A ground loop is then a single device is connected to ground more than once. A good example is a motor driver. It might in a "power" input called "+" and "-" with the minus side grounded to the AC mains ground or a chassis frame ground. The in addition there is a logic level control signal that is "signal" and "ground" wires. This is a classic gound loop.
How to break it? Use optical isolation on the signal. This places an air-gap in the control signal. Most of the time the system is not so simple as the above but the concept is the same, multiple ground connections are not good. Why? Because in theory current can flow if you have a loop but can never flow if there is not a closed loop. Then Ohm's law applies -- if there is current flow there is voltage drop. If the voltage drops across a gound then you have tow "grounds" that are not the same voltage. This can be really serious if the motors are large. There are a number of conventions that work. but they all do the same thing, they reduce the number of ground connects to one per "part" of the system. All the rules try to do the same thing, connect nuetral to ground ONLY at the building service entrance, use opto's on all signal lines. It is all the same idea _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
