Wiring, Grounding, And Shielding Techniques; Minimizing Emi Interference - Aerotech BA10 SERIES User Manual

Installation and Operation
2-4
2.3.

Wiring, Grounding, and Shielding Techniques

To reduce electrical noise in the BA Series amplifiers, the user should observe the motor
and input power wiring techniques explained in the following sections. This is suitable for
use on a circuit capable of delivering not more than 5000A, 240V.

2.3.1. Minimizing EMI Interference

The BA320 are high efficiency PWM amplifiers operating at a 20K Hz switching rate.
The switching time between positive and negative rails on each of the motor leads is less
than 50 nano-seconds for a 320 VDC bus. This switching rate can generate
Electromagnetic Interference (EMI) into the Mega Hz band. To minimize this EMI, it is
recommended that the motor leads be twisted together with the motor cable grounding
wire and surrounded with a foil shield. Refer to Figure 2-2.
In addition to the EMI effects, electro-static (capacitive) coupling to the motor frame is
very high requiring the frame to be grounded in order to eliminate a shock hazard.
Additional electro-static coupling exists between the three twisted motor leads and the foil
shield of the motor cable.
This coupling forces high frequency currents to flow through the returning earth ground
of the motor cable. To minimize this problem and maintain low levels of EMI radiation,
perform the following.
1. Use shielded cable to carry the motor current and tie the shield to earth ground. Refer
to Figure 2-2.
2. Place one toriod (ferrite) around the three motor leads (two leads for brush motors).
The toriod should have 10 turns for 16 AWG wire or 7 turns for 14 AWG wire. This
helps reduce the harmonics generated by the 20 KHz switching waveform. Use a
Ferroxcube 500T600-3C81 core or equal. Refer to Figure 2-2.
3. Use a cable with sufficient insulation. This will reduce the capacitive coupling
between the leads, which in turn reduces the current generated in the shield wire.
4. Provide strong earth ground connections to the amplifier, additional heat sink, and
the motor. Offering electrical noise a low impedance path to earth ground not only
reduces radiated emissions, but also improves system performance.
5. If possible, do not route motor cables near cables carrying logic signals and use
shielded cable to carry logic signals.
Aerotech, Inc.
BA10/20/30 Series User's Manual
Version 1.6