Hand Hygiene

The first test with this antenna, 7MM Test One, showed that we could maybe get some separation between distances and that the antenna was not angular dependent – except in some extreme cases. We decided to run the test again to verify these results but repeatedly came up with something different. The data from this second test show a clear dependency on angle and allow for no real separation between distances.

My first thoughts may be that the original test was just a fluke and it doesn’t represent the real data set. This has happened before, but never to this degree. Because the difference in spread is so much we are questioning whether this mote is the right choice. Here is a boxplot of the RSSI vs. Distance Height Angle that provides a summary of the data and allows you to see the angular dependency:

From this boxplot you can see that the RSSI appears to dip around 90 degrees at almost every distance and height. This is bad because if the antenna is angular dependent then if a person approaches from the wrong angle they might not get picked up, but a person passing by and not using the hand cleaner would.

The following plot is a CDF of this data:

From this plot it is appearant that there is not a good cutoff value to seperate a total distance of even 1m. That means that you cannot choose an RSSI cutoff such that you could get almost all the 0.25m values and none of the 1m values. There is just too much overlap

My second guess for why this is happening is that the broadcasting mote may have a different orientation than the first test. This is a possibility because I didn’t run the first test and couldn’t find any decent documentation on how it was oriented then. Luckily the person who ran the test is available, but we still need better documentation, or just better consistency at documentation.