Specifications

Doc Number: VIS-ANA-VER-01001-9002
Date: 27 May 2004
Issue: 5.0
Page: 61 of 80
Author: J. Delgadillo
Controls Preliminary Design Report Issue 5.doc
Altitude Tape Encoder Accuracy
Encoder Accuracy of Graduation +/- 3 microns = +/- 0.003 mm
Encoder Tape Circumference 5,824.5128 mm = 360°
= 0.0618 °/mm
Encoder Accuracy (One Read-Head) 0.0618 °/mm * 0.003 mm
= 0.00019 ° = 0.668 arc-sec peak
Encoder Accuracy (4 Read-Heads) = 0.668 arc-sec / 2 = 0.334 arc-sec peak
4.3.3 Cassegrain Rotator Tape Encoder Calculations
Cassegrain Tape Encoder Resolution
Tape Sitting Diameter: 1578 mm
Tape Sitting Circumference: 1578mm * Π = 4,957.433 mm
Graduation Distance 40 e-6 mm = 25 lines/mm
# of Encoder Lines 25 lines/mm * 4,957.433 mm
= 123,935.8302 lines
IK 320 Interpolation Factor 4096 counts/line * 123,935.8302 lines
= 507,641,160.5 counts
Encoder Resolution 360°/507,641,160.5 counts = 7.0916 e-7 deg
= 0.0026 arc-secs
Cassegrain Tape Encoder Accuracy
Encoder Accuracy of Graduation +/- 3 microns = +/- 0.003 mm
Encoder Tape Circumference 4,957.433 mm = 360°
= 0.07262 °/mm
Encoder Accuracy (One Read-Head) 0.07262 °/mm * 0.003 mm
= 0.00022 ° = 0.784 arc-sec peak
Encoder Accuracy (4 Read-Heads) = 0.784 arc-sec / 2 = 0.392 arc-sec peak