I'll look into firmware, should be rather easy to hack into.
Meanwhile, ran script to capture noise on short ppm/range once again, this time with 30minute sample window and LFILTER ON.
![](http://xdevs.com/doc/HP_Agilent_Keysight/3458A/test/comp_3458a.png)
Much closer to MM's 3458A, but still away from Dr.Frank (his results not using scripts, nor autozero, also no NPLC1000).
One thing I noted from reading manual that actual NPLC >10 is not increasing integration time, but just doing averaging of NPLC10 samples. There is other way to set speed, using APER command, with maximum integration time as 1 second. Should try that.
Running now without autozero, 5min window. No errors from meter so far.
![ThumbsUp :-+](https://www.eevblog.com/forum/Smileys/default/icon_smile_thumbsup.gif)
If anyone with 3458A want to jump in, just get
this EZGPIB script and
EZGPIB itself. It takes 17 hours to complete run on all ranges/NPLCs. It can be quicker if reduce window
const duration=30; // Acquisition time in minutes / cycle
Final internal view on both sides of meter before shields installed:
![](http://xdevs.com/doc/HP_Agilent_Keysight/3458A/img/final_bot_1.jpg)
![](http://xdevs.com/doc/HP_Agilent_Keysight/3458A/img/final_face_1.jpg)
![](http://xdevs.com/doc/HP_Agilent_Keysight/3458A/img/final_back_1.jpg)