HP Cesium Standards in the International Atomic Time Scale, the legend of Felix Lazarus, and the "top cover effect".
Hello Time Nuts,
I found this HP Application note in my archives, and attached a scanned copy:
Application Note 52-4. Contribution of HP clocks to the BIH's International Atomic Time Scale (IATS).
I also found a couple of archives for HP application notes for anyone who may be interested:
http://hparchive.com/appnotes
https://www.keysight.com/main/editorial.jspx?cc=US&lc=eng&ckey=1127547&id=1127547&cmpid=zzfindclassic-app-notes
It is an interesting snapshot at the method of keeping the official IATS time, and how HP Cesium standards are a major part of it, published in 1986.
The author, Felix Lazarus, was a legendary Field Application Engineer (or something like that) for HP in Europe, based in Geneva Switzerland. He was obsessively fussy, and insisted that any Cesium Standard shipped to key customers in Europe were first shipped to him, so he could verify acceptable performance before the customer received the instrument.
He would fire up the product, re-tune and re-align all the settings, and then compare it to his house standard. If it wasn't up to his exacting standards, he would keep tuning and testing until it was acceptable - to him. He was looking for performance several times better than our published specifications, which were 5 x 10e-12. He wasn't satisfied until is was less than 2, or something like that. It drove us factory guys crazy. He was a well-respected figure in the time keeping world, and would bash us for shipping product that were not beating the specs by enough margin.
I think he is the one that discovered the "top cover effect". If you removed the top sheet metal cover from the instrument, the offset would shift by a part in 10 to the 12th or so. If you put the cover on, and changed how tight the screws were tightened, it would shift differently. I recall he wanted us to fix this.
I was the "Production Engineer" on the Cesium standards, a young BSEE college graduate. I barely knew how a basic op-amp amplifier worked, and was completely overwhelmed by the complexity of the Cesium Standards. "Go fix the problem on the most accurate commercial atomic standard for sale in the world, where if you change how tight a screw is, the performance shifts a touch." It is safe to say that I didn't make this my highest priority. There were theories that the root cause was subtle changes to the ground loops with a change like this. The whole product used all the sheet metal as a common ground, meaning that the ground return paths were not designed at all, just left to chance.
A related issue that I didn't work on was the "oven controller cable offset." There was a big multi wire cable o the cesium oven heater controller, and if you twisted it left vs. right before plugging it in, the offset of the standard would change.
Working on the 5061B destroyed my confidence in my engineering abilities. I didn't think I could solve "real" engineering problems, because of issues like this. After working on the 5061B product for several years, I applied for a job as an engineering manager over the frequency counter production product line. During the interviews, my low technical self-confidence came through, and the R&D management partners to this position were worried I couldn't provide technical leadership to the other engineers. So, in true HP fashion, my they sent me through the full scale HP R&D engineering interview -about a half dozen deep 1:1 technical interviews with EE experts in the lab. Turns out that I wasn't a dunce after all, just scarred from my experience working on the cesium standards. I got the job.
I have a handful of other stories like this from my days inside HP frequency and time division. Let me know if you want to hear more. Maybe Rick Karlquist will tell some stories of developing the 5071!
Hugh Rice
Hugh,
Well I sure enjoyed the story and though I won't say I am scarred by
Cesiums, they have proven just how little I know more then a few times.
Like you it took some 3 years to get the monster working. Its called
Frankenstein. You guessed how its made.
Regards
Paul
WB8TSL
On Wed, Dec 19, 2018 at 8:07 PM Rice, Hugh (IPH Writing Systems) <
hugh.rice@hp.com> wrote:
Hello Time Nuts,
I found this HP Application note in my archives, and attached a scanned
copy:
Application Note 52-4. Contribution of HP clocks to the BIH's
International Atomic Time Scale (IATS).
I also found a couple of archives for HP application notes for anyone who
may be interested:
http://hparchive.com/appnotes
It is an interesting snapshot at the method of keeping the official IATS
time, and how HP Cesium standards are a major part of it, published in 1986.
The author, Felix Lazarus, was a legendary Field Application Engineer (or
something like that) for HP in Europe, based in Geneva Switzerland. He
was obsessively fussy, and insisted that any Cesium Standard shipped to key
customers in Europe were first shipped to him, so he could verify
acceptable performance before the customer received the instrument.
He would fire up the product, re-tune and re-align all the settings, and
then compare it to his house standard. If it wasn't up to his exacting
standards, he would keep tuning and testing until it was acceptable - to
him. He was looking for performance several times better than our
published specifications, which were 5 x 10e-12. He wasn't satisfied
until is was less than 2, or something like that. It drove us factory
guys crazy. He was a well-respected figure in the time keeping world, and
would bash us for shipping product that were not beating the specs by
enough margin.
