5491
General Mach Discussion / Re: Limit Switches and Interference
« on: October 28, 2012, 07:31:09 AM »
Just in general...
The shields of all cables are connected to GND at the controller end only and preferably to one single point or tag.
The machine frame and any other metal parts that you can touch are connected to protective Earth.
Earth and GND should be treated as two entirely separate circuits as far as wiring is concerned.
It is essential that you have no 'Earth loops' or 'GND loops' anywhere within your wiring.
The PC usually has its negative rail (GND) connected to Earth so this should be the only place where they meet.
Often points of conflict exist if the shielding of the LPT parallel cable or PC casing is connected to machine frame (Earth) or the heat-sink of a VFD is connected to the machine frame and also has it's own Earth wiring but there are many other areas where loops can easily be created.
As you have discovered, it is a difficult problem to resolve but unless it is resolved 100% then it may come back to bite you, at some future date - usually 3/4 of the way through a complicated and expensive job.
Tweakie.
The shields of all cables are connected to GND at the controller end only and preferably to one single point or tag.
The machine frame and any other metal parts that you can touch are connected to protective Earth.
Earth and GND should be treated as two entirely separate circuits as far as wiring is concerned.
It is essential that you have no 'Earth loops' or 'GND loops' anywhere within your wiring.
The PC usually has its negative rail (GND) connected to Earth so this should be the only place where they meet.
Often points of conflict exist if the shielding of the LPT parallel cable or PC casing is connected to machine frame (Earth) or the heat-sink of a VFD is connected to the machine frame and also has it's own Earth wiring but there are many other areas where loops can easily be created.
As you have discovered, it is a difficult problem to resolve but unless it is resolved 100% then it may come back to bite you, at some future date - usually 3/4 of the way through a complicated and expensive job.
Tweakie.