pypid 0.4

A modular PID control library.

This package provides general PID control software in Python with a Melcor MTCA backend. The idea is that experimentalists interested in temperature controlled experiments or other processes should not need to learn the inner workings of their PID controller before they can perform simple control tasks.

Module structure

This package provides both a high level controller that uses per-device backend drivers. The controller handles auto-tuning the PID feedback parameters and changing system temperatures, while the backends communicate setpoint changes, temperature read requests, etc. to the temperature control device.

Backends

The only physicsal backend that is supported at the moment is a Melcor Series MTCA Thermoelectric Cooler Controller, which we communicate with via Modbus packets over a serial port. That’s all I needed for my experiments, but I tried to write a framework that was flexible enough to swap in other backends. By subclassing Backend for your particular device, you can take advantage of the high-level Controller code that’s already written.

Melcor

Companies don’t stay in business forever, but lab equipment does ;). Our controller is still going strong since 1999, but Melcor has moved around. According to their 2005 announcement the Laird Group PLC purchased Melcor from Fedders Corporation, and by 2009 (according to the Internet Archive Wayback Machine) they phased out the old website at melcor.com in favor of their own thermal site, and it looks like there is no longer support for the older MTCA controllers. There seem to be a number of them on eBay though ;).

TestBackend

To get a feel for driving a PID system, look atcheck out the TestBackend, which simulates a standard first-order process with dead time (FOPDT).

Installation

Packages

Gentoo

I’ve packaged pypid for Gentoo. You need layman and my wtk overlay. Install with:

# emerge -av app-portage/layman
# layman --add wtk
# emerge -av dev-python/pypid

Dependencies

If you’re installing by hand or packaging pypid for another distribution, you’ll need the following dependencies:

Package	Purpose	Debian	Gentoo
aubio	Pitch detection	python-aubio	media-libs/aubio
nose	testing	python-nose	dev-python/nose
NumPy	Controller analysis	python-numpy	dev-python/numpy
pySerial	serial comminication	python-serial	dev-python/pyserial
pymodbus	Modbus stack	python-modbus	dev-python/twisted
SciPy	Controller analysis	python-scipy	dev-python/scipy

Actually, pymodbus may (depending on your packaging system) depend on pySerial via Twisted, so pymodbus alone may be enough to get you going.

The Debian package for pymodbus has not been accepted yet. Debian bug #578120 tracks the progress of the prospective package, but it seems to have stalled out at the moment.

Installing by hand

Pypid is available as a Git repository:

$ git clone git://tremily.us/pypid.git

See the homepage for details. To install the checkout, run the standard:

$ python setup.py install

Usage

See the examples in the examples directory.

Testing

Run the test suite with:

$ nosetests --with-doctest --doctest-tests pypid

Note that you should have your temperature control device connected to your computer before running this command, as backend tests require a connected backend.

Licence

This project is distributed under the GNU General Public License Version 3 or greater.

Author

W. Trevor King [e-mail] Copyright 2008-2012