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IR All-Sky (Cloud) Camera Rebuild Tom Reeves & Robert Barkhouser

IR All-Sky (Cloud) Camera Rebuild Tom Reeves & Robert Barkhouser. Instrument Design. Site Computer. IR Energy. Stepper Motor Drive Signals. RS-232 Link. Scan Mirror #2. LN 2 Cooled Detector (HgCdTe). Scan Mirror #1. Signal. Focusing Mirror (off-axis parabola). Preamp.

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IR All-Sky (Cloud) Camera Rebuild Tom Reeves & Robert Barkhouser

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  1. IR All-Sky (Cloud) Camera RebuildTom Reeves & Robert Barkhouser

  2. Instrument Design Site Computer IR Energy Stepper Motor Drive Signals RS-232 Link Scan Mirror #2 LN2 Cooled Detector (HgCdTe) Scan Mirror #1 Signal Focusing Mirror (off-axis parabola) Preamp Control Computer 10 mm Filter Chopper Wheel Chopper Wheel Motor Speed Signal

  3. Current Implementation Instrument Housing (plastic shipping container) Scan Mirror #2 Scan Mirror #1 Detector LN2 Dewar Power Supplies Detector Entrance Window 10 mm Filter Control Computer Chopper Wheel (seen edge-on) Focusing Mirror Mounting Bracket (mirror not visible) Vibration Damper (lead weight)

  4. Assessment Site Visit: We inspected the instrument at APO on June 8, 2000, during operation and while powered down. We also met with APO personnel (Jon Brinkman and Craig Loomis) most familiar with the instrument, to discuss current problems and suggested repairs or improvements. Conclusions: Several problems plague the instrument. Most significant is the lack of documentation and complete lack of control software source code, rendering maintenance and repair very difficult. The instrument computer hangs frequently, requiring a reboot of the system. The optics are dirty and scratched, due to repeated exposure to inclement weather and subsequent cleaning. One axis of the alt-alt scanning scheme exhibits significant wobble/backlash as the stepper motor increments. The chopper wheel induces significant vibration throughout the instrument, which is intensified by tall, slender mounting brackets. Initial positioning of the instrument to zenith must be done manually by rotating the scan mirrors.

  5. Summary of Existing Problems • Documentation • Hardware documentation is limited or nonexistent • Control software source code is nonexistent • System hangs frequently, requiring reboot • Optics are unprotected and in poor condition • Large wobble in scan axis #2 after each motor step • Excessive mechanical vibration from chopper wheel • Noise problems • ~200 Hz ripple evident in images • Preamplifier is noisy • No “home” position sensors implemented for initial alignment

  6. Recommended Remedies • Replace control electronics • Provide a documented, maintainable system • Implement a reliable communication link to eliminate frequent system hangs • Implement instrument status reporting • Replace optics • Replace detector preamplifier • Redesign chopper wheel assembly • Reduce excessive vibration • Implement chopper wheel position strobes to data acquisition system (will reduce software complexity and development time) • Incorporate mechanical adjustments for alignment

  7. Recommended Remedies (cont.) • Redesign scan mirror assembly • Reduce moment of inertia and eliminate wobble • Implement “home” position sensors • Replace old stepper motors with new units • Enclosure with remotely controlled cover • Provide rapid protection of instrument in case of inclement weather • Provide rapid return to operation after periods of inclement weather • Eliminate distraction and inconvenience to operator focused on other tasks • Will improve reliability and reduce maintenance

  8. Control Electronics • Replace existing system with single-board PC featuring: • Ram and flash memory • Multi-channel 12-bit A/D converter • Ethernet communication interface • 5.75” ´ 8.00” footprint • Replace existing stepper motor driver board with self-contained indexer/driver modules featuring: • Bi-directional serial communication with control computer • Non-volatile program memory storage • Ability to independently execute stored programs • Phase current up to 3 amps RMS

  9. Software • Control computer will run Linux • Control software developed with National Instruments LabVIEW • Application Builder will compile LabVIEW VI into stand-alone application • Stand-alone VI downloaded to control computer and executed under Linux • Ethernet TCP/IP link to remote (site) computer • Status and error reporting to remote computer

  10. Optics • 2 scan mirrors • Edmund #K32-090 • Elliptical flat, 2.25” x 3.182” x .625” thick • Protected gold coating • Focusing mirror • Janos #A8037-102 • 90° off-axis parabola, 1.0” Æ, 25.4 mm FL, 50.8 mm EFL • Gold coating • Bond fixture for scan mirrors • Needed for centering 45° mirror face to mounting shaft axis • Will reduce downtime if replacement occurs on site at APO

  11. Detector Preamplifier • Existing preamplifier is suspected source of noise • Replacement unit is available off-the-shelf • Judson Technologies (formerly EG&G Optoelectronics) #PA-101 • Low-noise, voltage mode preamplifier, 10 Hz - 1 MHz • Recommended for J15 series HgCdTe detectors • Bias resistor factory-matched to existing detector • Dual output channels with gains of 10´ and 100´ • 10 V maximum output (load ³ 10 KW)

  12. Chopper Wheel Holes for optical fork detectors (4) • Install optical fork detectors to sync to A/D converter • Sturdy mount for reduced vibration • Stabilizers on wheel for reduced vibration • Simple mechanical adjustments for alignment Wheel stabilizer (both sides) Optical fork detectors (2)

  13. Scan Mirror Assembly • Existing assembly exhibits excessive backlash/wobble • Scan mirrors are ~2´ oversized in relation to aperture stop • Oversized stepper motor on scan axis #1 • Massive counterweight required to balance oversized components • New design would incorporate: • Same scanning scheme • Smaller mirrors to reduce size and inertia of assembly • Smaller housing sized appropriately for smaller mirrors • New stepper motors, only as large as required for load • Bearing to couple assembly housing to mounting bracket • Hall-effect sensors to provide “home” position reference

  14. Enclosure • Cloud Camera is low priority when bad weather strikes • Current enclosure • Requires someone to walk outside to install cover • Results in periodic exposure of optics and electronics to rain • Enclosure should have remotely-controlled cover • Proposed enclosure would feature: • Aluminum extrusion framework using off-the-shelf hardware • Panels and gasketing to form weather tight seal • Motor-driven mechanism to open/close cover • Remote operation via TCP/IP interface • Local operation via external switch

  15. Cost Estimate

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