Problem reading voltages in a DC sweep setup with DC current source 6221 and nanovoltmeter 2182

Hello,

This sounds very much like the Delta Mode operations available to the 6221/2182A.
This mode creates a system of instruments with TLink and RS-232 between the instruments and sets the 6221 as the 'master' node.
All control operations and data will be handled on this unit, while the 2182A would only be used as a 'software' controlled voltmeter.
Typically, this removes any ability to communicate directly with the 2182A and all data would appear from the 6221 through that link.
I am not sure what additional handshaking occurs through the delta mode backend code to allow for this, unfortunately.
I have shared this post within our development group and hope others will comment with information that may be helpful to you.
 

Here is some additional information related to your request:

There’s 2 levels of communication here. Unlike with TSP link or TSP net where we can directly reference the nodes in the system and the lead node handles divvying out the responses, we have to explicitly tell the 6221 to communicate back and forth with the 2182A before communicating with the PC.

The SYST:COMM:SER:SEND sends a command to the 2182A. If that command is a query like TRAC:DATA? The 2182A places the requested information into the output buffer of the 2182A. The 6221 still has to read that information with the SYST:COMM:SER:ENT? Command which grabs the info from the 2182A output buffer and puts it in the 6221 output buffer so that it can be read to the PC. The SYST:COMM:SER:SEND command itself is not a query, nothing is put in the output buffer of the 6221, so when you try to read in python, there’s no response to read from the 6221 and an error is produced.

The code should do the following:

Write(SYST:COMM:SER:SEND “TRAC:DATA?”) – tell the 6221 to tell the 2182A to put the data in its output buffer

Query(SYST:COMM:SER:ENT?) – tell the 6221 to check for output from the 2182A and put the response in the 6221 output buffer where we can read it.

Hi Jake,

Thank you very much for your answer. That is exactly what I suspected, that in order to do a query from 2182A I needed to send the query to 2182A and then read the output of the RS232 link with the SYST:COMM:SER:ENT? command. However, using this method I cannot implement a sweep with more than 16 points, which is very inconvenient. Basically, using the code that I previously shared, everything works perfectly fine if the number of points for the sweep is smaller than 16. If I increase the number of points to 17, the variable 'voltage_meas' where I store the data read from Query(SYST:COMM:SER:ENT?) (see attached 'voltage_meas_17_points.png') only shows 16 values instead of 17 as we would expect. In addition, the first ('3\n') and last ('+8.21553742E) measured values do not correspond to voltage values. If I further increase the number of points to 25, we observe the same result (see attached 'voltage_meas_25_points.png') with only 16 read values, where the first and the last one do not correspond to voltage values. 

From the 2182A manual I know the maximum number of points that can be stored in 2182A buffer is 1024, hence I don't believe the problem comes from 2182A. The maximum size of the 6221 buffer is 65536 and I have tried to set it up so it corresponds to the number of points of my sweep, hence I neither think the problem comes from 6221 buffer. I suspect that the element limiting the number of data that can be read is the RS232 cable. However, if I use the example software KI622O.exe provided by Keithley, I am capable to perform a sweep with up to 1024 points using exactly the same setup described before (GPIB from 6221 to the PC and RS232 + Tlink between 6221 and 2182A). Therefore, I believe there must be a way to perform the sweep with high number of points using this setup. The reason why I do not use the KI6220.exe software is because I cannot save the measured voltage values, which is critical for my experiment.

I hope you can help me on how to increase the number measured points. Let me know if further information is required.

Thank you very much.
Javier

 

Hi Jake,

An update on the issue: I have noticed that the Query(SYST:COMM:SER:ENT?) function only reads 16 values from the 2182A buffer. Hence by repeating Query(SYST:COMM:SER:ENT?) several times I can retrieve all the data from 2182A buffer. I have updated my code (see attached) to repeat as many times as required the function  Query(SYST:COMM:SER:ENT?) until the 2182A buffer is empty. It seems to work quite nicely for a sweep with maximum 100 points. When I try with 150 points or more, I always find a -363 error message in 6221, which consists of an input buffer overrun. As I mentioned previously, I know the capacity of 2182A buffer is up to 1024, and I set up the buffer to have the same dimension as the number of points that I want to measure. Where does this buffer overrun comes from?

P/S: I have tried to set the flow control to 'XON' as from my understanding this should prevent any overrun in the input buffer of 6221, however the error -363 doesn't disappear.