1. December 3-4, Green Bank GBT PTCS In Progress Review Instrumentation K. Constantikes

2. GBT PTCS In Progress Review – December 3-4, 2003 2 Overview Conventional methods for improving pointing, focus are promising –JCMT inclinometry, LMT thermal model Instrumentation is simple, robust, relatively low cost Requires crafty approaches and antenna characterization Achievable on short time scales Thermal corrections: 8 months for –Sensor design, fabricate, install –Communications design, fabricate, install –Astrometric experiments –Correction algorithms, validation –Prototype real-time correction implementation

3. GBT PTCS In Progress Review – December 3-4, 2003 3 Status InstrumentPurposeStatusInitial Capability Notes Structural tempCorrect thermal deformation CommissionedUp to 10 additional Units RS232 Concentrators Sensor Communications Commissioned21 Ports Used, 48 Total Quadrant DetectorDedicated Feed Arm Position InstalledDecemberCalibrations InclinometersAlidade Thermals Wind Effects Structure Modal Tests In Design, Material ordered DecemberHighest Priority Star Tracker (Guide Scope) Differential Orientation of GBT Components In TestModerate Priority Data Acquisition System (GDAQ) High Resolution ADC and Discretes Material On Hand Device Testing No Date SetLow Priority Vertical air tempGroup Index QD Path Bending Structure Coupling Prototypes Installed No Date SetUp to 6 units AccelerometersStructural healthOn holdNo Date SetLow Priority

4. GBT PTCS In Progress Review – December 3-4, 2003 4 Structural Temperature 19 locations, 0.2C interchangeable accuracy, 0.01C resolution, 1Hz, range –35 to 40C. (actual accuracy is ~0.1C, temp control of conversion elex) Design documentation: –PTCS Wiki (AntennaInstrumentation) –PTCS Project Note PTCS/PN12 Accuracy tested in lab: –Solar/convective loading –Selected unit-to-unit accuracy, repeatability –Electronics temperature range RFI mitigated, ESD protected Two thermistor failures, forensics with YSI Integrated into M&C First cut pointing, focus predictive algorithms tested

5. GBT PTCS In Progress Review – December 3-4, 2003 5 Structural Temperature

6. GBT PTCS In Progress Review – December 3-4, 2003 6 Temperature Sensor Locations T SR T F1 T F4 T F5 T F3 T F2 T H2 T H3 T B2 T B1 T B3 T B5 T B4 T E1 T E2 T A3 T A1 T A2 T A4

7. GBT PTCS In Progress Review – December 3-4, 2003 7 Structural Temperature

8. GBT PTCS In Progress Review – December 3-4, 2003 8 Structural Temperature

9. GBT PTCS In Progress Review – December 3-4, 2003 9 Concentrators 8 port terminal servers, up to 115kb/sec. Fiber interconnect to GB net RFI mitigated, ESD protected, thermal tests 5 currently on GBT: 21 ports used, 40 available –1 alidade –1 actuator room –2 vertex –1 receiver room 6 th unit to be installed at actuator room location Units provide (will provide) RS232 for: –Structure and air temperature sensors –Quadrant detector status and control –Alidade inclinometers –Data acquisition units (GDAC) –Etc…

10. GBT PTCS In Progress Review – December 3-4, 2003 10 Air Temperature

11. GBT PTCS In Progress Review – December 3-4, 2003 11 Air Temperature Modified structure temp sensor package –Forced convection cell –1 sec time constant thermistor –Effective 5 sec time constant (swept volume) Applications: –More accurate LRF group index –Correct QD for path bending (gradient normal to ray) –Possible applications in model convective heat transfer to/from structure, improved night-time thermal pointing corrections

12. GBT PTCS In Progress Review – December 3-4, 2003 12 Quadrant Detector Used to measure feed arm motion WRT ~elevation axle, 10 Hz sample rate. Excellent for vibration measurements, wind effects. Need to resolve calibrations for 1 hour absolute accuracy (unmodeled elevation dependence) Prototype unit removed Fall 2002 for improvements Upgrades: –Reduced electronic thermal drifts –Reduced electronics noise –Monitoring and control functions Reinstalled Nov 2003, completed functional tests Engineering interfaces only

13. GBT PTCS In Progress Review – December 3-4, 2003 13 Quadrant Detector

14. GBT PTCS In Progress Review – December 3-4, 2003 14 Quadrant Detector Stability in lab ~ path refractive effects (~  200  m in lab) (Estler, et al., equivalent to 1C/m vertical air temp gradient) Resolution ~ 12  m (GBT equiv) Noise in lab ~100  m position (GBT equiv) Residual nonlinearity in lab cal ~ 1.3 millimeters RMS (GBT equiv) Works in foggy/rainy conditions Noise on GBT < 150  m Dynamic range from 10 to 85 deg elevation SR translation plate scale <4”/mm