I think he is the one that discovered the "top cover effect". If you
removed the top sheet metal cover from the instrument, the offset would
shift by a part in 10 to the 12th or so. If you put the cover on, and
changed how tight the screws were tightened, it would shift differently.
I recall he wanted us to fix this.
I was the "Production Engineer" on the Cesium standards, a young BSEE
college graduate. I barely knew how a basic op-amp amplifier worked, and
was completely overwhelmed by the complexity of the Cesium Standards. "Go
fix the problem on the most accurate commercial atomic standard for sale in
the world, where if you change how tight a screw is, the performance shifts
a touch." It is safe to say that I didn't make this my highest priority.
There were theories that the root cause was subtle changes to the ground
loops with a change like this. The whole product used all the sheet metal
as a common ground, meaning that the ground return paths were not designed
at all, just left to chance.
A related issue that I didn't work on was the "oven controller cable
offset." There was a big multi wire cable o the cesium oven heater
controller, and if you twisted it left vs. right before plugging it in, the
offset of the standard would change.
Working on the 5061B destroyed my confidence in my engineering abilities.
I didn't think I could solve "real" engineering problems, because of
issues like this. After working on the 5061B product for several years,
I applied for a job as an engineering manager over the frequency counter
production product line. During the interviews, my low technical
self-confidence came through, and the R&D management partners to this
position were worried I couldn't provide technical leadership to the other
engineers. So, in true HP fashion, my they sent me through the full
scale HP R&D engineering interview -about a half dozen deep 1:1 technical
interviews with EE experts in the lab. Turns out that I wasn't a dunce
after all, just scarred from my experience working on the cesium
standards. I got the job.
I have a handful of other stories like this from my days inside HP
frequency and time division. Let me know if you want to hear more.
Maybe Rick Karlquist will tell some stories of developing the 5071!
Hugh Rice
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.
Yup, I've seen plenty of "top cover effects," and other strange things.
That sort of thing is evident even when you don't have to reach E-12
resolution levels - like a million times less. The instrument cabinet
and hardware are indeed a part of the electronic system and circuits. So
are what it's hooked up to, and its various characteristics, and so on.
Coincidentally, just the other day I was working on reducing residual
line noise in my HP8568 SA and its homemade tracking generator project.
This involved line frequency and its harmonic spurs just above the noise
floor, around -95 dBm on screen. Minor changes to grounding, hardware
mounting, position, signal paths, etc, can make large differences in
result, due to effects on ground current distribution. Sometimes bad
things even cancel out, but only when just right, under certain conditions.
And that's just an electrical aspect - there are thermal and mechanical
stress and other effects in play too, as you go ever higher in resolution.
Ed
Warning: websites cited here can be seriously time-consuming rabbit holes!
An anonymous engineer using the pseudonym NwAvGuy http://nwavguy.blogspot.com/ got fed up with the subjective nature of discussions about DACs and amplifiers in the world of high fidelity audio. To clear away the smoke, in 2011 he started publishing independent measurements, along with some blog posts about what measurements and goals were detectable. As one might imagine, this was very controversial.
Later that year he (or she) concluded it was possible to build a replicable DAC and a headphone amplifier http://nwavguy.blogspot.com/2011/08/o2-summary.html that could exceed the performance of so-called high-end units being sold for 10e3 - 10e5 dollars, yet cost the consumer an order of magnitude less. His blog posts describe the design process from requirements to finished result.
Relevant to this thread was NwAvGuy’s long list of PC board routing and enclosure topics that significantly affect performance of otherwise identical parts and circuit:
ground routing, ground planes, floods & fills
EMI loops
inductive coupling
parasitics
failure to follow the PC layout developed by the component manufacturer
component placement, aka “rows and columns may not be your friend”
track placement: moving a single track can change increase distortion [by 26 dB] was one example given
all this at audio frequencies.
So, yes, I cringe at the thought of developing such systems at frequencies and performance levels we talk about here on Time-Nuts. There are not enough lifetimes to learn how to do this well, I feel. :-(
Hats off to all those people who’ve mastered and advanced this craft.
— Eric K3NA
p.s.: NwAvGuy’s resulting DAC/amp has been available in kit or assembled form since 2012 from companies such as JDS Labs https://www.jdslabs.com/products/48/objective2-odac-combo-revb/ ($280), built exactly according to the design spelled out by NwAvGuy.
NwAvGuy’s identity has been closely guarded by the few individuals who know it. (I am not one of those.) She stopped posting in 2012 and disappeared from the scene.
