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Current and projected requirements for increased angle readout accuracy on photo-optical instrumentation mounts create new demands on the angle encoding systems used to instrument the mount axes. In most modern system requirements, an output is required in real time digital form. In two basic applications, the mount angle readouts are 1. recorded (correlated to real time) as the instrument tracks a target, for the purpose of reconstructing the target trajectory. 2. used in real time as the position feedback reference to a digital position control loop which drives the mount along a specific tra-jectory so that a high resolution optical record of the object can be obtained. In addition to high static accuracy and fine resolution requirements, the above applications require high dynam-ic accuracy of the encoding system. In addition, the angle encoder system must be rugged enough to withstand field environment stresses, and reliable enough to cause negligible system downtime. Inductosyn plates, when correctly adapted to the instrument axis and when properly matched to the right set of electronics, satisfies the current and projected accuracy and resolution re-quirements. An electronic system for converting the Inductosyn* plate out-puts into digital form is discussed, following a pattern in which various alternate schemes are discussed, thus developing the rational for the chosen configuration.Error analyses, considering both static and dynamic conditions, are presented for the entire conversion process for the Inductosyn* plate to the digital output; the error analysis shows that the FSD angle encoder system, using an Inductosyn* plate, produces static and dynamic errors of + 1 arc sec, 1 arc sec/rad/sec, and 1 arc sec/rad/sec2, with resolution as fine as 0.15 arc sec. Techniques are described or mechanically coupling Inductosyn plates to the mount axes, with considerations depending on the mount bearing accuracies and overall system accuracy require-ments. Finally, static and dynamic test results are shown which depict angle readout error curves for a system using the FSD angle encoding systems, demonstrating the accuracy achieved. Several methods of performing accuracy tests are pre sented, emphasizing the care required to achieve consistent test results.
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