Epsilon Eb Digital Servo Drive Installation Manual
Achieving Low Impedance Connections
Noise immunity can be improved and emissions reduced by making sure that all the components have a low impedance connection to the same ground point. A low impedance connection is one that conducts high frequency current with very little resistance. Impedance cannot be accurately measured with a standard ohmmeter, because an ohmmeter measures DC resistance. For example, a
Low impedance connections can be achieved by bringing large areas of conductive surfaces into direct contact with each other. In most cases this requires paint removal because a ground connection through bolt threads is not sufficient. However, component materials should be conductive, compatible, and exhibit good atmospheric corrosion resistance to prevent loss through corrosion, which will hinder the low impedance connection. Enclosure manufacturers offer corrosion resistant, unpainted mounting plates to help.
Bringing components into direct contact cannot always be achieved. In these situations a conductor must be relied upon to provide a low impedance path between components. Remember a flat braided wire has lower impedance than a round wire of a large guage rating.
A low impedance connection should exist among the following components:
•Enclosure and mounting plate
•Servo amplifier chassis and mounting plate
•EMI/RFI AC line filter chassis and mounting plate
•Other interface equipment chassis and mounting plate
•Other interface equipment chassis and electrical connectors
•Enclosure and conduit fittings or electrical connectors
•Enclosure mounting plate and earth ground
•Motor frame and conduit fittings or electrical connectors
•Encoder chassis and electrical connector
A good rule to follow when specifying conductors for high frequency applications is to use a metal strap with a length to width ratio that is less than 3:1.
4