Scripts to measure specific resistance with a 4-point-probe.
The project is developed and maintained by the Model experiments group at the Leibniz Institute for Crystal Growth (IKZ).
This project is used to measure voltage and specific resistance with the 4-point method. The Python script completely automates the process.
The 4-Point method uses four probes to measure voltage at a set current, which is induced by two of the four probes. The specific resistance can be calculated with the known and measured values. For additional information, read here: https://iopscience.iop.org/article/10.1088/0953-8984/27/22/223201/pdf.
A Raspberry Pi 400 is used as the computer. Connected to the Pi are the "2450 SourceMeter" with USB, the "DAQ6510" with RS232 to USB, and the "IKA C-MAG HS 7" with RS232 to USB. The sample is placed on the heating plate. The four probes are placed on the sample with sufficient weight (!) and are connected to the "2450 SourceMeter"which is capable of the 4-point-measurement method. Two more probes are placed at the back of the probes that measure the voltage and are connected to the "DAQ6510," which ensures higher accuracy.
The internal script "Setup00" of the "2450 SourceMeter" has to be configured for 4-point-measurement.
To use usbtmc (which is used to control the "2450 SourceMeter" ) without root, the following steps have to be taken:
Go to the rules.d folder.
cd /etc/udev/rules.d/
Find (or create) the usbtmc.rules file and open it:
sudo nano usbtmc.rules
Add the following line:
SUBSYSTEM=="usb", ATTRS{idVendor}=="05e6", ATTRS{idProduct}=="2450", MODE="0666"
If the file is not empty, delete all the other lines. If you use another device, then the "2450 SourceMeter" use lsusb to find the vendor ID and the product ID.
Restart udevadm:
sudo udevadm control -R
Close and reopen your script. usbtmc should now be usable without root.
The following external libraries are used: yaml, atexit, matplotlib, numpy, usbtmc
Before using "hauptprogramm.py" "config.yml" and "settings.txt" have to be configured.
"config.yml" is used to configure the DAQ6510 and the heating plate (IKA or Eurotherm).
"settings.txt" is used to configure the depth of the sample, the currents used and the temperature settings. Read settings.txt for detailed information.
The "2540 SourceMeter" is configured directly in the script, no configuration should be needed.A method to control the "2540 SourceMeter" over the Internet and Selenium can be found in 2450SourceMeterWithInternet.py, but it is not used.
If all settings are configured, hauptprogramm.py can be started. The program should start and run automatically, with no further action needed. If a plot appears and moves once a second, the program runs as intended. The program is finished when the plot closes. If the plot is closed early, the program will halt.
Results are stored in the "data" folder. A list of every value record can be found in "data.csv". A list of average measurement data and standard deviations can be found in "measerment_data.csv". Also, a screenshot of the plot is found in the folder.
This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No 851768).
