KX-LTZ1000 based 10v transfer standard journey and tuneup

[kj7e]

Over the past year, I have been building a battery powered 10v reference based on TiN's KX-LTZ1000 board.  This was not really a project out of need, but just a project I wanted to build and experiment with.  I ended up building three of the KX boards, the first one I had accidentally revered the polarity from the 15v power supply feeding it.  The power supply was not current limited and spiked 20 amps as the input filtering 47uF tantalum caps smoked.  I replaced all three caps and two current limiting resistors and it came back to life, but the voltage shifted a bit so I was skeptical (after 6 months of testing turns out this board is rock solid).  Then I built a second KX board, this one looked very promising but I was seeing a voltage jump of a few PPM randomly, I fought this for a month and never did figure out what the deal was, I suspect its the LTZ1000 chip itself.  Since I had all the parts to build a third, minus another LTZ1000, I decided to try a third time.  Third time was the charm!  Unfortunately I had calculated and spec'ed a Vishay VHD200 for the 7->10v buffer based on a slightly different voltage, but I was able to compensate in the trimming section.

The KX ref and buffer board would be placed in an oven held at 35C, to stabilize the buffer resistors mostly.  Rather than post duplicate photos and info here are some links to the build already posted.

Initial KX build;
https://www.eevblog.com/forum/metrology/kx-reference/msg1230341/#msg1230341

Experimenting with draft shields on the LTZ1000 can and leads;
https://www.eevblog.com/forum/metrology/kx-reference/msg1230535/#msg1230535

The oven build begins (oven controller schematic attached here);
https://www.eevblog.com/forum/metrology/kx-reference/msg1236890/#msg1236890

Planning and building the portable enclosure;
https://www.eevblog.com/forum/metrology/kx-reference/msg1244824/#msg1244824

Completed enclosure and external power supply;
https://www.eevblog.com/forum/metrology/kx-reference/msg1263564/#msg1263564

Temperature Coefficient concerns;
https://www.eevblog.com/forum/metrology/kx-reference/msg1301155/#msg1301155

KX #2 build (possible jumpy chip);
https://www.eevblog.com/forum/metrology/kx-reference/msg1317082/#msg1317082

Temperature Coefficient testing and resolution + reasoning to buy a new 7.5 digit DMM;
https://www.eevblog.com/forum/metrology/kx-reference/msg1369941/#msg1369941

7v reference noise testing;
https://www.eevblog.com/forum/metrology/kx-reference/msg1402418/#msg1402418

Building a worthy 10v buffer (schematic included on post #1);
https://www.eevblog.com/forum/metrology/ltz1000-10v-buffer/msg1435737/#msg1435737

All of this has taken a bit longer than a year to get to this point.  Its built, I'm satisfied with the performance and now its time to make use of it.  Late last year I contacted a fellow forum member, Ryan (CalMachine), who also was building some KX references along with his own design who also happened to have access to traceable standards at his work.  The conversations started off just as wanting a second pair of eyes to verify my results but being a voltnut he went far beyond my expectations.

With fully charged batteries my reference can run on battery power for 7 days powering the KX and Buffer boards or 72 hours with the oven on (at normal room temp).  The idea was to ship the reference to Ryan in Indiana with the reference powered on (oven off) so the LTZ1000 would not be subject to extreme cold temp swings during transport this time of the year.  The oven is insulated well enough there is a 5C rise in internal temp from ambient from the KX board and buffer being powered alone.

Final test prior to shipment;
https://www.eevblog.com/forum/metrology/usa-calibration-club/msg1470038/#msg1470038

Ryan went out of his way, comparing my reference to no less than three HP 3458's, two recently calibrated units and one with option 002.  He also spent some time recording some data with the oven off, on and during warming.  After a few days he made a small adjustment to my 10v trimmer and netted the 10v within 0.2ppm from his 732B which is keep in agreement with his work standards.  After about two weeks, the reference was sent back powered on, there was some delay in shipping as it arrived exactly 7 days after it was sent.  It was still running on battery power which had 10% capacity left.

