Apologies, the last message went out before I was finished drafting it. See these links:
https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/ https://www.eevblog.com/forum/metrology/factory-2dw23x-order-aggregation-thread/ Note that these zeners are quite cheap. You could parallel a number of them for ever further noise reduction, yet still be cheaper than an LTZ. Sent from my iPhone > On Feb 17, 2018, at 7:24 PM, [email protected] wrote: > > Hello, > > Are you familiar with the 2DW232, a Chinese zener? There is one particular > factory in China which is somehow producing exceptionally low noise units > (much lower noise than the LTZ1000). > > There is an EEVBlog forum member who lives in China and has graciously > volunteered to perform group buys from this factory and then distribute the > pets to the individual buyers. > > > > Sent from my iPhone > >> On Feb 17, 2018, at 9:07 AM, Randy Evans <[email protected]> wrote: >> >> Thanks for the feedback. I don't think I am having problems with leakage >> in the test setup, thermal, or shielding issues. I used aluminum cast >> boxes (Pomona 2391) which have BNC M and F connectors, which use teflon >> insulators. The cast boxes have enough thermal mass and not subject to >> moving air currents, so it is unlikely that the wide voltage extremes, over >> periods of a few to 10's of milliseconds, I am seeing are due to thermal >> changes. Also, I had a typo in the original message (I said pA when I >> meant to type nA) in that the last sentence in the second paragraph should >> read: "and around 1 nA at 0.1V, but with widely varying leakage current of >> 0.5 to 1.5 nA, with occasional peaks of -0.5 to 2 nA. This would equate to >> about +/- 2 uV voltage variation across R1, making a 10 V 0.1ppm stable >> voltage reference of questionable value." the first sentence in the fourth >> paragraph should also be referencing nA's. Sorry about the brain lapse. >> >> The wide variations in current through the 100uF cap-1Kohm resistor are my >> main concern since I can't explain it. It is absolutely not present in the >> 100 Mohm cal resistor in the same type aluminum cast box and is completely >> stable. I originally suspected interference but the cap-resistor and >> calibration resistor are mounted in identical shielded boxes but the 100 >> Mohm cal resistor is clean and stable. >> >> I suppose I need to bite the bullet and build the circuit and see how >> stable it is. I can check it with my two Fluke 732As and two HP-3458As. >> >> Rrandall Evans >> >> >>> On Sat, Feb 17, 2018 at 4:38 AM, Andre <[email protected]> wrote: >>> >>> also see https://workmanship.nasa.gov/lib/insp/2%20books/links/ >>> sections/407%20Splices.html >>> >>> -Andre >>> >>> ________________________________________ >>> From: volt-nuts <[email protected]> on behalf of Randy Evans < >>> [email protected]> >>> Sent: 16 February 2018 18:39 >>> To: Discussion of precise voltage measurement >>> Subject: [volt-nuts] Low noise reference >>> >>> I have a question for the group. I was looking at an article for building >>> an ultra-low noise voltage reference by Walt Jung, published in Electronic >>> Design June 24, 1993 and a URL to the article is below. I want to filter >>> the output of an LTZ1000 based 10V reference I am building and this circuit >>> has a very low freq corner of 1.6 Hz. I was concerned about the leakage >>> through R1-C1. If C1 had as little as 1ua leakage, it would drop the >>> voltage through R1 by 1 mV. The spec on 100 uF electrolytic and tantalum >>> capacitors show a leakage of 20 ua at rated voltage so this could be of >>> great concern. However, at the low few tenths of a volt that should be >>> across C1, the capacitor should have a much lower leakage amount, which is >>> the theme of the article. >>> >>> To get a better appreciation of the issue, I connected a precision 0 to 10 >>> V source (100uV resolution steps) to a series combination of a 1 Kohm >>> resistor and a 100 uF electrolytic and, later, another 47uF tantalum and a >>> 47 uF electrolytic capacitor. In all cases the leakage, as measured with a >>> Keithley 414 picoammmeter, showed a leakage or around 0.08 uA at 10V and >>> varying 0.04 to 0.12 uA, around .1uA at 1V and varying , and around 1 pA at >>> 0.1V, but with widely varying leakage current of 0.5 to 1.5 pA, with >>> occasional peaks of -0.5 to 2 pA. This would equate to about +/- 2 uV >>> voltage variation across R1, making a 10 V 0.1ppm stable voltage reference >>> of questionable value. >>> >>> I also tried a 0.68 uF polystyrene capacitor and also saw leakage current >>> variations, although much less than the electrolytic and tantalum >>> capacitors, as one would expect. >>> >>> Thinking the problem might be the the picoammeter, I put a 100 megohm 0.1% >>> precision resistor in place of the capacitor across the precision voltage >>> source set for 0.1 V and measured the current through the resistor at a >>> very stable 0.9 pA on the Keithley 414 (sb 1pA but accurate enough for my >>> measurements - the resistor shielded box likely has some sub pA leakage >>> also). Note that I used shielded cables for all measurements, and the >>> resistor and capacitor were in a shielded box, as well as the 100 Mohm >>> calibration resistor. Touching the cables or boxes did not change the >>> picoammeter reading at all, indicating to me that the shielding was >>> reasonable. >>> >>> I suppose the best approach is to build it and characterize it, but it's >>> not fruitful if someone has already done this. So my question is: has >>> anyone built this circuit and characterized it, particularly over >>> temperature for stability at the sub ppm level? >>> >>> Thanks, >>> >>> Randall Evans >>> >>> >>> >>> >>> >>> >>> >>> http://waltjung.org/PDFs/Build_Ultra_Low_Noise_Voltage_Reference.pdf >>> _______________________________________________ >>> volt-nuts mailing list -- [email protected] >>> To unsubscribe, go to https://www.febo.com/cgi-bin/ >>> mailman/listinfo/volt-nuts >>> and follow the instructions there. >>> >>> _______________________________________________ >>> volt-nuts mailing list -- [email protected] >>> To unsubscribe, go to https://www.febo.com/cgi-bin/ >>> mailman/listinfo/volt-nuts >>> and follow the instructions there. >>> >> _______________________________________________ >> volt-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts >> and follow the instructions there. _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
