I just finished my boxes. The refs are isolated in RF boxes with some capacitors on Vin then those boxes are soldered shut(two spots to make sure shielding is continous. Those boxes are put into some Hammond boxes with a wire soldered to the RF box for earth connection and closed up. My reading offsets dropped by 50%. Was -40uV from nominal, down to -20uV.
Hello,
do you have a cirquit diagram of those references?
do you supply them by a switchmode power supply.
Is there any switch mode power supply (or LED lamp) near the cirquit?
What happens with battery supply?
In principle I see two possible issues:
- either instability due too much capacitive loading if the output has no measure for isolating capacitive loads.
- or instability due to EMI/switchmode supplies.
Sealed? No ventilation? I've read in this very thread (somewhere, can'f find it now--sorry!) that no ventilation is bad because the LTZ1000 will lose regulation at some point...
but not at room temperature. Most of the heat is transported by the component leads and by the copper on the PCB. So the chance of over isolation is very small.
I suggest to do a measurement of T.C. then you can see where the regulation begins to be weak (non-linear) and when it is completely failing (with 40-50 ppm/K).
with best regards
Andreas