On quite a few industrial grade PCBs which are mounted in plastic enclosures, I saw these frame earth tracks going a long the perimeter of the PCB. They typically are on both sides of the PCBs, form a loop, top and bottom track are connected with plenty of vias and are connected to the protective earth terminal of the enclosure. The circuit ground (GND) is typically connected via a 1MOhm/10nF to this track.
The purpose seems to be an EMI shield.
Is this a useful thing and recommended to do on a 2-layer PCB?
As the track forms a loop I am concerned that it could be EMI wise counter productive.
Ricky