keysightoscilloscopeacquire 2.0.1

Obtain traces, save to files and export raw plots from Keysight oscilloscopes using PyVISA.

Keysight oscilloscope acquire package

v2.0.1 // August 2019 // Andreas Svela

Overview

This package gives functionality for acquiring traces from Keysight oscilloscopes through a VISA interface, and exports traces as a chosen ASCII format file (default csv) and a png of the trace plot. The Python library visa is used for communication. The code has been tested on a Keysight DSO2024A model using a USB connection.

The code is structured as a module keyoscacquire/oscacq.py containing the engine doing visa interfacing in a class Oscilloscope, and support functions for data processing/saving. Programmes are located in keyoscacquire/programmes.py. Default options are found in keyoscacq/config.py, the files in /scripts can be ran from the command line and are essentially the same running the installed executables.

Installation

Install the package with pip:

$ pip install keysightoscilloscopeacquire

or download locally and install with $ python setup.py install or by running install.bat.

Default options

The package is installed with a set of default options found in keyoscacq/config.py:

# Default options in config.py
_visa_address = 'USB0::XXXX::XXXX::MYXXXXXXXX::INSTR' # address of instrument
_waveform_format = 'WORD' # WORD formatted data is transferred as 16-bit uint.
                          # BYTE formatted data is transferred as 8-bit uint.
                          # ASCii formatted data converts the internal integer data values to real Y-axis values.
                          #       Values are transferred as ASCii digits in floating point notation, separated by commas.
_ch_nums = ['']           # list of chars, e.g. ['1', '3']. Use a list with an empty string [''] to capture all currently displayed channels
_acq_type = "HRESolution" # {HRESolution, NORMal, AVER<m>} where <m> is the number of averages in range [1, 65536]
_num_avg = 2              # default number of averages used if only AVER is given as acquisition type
_filename = "data"        # default base filename of all traces and pngs exported, a number is appended to the base
_file_delimiter = " n"    # delimiter used between _filename and filenumber (before _filetype)
_filetype = ".csv"        # filetype of exported data, can also be txt/dat etc.
_export_png = True        # export png of plot of obtained trace
_show_plot = False        # show each plot when generated (program pauses until it is closed)
_timeout = 15000          # ms timeout for the instrument connection

For changes to these defaults to take effect, the package must be reinstalled locally after doing the changes in config.py, simply by navigating to the directory containing setup.py and running $ python setup.py install or install.bat. Note that none of the functions access the global variables directly, but they are feed them as default arguments.

The _waveform_format dictates whether 16/8 bit raw values or comma separated ascii voltage values should be transferred when the waveform is queried for (the output file will be ascii anyway, this is simply a question of how the data is transferred to and processed on the computer). Raw values format is approx. 10x faster than ascii.

The command line programmes will save traces in the folder from where they are ran as_filename+_file_delimiter+<n>+_filetype, i.e. by default as data n<n>.csvand data n<n>.png.

Known issues/suggested improvements

• Known issue: Sometimes WORD waveform does not give the correct trace data, just random noise (but switching to ASCii or BYTE gives correct traces). If this happens, open KeySight BenchVue and obtain one trace through the software. Now try to obtain a trace through this package -- it should now work again using WORD.
• Add optional argument to supply visa address of instrument to command line executables and scripts

Usage

In order to connect to a VISA instrument, NI MAX or similar might need to be running on the computer. The VISA address of the instrument can be found in NI MAX, and should be set as the _visa_address variable, see below, before installation.

Four command line programmes get_single_trace, get_num_traces, getTraces_connect_each_time and getTraces_single_connection can be ran directly from the command line after installation (i.e. from whatever folder and no need for $ python [...].py).

The two first programmes will obtain one and a specified number of traces, respectively. The two latter programmes are loops for which every time enter is hit a trace will be obtained and exported as csv and png files with successive numbering. By default all active channels on the oscilloscope will be captured (this can be changed, see below). The difference between the two latter programmes is that the first programme is establishing a new connection to the instrument each time a trace is to be captured, whereas the second opens a connection to start with and does not close the connection until the program is quit. The second programme only checks which channels are active when it connects, i.e. the first programme will save only the currently active channels for each saved trace; the second will each time save the channels that were active at the time of starting the programme.

Optional command line argument sets base filename, acquiring mode or number of traces to obtain

Furthermore, both programmes takes up to two optional arguments: -f "custom filename" set as the base filename to "custom filename" -a AVER8 sets acquiring type to average with eight traces -n 10 sets number of traces to obtain (only for get_num_traces)

For example

$ getTraces_single_connection_loop -f measurement

will give output files measurement n<n>.csv and measurement n<n>.png. The programmes will check if the file "measurement"+_file_delimiter+num+_filetype) exists, and if it does, prompt the user for something to append to measurement until "measurement"+appended+"0"+_filetype is not an existing file. The same checking procedure applies also when no base filename is supplied and DEFAULT_FILENAME is used.

Obtaining single traces

Running the module with $ python -m keyoscacquire obtains and saves a trace with default options being used. Alternatively, the filename and acquisition type can be specified as per the paragraph above using the executable, e.g. $ get_single_trace -f "fname" -a "AVER".

Obtaining traces when the scope is running vs when stopped

When the scope is running the capture_and_read functions will obtain a trace by running :DIGitize, causing the instrument to acquire a trace and then stop the oscilloscope. When the scope is stopped the current trace on the screen of the oscilloscope will be captured (Warning: This might mean the settings specified with :ACQuire are not used, i.e. acquiring mode and number of points to be captured).

The scope will always be set to running after a trace is captured.

Scripts in ./scripts

These can be ran as command line scripts from the folder with $ python [script].py. Optional arguments for filename and acquisition mode can be used, such as $ python [script].py "otherFileName", or $ python [script].py "otherFileName" "AVER8". Note, no flag specifiers are needed (or allowed) and the sequence of arguments is fixed.

Logging

The module gives output for debugging through logging. The output can be directed to the terminal by adding the following to the top level file using the keyoscacquire package

import logging
logging.basicConfig(level=logging.DEBUG)

or directed to a file mylog.log with

import logging
logging.basicConfig(filename='mylog.log', level=logging.DEBUG)