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On 10/18/2012 02:05 PM, Andreas Jahn wrote: > Hello Bob, > > whats the matter with you. Infected by precision virus like me? Yep - and I have a question. What does the spec of Xppm/sqrt(1,000 hrs) mean? If we expect Xppm over the first 1,000 hours, does the stability improve with long term operation? What would be expected over the second 1000 hours, etc? Would we expect a drift of 1.4 * X ppm over 2000 hours, sqrt(10) * X ppm over 10,000 hours, and so on? Thanks, -- ======================================================================= Bob Smither Circuit Concepts, Inc. “Three groups spend other people's money: children, thieves, politicians. All three need supervision.” -- Dick Armey Smither@c-c-i.com www.c-c-i.com 281-331-2744 =======================================================================

Date: Fri, 19 Oct 2012 21:34:38 -0500 From: smither@c-c-i.com To: volt-nuts@febo.com Subject: Re: [volt-nuts] Traveling Standards On 10/18/2012 02:05 PM, Andreas Jahn wrote: > Hello Bob, > > whats the matter with you. Infected by precision virus like me? Yep - and I have a question. What does the spec of Xppm/sqrt(1,000 hrs) mean? If we expect Xppm over the first 1,000 hours, does the stability improve with long term operation? What would be expected over the second 1000 hours, etc? Would we expect a drift of 1.4 * X ppm over 2000 hours, sqrt(10) * X ppm over 10,000 hours, and so on? In theory yes, but there are some aspects like continuing corrosion of the wirewound resistor wire I suspect that will be closer to linear, but if the oxide is very adherent then it may well be root time. a poorly adhering film will have steps in its corrosion rate as fragments of oxide etc fall off. Regards, MK

Hello Bob, yes you are right. The absolute ageing drift gets lower the more working hours are on the reference. But the ageing rate is only a statistically value (averaged over a large quantity of individual references) And: the environmental condititons have to be constant during the ageing. Each mechanical stress (eg due to soldering) to the package may issue a new level of ageing. For well aged plastic references the ageing effects may be invisible against humidity drift. See also: http://cds.linear.com/docs/Design%20Note/dn229f.pdf At the moment I am doing some longterm drift measurements on some references. The first was a hermetically sealed AD586LQ with stress reduced mounting in my ADC13 voltage converter. On the attached picture you can see that the drift against a LTZ1000 #2 (dark blue) was initially around 3.4 ppm/sqrt(kHr) (light blue extrapolated line) from "day of birth" = day 200 on the x-axis. Around day 410 I tried some "accellerated ageing" by loading the reference with 15 mA load during night. The result is extrapolated by the pink line with 2.4ppm/sqrt(kHr) from day 410 on. Suddenly around day 470 the ageing stopped nearly. Except of some noise it seems to be stable. I dont know the reason for this. The last 5 days on the diagram is now without the 15 mA loading during night. Best regards Andreas ----- Original Message ----- Yep - and I have a question. What does the spec of Xppm/sqrt(1,000 hrs) mean? If we expect Xppm over the first 1,000 hours, does the stability improve with long term operation? What would be expected over the second 1000 hours, etc? Would we expect a drift of 1.4 * X ppm over 2000 hours, sqrt(10) * X ppm over 10,000 hours, and so on? Thanks, -- ======================================================================= Bob Smither Circuit Concepts, Inc.

