My current measuring tools may be of interest also for other people. Here is a brief description of the process.
Lab setup --------- This image shows the lab setup: http://downloads.qi-hardware.com/people/werner/anelok/tmp/isys-lab.jpg The lab power supply provides the voltage, with the current limited to something circuit and multimeter can handle. The negative terminal (ground) is connected directly to the test circuit (black arc). The positive terminal is connected to the multimeter (small red arc). >From there, the current goes to the test circuit (large red arc). The arrows indicate the direction in which the current flows. The multimeter is set to operate in the lowest range in which the current measured during the test fits. This is important because measurements can become quite inaccurate if the meter is operating at too high a range. Data collection --------------- The meter is connected to the PC and the PC continuously requests measurements. The script that does this is here: https://gitorious.org/anelok/anelok/source/meas/isys/m.py Nice and simple. It uses my TMC library, which now lives here: https://gitorious.org/lab-tools/tmc/ The TMC library is originally from Openmoko: http://svn.openmoko.org/developers/werner/ahrt/host/tmc/ The version on gitorious lacks the examples/ and demo/ directories, which contain things that can be useful but many of them are obsolete, which is why I didn't just copy them over. In the m.py script, you may notice the error handling. This is needed because my Fluke occasionally doesn't flush its output buffer properly and the read then waits forever. I've now added a timeout with automatic reconnect and repetition of the last command. Since a series of samples that includes such a recovery would have a different timing than one that had no problems, I discard such a series. Skewed timing may acceptable in other applications, though. Plotting -------- This is the script that does all the plotting: https://gitorious.org/anelok/anelok/source/meas/isys/plot Things of interest (gnuplot features that I have not or only rarely used before): - use of the greek mu in PNG and X11 output. For X11, the trick is to use WxT, which has an "enhanced" mode with special symbols, and not X11, which doesn't. - use of very thin lines (lw 0.1) combined with Bezier curves, which makes them look very nice. - parameter fitting ("fit" command) of an arbitrary function. There is also a new averaging mode that is better suited for plotting the long-term consumption. The result looks like this: http://downloads.qi-hardware.com/people/werner/anelok/tmp/anelok-idle-20140801-2029-0029-avg.png The little bump at 23:45 was caused by a heat source approaching the board. That was me taking the picture at the beginning of this post. - Werner _______________________________________________ Qi Hardware Discussion List Mail to list (members only): [email protected] Subscribe or Unsubscribe: http://lists.en.qi-hardware.com/mailman/listinfo/discussion
