Hello,
So you have checked that its not the input buffer of the DMM. The voltage reference(s) can be still affected.
You can use 2 of your LTZ references with ground pin connected and measuring the difference in 10V range.
Andreas
Well this is how was obtained first chart.
Reference where running on insulated power supply (KX on a mains powered with transformer, HBDR107A on batteries).
- Ground pin of both ref connected.
- The two 7V connected one to HI and one to LO.
I attache here also this night run with ratio measurement.
Noise in ratio mode is around 250nV RMS with some spike, a little bit more than when it was back 2 back but still I cannot see any multiple minute 1uV jump.
I was expecting ratio mode to have similar noise than back to back ... I have to think at this.