Transport Measurements

Overview

This set of Python scripts represent my first attempt at real-time data acquisition and plotting with PyVISA and pylibnidaqmx.

The goal was to keep the plotting as simple as possible to facilitate easy writing of new experiment classes. These measurements do work, but they aren't nearly as reliable as I'd like and adding additional feedback forthe user quickly becomes very complicated.

Structure

• instruments.py creates a class for each GPIB/RS232 device in our lab as a subclass of some PyVISA instrument
• specific instrument/measurement classes (e.g. nanovoltmeter.py). These create subclasses out of the instruments classes in instruments.py. The idea was to create a class for a specific type of measurement using that particular instrument (IV curve, differential conductance, ...).
• measurement classes (e.g. keithleypair_IV_swpVar.py) -- These classes/functions build specific experiments around the measurement classes defined for each instrument.

Example

If I want to take several IV curves, each at a different magnetic field, using the Keithley 6220 and 2182A, I can use keithleypair_IV_swpVar.IV_MagField. This class uses instruments.oxford_magnet to control the magnetic field and keithleypair.IVmax1024 (which is a subclass of instruments.K6220_2182A) to run an IV curve at each magnetic field value.

The experiment itself is written in the run_simple() function, which saves the data without attempting to plot it. Plotting is possible through the run() function. This function calls run_simple() as a thread while monitoring the class variable self.data and updating a plot with matplotlib.animation

Dependencies

• PyVISA -- http://pyvisa.sourceforge.net/
• pylibnidaqmx -- https://code.google.com/p/pylibnidaqmx/
• Numpy
• matplotlib

Author and Future Work

This work was completed by Nik Hartman as a part of his PhD thesis in the Markovic lab at Johns Hopkins University. The author can be reached at: [email protected]

I'm interested in continuing this work, but it has reached a point where it has become too distracting from the main focus of my experiments. Any collaboration or comments are welcome.