the better specs of the 7510.

This reminds me of the HP 3468A (portable brother of the 3478A) Multimeter designed in 1982/83 and the design-philosopy named in the Hewlett-Packard Journal 2/1983 on Page 8. http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1983-02.pdf
 

Online Marco

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Re: EEVblog #731 - Keithley DMM7510 7.5 Digit Multimeter Teardown
« Reply #18 on: April 09, 2015, 04:05:19 pm »
I actually spy two AD7982's on the board.

Might use one to determine how to do the multislope run up ... it would be silly overkill for that, but not compared to all the overkill in the thing any way.
 

Offline 6thimage

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Re: EEVblog #731 - Keithley DMM7510 7.5 Digit Multimeter Teardown
« Reply #19 on: April 09, 2015, 05:41:51 pm »
Great video!

I'm a little surprised at what it looks like inside - after Agilent's/Keysight's multimeters, I was expecting the same kind of system design. But it looks like they designed the measurement board and then tacked leftovers from other products together to get the finished device - it's not particularly impressive. I would be interested in seeing the difference between Keithley's special low-noise power supply and a linear supply, to see if there are any differences or whether Keithley are using it as a hacked together method to back themselves out of a corner, that they designed themselves into.

I hoping that the review videos for both the 34470A and the DMM7510 are in the works, as a high-end multimeter comparison would be very interesting. From the few minutes at the beginning of the video, it seems that Keithley aren't using the screen very well - with smaller digits, harder to read colours and harder to see which mode the meter is in. I do wonder about the usability of the multimeter, with the touch screen being the main input method - it looked like changing the range is a little more awkward than having dedicated buttons.
 

Offline RupertGo

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Re: EEVblog #731 - Keithley DMM7510 7.5 Digit Multimeter Teardown
« Reply #20 on: April 09, 2015, 06:05:08 pm »
That secondary PSU for the analogue board is frankly bizarre. It must be switching a fair amount of current at a fair few MHz - is that really going to be a lower-noise system, even if it's locked to the sample clock,  than a decently-filtered linearly regulated bog standard mains toroid system? I'd love to see some RF EMI readings of that beast, although not as much as I'd like to see the circuit.

 

Offline FrankBuss

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Re: EEVblog #731 - Keithley DMM7510 7.5 Digit Multimeter Teardown
« Reply #21 on: April 09, 2015, 06:56:51 pm »
Nice multimeter, but I still don't understand why they need the laser trimmed resistors. I understand this for older multimeters, with less processing power, but should be no problem to use just 1%, low tempco resistors and then calibrate it in software. The Freescale microcontrollers on the board have even a double precision floating point unit, and they run at 800 MIPS, so even at 1 MHz samplerate should be no problem to do one more multiplication per sample.
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Offline SeanB

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Re: EEVblog #731 - Keithley DMM7510 7.5 Digit Multimeter Teardown
« Reply #22 on: April 09, 2015, 06:57:47 pm »
I would guess that the analogue supply is using a sine wave drive, probably at a fair amplitude and able to give a low distortion output. That will give low noise ( aside from the fundamental) and will provide enough power using the simple 2 turn primary and probably a resonant secondary with some fast switches as synchronous rectifiers on the secondary side. 1MHz as a drive looks about right for the size, and you will get a fair power as well.

I think the 21V rails are used for the relay drive, as they probably want to reduce the current in the coils, and a 24V coil will operate reliably with 21V, and still switch fast enough. There must be some switchers on the supply board though, as getting 5V off 21V with a linear regulator will involve some cooking. The converters are probably on the other side of the board, shielded by the transformer shield, and using those large collection of Nichicon and polymer caps as final filtering.
 

Offline lampbus

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Re: EEVblog #731 - Keithley DMM7510 7.5 Digit Multimeter Teardown
« Reply #23 on: April 09, 2015, 07:14:41 pm »
"spiral PCB cutouts for vibration isolation..." not.

When the plastic box/lid is in place, it holds it all tightly in place, bridging the gaps in the spiral. Effectively the box hangs directly on four tabs to the main PCB, and the internal circuitry hangs by four tags inside the box.

Thermal isolation. Not seismic isolation.

The plastic boxes look like standard off the shelf enclosures - and cheap ones at that : no gasket or cover interlocking, best can be said of them is the metal thread inserts.
« Last Edit: April 09, 2015, 07:17:11 pm by lampbus »
 

Offline SeanB

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Re: EEVblog #731 - Keithley DMM7510 7.5 Digit Multimeter Teardown
« Reply #24 on: April 09, 2015, 07:26:05 pm »
The boxes are not off the shelf, you can see the diagonals have 2 locating pips, and a corresponding hole in the PCB for them as well, and the bottom sections have the same 2 pips on the other diagonal. Makes it easy to put on the board and align so the screws are going to be in the centre of the holes in the board and will not bind on the GRP material, and positions the box very accurately.

Not cheap styrene or PVC boxes, more like a precision moulded polycarbonate, polypropylene or glass filled nylon, in a rather expensive mould.
 


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