I am designing a circuit with a very sensitive analog part. In order to eliminate SMPS noise from a regular power supply, the device has its own non-SMPS power supply followed by an ultra low noise linear regulator (LT3042). However even after this, the device still sees some noise coming from mains socket if a noisy equipment is connected on the adjacent socket.
Usually, simply choosing a socket on a different wall, or moving the equipment power cables apart, significantly reduces noise. I see this as free noise reduction over and above what can be done in the circuit.
I would like to have some mechanism in the device that can inform the user about noise on the line. I don't need exact ripple voltage measurements just something good enough to tell that cable arrangement B is better than cable arrangement A. This would allow the user to try different sockets and choose one that has the least noise.
Alternatively, the device can simply have a noise threshold below which a "Power Good" indication will be provided to the user.
Just FYI, this is for an industrial application and the position of the device or its wiring won't change very often. If during operation the noise level rises above threshold, say due to some other equipment connected nearby, the device can notify the master via RS485.