By Alan Bradford
Electrical Noise or Radio Frequency Interference (RFI) has once again become a concern, with the new network enabled crop of CNC/Motion Controllers. The design and installation of retrofits (and new machines) requires more attention to shielding, internal and external. Noise was a major problem in the early days, as not much was done with shielding and grounding until a problem occurred. The next generation (Hypertherm’s Edge series and Burny 10 models) did a better job with the internal shielding and external signal conditioning, that noise wasn’t as much of an issue as long as one kept with the shielded cables and proper routing/grounding procedures.
The new digital design, with EtherCAT, networking all the major components, we have to worry more about radiated noise. The CNC producers have reduced their responsibility by offloading the engineering and signal conditioning to the Drive Engineers and System Integrators. On top of that we now have additional noise generators and more sensitive receivers.
The Noise Generators are, the new family of Plasma Systems. The High Frequency Starter is now a lower frequency, but they also reduced the shielding for a net gain, on reducing noise, of zero. Brushless DC and AC Servo Drives are a high power source of PWM generated RFI and the Switching Power Supplies (Direct Switching Line to Load Power Converters) are a new source, since replacing the old linear devices with the heavy, expensive power transformers.
The high speed EtherCAT cables make great antennas to absorb all this new energy. Additionally the I/O, for Limit Switches and Solenoid Drivers are not built into a nice isolation board, like the last generation of CNC’s. The signals go directly to an EtherCAT to I/O processor, and the filtering is minimal.
We now have to make sure that all grounding and shielding is done properly. Only ground 1 end of the drain wire, on shielded cables. Limit Switches must now use shielded cables. Star grounds need to be utilized, and keep the noisy Plasma Cables away from the clean Network and Control cables. Cross noisy and clean cables at 90 degrees to reduce noise coupling.
If you or a customer are having noise issues and need expert help call Plasma Technologies at 603 632 4567 or email us firstname.lastname@example.org our team of system integrators are here to help.
About the Author:
Alan Bradford has been rebuilding and servicing cutting machines for over 30 years. Alan is President of Plasma Technologies Located in Canaan NH.