Ten years of PowerSense: non-contact power monitoring for railway switches
In 2016 DB Netz called. The result was a PoE sensor that measures voltage without galvanic contact, and our rule 'PoE first'.
In January 2016 DB Netz AG was looking for a better way to monitor the power supply of railway switch drives: three-phase, 16 A, retrofit by clip-on, no rewiring, no outages. The proposal on the table was an RS-485 sensor. We declined and proposed Power over Ethernet, for the first time in critical infrastructure.
Four requirements shaped the following years: under 2 W total, EMC to railway standards with high demands on dielectric strength, installation in seconds without tools, and voltage measurement without a galvanic connection. The last one we solve with patch antennas on the top and bottom of a thick PCB: the difference between the two E-fields scales with 1/r², and from it we reconstruct the voltage waveform. Embedded ferrite cores take care of the current.
PowerSense runs today in Deutsche Bahn's DIANA system, among others. Two rules from the project are in every DAQ system we build: PoE first, and digitise as close to the source as possible.
Blood, sweat and ferrite cores: the whole ten-year story is on Stephan Bökelmann's blog.