IP-Quadrature Greenspring Four Channel Decoder IndustryPack

The Abaco Systems / SBS / Greenspring IP-Quadrature Four Channel Decoder IndustryPack Module provides high density, cost-effective flexible implementation of four quadrature decoder channels. Channels may also be used as general purpose counters. Four independent channels provide 24-bit resolution, programmable modes, programmable polarity, interrupt capability, differential or single-ended (RS-422 or TTL/CMOS) input, read-on-the-fly capability, and a count frequency of 0 to 10 MHz.

Quadrature encoders are popular sensors that provide accurate, low cost incremental motion sensing. Most commonly, they are shaft encoders that provide 512 to 2048 counts per revolution. They are also commonly used as linear encoders with resolutions down to 0.005 inch. They are available in nearly any length desired. Most encoders are now optical, using molded assemblies consisting of a pair of LEDs, lenses, photo-sensors, and simple electronics. For rotary motion the assembly senses alternating opaque and clear lines on a rotating wheel. For linear motion the alternating lines may be on a fixed bar and the sensor assembly moves, or vice-versa. The pair of LED and photo-sensors are offset about one-half line width so that direction of motion may be sensed by observing the relative phase of the two outputs. Typical quadrature encoder outputs are a pair of digital logic signals that are nominally 90° out of phase. Some encoders also provide an "index" pulse output once per revolution to provide absolute position information. Most modern encoders run from +5 volts and provide CMOS/TTL logic outputs and/or RS-422 differential logic outputs. RS-422 is recommended where possible because of its inherent noise immunity and the ability to run long distances. TTL logic levels should normally be restricted to cables less than ten feet in length. Quadrature encoders are available from Hewlett-Packard, US digital, and other sources.