Process Plants

EMC Solutions for Processing Plants and Large Facilities

It is no secret that machinery in a plant generates noise but the question has always been “how much noise?”  With increasing frequency, machinery is behavior in ways never intended in the original design. This behavior could manifest as a machine that occasionally or constantly resets, machinery that goes off track, or machinery that stops working properly. Much of this behavior can be traced to inter-machine noise.

What creates this noise? Many machines use servo drives and variable frequency drives (VFDs) to control rotating machinery. These VFDs create high frequency noise that radiates out on the input power cable. If a drive cable is close enough to a signal cable that the two cables couple, then the noise from the drive cable will radiate onto the signal cable. The signal can be overwhelmed by the noise and cause false readings. This can then cause the PLC to make incorrect decisions.

Another source of noise is the silicon controlled rectifier (SCR). These devices are often seen in welding and brazing equipment, industrial ovens, and other large applications where systems need to develop or maintain temperatures in the system. As the SCR turns on, the voltage on the input power line momentarily drops because of insufficient power to feed the load. This causes glitches on the power lines within the plant. This glitch may cause a nearby PLC to reset if the glitch duration is long enough.

Enerdoor's solution to noise problems is to install EMC filters on each panel that controls a VFD or an SCR. These filters help in two ways. First, the filter stops noise from leaving the machine and then it prevents noise from within the plant from entering the machine.

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