I take a look at the Precision Digital Voltage Source by Ian Johnston.

Buy one here:
http://www.ianjohnston.com/index.php/…

Learn more about it here:
http://www.ianjohnston.com/index.php/…

FUNCTIONS & FEATURES:-

PDF version of the latest manual here.

– 50mV to 10Vdc user adjustable output (4d.p’s, 5d.p’s extended, i.e. 10’s of uV’s).
– Voltage setting or ramp up/down controls via the 12 button numeric keypad.
– Soft power switch.
– Based on the industry standard LM399AH (0.5 ppm/degC) voltage reference.
– No potentiometers inside or outside.
– 18bit DAC with an accuracy/stability down in the tens of uV’s (using a PLC filter of 1.0 or higher).
– Battery voltage monitor, including low voltage warning and auto-shutdown.
– Output voltage monitor including overload / short circuit protection.
– 3” Graphics LCD (128×64 pixels).
– Atmel 328P micro-controller (uses Arduino bootloader).
– Precision chopper op-amp on final output with extra stability achieved using low tempco resistors.
– Re-calibration by the user possible via keypad/LCD and saved to flash rom.
– Battery powered.
– Battery reverse polarity protection.
– Quality Hammond 1599 case.
– Quality aluminium anodized & engraved front panel.
– Quality 4mm banana sockets.
– Single PCB integrating the analog & digital electronics, LCD, keypad & battery terminals.
– Printed manual including factory calibration/settings record supplied. Unique serial number.
– NEW: Latest software V1.2 includes PLAYBACK mode.

Prior to shipping each unit:

– Hardware assembled and powered-up/tested using a strict procedure.
– Test point check at various places around the circuit for compliance.
– LM399AH aged/burned-in for 48hrs in unit, including numerous power cycles.
– Calibrated against a Keysight 34461a 6.5 digit multimeter (with current calibration certificate).
– Output load tested.
– Calibrated at approx. 23degC ambient.
– Unique serial number assigned.
– Calibration/setting record generated.

SPECIFICATION SUMMARY:-

– Voltage reference IC = LM399AH (0.5 – 1 ppm/degC temperature coefficient).
– Range = 0.05Vdc (50mV) to 10.0Vdc in 38.146uV steps (minimum).
– Load = 5mA (whilst maintaining output within approx. 10uV).
– Accuracy = 0.001% (within 100uV & using a PLC filter of 1.0 or higher).
– Stability = 0.0001Vdc variation max. 4d.p. mode.
Stability = 0.00004Vdc typical variation in extended 5d.p. mode.
– Temperature coefficient (output voltage) = Less than 1 ppm/degC (tested across a temperature variation of 11.5degC – See the project page here for more info).
– Stabilization time = typically 10mins when stored at approx. 23degC. Can be quicker, or longer depending on ambient and storage conditions.
– Output short circuit = indefinite.
– Power Source = Two 9V PP3 batteries.
– Battery life = 14hrs (600mAh batteries) typical continuous operation.
– Current drain = 40mA (after LM399AH stabilizes).
– Dimensions = 158mm x 83mm x 35mm (case size).