Hi, Mr. Mickle.T and Mr. Kleinstein ,
Thanks a lot!
Yes it is time to analize upon the circuit. I will try to get the draft.
Acturely I had repaired nothing but find the way to perform the external calibration. The DCV and DCI zero is improved after that, especially for the lower range. For example ,the DCI 0.1ma is used to be as 0.07177ma and now is nearlly same with my 34401.
For the further test, I connect the DCV port to 6144 DC source and it is 0.32na when apply 0v, and 0.34na when add +10v, and 0.29na when add -10v. It is 0.29na when left all port open or short the DCV port, and 0.35na when short the DCI port. Both are in 100na range. I must point out that the reading changed when open all the port from 0.1737na ,the data recorded yestoday, to 0.29na, and this might be caused by the drift.
Re-test the DCI zero and attached FYI.
100na 1000na 10ua 100ua 1000ua 10ma 100ma 1000ma
open 0.2752 0.2034 0.000141 -0.00011 0.0069 -0.000052 -0.00032 -0.0124
short 0.3511 0.2941 0.000651 0.00454 0.0405 0.000285 0.00112 -0.0047
delta 0.0759 0.0907 0.00051 0.00465 0.0336 0.000337 0.00144 0.0077
ppm 759 90.7 51 46.5 33.6 33.7 14.4 7.7
delta uv 75.9 9.07 5.1 4.65 3.36 3.37 1.44 0.77
Pls look at the delta uv on shunt , the trend is very clear and the number is become smaller with the DCI range increasing. That is the correct data compared to yestoday's, which might be some mistake. That might imply something?
I had found a occurrence that the DCV zero will be a large number like -50uv when in cold state and will slowly come down to -3uv after warming up for 2 hours and stay there,all with AZ off. After I turn on the AZ, the reading become smaller like around -1uv and then turn off AZ ,it will stay there around -1uv , more like that the AZ on fixed the zero offset from the 1st time it was turned on in this power on cycle. I don't know if it will cause the DCI zero offset issue. Does it fine in the DCV zero offset ?
Best Regards,
szszjdb