Rockwell Automation System Design for the Control of Electrical Noise - Manual (Page 87)

Publication GMC-RM001A-EN-P — July 2001
Chapter
10
Encoders
Chapter Objectives This chapter describes bonding, segregating, shielding, and filtering
techniques for use with encoders. This chapter covers the following
topics:
• Understanding encoders
• Noise reduction methods
• Power supply wiring options
Understanding Encoders Encoder input circuits are, by their nature, potentially sensitive to
noise. The signal is typically a square wave of about 500kHz at
maximum speed. In order to preserve a reasonable square pulse, the
circuit must handle at least ten times higher frequencies.
Unfortunately, a response of 5MHz is ideally suited to detecting the
noise spikes in a drive system.
The internal encoder circuitry should be relatively immune if it is well
designed but there is often a long cable run to the control input
circuitry. Coupling is usually due to voltage differentials between the
encoder mounting and the drive input.
Noise Reduction Methods This section provides installation guidelines for reducing noise sources
near encoder input circuits.
Driver Type
IMPORTANT
Driver type is generally dictated by the drive product
but A quad B, differential, or line driver outputs are
preferred.