Buyers beware, misleading 34470A reference modules (clones) on eBay.

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In the 34465A, I replaced the 4 pin precision DIL socket by 8 pin golden sockets, about 5 mm in height, so that it's possible at any time to plug in the LM399 again.

What is the spec (or part number) for the 8 pin golden socket? 

Thanks,
Donal

[TiN]

Good morning Illya,
maybe you need a strong coffee first 

Prefer herbal tea, thanks

Ok, so I was looking at "Stab_1h_LTZ_without_hat.jpg" and "34465A_1h_stability.jpg" which is LM399, which looked about same. Didn't see previous post at first, my bad.  .

You're right, ScoobyDoo just sent me a picture of top and bottom cover, which I've never seen before.

Dave's EEVBlog 34470A teardown video shows reference assembly in great details, including covers and everything. That's my only source of knowledge about these meters, as I don't have any 3446*A or 3447*A.

The 34465A currently reads the M7000 you've calibrated, 9.999 873 2V at -1°C compared to 9.999 877 6V what you have measured recently.
T.C. w/o ACAL is determined to be +0.3ppm/K

What is M7000? That is 7000 cell from 7004T unit? What M means? You guys all supersecretive about all these 7000 versions and info adding slight amount of confusion

Concerning the 24h specification: That's easy to believe, just read the specification. It's so barn door wide, i.e. 20..30 ppm in DCV, even for the 470A, that this will be easily met.
All DCV ranges were inside +/- 4ppm during the last 5 years.

Just checked spec, its not that wide for 24 hours, +/-13ppm for 34465A and +/-10ppm for 34470A. Pretty decent for just 6.5d/7.5d meters.

[Dr. Frank]

The 34465A currently reads the M7000 you've calibrated, 9.999 873 2V at -1°C compared to 9.999 877 6V what you have measured recently.
T.C. w/o ACAL is determined to be +0.3ppm/K

What is M7000? That is 7000 cell from 7004T unit? What M means? You guys all supersecretive about all these 7000 versions and info adding slight amount of confusion

Concerning the 24h specification: That's easy to believe, just read the specification. It's so barn door wide, i.e. 20..30 ppm in DCV, even for the 470A, that this will be easily met.
All DCV ranges were inside +/- 4ppm during the last 5 years.

Just checked spec, its not that wide for 24 hours, +/-13ppm for 34465A and +/-10ppm for 34470A. Pretty decent for just 6.5d/7.5d meters.

Hello Illya,
sorry for the confusion with the designators, this 'M7000' was somehow taken over since the Metrology Meeting 2019 where somebody brought a reference which was labeled 'MODEL 7000'.

There were also version from Metron, Wavetek (like the 4th cell) and Fluke, so mine would be better called an F7000, as it has several FLUKE cal stickers .. it is the third reference in the 7004T rack, which you kindly have measured to 0.3ppm uncertainty, thanks again for that!

The specification for the 10V DC range might be relatively tight, but the other DCV ranges and OHM are about 25..35ppm/24hr only, but all these ranges do perform much better than that, over years.
I'm under the impression, that the 34465A and 470A as successors of the 34401A / 410A / 411A simply have gotten the same specification for sort of historic reasons, instead of updating to the real, better data.. and the predecessors might already have performed better than specification.

However, it's not a good sign, that the 34470A was not specified tighter, like a 7.5 digit instrument. But that's no wonder either, as both instruments share an identical main board

Frank

[Kleinstein]

The ADC of the 34401 is quite different from the others. As much as I have read the ADCs in the 34410 to 34470 are still quite similar. There may be some changes in the parts used (one of the OP27 in the 34410 would be a prime candidate for an update for lower noise), but the architecture seems to be the same. So the linearity and stability are probably very similar, though it may only take minor changes to effect the INL likely more toward the better from experience and improved test tools.

The improved the reference for in the 34470 would change that much, mainly reference noise and maybe a little on the reference drift. A LTZ1000 with a 15K-1K temperature set point may not be that much lower drift than a burnt in LM399.
The ACAL  steps should not be effected much from reference noise - this is more a question of the linearity.

