You can also try a temperature compensation by NTC like in the Geller SVR-T reference.
The link to the schematic for SRV-T is broken here
http://www.gellerlabs.com/Voltage%20References.htm
Does anyone have it at hand?
Got a request offline so here is my copy. /Lars W
This schematic is based on the original SVR that I just added the NTC + series resistor to. I have done temperature compensations to many AD587, REF102, LT1021 and LT1236 and my preferred way today is to have a separate trimpot for temperature compensation with a NTC+ series resistor.
The AD587JQ from Digikey (or Mouser) is right now my preferred DIY10V ref as it isn´t humidity sensitive. The last years I have bought AD587JQ´s a couple of times and no one have been over 5ppm/C (probably been lucky but am not sure). So it should be quite easy to get them down below 0.5ppm/C with some temperature tests and NTC compensation.
As pin 5 on the AD587 is at about 7V I have had two 20 k trimpots in series between 0 and +10V (pin 6). The upper has been connected to the NTC (680+680k SMD near pin 5)) in series with a resistor of 1.5M. This gives a range of about +-10ppm/C adjustment if I remember correct. If the temperature coefficient is positive I sometimes calculates a higher value resistor to get some second order compensation, this also gives lower sensitivity to the components (TC, res, pot). The other pot is connected with a 10Mohm resistor to pin 5 to give about +-135ppm trim. A third resistor is connected between 0 or 10V to get the trim range for the pot.
This compensation scheme works well with the other IC´s mentioned but values will be different. If the trim pin is at +5V (eg LT1021+1236) don´t put the trimmers in series but instead in parallell. To set up your own calculation just hook up a 1Mohm resistor to the 0v respective 10v and see the change in ppm. Use these values together with say values for the NTC at 20-25-30C and put in a spreadsheet.
Another important thing that is missing in the schematic is a 100nf capacitor on the output (pin 6 to 0V). Without that the SVR is very EMI sensitive as I have seen a lot of times in my lab before I understood that. I also normally use ferrite beads to the connecting pins (in and out)