I have made a LM399 standard, dead bug build, at 10V. A uA723 for powersupply at 15V. In a metalhousing and shielded internal extra using double sided pcb. It is now 24/7 on for about 5 weeks. I modified my solartron 7601 so it stays at 38C plus/minus 1 degree internal. ( mounted two heatsincs on top, one above the transformer, a ntc inside, and a speedregulated fan on the main heatsinc. Thanks to your post i started monitoring it. So since a few days that meter is also on 24/7. A few times a day Zi take readings ( i am digital disabled so logging probably always will stay a dream) Room temp changes from 19 to 24 degrees. I made a 10 turn potentiometer on the front that gives me some adjusting. Still more as needed but until it is aged enough I keep it like this. Resistors are all 0.02% or 0.01% One whole turn of the multiturn is around 100 uV. I adjusted it to 10.000,000 Volt at 19 degrees Celcius. This was a cold mornig and a lot of rain. According to my bones humidity was high. Later that day it became 21 degrees ( heath from instruments and light spots) It was the 10.000,030V, yesterday a dry and warm day it ( 21 to 24 degrees) raised to 10.000,052) this moring 20 degrees, rain outside, it was 10.000,058 The ten turn pot has a reading ( a dial with two arms like a clock) and i made the standard so that the pot at 10.000,000 V was at the 5.00 position. Until that, I had to turn it between 4.45 and 5.15 to get it back at 10V. So it still has a total drift around 50 to 100 uV ( monitored it als a few days three weeks back using two meters and they showed the same trend. But i think I have a problem regarding magnetic fields or other sources because I have strange issues while meauring using the 332 and KV deviders or my LM399. I looked to it with a friend and he thinks it is some magnetic field or common mode thing. I had powered everything off, even the lights. Then both 7,5 digit meters showed the same values, turning the polarity did not matter. Both KVs were lineair upto 1 uV. Using my 399 or Fluke 332, also tested the 332 divider dircect. Then with the lights on severa instruments ect. A big difference if i change polarity, both meters gave different readings, both KV dividers gave excact the same non lineairity. I did this several days and up to about 1 mV !! between 100 mV and 10V but an verage of a few hundered mV) if I power all stuff down exept the 332 and 7106 all is perfect again. All intruments are grounded. I use shielded cables to the meters and from 332 to KVs from Beats me :-( So I think your standard performs well if it is this stable while tossing around, i wish my 332 and LM399 was that stable ( or more, the environment was more standard friendly becaus all powered down things are much more stable) Fred PA4TIM Op 20 okt. 2012 om 04:27 heeft Bob Smither <smither@c-c-i.com> het volgende geschreven: > On 10/18/2012 02:05 PM, Andreas Jahn wrote: >> Hello Bob, >> >> whats the matter with you. Infected by precision virus like me? >> You wanted to have a standard with about 10ppm and now you blame a 3-4ppm drift. > > :-) - afraid so Andreas! > >>> >>> The LM199A is hermetically sealed. >>> >> >> The PCB, the 8K Resistor and the voltage Regulator are not. >> >>> Although a small sample, the two references appear to be similarly affected by >>> whatever caused the drift - similar range of drift, similar time constant. >>> >> On the first view I would blame it on the meter. >> It is very unusual that the drift of 2 different references has nearly exact the >> same amount of ppm and direction. >> But on the other side you state that there are several HP3458A which recorded >> the drift. >> It is not probable that all came freshly from calibration of a other location. >> >>> Any ideas about what could cause the drift we are seeing? >> >>> From time constant it could be the humidity change. > > This is my best guess. > >> My 2 LT1027CCN8-5 references which ara mounted only with 1 Pin >> to the PCB have time constants in the range of 4-7 days. >> The epoxy material of a PCB should lie in the same ball park area. >> The LT1027 are influenced by around 0.5 ppm per percent humidity change. >> >> For the hermetically sealed brand new references LT1236AILS