Hello,
Mhm, there should be also a 5 V output to distinguish ageing of the reference and ageing of the rest of the cirquit.
I guess that that drift what you see is not the ageing of the reference.
With best regards
Andreas
What I have preferred the last years are actually the AD587 JQ as the LQ isn´t available. That the KQ and LQ isn´t available and that the UQ seems to be trimmed in another way is one reason I think it reasonable to believe a lot of JQ’s will be within 5ppm/C. And of course, I was lucky to get all my AD587JQ within +-5ppm/C. I have nine AD587JQ’s of date codes 1028, 1247, 1517 and 1609 bought from Digikey and RS components.
The datasheet for the AD587JQ says 20ppm/C temperature coefficient and that with the box method. So, at 25C you can have even worse TC. As I, Andreas, Joe Geller and a report from the LISA-project shows the AD587UQ has more like 7-11ppm/C at 25C but the box specification is 5ppm/C.
Joe used the LQ and I think all had the date code 0045. Most of the LQ Joe had were around +2ppm/C at 25C so the simple add-on with a NTC+ resistor worked well.
I have temperature compensated many 10V references at home (never in a design at work) with NTC’s but mostly used other designs than the SVR-T design. The SVR-T design was just because the trimpot value was already fixed. Enclose a sketch for what I tried to describe earlier as an example for a more general design. It will give an adjustment range to compensate -8ppm/C to +12ppm/C. In this design the sensitivity to drift of all trim components are quite low compared to the SVR-T design. If I know the AD587 have a slight positive TC I can calculate a larger value instead of 1.5M to get less range and some second order compensation. Most AD587 seems to have a slight negative second order component of about -0.03ppm / (°C * °C) around 25C so a larger resistor gives some compensation for this. 1.5M together with 1.36M NTC gives a quite linear compensation, so no second order compensation, but useful for a broad range. I myself has set up an excel sheet for calculation of the NTC compensation.
That I say I prefer the AD587JQ is only true from a hobbyist point and to get a good “transfer standard” to compare and maintain 10V. In my professional work as a design engineer I haven’t designed in an AD587JQ and probably will not. Long long ago I designed in AD688AQ and BQ as they were good choices for +-10V refs with reasonable accuracy in data acquisition systems. As the AD588BQ are similar I guess it is a good choice for 15EUR/USD from eBay if they are not fake. My experiences with AD688xQ compared to AD587xQ are that the 587 is slightly more stable over time and draw much less power (10x) and don´t need dual supplies, so if you don’t need +-10v I prefer the AD587 in all aspects. Having just 2mA current draw is a plus when using say two 9V batteries to power your reference. Today most volt refs I design in are 2.5-5V in SMD of course.
Why 10V even for a hobbyist? I should say because of the traceability chain and uncertainties. If you, like me, after some years comes below 10ppm uncertainty the extra step from say 5 or 7.xV gives extra uncertainty. Not all have a super linear 8 ½ digit DMM or a KVD. My best DMMs are only 6 ½ digits and I never paid more than 100USD for a DMM yet. If you go for a couple of 10V references adjusted close to 10V it is also easy to make a simple x100 amplifier and with just a 3 ½ digit DMM to get 0.1ppm resolution when you regularly compare your references. Of course, after a while you will find it is difficult to measure the absolute long-term drift without repeated calibrations with known uncertainties. But even before that you have learned a lot about drifts between your samples. And temperature coefficients can be checked and adjusted with simple means. My first NTC temperature compensated REF102CM’s I adjusted with just a lamp above the DUT and a 3 ½ digit DMM + amplifier. Three out of four are below 0.1ppm/C at 23C. The fourth I must have made some mistake as it is +0.4ppm/C but as I have a second 10K NTC connected to banana jacks on the front of the box it is easy to compensate afterwards. Some other of my references aren’t compensated but I only compensate afterwards. I prefer the 10V adjusted to within say +-100ppm but some of my better reference have up to 400ppm offset (and 2ppm/C).
As Andreas pointed out you cannot temperature compensate away all TC on the IC. My estimate is maybe 10-20 times for a reference with about 5ppm/C from my experiences with an NTC very close to the IC (and of course mounted in a box, so outside gradients will not affect so much).
