Emerson SI-Universal User Manual page 29

Figure 5-1 Galvanic Isolation
Housing
between motor housing
and encoder housing
An example of this is the Unimotor, where isolation from the motor is achieved by inserting a plastic
mounting plate between the motor housing and encoder housing and a plastic insert fitted in the
motor shaft for encoder mounting to the motor shaft. With this preferred method of mounting, noise
currents are prevented from passing from the motor housing into the encoder housing, and hence
into the encoder cable.
The ground connection of the cable shield is optional, but this may be required in order to comply
with safety measures, or to reduce radiated radio frequency emissions from either the drive or
encoder.
5.2.2 Encoder circuit with galvanic isolation from encoder body
In this case, the encoder device is mounted directly on the motor housing with contact being made
between the motor housing/shaft and encoder. With this mounting method, the encoders internal
circuits are exposed to electrical noise from the motor housing through the stray capacitance, and
must therefore be designed to withstand this situation. However, this arrangement still prevents
large noise currents from flowing from the motor body into the encoder cable.
The ground connection of the cable shield is optional, this may be required to comply with safety
measures or to reduce radiated radio frequency emissions from either the drive or encoder.
SI-Universal Encoder User Guide
Issue: 2
Isolation
between motor shaft
and encoder
Motor
Motor
Shaft
Isolation
0V
A
A
+5V
0V
B
B
+5V
Encoder
Housing
Encoder
Circuit
Encoder
Connection
Encoder
Body
29