they state in their >> new product catalog >> a humidity change of less than 10ppm for 25% humidity change. (page 36) >> http://cds.linear.com/docs/Product%20Info/NPC.pdf > > This is most interesting - so even "hermetically sealed" units are influenced by > humidity! > >> I asked them whether this is from mechanical stress from the PCB and they >> confirmed to me >> that with a dead bug mounting the influence of humidity will be virtually >> unmeasurable. >> So they will delete the parameter from the data sheet. > > Mine are not "dead bug" mounted. The 'PCB' is in fact a Radio Shack perf board > - certainly not the best substrate to mount them on - I don't think it is FR-4 > material. > >> So for the LM399 it might be mechanical stress introduced by the PCB. >> >> >> When looking at your cirquit there are several points to mention: >> One common failure source will be the LM78L15. A output voltage change will >> influence the supply of MAX6350 and the reference current of LM399. >> PSRR of MAX6350 is about 2-5 ppm/V above 10V supply. (without self heating >> effects). > > LM78L15 spec is 1mV/C. This would result in .02 ppm/C on the LM199A (operated > at 1 mA with 8K resistor providing the current). > > For the MAX6350 1mV/C and 5 ppm/V => .005 ppm/C > >> The LM399 resistor will give a current change of about 10% per Volt (100uA) >> resulting with 0.5 Ohm impedance in about 50uV/V or 7ppm/V > > see note above. > >> Other weak points of the cirquit are: >> The LM399 heater voltage is not stabilized. this will give about 0.5ppm/V > > It is stabilized by the power supply - a 24 volt, .02%/C unit => 5mV/C => .0025 > ppm/C. > >> And finally: was the LM399 always in the same orientation during measurements? >> (will be difficult with a cylindrical housing). >> My LM399 drift 3-4 ppm by tilting orientation. > > Not sure - but from the consistent results (consistent drift and apparent > settling) it likely was. > > The above still leaves humidity induced PCB changes causing mechanical stress as > likely. I am going to look for some better board material for when I construct TS2. > > Thanks Andreas! > > -- > "As we act, let us not become the evil that we deplore." > <smither.vcf> > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there.

Hello Fred, I also had large common mode effects on the LM399 until I spent 2 100nF ceramic multilayer capacitors to the heater and the zener See C6 and C8 on Bobs cirquit. http://c-c-i.com/sites/default/files/reference_voltage.pdf Further you could try using batteries during measurement for the standard. And charging only when no measurement is made. Without these capacitors there was a difference up to 100uV depending where I put my hand on the wiring. (either near the Reference or directly to the NiMH-Batteries of one of the references). The voltage was measured as difference of 2 references to get improved resolution. The common mode effect came from the switch mode supply of my personal computer. With these capacitors the common mode effect was reduced to My first ADCs did not have photocouplers and where galvanically coupled to the PC. With the decoupling capacitors the common mode effect was below 2uV. Maybe also this were resulting thermocouple effects. Now I have galvanic decoupling between PC and ADCs further reducing effects. Common mode problems are only visible when I forget to disconnect the switchmode chargers for my batteries. With best regards Andreas ----- Original Message ----- From: "Fred Schneider" <pa4tim@gmail.com> To: "Discussion of precise voltage measurement" <volt-nuts@febo.com> Sent: Saturday, October 20, 2012 10:47 AM Subject: Re: [volt-nuts] Traveling Standards >I have made a LM399 standard, dead bug build, at 10V. A uA723 for >powersupply at 15V. In a metalhousing and shielded internal extra using >double sided pcb. > It is now 24/7 on for about 5 weeks. > I modified my solartron 7601 so it stays at 38C plus/minus 1 degree > internal. ( mounted two heatsincs on top, one above the transformer, a ntc > inside, and a speedregulated fan on the main heatsinc. Thanks to your post > i started monitoring it. So since a few days that meter is also on 24/7. A > few times a day Zi take readings ( i am