Andrea C

Can you explain the 3-sigma value?  How compute it?

In your config, what sort of speed settings?  Use Quiet if looking for small standard deviations.

It looks like your DUT value is a few single digit pF.
At 1KHz, it will be very big Z and very small current relative to using higher test freq.
In our datasheet for CVU, we do not publish value for pF at 1KHz.

 

Sure, it is possible.

For older 4200, they can connect to external instruments on gpib or LAN (raw socket).
The newer 4200A-SCS adds usb and VISA for connection to external instruments.

The scope you mention has both LAN and USB.

For the software environment to send commands to scope and read data back, a library would be written using KULT tool.  Depending on your overall objectives, the code you write with KULT can also interact with the SMU, CVU or PMU hardware in your 4200/4200A.  The compiled library is run from KITE or Clarius UTM (user test module).  KXCI can also call user libraries.

Take a look at example KULT libraries on your system.  Ones for temperature control or for external LCR meter can give you an idea of interaction with external instruments.
 

Yes, that can be done.

In general, follow the Guidelines for combining SMU outputs in the Reference manual (section 2).

For two current sources in particular, make sure to have the voltage compliance limits a little bit different from each other.

To have same timing behavior from each SMU, use same ranges and other settings on each.

Also, sometimes the order of starting their trigger models matters.  For example, if SMUB is consuming an output event from SMUA to get things started, make sure to call the trigger initiate for SMUB first so that it can be fully armed and awaiting the events.

Are you using a fixed source range?  If the source range is also using auto, then the discontinuity could be for the hand-off of 200mV to 2V range as you sweep to 250mV.  A source range can go to 101% of its full-scale value.

For the data in the buffer, look at the measurerange and sourcerange attributes.  And perhaps post a CSV with your I, V, timestamp and the range information.
Try setting the smu sourcerange to a fixed value that can handle all the desired source levels (2V in your case).

When was last time your instrument was calibrated?
 

The CVU can source the DC bias at both CVUHI and CVULO.
To put the bias tees into CV mode, source -10 at each terminal from CVU.
The blocking cap of the bias tee will prevent this -10V from reaching DUT;  instead the bias from the SMU passes thru.

You are writing custom code to control it all?
Our ACS or ACS-Basic software has HVCV libraries for this configuration.

Depending on the connection rule in use, when moving to next channel in a scan, the opening of prior channel and closing of next can occur simultaneously or can be configured for break before make, etc.

In general the scan is just closing, measure, open/close next channel, measure, etc.

Since a measure function is associated with the scan, the instrument will also manage the backplane relays to connect the switch to the internal DMM.

Measure count of 10 would give 10 individual readings in the buffer.
To obtain an average, you could use a digital filter.  The instrument has both moving and repeating average filter.
Or there are buffer statistics that you can query to obtain mean, std dev, etc.

Yes.
Next to last page of data sheet lists the PC recommendations/requirements.
Windows 11 is supported.
Datasheet

In event log on the instrument, try turning on command logging.
Sounds like a syntax error.
Video on command logging:  https://www.youtube.com/watch?v=cVU_C308EUc

Or try NI IO Trace to see what is happening on the bus.

I failed to notice in my first post that you have auto range for the current measure still turned on.
You are setting fixed source range and fixed measure range v, but the measure range i is not set, so will default to auto range on.  Is that correct?

That is most likely the reason for loss of synchronization and the one SMU getting stuck in the trigger model awaiting a trigger that it missed due to taking extra time during a range change that maybe other SMU did not do.

Are your two 2651A at the same firmware level?  If not, please do that.

For pulsing, it is generally not feasible to also have auto range enabled.  Need a time budget on pulse width vs time for range changes and repeated measurements.

For low measure ranges in effect and large capacitive loads such as a solar device, there can sometimes be source stability issues.
In that case, try restricting the measure range by using fixed range or use of smuX.measure.lowrangei = XX

There is a high capacitance mode you can turn on.
Sometimes, just going to higher ranges fixes things up without the use of high C mode.

If you do not need pulse mode, have long pulses or otherwise want to use current measure auto range, you can maintain synchronization by making sure both SMU have completed a measurement before sourcing next value.  To do it, use the meas complete event from node[2] as stimulus for a tsplink trigger.  Then on node[1], use an event blender to logically AND the node[1] measure complete event with the node[2] meas complete relayed over the tsplink trigger.
The event_id of the blender can then be used to influence when sourcing occurs.
In this case, typically use a second event blender to do logical OR of the armed event id (first src value) or the blender id serving up the combined meas complete events (subsequent src values).
Make this OR blender to be the stimulus for the sourcing action.