As the thread started with suggestion for 10v for MML I would say: DIY with AD587JQ and/or VREF10-003 from voltagestandard.com if you can afford 53USD for it. With the VREF10-003 you get 30ppm for 6 months and as far as I know it is a serious offer compared to many other Vref boards or boxes on eBay. I have only one VREF10-003 but at arrival it was very close and now after more than 1 year it is still just +12ppm. Of course it is humidity sensitive as all plastic refs. It has a cut-out on three sides of the IC but I am not so sure it helps. I think the humidity sensitivity comes from the epoxy in the DIP8 package. Enclose my measurements of it. The result is compensated for temperature (1.3ppm/C).
Having at least three 10V refs is nice as you can compare them. I try to compare my 10V refs each second or third month as that give multiple points over a year, which is nice to see seasonal variations.
Lars
A note: I usually say just “uncertainty” but more mean “expanded uncertainty” as it often is written in calibration protocols with k=2 or a confidence of 95%.
Have you measured the tempco-curve of your reference?
I have tested a lot of different voltage references and put together a chart detailing their specifications along with their output voltage as measured on my 34401A.
I tried to list the specification limit, not the "typical" deviation figure. I didn't want to compare one model's typical as compared to another's maximum. Occasionally I had to make an educated guess as to its maximum value. Case-in-point: the beloved LTZ1000. Linear likes to play up its 0.05ppm/C temperature drift specification without defining it. It appears to be a typical value. I guessed that its maximum might be 0.2ppm/C. The LTZ1000CH is the only voltage reference detailed on my attachment which I didn't have on hand to measure its actual output voltage.
I colored coded my opinion of the specification. For example, The LTZ1000 and LM399 have red accuracy specifications, but bright green temperature and long term stability ratings. I tried to be fair in those ratings and based them on their relative figures compared to the others listed.
The LM4128AMF-3.0 which I tested had a high noise level and poor voltage stability. It was by far the worst one tested in those regards.
I included a temperature compensated 1N4573A-1 zener in my tests for comparison. It had good voltage stability and a noise level comparable to the average voltage reference. The economy BZX79-B6V8,143 zener that I also tested for comparison had both a high noise level and poor voltage stability.
Most of the voltage references tested were purchased either from Mouser, Digi-Key or Arrow. The two AD584's tested were inside the eBay Chinese boxes which are available. The AD688BQ was recently obtained from http://www.ebay.com/itm/182537476611 for $18.91 + $4.00 shipping. It meets its 0.02% voltage accuracy specification for its +/-10V output. I'll probably add some trimmers to improved that accuracy further. Its voltage stability has been good in its initial tests. It's nice not to have to play games to alter the voltage to obtain 10 volts. Having a similarly accurate 20 volts output can double the precision of tests of some equipment.
Only testing one of most voltage references makes my test of them be not that meaningful. The LM399AH was the only one where I tested two. I wish that the tested ISL21009BFB's wouldn't have been discontinued. The specs of their replacements aren't as good.
Hopefully the attachment is useful for some. I tried to provide a fair comparison of the different models. Hopefully I didn't let any typical values slip through and that my approximations of a few maximum specifications aren't too far off the manufacturer's limitations. Several additional models were just added 6July2017.
I colored coded my opinion of the specification. For example, The LTZ1000 and LM399 have red accuracy specifications, but bright green temperature and long term stability ratings.
how about LH0070/LT1031B (metal cans)? reportedly pretty good tcr ca. 5ppm and good initial accuracy (+- 3mv for LT1031BMH).
is it a wise, to go with plastic, and adding some humidity countermeasures ?
can someone has opinion to immerse board in some electronic liquid ?
does lt1021 comparable with AD567 for a long term?
Silly question: wonder, if "soft start" ( V supply rising during seconds may help with accidental Vref shift ? )
My most stable 10V reference at this time is an original Geller SVRT, about 5 years old and was turned ON most of the time.
The picture here shows a recent measurement over night with "cheap normal cables" and around 2 °C change over night.
Actually I am surprised how stable the SVRT really is.
When it is turned off for a few days it needs about 30 h to stabilize again.
Note that the VRE305AD was pulled from the test because it clearly was out of spec
Note that the VRE305AD was pulled from the test because it clearly was out of specHello,
What do you mean with clearly out of spec?
The initial output voltage +1mV against 0.5mV max. (on production, before soldering).
or the -40 ppm drift over 600 hours against typical 6 ppm/kHr?
Did you also measure 0.1 .. 10 Hz noise?
with best regards
Andreas