digital disabled so logging > probably always will stay a dream) Room temp changes from 19 to 24 > degrees. > > I made a 10 turn potentiometer on the front that gives me some adjusting. > Still more as needed but until it is aged enough I keep it like this. > Resistors are all 0.02% or 0.01% > One whole turn of the multiturn is around 100 uV. > I adjusted it to 10.000,000 Volt at 19 degrees Celcius. This was a cold > mornig and a lot of rain. According to my bones humidity was high. Later > that day it became 21 degrees ( heath from instruments and light spots) > It was the 10.000,030V, yesterday a dry and warm day it ( 21 to 24 > degrees) raised to 10.000,052) this moring 20 degrees, rain outside, it > was 10.000,058 > The ten turn pot has a reading ( a dial with two arms like a clock) and i > made the standard so that the pot at 10.000,000 V was at the 5.00 > position. Until that, I had to turn it between 4.45 and 5.15 to get it > back at 10V. So it still has a total drift around 50 to 100 uV ( monitored > it als a few days three weeks back using two meters and they showed the > same trend. > > But i think I have a problem regarding magnetic fields or other sources > because I have strange issues while meauring using the 332 and KV deviders > or my LM399. > I looked to it with a friend and he thinks it is some magnetic field or > common mode thing. > I had powered everything off, even the lights. Then both 7,5 digit meters > showed the same values, turning the polarity did not matter. Both KVs were > lineair upto 1 uV. Using my 399 or Fluke 332, also tested the 332 divider > dircect. > Then with the lights on severa instruments ect. A big difference if i > change polarity, both meters gave different readings, both KV dividers > gave excact the same non lineairity. I did this several days and up to > about 1 mV !! between 100 mV and 10V but an verage of a few hundered mV) > if I power all stuff down exept the 332 and 7106 all is perfect again. All > intruments are grounded. I use shielded cables to the meters and from 332 > to KVs from Beats me :-( > So I think your standard performs well if it is this stable while tossing > around, i wish my 332 and LM399 was that stable ( or more, the environment > was more standard friendly becaus all powered down things are much more > stable) > > Fred PA4TIM > > Op 20 okt. 2012 om 04:27 heeft Bob Smither <smither@c-c-i.com> het > volgende geschreven: > >> On 10/18/2012 02:05 PM, Andreas Jahn wrote: >>> Hello Bob, >>> >>> whats the matter with you. Infected by precision virus like me? >>> You wanted to have a standard with about 10ppm and now you blame a >>> 3-4ppm drift. >> >> :-) - afraid so Andreas! >> >>>> >>>> The LM199A is hermetically sealed. >>>> >>> >>> The PCB, the 8K Resistor and the voltage Regulator are not. >>> >>>> Although a small sample, the two references appear to be similarly >>>> affected by >>>> whatever caused the drift - similar range of drift, similar time >>>> constant. >>>> >>> On the first view I would blame it on the meter. >>> It is very unusual that the drift of 2 different references has nearly >>> exact the >>> same amount of ppm and direction. >>> But on the other side you state that there are several HP3458A which >>> recorded >>> the drift. >>> It is not probable that all came freshly from calibration of a other >>> location. >>> >>>> Any ideas about what could cause the drift we are seeing? >>> >>>> From time constant it could be the humidity change. >> >> This is my best guess. >> >>> My 2 LT1027CCN8-5 references which ara mounted only with 1 Pin >>> to the PCB have time constants in the range of 4-7 days. >>> The epoxy material of a PCB should lie in the same ball park area. >>> The LT1027 are influenced by around 0.5 ppm per percent humidity change. >>> >>> For the hermetically sealed brand new references LT1236AILS they state >>> in their >>> new product catalog >>> a humidity change of less than 10ppm for 25% humidity change. (page 36) >>> http://cds.linear.com/docs/Product%20Info/NPC.pdf >> >> This is most interesting - so even "hermetically sealed" units are >> influenced by >> humidity! >> >>> I asked them whether this is from mechanical stress from the PCB and >>> they >>> confirmed to me >>> that with a dead bug mounting the influence of humidity will be >>> virtually >>> unmeasurable. >>> So they will delete the parameter from the data sheet. >> >> Mine are not "dead bug" mounted. The 'PCB' is in fact a Radio Shack perf >> board >> - certainly not the best substrate to mount them on - I don't think it is >> FR-4 >> material. >> >>> So for the LM399 it might be mechanical stress introduced by the PCB. >>> >>> >>> When looking at your cirquit there are several points to mention: >>> One common failure source will be the LM78L15. A output voltage change >>> will >>> influence the supply of MAX6350 and the reference current of LM399. >>> PSRR of MAX6350 is about 2-5 ppm/V above 10V supply. (without self >>> heating >>> effects). >> >> LM78L15 spec is 1mV/C. This would result in .02 ppm/C on the LM199A >> (operated >> at 1 mA with 8K resistor providing the current). >> >> For the MAX6350 1mV/C and 5 ppm/V => .005 ppm/C >> >>> The LM399 resistor will give a current change of about 10% per Volt >>> (100uA) >>> resulting with 0.5 Ohm impedance in about 50uV/V or 7ppm/V >> >> see note above. >> >>> Other weak points of the cirquit are: >>> The LM399 heater voltage is not stabilized. this will give about >>> 0.5ppm/V >> >> It is stabilized by the power supply - a 24 volt, .02%/C unit => 5mV/C => >> .0025 >> ppm/C. >> >>> And finally: was the LM399 always in the same orientation during >>> measurements? >>> (will be difficult with a cylindrical housing). >>> My LM399 drift 3-4 ppm by tilting orientation. >> >> Not sure - but from the consistent results (consistent drift and apparent >> settling) it likely was. >> >> The above still leaves humidity induced PCB changes causing mechanical >> stress as >> likely. I am going to look for some better board material for when I >> construct TS2. >> >> Thanks Andreas! >> >> -- >> "As we act, let us not become the evil that we deplore." >> <smither.vcf> >> _______________________________________________ >> volt-nuts mailing list -- volt-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts >> and follow the instructions there. > > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there.

Hello Fred, > It is now 24/7 on for about 5 weeks. 5 weeks is nothing in the life of a reference. During the first year my 2 LM399 references drifted 500uV against each other The 2nd year it was only 220uV now I know that LM399 #1 is drifting much more (200uV) than LM399 #2 (20uV) in the 2nd year. In the 3rd year LM399#1 drifted around 140uV and LM399#3 less than 10uV. So not all references seem to be usable for precision measurement. Its shurely no fault to start with a set of several references and select out the bad ones. With best regards Andreas

So I have nothing to complain, after the first week changing " much" it now goes up/ down a bit with temp and probably humidity. At 10V, 1ppm is 10 uV so it is changes 5 to 6 ppm over 5 degrees. Today it changed less then 1 ppm over 3 degrees so I that leaves humidity. I do not have a hygrometer so it becomes time I get one. Thanks for the tips for the common mode, i will try it soon, http://www.pa4tim.nl/wp-content/uploads/2011/06/lm399schema_1.jpg This is the schematic ( completely my own design but I'm no EE so it probably will not be to great) but I appriciate comments for improvement. http://www.pa4tim.nl/?p=2531 pictures are at the bottom of the page, all my reference experiments are here together. Fred PA4TIM Op 20 okt. 2012 om 17:41 heeft "Andreas Jahn" <Andreas_-_Jahn@t-online.de> het volgende geschreven: > Hello Fred, > >> It is now 24/7 on for about 5 weeks. > > 5 weeks is nothing in the life of a reference. > During the first year my 2 LM399 references drifted 500uV against each other > > The 2nd year it was only 220uV > now I know that LM399 #1 is drifting much more (200uV) than LM399 #2 (20uV) in the 2nd year. > > In the 3rd year LM399#1 drifted around 140uV and LM399#3 less than 10uV. > > So not all references seem to be usable for precision measurement. > Its shurely no fault to start with a set of several references and select out the bad ones. > > With best regards > > Andreas > > > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there.

