Communicat​ing with Keithley 2602A using python script

Question

Hi everyone,
I want to enable communication between my PC and Keithley 2602A SourceMeter Instrument so that I can send commands to the SMI without using Test Script Builder (TSB) - a scripting/remote controlling program that enables communication between itself and the host computer.
The reason why I want to do this is because I want to program in Python to carry out a series of tasks involving other hardwares and adjusting the voltage on the SMI at the same time. I can't use TSB to do this because TSB is solely for controlling the SMI and not other hardwares. I need to use Python scripts to consolidate all the hardware control. So far, communicating with other hardwares from my PC using Python scripts is not a problem because I have readily available libraries for them.
I have found PyVisa which I thought could solve the communication problem. So I installed PyVisa and wrote the following code to test the communication.
import visa
keithley = visa.instrument("COM1")  #SMI connected to COM1
keithley.write("smua.source.output = smua.OUTPUT_ON")  #send this command to SMI
 However, the communication was not successful as I got the error message as shown below:
C:\Documents and Settings\cho\Desktop\Python Ex>keithley_test.py
Traceback (most recent call last):
  File "C:\Documents and Settings\cho\Desktop\Python Ex\keithley_test.py", line 2, in <module>
    keithley = visa.instrument("COM1")
  File "C:\Python26\Lib\site-packages\pyvisa\visa.py", line 292, in instrument
    return SerialInstrument(resource_name, **keyw)
  File "C:\Python26\Lib\site-packages\pyvisa\visa.py", line 680, in __init__
    "delay", "send_end", "values_format")))
  File "C:\Python26\Lib\site-packages\pyvisa\visa.py", line 358, in __init__
    "lock")))
  File "C:\Python26\Lib\site-packages\pyvisa\visa.py", line 132, in __init__
    keyw.get("lock", VI_NO_LOCK))
  File "C:\Python26\Lib\site-packages\pyvisa\vpp43.py", line 753, in open
    byref(vi))
  File "C:\Python26\Lib\site-packages\pyvisa\vpp43.py", line 398,
in check_status raise visa_exceptions.VisaIOError, status
pyvisa.visa_exceptions.VisaIOError: VI_ERROR_RSRC_BUSY: The resource is valid, but VISA cannot currently access it.
Can anyone tell me what went wrong? How can I control the Keithley 2602A using a Python script run from my PC?

Answer 1

Hi DavItron, this is a very old thread but it's one of the top google results when I looked up info on how to implement some Python code with PyVISA to drive the Keithley 2602A so I will post this response so that other searchers can find the info.
You can store data in named variables in the Keithely 2602A and then "print" them to the remote interface using something like the following:
import visa
ps = visa.Instrument("GPIB::Address of your instrument")
ps.write("smua.source.levelv=10")
ps.write("smua.source.output=smua.OUTPUT_ON")
ps.write("currenta, voltagea = smua.measure.iv()")
ps.write("smua.source.output=smua.OUTPUT_OFF")
current = ps.ask("print(currenta)")
voltage = ps.ask("print(voltagea)")
For what I do which is mostly setting and measuring a bias point, then holding that while I trigger a measurement on another instrument, this is fine for me.  If you want to do  sweeps with a lot of data points it's probably more efficient to use the buffers directly, but I haven't needed that yet.
Hope that helps somebody!