Cloud Camera Rebulid

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

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

Instrument Design : 

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

Current Implementation : 

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

Assessment : 

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.

Summary of Existing Problems : 

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

Recommended Remedies : 

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

Recommended Remedies (cont.) : 

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

Control Electronics : 

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

Software : 

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

Optics : 

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

Detector Preamplifier : 

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)

Chopper Wheel : 

Chopper Wheel 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 Optical fork detectors (2) Wheel stabilizer (both sides) Holes for optical fork detectors (4)

Scan Mirror Assembly : 

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

Enclosure : 

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

Cost Estimate : 

Cost Estimate