National Instruments NI 9514 User Manual

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© National Instruments | 3-11NI 951x User ManualA typical encoder with a specification of N (N = number) lines per unit of measure in revolutionsor linear distance, produces 4 × N counts per unit of measure. The count is the basic incrementof position in closed-loop motion systems.Note To determine your encoder counts per revolution, multiply the specifiedencoder counts per revolution by four. For example, a 500 line encoder has2,000 counts per revolution.If an encoder resource is not needed for axis control, it is available for other functions includingposition monitoring, as a digital potentiometer encoder input, or as a master encoder input forelectronic gearing or electronic camming applications.Encoder IndexThe Index input is primarily used to establish a reference position. The Index signal produces asingle pulse per revolution. You can use software to capture the Index pulse position andestablish a reference zero position for absolute position control. Figure 3-10 shows thesingle-ended representation of the encoder pulses.Figure 3-10. Incremental Encoder Phasing DiagramYou can set the index reference criteria in software to change the line state of Phase A and PhaseB used in the Index search. Refer to the NI SoftMotion Module book of the LabVIEW Help formore information about encoder settings.Encoder Input CircuitThe NI 951x drive interface modules support RS-422 differential and single-ended inputs forPhase A, Phase B, and Index signals, and provide a +5 V output for encoder power.You also can set the encoder active state for Phases A, Phase B, and Index to high or low usingsoftware. Refer to the NI SoftMotion Module book of the LabVIEW Help for more information.Tip Refer to the Signal Connection Recommendations section of Chapter 4,Accessory and Cable Connections, for additional wiring and cablingrecommendations.Phase APhase BIndex