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HP-34401A-Python

This is a simple driver (but with nice features) to read data from the HP 34401A multimeter.

What this driver offers?

  • A simple API with raw output in scientifc notation and float output
  • You can plug more than one multimeter
  • The serial is already configured and YES it works more stable with xonxoff instead of hardware flow control. It's a bug in the pySerial library
  • Works in Python 2.7 and Python 3.X

What's to be implemented in the future?

  • Config the 34401A via the Python Script

How to use this driver?

You need to import the DMM_34401a.py file with:

import DMM_34401a as dmm

Them you init your multimeter and store a handler, like the next line, the handler in this case is dmm0, and everytime you want to do anything with this multimeter you MUST use this "handler". Inside the DMM_init function you just need to pass the serial port you're going to use.

dmm0 = dmm.DMM_init("/dev/ttyUSB0")

Now you wanna read something from your multimeter, you got two options:

  • DMM_read_float(handler) In this one you will get a float number like 10.0010310
  • DMM_read_raw(handler) In this one you will get the raw output from the multimeter it's usually something like: +1.00010310E+01

Example of usage:

import DMM_34401a as dmm
dmm0 = dmm.init("/dev/ttyUSB0")
print(dmm.DMM_read_float(dmm0))

In the example above you will get a reading from the actual function set on the multimeter, so you need to set it before using the script. You should really prefer using the float version of the read, as it's protected with a REGEX, and it's impossible to get trash saved into your data (if you're going to use the 34401a to log something)

Tricks with the HP 34401a serial comm

  1. I spent a lot of time testing the serial port with the HP 34401a. Sometime this script will not work, go into the menu in your 34401a and set the baudrate again!
  2. Make sure you're not trying to get data faster than the multimeter does the acquisition ( 6 digit FAST, 6 digit SLOW, etc in the config of the multimeter)
  3. I don't know why but there is some bug with the pySerial library. The driver works with xonxoff and also dsrdtr (but it's not stalbe enough), the problem is the 34401a uses full serial flow control.