Yes they are similar but I have used the old Philips/BC Components like Digikey BC2301-ND for more than 20 years. Ordinary SMD NTC will also work. I normally check the trimpin on for example an AD587 with a 1M or 10Mohm resistor to +10 and Ground. By checking how the trimpin voltage and output voltage changes it has been quite easy to set up a model in Excel for calculation. That together with a temperature scan can be used to select components compensation. I think Joe Geller used an automated model with Labview to calculate the NTC and resistors to get the right compensation. Lars​ Från: Russ Ramirez Skickat: ‎tisdag‎ den ‎24‎ ‎november‎ ‎2015 ‎17‎:‎52 Till: Discussion of precise voltage measurement Wow, there's a ton to know about NTC thermistors by themselves! Lars, is the part for the Geller style of unit similar to this one, ( http://www.digikey.com/product-detail/en/NXRT15XH103FA1B030/490-8601-ND/3788625) or very different? Russ On Tue, Nov 24, 2015 at 8:51 AM, Lars Walenius <lars.walenius@hotmail.com> wrote: > Hello, > > > My name is Lars Walenius and I live in Sweden. I am new to this forum but > a volt nut for decades. I must admit I have to many DIY voltage reference > boxes. Some years ago I was fortunate to work with Joe Geller on the SVR-T. > For me the SVR-T still is the best 10V hobby reference sold. So it is a > pity the AD587LQ isn´t available any more as my opinion is that the > reference IC is the most important in a DIY reference. > > > I can just second what Andreas say. Maybe the comment about metal cans > need to be commented. Metal cans are good for humidity but I have seen high > long term drifts on LT1031 that I have several powered on for years. Also > if power is off for a or two month they go back many ppms. On REF102CM in > metal cans (obsolete) I have seen about 5ppm if turned off a longer time. > In the same test AD587LQ (obsolete) changed less than a ppm. AD587JQ and > AD587UQ are still available but I would not recommend the UQ as my and > others observations are in the 10ppm/C class ( probably due to adaption to > a very wide temp range). I have several JQ with reasonable (less than > 5ppm/C that can be compensated with NTC) but you should check noise (LF). I > have seen several ppm p-p on some. So by selection I think the AD587JQ is > the best 10V ref available today (from eg Digikey). > > > Charles, I have to say thank for all your good comments both here and in > time nuts but if the 130USD ref is the D105 on Ebay have a look on EEVBlog > and my humidity tests. The 2ppm ref has 20ppm drift for a change 40 to > 90%RH in just a week!! > > > > http://www.eevblog.com/forum/testgear/calibratory-d-105-dc-precision-voltage-reference-standard/630/ > > > > > > > Lars > > > > > > > Från: Russ Ramirez > Skickat: ‎tisdag‎ den ‎24‎ ‎november‎ ‎2015 ‎15‎:‎29 > Till: Discussion of precise voltage measurement > > > > > > Thank-you all for your valuable insights and the book reference Jahn. I can > see clearly now that doing such a project with a LM399 for example as a > learning project would be interesting. Designing the board to use the > MAX6126, and finding reasonably priced low tempco parts was a useful > exercise. > > Russ > > On Tue, Nov 24, 2015 at 5:55 AM, <acbern@gmx.de> wrote: > > > There are many things to factor in. Drift of reference itself over time > > and temperature (399 is 1ppm/K worst case alone, over say 10K, i.e. > > 23C+/-5K). Drift of the gain setting resistor is critical (assuming you > > have an amp generating 10V out of the 399 output voltage). and so on. > > Also, you need a precise reference to calibrate the units (low cal > > uncertainty and low drift). > > Selection, statistical validation and aging is needed. > > All doable but costly and more complicated than one might expect. > > > > Thats why I think the target price has to be reasonable, any thoughts > here? > > > > > > > > > > > Gesendet: Dienstag, 24. November 2015 um 10:05 Uhr > > > Von: "Ian Johnston" <ian@ianjohnston.com> > > > An: "Discussion of precise voltage measurement" <volt-nuts@febo.com> > > > Betreff: Re: [volt-nuts] Low-cost voltage reference questions > > > > > > Hi all, > > > > > > I can relate to this.......and only last night I was pouring over it > > > wondering what to do! > > > > > > I have just designed a Handheld Precision Digital Voltage > > > Source.........LM399AH & uController controlled. > > > > > > About to start selling them, and so I am writing the manual & spec > sheet > > for > > > it.......but can't decide without a years worth of data & testing > behind > > me > > > what figures to use! > > > I've got the reference, DAC and op-amp figures, all the tempo's I need > > etc > > > etc. > > > > > > Hmmmm! > > > > > > Ian. > > > > > > > > > > > > -----Original Message----- > > > From: acbern@gmx.de > > > To: volt-nuts@febo.com > > > Date: Tue, 24 Nov 2015 09:35:24 +0100 > > > Subject: Re: [volt-nuts] Low-cost voltage reference