I am building a shield that contains an AC power supply and relay for an Arduino-like board. The problem I am having is that the relay is quite noisy with respect to EMI, and I can see a few jitters or jumps in my system during normal operation even with a zero cross detector.
I have added in another shield between the 'relay' shield and the main board, which has helped the problem by creating a larger gap, but I would like a more permanent and robust solution.
I was thinking of building a simple shield that has nothing much on it and is simply a large ground plane that sits in between the relay shield and the main board. This would be a simple solution that does not involve making any shielding cages.
This ground plane would be connect to the chassis of my device, which is then earthed.
Since the device has both a DC ground voltage (0V DC) and a AC earth (0V AC) I was thinking maybe I should use both as part of my shielding. Since the board has layers on both sides perhaps I could design it to have the side facing the relays to be earthed, while on the other side, facing the CPU, would be DC ground. I could even couple the two planes with a capacitor, if it helps.
On the one hand I think the earthed option should be fine, but on the other hand I would like to know more about using the DC ground as an EMI shield. Would the simple earth only option work? Would even a DC ground only option work? Does it help to use the DC ground as an EMI shield for the DC components or am I over complicating it?