Hi! It is possible to reduce the reference instability by the simple statistical methods. This is the my 10V DIY reference with triple LM399H and "statistical" 7-10 step-up divider (16 metal-foil hermetically sealed resistors S5-61 type): http://www.mediafire.com/view/?a8vm5tkx7knbady http://www.mediafire.com/view/?59nva8mi5bxfy6n http://www.mediafire.com/view/?pbgq9va0mog5l5h Regards, Mickle T. 16

Fred, You may have some light-sensitive components. Diodes with glass packaging are especially bad. Try blocking the light with cardboard and see what happens. Keep your hands away from your meters while moving the cardboard around. Brent On 10/20/2012 2:47 AM, Fred Schneider wrote: > But i think I have a problem regarding magnetic fields or other sources because I have strange issues while meauring using the 332 and KV deviders or my LM399. > I looked to it with a friend and he thinks it is some magnetic field or common mode thing. > I had powered everything off, even the lights. Then both 7,5 digit meters showed the same values, turning the polarity did not matter. Both KVs were lineair upto 1 uV. Using my 399 or Fluke 332, also tested the 332 divider dircect. > Then with the lights on severa instruments ect. A big difference if i change polarity, both meters gave different readings, both KV dividers gave excact the same non lineairity. I did this several days and up to about 1 mV !! between 100 mV and 10V but an verage of a few hundered mV) if I power all stuff down exept the 332 and 7106 all is perfect again. All intruments are grounded. I use shielded cables to the meters and from 332 to KVs from Beats me :-( > So I think your standard performs well if it is this stable while tossing around, i wish my 332 and LM399 was that stable ( or more, the environment was more standard friendly becaus all powered down things are much more stable) > > Fred PA4TIM

Hello Fred, When looking at the cirquit of your reference the OP-Amps may be a source of common mode error too. With my LTZ1000 Reference I tested each Pin of each semiconductor with a metallic needle (held with my hand) if it is sensitive to common mode effects. The resulting cirquit diagram is in the archive from 6. November 2010. Usually Im cleaning the PCB after soldering with denatured alcohol to remove the dirt which might cause leakage currents. And finally: I would never put trimmers with several hundreds of ppm/degree tempco within the direct signal path. If you look at the internal cirquit of a precision reference the external trimpot is always used as voltage divider where the tempco cancels nearly out. The wiper of the trimmer is fed over a reference internal series resistor to a voltage divider. The series resistor and the voltage divider on the chip have again equal tempco which cancels out. So the trimming of the output voltage has only little influence on the tempco of the output. With best regards Andreas ----- Original Message ----- From: "Fred Schneider" <pa4tim@gmail.com> To: "Discussion of precise voltage measurement" <volt-nuts@febo.com> Sent: Saturday, October 20, 2012 7:34 PM Subject: Re: [volt-nuts] Traveling Standards > So I have nothing to complain, after the first week changing " much" it > now goes up/ down a bit with temp and probably humidity. At 10V, 1ppm is > 10 uV so it is changes 5 to 6 ppm over 5 degrees. Today it changed less > then 1 ppm over 3 degrees so I that leaves humidity. I do not have a > hygrometer so it becomes time I get one. > > Thanks for the tips for the common mode, i will try it soon, > http://www.pa4tim.nl/wp-content/uploads/2011/06/lm399schema_1.jpg > This is the schematic ( completely my own design but I'm no EE so it > probably will not be to great) but I appriciate comments for improvement. > http://www.pa4tim.nl/?p=2531 pictures are at the bottom of the page, all > my reference experiments are here together. > > Fred PA4TIM > > Op 20 okt. 2012 om 17:41 heeft "Andreas Jahn" <Andreas_-_Jahn@t-online.de> > het volgende geschreven: > >> Hello Fred, >> >>> It is now 24/7 on for about 5 weeks. >> >> 5 weeks is nothing in the life of a reference. >> During the first year my 2 LM399 references drifted 500uV against each >> other >> >> The 2nd year it was only 220uV >> now I know that LM399 #1 is drifting much more (200uV) than LM399 #2 >> (20uV) in the 2nd year. >> >> In the 3rd year LM399#1 drifted around 140uV and LM399#3 less than 10uV. >> >> So not all references seem to be usable for precision measurement. >> Its shurely no fault to start with a set of several references and select >> out the bad ones. >> >> With best regards >> >> Andreas >> >> >> _______________________________________________ >> volt-nuts mailing list -- volt-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts >> and follow the instructions there. > > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there.