questions > > > > > > > > > Charles and group, > > > another persons opinion: > > > > > > I guess the reference to the "standards" means those sold on ebay US. > If > > so, > > > I would think it is a false expectation this would meet 3ppm acc. > > guaranteed > > > within a year. > > > There is a lengthy chat in eevblog about it, in case you are not aware, > > and > > > while the unit typically may not be too bad, it is certainly not > > seriously a > > > 3ppm guaranteed standard (even in its best version). It starts with the > > > traceability, and goes on with the design and build standard. Details > in > > the > > > blog. In summary, it is not even really spec'ed, also because it can't > be > > > (at least not close to what it seems to raise in expectations). But at > > that > > > price, it would be unfair to expect more than a hobbyist item with > > > relatively unclear real specs. But if you mean another item, let us > > know, I > > > guess the group would be interested. > > > Keep in mind, the Fluke 732B is specified/guaranteed to 2ppm per year. > > There > > > is data available from Fluke about 732B drifts ("Predictability of > Solid > > > State Zener References"), and it can be seen how hard it is for them to > > > guarantee 2ppm/year. > > > So I think your price target and spec expectation ("guaranteed to > > > remain"...) just does not match. > > > > > > I would think a unit that has a traceable specification to a National > > > Standard (including an error propagation analysis for the factory > > > calibration how to get there), and be within say 5ppm a year, over a > > defined > > > (limited) temperature range, with a good build standard (CU-TE spades, > > metal > > > case, EMI filtering, PSU...), targeted at those who cannot afford/do > not > > > need a 732B could easily have a fair price of a couple hundred usd. > > > Other opinions welcome. > > > > > > > > > Cheers > > > Adrian > > > > > > > > > > Gesendet: Montag, 23. November 2015 um 23:26 Uhr > > > > Von: "Charles Steinmetz" <csteinmetz@yandex.com> > > > > An: "Discussion of precise voltage measurement" <volt-nuts@febo.com> > > > > Betreff: Re: [volt-nuts] Low-cost voltage reference questions > > > > > > > > Russ wrote: > > > > > > > > >What is considered the break-over point of precision with low > > uncertainty > > > > >versus cost to a group like this? Is there a rule-of-thumb for the > > cost > > > of > > > > >each additional digit of precision after N digits? > > > > > > > > One person's opinion: > > > > > > > > To a group like this, I'd be inclined to say that interest begins at > > > > a room-temperature (say, 20C +/- 3C) accuracy of 3ppm (i.e., > > > > guaranteed to remain within 3ppm from 18-22C for at least one year > > > > after purchase). 3 ppm is 0.0003%. There is at least one 10v > > > > reference with specifications in this ballpark available at an asking > > > > price under $130 (I'm told the seller has accepted offers > > > > significantly lower than this). > > > > > > > > >If I sell someone a reference > > > > >that I've ascertained is 2.50163v @70.3 F with a calculated > > uncertainty, > > > is > > > > >it valuable as a 0.1% reference even though the error may be much > > less, > > > > >like +/- 0.08%? > > > > > > > > I, for one, do not consider 0.08% to be "much less" than 0.1%. One > > > > sneeze and it's out of spec. Indeed, I would consider a claim of > > > > 0.1% accuracy to be bordering on fraudulent based on a calibrated > > > > measurement at 0.08%, unless the spec was qualified as "within 0.1% > > > > at [temperature within 0.1C] as is, where is -- no claim as to > > > > accuracy after it has been shipped to the buyer." > > > > > > > > Speaking as someone with substantial commercial design experience, I > > > > would never offer a voltage reference for sale as a claimed "0.1% > > > > standard" that I did not have excellent justification for believing > > > > would stay below 0.05% for a year over a several-degree range of > > > > temperature and multiple trips across the country via commercial > > > > carriers. I wouldn't expect to be able to charge more than $10-15 > > > > for the product just described, and then only if the nominal output > > > > voltage were 10v (I think you will find that there is a very strong > > > > preference for 10v references over 5v, 2.5v, or other voltages). > > > > > > > > Best regards, > > > > > > > > Charles > > > > > > > > > > > > _______________________________________________ > > > > 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. > > > > > > > > > > > > > > > [Sent by MDaemon Mail Server at IanJohnston.com] > > > _______________________________________________ > > > 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. > > > _______________________________________________ > 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. > _______________________________________________ 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.