You can’t afford it, if you have to ask the price…
Layout of the 6-layer custom ceramic PCB:
Cross-section of the PCB
Module assembled with some additional shielding
Air baffles to reduce thermal gradients around LTZ1000A chips.
Module installed in Keysight 3458A DMM, replacing onboard A9 LTZ1000A-module
Preliminary 0.1 – 10 Hz noise test results, room temperature.
QVR Unit #1 was mostly kept unpowered to evaluate deviation and instability of the quad LTZ1000A-based reference module. Measurements were handled at two different locations with international shipping of the unit with regular postal service (USPS at US end, EMS at NMI location).
Calibration reference value T23°C = 9.990901 VDC ±0.8 ppm , 10.SEP.2019
Calibration result from NMI (Calibrated 3458A readout)
Calibration reference value T23°C = 9.990904 VDC ±0.6 ppm , 17.JAN.2021
Then standard was returned and tested again, powered from Fluke 792X battery power pack.
Calibration reference value T17°C = 9.9909107 VDC ±0.6 ppm , 1.APR.2021
Calibration reference value T23°C = 9.9909107 VDC ±0.6 ppm , 1.APR.2021
Calibration reference value T30°C = 9.9909107 VDC ±0.6 ppm , 1.APR.2021
Calibration reference value T45°C = 9.9909107 VDC ±0.6 ppm , 1.APR.2021
Modified: April 1, 2021, 9:50 p.m.