Electronic Design

Encoder Cable Eliminates Interference, Noise Problems

The MR121 ZapFree multifiber-optic encoder cable from Micronor Inc. is guaranteed to solve nagging ground-loop and interference problems in motion-control systems. It handles signals up to 500 kHz per channel with a maximum pulse uncertainty of 0.5 µs. Error-free communications are possible over 1000 m (3280 ft).

This patent-pending ZapFree technology transports all controller-encoder signals from the cable, end to end, via industry-standard 12-pole M23 electrical connectors found on most popular encoders. The encoder's A, B, and M outputs (either single-pole or differential line-driver formats) are internally converted from electrical to optical form on the encoder end. Then, they're transported through the optical fibers within the cable and converted back to an electrical form at the controller end.

Controller-sourced shield, power, ground, and power/ground sense paths are transported electrically. Internal optical-to-electrical and electrical-to-optical converters require minimal current. A small regulated tap provides all internal interface power requirements.

The input voltage ranges from 5 to 12 V. Besides optical fiber's natural resistance to radio-frequency interference and electromagnetic interference, ZapFree takes advantage of its exceedingly low loss over distance, which allows separation of the controller and a remote sensor over long distances.

The cable's RDE connector conforms to the MIL-I-5015 standard. The electrical interface is an RS422 line driver. The cable operates from −25°C to 85°C, and it can withstand a minimum 10-cm bend radius.

Cable can be ordered to any length from 3 m (10 ft) to 1000 m (3280 ft). Other connector options are available as well. A typical 50-ft cable costs $589 each in lots of 100.

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