More recently, Audio Science Review https://www.audiosciencereview.com/forum/index.php has started publishing objective measurements of commercial audio equipment, including DACs https://www.audiosciencereview.com/forum/index.php?threads/review-and-measurements-of-wesiontek-khadas-tone-board-dac.4823/ and headphone amps https://www.audiosciencereview.com/forum/index.php?threads/review-and-measurements-of-massdrop-thx-aaa-789-amp.5001/ that somewhat exceed the performance of the NwAvGuy’s solution but remain in similar price ranges. The site’s admin and principle author employs a pseudonym amirm https://www.audiosciencereview.com/forum/index.php?members/amirm.2/, claims to be in the Seattle area — and some wonder if this is the same person as NwAvGuy.
On 2018 Dec 20, at 01:41 , ed breya eb@telight.com wrote:
Yup, I've seen plenty of "top cover effects," and other strange things. That sort of thing is evident even when you don't have to reach E-12 resolution levels - like a million times less. The instrument cabinet and hardware are indeed a part of the electronic system and circuits. So are what it's hooked up to, and its various characteristics, and so on.
Dear Hugh,
I really enjoyed reading this! You have several cliff-hangers in there:
Did you (HP) fix/reduce the top cover issue? Did you alter the setup to
meet tighter specs? Did you fix the oven controller cable offset?
What else war-stories do you got?
It is by war-stories one shares knowledge, lessons learned is not
without its background and at least you have a great story.
Cheers,
Magnus
On 12/20/18 12:36 AM, Rice, Hugh (IPH Writing Systems) wrote:
Hello Time Nuts,
I found this HP Application note in my archives, and attached a scanned copy:
Application Note 52-4. Contribution of HP clocks to the BIH's International Atomic Time Scale (IATS).
I also found a couple of archives for HP application notes for anyone who may be interested:
http://hparchive.com/appnotes
https://www.keysight.com/main/editorial.jspx?cc=US&lc=eng&ckey=1127547&id=1127547&cmpid=zzfindclassic-app-notes
It is an interesting snapshot at the method of keeping the official IATS time, and how HP Cesium standards are a major part of it, published in 1986.
The author, Felix Lazarus, was a legendary Field Application Engineer (or something like that) for HP in Europe, based in Geneva Switzerland. He was obsessively fussy, and insisted that any Cesium Standard shipped to key customers in Europe were first shipped to him, so he could verify acceptable performance before the customer received the instrument.
He would fire up the product, re-tune and re-align all the settings, and then compare it to his house standard. If it wasn't up to his exacting standards, he would keep tuning and testing until it was acceptable - to him. He was looking for performance several times better than our published specifications, which were 5 x 10e-12. He wasn't satisfied until is was less than 2, or something like that. It drove us factory guys crazy. He was a well-respected figure in the time keeping world, and would bash us for shipping product that were not beating the specs by enough margin.
I think he is the one that discovered the "top cover effect". If you removed the top sheet metal cover from the instrument, the offset would shift by a part in 10 to the 12th or so. If you put the cover on, and changed how tight the screws were tightened, it would shift differently. I recall he wanted us to fix this.
I was the "Production Engineer" on the Cesium standards, a young BSEE college graduate. I barely knew how a basic op-amp amplifier worked, and was completely overwhelmed by the complexity of the Cesium Standards. "Go fix the problem on the most accurate commercial atomic standard for sale in the world, where if you change how tight a screw is, the performance shifts a touch." It is safe to say that I didn't make this my highest priority. There were theories that the root cause was subtle changes to the ground loops with a change like this. The whole product used all the sheet metal as a common ground, meaning that the ground return paths were not designed at all, just left to chance.
A related issue that I didn't work on was the "oven controller cable offset." There was a big multi wire cable o the cesium oven heater controller, and if you twisted it left vs. right before plugging it in, the offset of the standard would change.
Working on the 5061B destroyed my confidence in my engineering abilities. I didn't think I could solve "real" engineering problems, because of issues like this. After working on the 5061B product for several years, I applied for a job as an engineering manager over the frequency counter production product line. During the interviews, my low technical self-confidence came through, and the R&D management partners to this position were worried I couldn't provide technical leadership to the other engineers. So, in true HP fashion, my they sent me through the full scale HP R&D engineering interview -about a half dozen deep 1:1 technical interviews with EE experts in the lab. Turns out that I wasn't a dunce after all, just scarred from my experience working on the cesium standards. I got the job.
I have a handful of other stories like this from my days inside HP frequency and time division. Let me know if you want to hear more. Maybe Rick Karlquist will tell some stories of developing the 5071!
Hugh Rice
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