[Dr. Frank]

Having calibrated the DMM with the LTZ inside in all DCV ranges, I cooled it down from 23°C to 15.8°C.
The reading was -1.9ppm low, which gives an overall TC, w/o ACAL, of about +0.3pp/K.
At cold using ACAL, the reading was +3.7ppm, so I estimate the TC of the resistor network to +0.7ppm/K, and of the LTZ circuit to +0.5ppm/K, if a perfect ACAL compensation is assumed.

At normal r.t., I made many ACALs, one after the other, the readings in all DCV ranges  then were always within +/- 1ppm to nominal again, no sign of getting that mysterious offset phenomenon.
If you look at all the stability graphs over several hours, you will always see a -1.. -2ppm decrease of reading in the first 8h, or so.
I first assigned that to a warm -up effect, but that's obviously a drift right after each ACAL, instead.
This behavior was not observed when the instrument was new, and I don't understand why this is happening.

As ACV, ACI and most DCI ranges were off by 2% even after DCV calibration, I re -assembled the LM399, put the box over it, and made another DCV calibration.
Again, many ACALs always brought the DMM back to nominal within 1ppm, w/o any shift.   

I cooled it down to 8.1°C, reading w/o ACAL was -14.5ppm, which gives a total of +1ppm/°C.
ACAL brought the reading to - 6ppm of nominal.
That gives an estimate for the resistor network of +0.6ppm/K, and -0.4ppm/K for the LM399.

I made another 12h stability run. Noise was evidently less than the unprotected LM399, about 650nV_rms, but it showed some popcorn noise, therefore having about 1.5 times the noise of the LTZ reference.
Therefore the fan, which is blowing to the outside, creates some noise on both references due to air draught, confirming TiNs hint about the blocked fan.

I will later measure the LTZs T.C. directly and if its calculated T.C. is confirmed, I will probably trim it to zero, assemble it into the 34465A and have it completely calibrated.
Myself I'm missing several stimuli, or a 5720A / 5725A to do that on my own.

Frank

[Andreas]

and of the LTZ circuit to +0.5ppm/K,

 and -0.4ppm/K for the LM399.

Hmm,

what do you mean when you say LTZ cirquit and LM399? is it including the 7 to 10V transfer?
Otherwise the values look rather high to me (near room temperature).

For the LTZ + the 5 Resistors I would expect below 0.2-0.3 ppm/K and for a
LM399 I have typical 2-4 ppm deviation over 10-40 deg C.
Question: which output voltage do you measure at the LM399 (is it far away from the sweet spot of 6875 mV ?)

with best regards

Andreas

[dietert1]

I think every engineer should be able to understand the difference between Dr. Franks LM399 and "the LM399", which is an abstract entity: a multitude of voltage reference parts made after a certain receipt. Dr. Franks part is one instance and he may have caused popcorn noise when unsoldering it, maybe without using his special copper plated tool.
If Dr. Frank wanted to compare "the LTZ1000" and "the LM399", he would have to compare at least several of those parts. In this sense his statements above are a bit subjective. I'd guess using the LTZ1000 in a mezzanine  and plugging the LM399 with its hot pins into that IC socket already causes confusion.

Regards, Dieter

[Tj138waterboy]

 Don't mean to hijack the thread but have also found another semi populated board on ebay  https://www.ebay.com/itm/1-Semi-finished-Board-Ultra-Precision-Voltage-Reference-LTZ1000ACH-LTZ1000CH-/333584715972?_trksid=p2349624.m46890.l49292
I was wondering if this board was designed by any members here as well if anyone sees any issues as pics show its populated with 5ppm .5% resistors.

[Dr. Frank]

and of the LTZ circuit to +0.5ppm/K,

 and -0.4ppm/K for the LM399.

Hmm,

what do you mean when you say LTZ cirquit and LM399? is it including the 7 to 10V transfer?
Otherwise the values look rather high to me (near room temperature).

For the LTZ + the 5 Resistors I would expect below 0.2-0.3 ppm/K and for a
LM399 I have typical 2-4 ppm deviation over 10-40 deg C.
Question: which output voltage do you measure at the LM399 (is it far away from the sweet spot of 6875 mV ?)

with best regards

Andreas

Hello Andreas,

this specific LM399 has a voltage of about 7.020V, and this LTZ circuit has an exactly 2% higher voltage of 7.161V.

