Instrumentation Grounding

On instrumentation usually low amplitude and high impedance signal world, a few millivolts is enough percentage to ruin the result. And since ground is often used as AC or as DC signal reference, and neither dimensionless nor zero impedance conductors have to be used for grounding, those few mV are easy to pick in an EMI rich environment, so "ground" is NOT always and everywhere in your system at ZERO potential. Not to mention the relativistic latencies and reflections that get more significant as system bandwidth goes up and everything becomes a transmission line, or the potential danger to use a power ground with low enough impedance to protect user from mains leaks, but really crappy on surges and EMI for the circuit. Now one practical way to minimize problems like noise susceptibility and instability is by avoiding "ground loops", and use one point as ground, connect everything that must be grounded there, star-like. What we mainlly achieve by that is unknowingly common mode cancelling of picked-up and thus unwanted interference (either from outside, or from other parts of the cirquit, like from a noicy digital bus). Making loops, you form coils AND antennas, cancelling is ruined, and of course chance of instability and oscillations due to delay mismatch-phase shifts increases (...) S.M.