Knowing the voltage as I sent the reference and knowing what Ryan measured on his calibrated equipment and knowing the amount of change he adjusted I should be able to calculate what my new readings would be if everything remained stable during the return trip.  After letting it stabilize in my lab overnight here is a quick summery;

As measured by my Keithley DMM7510 prior shipping;
10.000000

As measured at ENI Labs;
9.9999637 -  3458 option 002, cal'ed at Fluke Std Labs 5 moths ago

Dif;
0.0000363 (3.6 ppm low)

Ryan adjusted the buffer trim upward by 37.7uV to the reference now measured;
10.0000014 (0.14ppm high)

I should now “theoretically” measure;
10.000038

My real measurement now is;
10.000039

I love it when the math checks out, this gives me a very high level of confidence the reference remained stable during its transport back and I now have a very good realization of 10v.

At ENI Labs (using my supplied test leads for consistency);


Back on my DMM7510, new as of 8 months ago;


And on my 34465A (calibrated by Keysight 6 months);


Ryan sent along some data, Ill try to put some of this together in my next post

Attached are some general notes I put together regarding the build and operation.

[kj7e]

Attached, scanner plot comparing the outputs from a Datron 4911, Fluke 732B and Fluke 732A over two days and my reference.

[cellularmitosis]

It was still running on battery power which had 10% capacity left.

 

[CalMachine]

I thoroughly enjoyed working with you on this and I was very impressed with your reference!  You built yourself a nice little compact unit there, with a great battery life.   I had let it run on battery power with the oven on for a few days during scanning.  One morning I came down to a battery low light blinking   

ENILABS 732B just arrived back from Fluke yesterday.  I can throw that on the 3458A to get its delta for a more accurate absolute reference value.


All in all, it looks like it was a huge success!  I enjoyed playing with your unit and thank you for allowing me to set your reference value 

[kj7e]

One morning I came down to a battery low light blinking   

Sweet!  Glad to know the low battery circuit works!

[TiN]

What a blast, when I published KX reference designs, I never expected anyone to follow thru to the end like this. 

I'd like to include reference to this and hi-res photos into the KX article, if you don't mind. As example what DC reference design might look like, departing from prototyping module only to finished device.

[kj7e]

TiN, absolutely!  Have at it,  if you need me to send you any hi-res photo directly let me know, but you may be able to pull them off photobucket.

[kj7e]

My old job of 17 years ended suddenly and my new job is having me commute 126 miles/day.  So time at home and in the lab has been limited over the last few months.  The home built 10v reverence has been continuously powered on where as the Keithly DMM7510 has only been powered on a few times for a day at the most since last May.  After warming up the room to 23C steady for a few hours and running a self cal on the 7510, here are the results.  Last time I checked between them was over in July.  Not much drift between the two.  Forgot to add, the DMM7510 was sent out for calibration just after my reference returned.  Both the reference and 7510 read within 0.5ppm back in may.

[CalMachine]

My old job of 17 years ended suddenly and my new job is having me commute 126 miles/day.  So time at home and in the lab has been limited over the last few months.  The home built 10v reverence has been continuously powered on where as the Keithly DMM7510 has only been powered on a few times for a day at the most since last May.  After warming up the room to 23C steady for a few hours and running a self cal on the 7510, here are the results.  Last time I checked between them was over in July.  Not much drift between the two.  Forgot to add, the DMM7510 was sent out for calibration just after my reference returned.  Both the reference and 7510 read within 0.5ppm back in may.

Sorry to hear about your previous employment!

The Volt Ref is looking pretty stable 

[kj7e]

Its been over a year since Ryan had calibrated and adjusted both my DMM7510 and 10v reference, after a 24 hour warmup and the home lab stabilized to 23c, performed a self cal on the 7510 and this is what I get;



The 10v reference has been powered on 100% of the time, going on now for over a year, the DMM7510 has seen very little power on time over the last year.  So I can say it appears neither device is drifting much as it would be extremely unlikely for them to both drift the same amount in the same direction with vastly different power on times.

[hwj-d]

Hello Damon,

thanks for your work and report.

Do you have a defbuffer1.csv (LXI extract data) from a slightly longer session, maybe 3h? What are your filter settings?

Thanks
H.-W.

[kj7e]

Hello Damon,

thanks for your work and report.

Do you have a defbuffer1.csv (LXI extract data) from a slightly longer session, maybe 3h? What are your filter settings?

Thanks
H.-W.

Line sync on, 5 NPLC, 10x repeat filter, Auto Z, Manual 10v.  Buffer CSV attached for your pleasure.

Edit, I just averaged the readings column from the buffer, 9992 readings = 10.000 001 56

[hwj-d]

Just enjoying. 
Thanks a lot.