I only can estimate the T.C.s from the different temperatures and the ACAL procedure, by neglecting the 7=> 10V transfer non linearity.. but as these shifts are in the 10ppm region, I would assume that that is far less than the 0.5..1ppm non linearity error of the ADC. The ACAL procedure is good for about 1ppm in the 10V range, so you could really have greater deviations of T.C.s..

Yes, the calculated LTZ T.C. seems to be really high, I also have never seen more than 0.3ppm/K, so please regard this as an upper limit/estimation.
At the moment I have no chance to give more accurate results.
I promise to determine it's real T.C. within the next few weeks. 

For the LM399 I have absolutely no alternative experience, but these 0.4ppm/K seem to be in accordance with yours.

Frank

[Dr. Frank]

I think every engineer should be able to understand the difference between Dr. Franks LM399 and "the LM399", which is an abstract entity: a multitude of voltage reference parts made after a certain receipt. Dr. Franks part is one instance and he may have caused popcorn noise when unsoldering it, maybe without using his special copper plated tool.
If Dr. Frank wanted to compare "the LTZ1000" and "the LM399", he would have to compare at least several of those parts. In this sense his statements above are a bit subjective. I'd guess using the LTZ1000 in a mezzanine  and plugging the LM399 with its hot pins into that IC socket already causes confusion.

Regards, Dieter

dietert1,

I don't think it's good practice that you again completely misinterpret my findings. Are you doing that intentionally? 

At first I have NEVER soldered on this LM399, and never made a statement that I needed to unsolder this device, because inside the original 34465A, it's ALWAYS plugged with its short cut legs into a precision socket. I have clearly documented this original socket, and the alternative, better socket I used, and I really wonder why you make such false statements, instead.

I also have NEVER made a claim that my findings are sort of a general ones, I simply reported what I found on my specific unit, and on my specific LTZ1000 parts which I have used.

Therefore this - sort of - popcorn noise I see on my LM399 is clearly specific to my unit, and I have again nowhere claimed any generality about this.

dietert, please publish your own findings on your own specific 34465A / 470A, that would help everybody else much more, instead of such grumbling.

Frank

[Dr. Frank]

The noise and stability at first sight is disappointing, 782nV_rms, apparently same figure as with LM399.

Did you check the noise of the LTZ1000A alone (with 1/f amplifier) before mounting into the 34465a?

with best regards

Andreas

'Aber isch 'abe gar keine 1/f Verstärker..'

Hello Andreas,
unfortunately, I don't have this low noise amplifier you're always using. I have to live with with the limitations of my equipment, but most important, to keep everything in a comparable manner.
Therefore I will measure the noise of this PCB compared to my 3458A, or differentially to another 7.161 V source, when I make the T.C. measurements.

Frank

[Kleinstein]

Seeing some popcorn noise with the LM399 is more the normal case. Selected ones may have need of the popcorn noise, but hardly none. With more other noise it may not be so visible in the initial curve, but it likely was still there and it looks like this too.

For the LTZ1000 reference it is not clear which pins are used for the negative side. It may very well be that the "wrong" (the one with the resistors and zener current) pin of the connector is used. As there is no other hardware change chances are high the normal ADC operation uses that wrong pin, possibly also in an original 34470. ACAL may use the separate negative side contact.
Depending on the way ACAL is done the contribution from using the "wrong" negative side may be seen as part of the reference TC or as part of the ADC's (resistors)  TC.

[maat]

Seeing some popcorn noise with the LM399 is more the normal case.

Indeed. From the last genuine batch (ordered from Mouser) , out of 25, I had to toss 10 due to popcorn noise.

[eplpwr]

I placed an order with Keysight for the board (USD441 with tax on my CC) and if their shipping is as I have had in the past, the board should arrive in a week or so.

I don't expect that it will come with its housing--that would be too nice--so perhaps someone will 3D print the enclosure parts? I'll update once the part arrives.

If you ordered 34470-66303 you get the board without the two housing parts. I ordered an original board 2 years ago, and it didn't come with any shields. When the clone boards appeared, I bought one to disassemble it and figure out the connections, like those under the 8-way connector. My (clone) board arrived days before christmas and has been sitting on a shelf, while I was away. Then, Dr Frank did most of the things I had planned to do, with stunning speed.

Regarding the shields, a modified version with room for better resistors would be most welcome. Maybe the bottom shield also would need a modified version, if thru-hole components are used for an improved board.

