Well, here now the next development step of my poor man’s 10 V reference based on the venerable LM 317 with its internal bandgap reference. The LM 317 is now heated by two BD 139 trannies on each side with a third BD 139 serving as a temperature sensor sandwiched in between making a single compact block bolted together with a M3 bolt. The arrangement is now insensitive to air movements although not yet contained in a metal box.
The next development steps will be:
1.) Replace the metal M3 bolt and nut of the block with a plastic M3 bolt and nut.
2.) Put the LM 317 block with the heating circuit on an new and clean hole dot matrix epoxy pcb. (instead of the currently used hard paper hole dot matrix pcb. material and avoiding flux residues) in a small metal box.
3.) Provide separate power supplies for the LM 317 block (+15 V) and the heater (+15 V, -15 V and - 5 V)
4.) Do some extended burning-in and subsequent ppm measurements. Watch this space.
By the way, my Keysight 34465A DMM set to the 10 V range and with its input shorted produces an output fluctuating at about 0.2 ppm (as measured over 1 hour). So my measurement limit, i.e the contribution from the 34465A in the enclosed graph will be about 10 times that at 2 ppm re. 10 V.
My aim is to produce a voltage reference circuit specc’d for around +/- 10 ppm (20 ppm total) perhaps, using cheap off-the-shelf components only.
What do you think?
Yours – Messtechniker
P.S. Still having fun with this.