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[fisico32]

Hello Forum,
I am a little confused about grounding.

Here my dilemmas:
1) Let's consider a simple DC circuit with a constant voltage source and a bunch of resistors connected in a certain configuration. The voltage across each resistor can be measured using a voltmeter. The voltmeter works on its own: it does not require the circuit to have a point that was selected a priori to be the reference point (i.e. the point in reference to which every other voltage is measured).

I think understand what earth ground is: pick a point in the circuit and connect it with a low resistance path to planet Earth. (for safety).

Chassis ground: we pick a point in the circuit and assign to it a zero voltage value. That is the reference point for all other voltages. For instance, in the car, the negative terminal of the battery is connected to chassis (the car body). All other electrical components don't need to connect directly to the negative terminal but only to the positive terminal. That saves wires.....All components simply connect one of their terminals to chassis too. That is an example of chassis ground, correct?

Then there is floating ground. Is that the same a chassis ground? If not what is it?

In the voltmeter, there is a connection called COM. I know how to use that COM port but I don't really know what it represents. Is it sort of an internal chassis ground for the voltmeter? Again, to measure voltage with a voltmeter we don't need the circuit to have a pre-selected zero voltage point. I have read that Common is the return to the source...so is it simply a normal wire? I am confused.....

Then I have heard of signal ground. What is that? Any example?

I also read about multi-point ground. What is it? Each component has some sort of direct connection to a metal component....that sounds like chassis ground....

High frequency and low frequency circuits: they require different types of grounding (ground planes, metal planes, etc....) Why? I understand what impedance is: a frequency dependent type of resistance (involving inductance and capacitance).....

In DC circuits it does not seem to matter which point we choose as the reference voltage point. Is that true also in AC circuit? For instance, if we "earth ground" an AC circuit, does it matter where we make the earth ground connection? If so, Why?

thanks
fisico32