[Dr. Frank]

For the LTZ1000 reference it is not clear which pins are used for the negative side. It may very well be that the "wrong" (the one with the resistors and zener current) pin of the connector is used. As there is no other hardware change chances are high the normal ADC operation uses that wrong pin, possibly also in an original 34470. ACAL may use the separate negative side contact.
Depending on the way ACAL is done the contribution from using the "wrong" negative side may be seen as part of the reference TC or as part of the ADC's (resistors)  TC.

Exactly, using the correct pin for REF- is possible only if the 470A uses a special SW switch to take this into account.
If you simply plug the LTZ into the 465A, the instrument has probably no other chance than to use the LM399 REF- pin.
As the LTZ board features a GND current compensation via the 4k22 resistor to V-, I assume that this difference / error on the REF- pin can be neglected, because virtually no current is flowing out of /into this pin. To complete this picture, you might take the 34410A schematic of its reference assembly, page 7, and draw the connection to this LTZ circuit..simply replacing the LM399 zener.
Then you'll recognize, that the 2.7mA supply current nicely complements the 4mA which is required from V+, anyhow.

Hint: 34410/411A share the same Multislope IV converter with the 3446xA/470As, therefore schematics should be identical or very similar.

Frank

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Hello Frank.
Firstly, thank you for the time you spent researching and documenting the possibility of making a '65 into '70 whether by way of China or in my case, by purchase from Keysight. The board should be in my hands next week, so before I do something stupid, I hope you and other contributors will take a minute to review my update plan.

My Plan:
1) From the photos posted it appears the the '65 board is populated with the through holes for the 8-pin connection, so that replacing 2x2 with 2x4 is sufficient modification.
2) Also, Frank's photo shows a new board installed, from which I infer that no changes to circuits with bodge-wire will be needed.
3) If I have read the comments correctly, the firmware (I updated to current version in December) will work with the new board.
4) A calibration may be required to account for differences in reference voltage, however this can be done without shipping to Keysight.(assume that skill, standards, etc. are available)

If anyone has a warning, suggestion or other tip, it will be appreciated. (like a source for the sockets, otherwise I'll find on Mouser)

Thanks in advance,
Donal

[Dr. Frank]

Hello Donal,
you need to desolder these 4pin female connectors and replace them with 2x4 male ones. That's pretty easy because the holes are big, but a bit flimsy to desolder these 4 lead free solder joints. I needed 3 attempts by feeding additional solder.
I used 8 pin female ones, due to using the LM399 again, but for the original board that's not optimal. see picture of the required pin connectors, on the left, these are gold plated standard ones
Just plug the KS board on the pins, no bodge required, also no SW change. Don't forget a proper air shield.
The original circuit heats up to 95°C,unfortunately,  therefore think about paralleling a 100k resistor or less to decrease the oven temperature.
This avoids melting the plastic, and gives much better timely stability. The interior doesn't heat up as the 3458A, so that's easy going.
Calibration for DCV, ACI, DCI and ACV is definitely necessary, lucky if you have all signals available

[TiN]

Melting plastic? LTZ1000ACH barely gets warm thanks to it's blessed bubble foam die attach. 

I decided not to return the module, it's just not worth it and will drop my both reference modules into tecbox to run some tempco slopes. I'll keep one original (after cleaning crap with IPA) and one will modify with Susumu 5ppm/K resistors.

[Dr. Frank]

Melting plastic? LTZ1000ACH barely gets warm thanks to it's blessed bubble foam die attach. 

I decided not to return the module, it's just not worth it and will drop my both reference modules into tecbox to run some tempco slopes. I'll keep one original (after cleaning crap with IPA) and one will modify with Susumu 5ppm/K resistors.

Hi Illya, you're probably correct.
Anyhow HP and also National Semiconductor used a high temperature plastic for the LTZ and LM 399 at 95°C. polysulfone (up to 150°C, glass temperature 190°C) is specified in the LM 399 data sheet or white paper, afaik.
The interior might heat up higher , even if the surface is luke warm only.. and polystyrol or other plastics will disintegrate over longer times, that's the reason why they are using these special plastics.
I've seen many XTAL ovens and similar, where the styrofoam was simply toast after 20..30 years.

