Continuation of emontx testing - feed comparison tool

Glyn has been running a parallel test of the new emontx v3 vs the old emontx v2 for over a month now. See Glyn's original post introducing emontx v3 here: http://openenergymonitor.blogspot.co.uk/2013/02/emontx-smt-update-introducing-emontx-v3.html

In testing a new emontx version here are a few questions that we would like to answer:

How does emonTx v3 accuracy compare at lower power's?

Is there any difference in low power readings with or without the powered from AC-AC adapter feature?

Can differences be explained by calibration error?

Are there any other measurement variations that need investigating?

To make it easier to compare the parallel test power feeds I though Id create a visualisation tool in emoncms that made it easier to see the difference between the feeds.

If difference is caused by calibration error then applying a calibration to the measured data should bring the difference down close to zero.

Any deviations in measurements that remain should be non-calibration errors, and they will appear off to one side of the linear PowerX vs PowerY plot.

The above visualisation can be viewed here:

This visualisation tool is available in the emoncms visualisations list if youd like to try this on your own monitor, even comparing say two different CT channels on a single emontx.

There are some issues I need to fix with the visualisation tool implementation that gives rise to some incorrect comparisons at some scales to do with the way it selects datapoint id's to compare.

In the next post I will explore differences between the two parallel test power feeds.

One of the interesting things I did yesterday was use the raspberrypi emoncms module on my ubuntu laptop. I used a jeelink connected to the usb port of the laptop and then configured raspberrypi_run.php to connect on port /dev/ttyUSB4 instead of the default raspberrypi port, this could be a useful configuration for anyone who just wants to log data from the nodes locally to their laptop and as Jerome pointed out here, maybe the emoncms raspberrypi module should just be called the emoncms linux board module or just serial interface module.