Programming the 9103 With Python – Part 1: Standard Speed

New sample Python code for the 9103 is now available on RBD’s website. The 9103’s API is easy to program with any language and documented fully, but as always with any device programming, a few examples always help. We chose Python because it’s well supported, easy to understand even if you’re using another language and compatible with a number of popular lab control and analysis environments.

The sample code we provide is open-source and free for you to use and distribute as you see fit.

(If you haven’t taken a look at the 9103 USB auto-ranging picoammeter, everything you need to know can be found here. Measure bi-polar DC current from picoamps to milliamps, with optional built-in bias and 5 kV isolation.)

Programming the 9103 with Python

A Quick Look at the Standard Speed Sampling Code

Python’s pySerial module abstracts the calls to class-compliant USB serial COM port drivers, so setting up communications with the 9103 is a matter of a few simple calls:

port=serial.Serial(
    'com' + port_number,
    baudrate=57600,
    bytesize=serial.EIGHTBITS,
    parity=serial.PARITY_NONE,
    stopbits=serial.STOPBITS_ONE,
    xonxoff=False,
    timeout=1)

With the addition of a few helper functions for handling ASCII, it’s simple to write functions to send individual commands to the 9103. The following sets the auto-range and filter settings:

def message(message_string):
return bytes('&'+ message_string + '\n','utf-8')

def command_range_auto():
port.write(message('R0')) # put in autorange

def command_default_filter_32():
port.write(message('F032'))

Similarly, with the addition of a few helper functions, the 9103 samples can be read with a simple loop that reads lines from the port buffer: In this case, we’ve setup the 9103 to read in interval mode, and poll the port for incoming samples, with a simple keyboard interrupt. This code also writes the sample information to a text file.

try:
while True:
msg=port.readline().decode('utf-8').rstrip()
print(msg)
parsed = parse_message_for_sample(msg)
if parsed:
samplefile.write( parsed + '\n')

except KeyboardInterrupt:
pass

All of the code is commented and documented in the Python file.

Using Python with LabView and MATLAB

The Python code samples can be helpful to both LabView and MATLAB users.
LabVIEW now supports Python through the Python Node, which features low-latency calls from a LabVIEW Block Diagram using LabVIEW primitives.

The MATLAB Engine API for Python allows you to call MATLAB as a computational engine from Python, and you can call functions and objects in Python from MATLAB.

More to Comeā€¦

Next up we’ll be posting some sample code to write and read using the high-speed version of the 9103. Since high-speed data from the 9103 arrives in packets, there are some minor differences in parsing the message samples.