Good to hear that you're also experimenting on this PCB, Susumu 5ppm/K sounds good.
Maybe that's also a recommendation for others who bought this PCB, or for pimping the original KS one,

regards Frank

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You need to desolder these 4pin female connectors and replace them with 2x4 male ones. That's pretty easy because the holes are big, but a bit flimsy to desolder these 4 lead free solder joints. I needed 3 attempts by feeding additional solder.
I used 8 pin female ones, due to using the LM399 again, but for the original board that's not optimal. see picture of the required pin connectors, on the left, these are gold plated standard ones

Hello Frank,
I missed seeing the gender switch, thanks for calling it to my attention. Turns out I have some gold plated round pins left over from building a test fixture for some 3458 ref boards. Once the KS board arrives and I open up the '65 I'll have a better idea of what space is available. Might it be possible to trim four pins to fit the existing female sockets with the other four soldered to the board? We'll see . . .

Any reason for round to be better than square?

Thanks again,
Donal

[Fidel]

Here are some ~50mp images of the 34470a rev3 reference board if this provides some help for anyone, including a close up of underneath the female header.

I can also confirm this successfully works in our 34465a,  but I replaced R4/R5/R91 with some nice VPG smd foil parts 

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The reference board I ordered from Keysight arrived about three hours ago and I could not resist the urge to put it to work. As Frank reported, unsoldering "lead-free" is a task that requires patience, for me at least an hour, and a good solder-sucker. I fabricated some gold pins (see photos attached) and fitted them in the new board to act as a fixture to aid alignment for soldering. Soldering and cleanup went as usual. A smoke test-before reassembly went without incident.

I removed the built in fan (temporary) and did not install any protection other than replacing the metal shields that surround the reference. I did an ACAL and hooked up a very reliable voltage source (KY 230) just to see how VDC compared. The '65 had been calibrated by Keysight a couple of years back. Now it is about 130mV too low over range 1 VDC to 100VDC consistently. Should be no problem getting it calibrated.

Many thanks to forum for help with this project. Once the calibration is completed, my plan is to do some analysis of measurements and post the results.

Cheers,
Donal

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The new ref board was installed yesterday and ran overnight connected to a 10VDC reference source. Calibration started about 10AM and finished around 12:30PM. Note: I did not run the full calibration and I did not run it in the sequence suggested. The ADC cal and zero cal were done first, followed by all the low-voltage VDC cal steps. The I stopped to check progress. DC Volts looked good and I ran the 100VDC cal, no problems. Next came the ohms cal followed by DC current cal.

At first I was discouraged by the "dissing" of the Fluke 5720A in favor of the "more accurate" Keysight 33500B series arb function generators to generate the "Frequency Accuracy Calibration" of a 10KHz sine wave at "9 to 10 VRMS." Then I used my little SDG1032 (synced to Rh time) at 7 VRMS and the cal was accepted. Then the low freq cal and finished off with a shot of 500 VDC to close out the HVDC cal.

Left for another day are all the AC flatness curves, AC current and DC amps on the 10A scale.

The work-in-progress is an overnight face-off between my 3458A and the 34465+ both connected to the same 10VDC reference. I'm capturing internal temperature and volts as well as the temperature in the lab at various locations.

More to come . . .

[TiN]

Looking at the photos, I'm concerned of using massive brass pogo pins for precision DC voltage interconnect.
Worth to check tempco on DCV as it could be affected. Also adjusting meter without at least few weeks of warmup for new reference is somewhat wasted effort, other than to check that adjustments still work.

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Hello Illya,
The pins are similar, if not identical, to the ones used in the 3458a and are not as massive as they appear in the photo. I have some a size smaller, however they seemed a bit loose fit in the ref board. Replacement is certainly possible, what would you suggest as a way of measuring the effect of temperature changes beyond correlating voltage measurement and internal temperature over an extended period of time?

Yes, the sole function of the meter for at least the next week will be to verify whether the new board yields better results against the specifications and I rely on the experience of users such as you and others on the forum for advice.

I’ll post the overnight run later today.

Many thanks,
Donal

The new update is an overnight comparison of voltage from a calibrated 10VDC reference connected to both a Keithley 6510 (KY6510) and a Keysight 34465A (KS34465). The test ran from roughly 21:00 on 20210106 to 10:00 on 2021017 over which time the temperature ranged from 24C down to 21.8C and up to 22.9C this morning. Samples were taken at NPLC=10 on the KS34465 and NPLC=15 on the KY6510.