Considering Decided to make 10 completely assembled and tested modules to provide +10.00000 +/-4 ppm buffered output.
One of the challenges is cost and time involved to test and calibrate these things.
Device is based around
xDevs.com FX module PCB, which have next design specifications:
Reference source: LTZ1000ACH with datasheet schematics, using LT1013ACN.
LTZ Temperature SP: 13K/1K which provide about +55C oven temp
Resistors: VPG BMF HZ for 120ohm, temperature SP. PTF56 5ppm/K for 70-80K bias resistors
Output 7V->10V stage: Chopper opamp ADA4522-2 in SO8, Hermetic resistor network or BMF resistors. Each unit adjusted by trim resistor for tight output tolerance.
Onboard supply: Linear LT3042 LDO, configured for +11V output to LTZ circuit.
PCB: 4-layer FR4 with ENIG plating
Input power requirements: +12V and -12V.
Power consumption : ~0.6W when operated with +24C ambient
Additional features : isolated section with I2C EEPROM with calibration data/config/history (RPI python app to be provided to maintain data), MAX6610 PCB temperature sensor for tracking
Calibration traceability: <4 ppm to 732B, uncertain with 0.6ppm.
Expected performance: <4 ppm/year long-term stability, <0.1ppm/K tempco over 18-28C ambient temperature.
Assembly type: Hammon metal box with Pomona 3770 low-thermal binding posts.
I'd like to check if there is any interest in expensive hobby-level reference among the members here.
If enough people would be willing to buy one, it will be easier for me to pull the trigger and tie in 4-5K$ into this project.
Estimated delivery date would be
March 2018 October 2018, with final good cost $500 USD.
Specs above are on safe side, so the module likely to be 2-5 times more stable, however I wouldn't guarantee it just yet. There is no replacement to actually running reference for 3+ years to determine actual long-term annual stability.
Feel free to comment
Member list, who interested in modulemontemcguire - 1 unit [CONFIRMED] [DELIVERED]
dr.diesel - 1 unit [CONFIRMED] [DELIVERED]
chriswebb - 1 unit [CONFIRMED] [DELIVERED]
PeLuLe - 2 unit [CONFIRMED]
MM - 1 unit [CONFIRMED] [DELIVERED]
bck - 2 unit [CONFIRMED] [DELIVERED]
USA cal club - 1 unit [CONFIRMED] [DELIVERED]
CM - 1 unit [CONFIRMED] [RESERVED]
zucca - 1 unit [CONFIRMED] [DELIVERED]
No more units available., unless somebody change their mind.
Prototype board overview, test data samples Initial output after first assembly.