by cncdrive » Tue Apr 03, 2018 9:25 am
Noisy environment is in other words industrial environment where there are other equipments too, not only the CNC machine which equipments can generate noise and transmit it though the mains.
Noise can be also caused by the machine itself, e.g. a spindle motor, a plasma unit etc. In general, devices which switching high voltage and or high current causing voltage spikes and possible noise.
USB is more sensitive to noise, because USB is ground referenced communication which means that both the PC and the USB device are referenced to the same 0Volts ground potential.
The USB endpoint device and the PC ground are connected with a wire in the USB cable.
The issue with this is that if the PC ground gets noise, the ground potential is fluctating with high frequency and/or with high amplitude can cause communication problems, because the wire which makes the ground connection has inductance and resistance and so the 2 ground points will not move instantly together.
Ethernet is isolated communication. There is no common ground points on the PC side and the endpoint device. The data is transfered through high frequency mini transformers called ethernet magnetics which are built into the RJ45 jack of the UCxxxETH controllers and also one transformer is on the PC's LAN card.
Because the 2 endpoints are isolated the above mentioned ground point fluctaction caused by electrical noise can't cause problems to ethernet communication.
Ofcourse noise can be usually filtered and with proper grounding scheme it can be kept under control when it causing no issue, but especially plasma units are often heavy noise generators and especially cheap chinese ones often have no sufficient mains filter which makes things worse and so we recommend to use ethernet controllers for plasma applications.