15. GBT PTCS In Progress Review – December 3-4, 2003 15 Quadrant Detector Before upgradeNotesCurrent Quantize 12  m 15 bits 12  m Path and Elex Noise <230  m Measured in lab <100  m PSD Nonlinearity 4000  m Measured in lab < 1300  m Electronic Thermal 400  m 10°CNo noticable trend on 2C Tipping calibration, ½ hour ~< ± 2000  m Residual repeatable cross- el error Mechanical/Therm al Drift, Path ± 3500  m Guess. Need to characterize Quantities in GBT configuration with 87M path

16. GBT PTCS In Progress Review – December 3-4, 2003 16 Quadrant Detector

17. GBT PTCS In Progress Review – December 3-4, 2003 17 Quadrant Detector

18. GBT PTCS In Progress Review – December 3-4, 2003 18 Inclinometers Plan to install two-axis inclinometers on each el bearing… –Dynamic range of angle motion is small, can use conventional inclinometers –Tilts of el bearings directly cause pointing errors –Might be able to use alidade as spring-balance (along with observations) to infer primary shift/rotation, FA bending as fcn of wind speed and relative azimuth- generate lift/drag relations semi- empirically –Can also distinguish thermal from other distortions via NCP experiments with range of wind speeds… –Can be used as accelerometers for structure mode shape and frequency analysis –Will use existing concentrators for communications

19. GBT PTCS In Progress Review – December 3-4, 2003 19 Inclinometers ± 1° Gas-damped capacitively coupled pendulum Design goal 0.2 arcsec over one hour –24 Hour limits of error (20C)= 0.6” + 0.07% RO –Uncompensated temp coef = 1.4”/C +0.2% RO –Resolution 0.46” @ 10 Hz, 0.14”@ 1 Hz, 0.07” @ 0.1 Hz Will thermally couple to el bearing casting,  T/  t < 5C over 24 hours, max rate ~< 1C/hour –Factory temp compensation curves will improve this… Natural frequency of inclinometer? –During real-time correction, average out. –During modal testing? Correction for az rate centripetal effects (a=  2 r) ~ 14e-9 G at 15”/sec, => 18” error  a = (da/d  )  = 2  r , so ~0.2” error =>  < 7”/sec

20. GBT PTCS In Progress Review – December 3-4, 2003 20 Star Tracker Need to measure/infer rotations of components on tipping structure –Dynamic range (5 to 95° elevation) prevents fixed conventional inclinometer –Primary rotations wrt el axle –SR rotations wrt el axle Guide cameras have been used to stabilize tracking to ~ 1” Propose use of star tracker to measure structure rotations (differentially) Additional use as optical guide scope

21. GBT PTCS In Progress Review – December 3-4, 2003 21 Star Tracker Acquired SBIG ST7-XE with 100mm F5 optic –CCD Kodak KAF-0401E + TI TC-211 Pixel Array –765 x 510 pixels,6.9 x 4.6 mm –Pitch 9 x 9 microns –Full Well Capacity ~100,000 e- –Dark Current 1e¯/pixel/sec at 0° C –Electromechanical shutter, min exposure 0.1sec IFOV ~20” Have started testing w/ 100mm and 300mm optics Need to prove that sub-pixel interpolation yields ~ 1” tracking Interface to M&C though USB/fiber Small form factor, will be easy to mount and move…

22. GBT PTCS In Progress Review – December 3-4, 2003 22 Accelerometers Silicon Designs 1221 MEMS accelerometers, 2  G/root-Hz. 3-axis design Signal conditioning PCBs completed Will test with existing QD Laser data acquisition system Will be used to –replace existing FA accelerometer –Additional accelerometers for structure modal analysis –Potential for less-accurate inclinometry, but thermal stability is poor.

23. GBT PTCS In Progress Review – December 3-4, 2003 23 Data Acquisition Need for 24-bit, up to 1kHz modules to service –Accelerometers –Replace existing QD VXWorks ADC Identified Analog devices ADUC845 –24 bit, sigma-delta, 10 single-ended or 5 differential –Embedded 8051 core –Have samples in hand –Have prototyping system in hand –Will evaluate (soon?) –Communications via RS232 Remaining technical issue is time-distribution protocol –Will evaluate round-robin latency measurement and 10 -5 sec/sec local clock: Estimation window of 100 secs for 1ms accuracy?

24. GBT PTCS In Progress Review – December 3-4, 2003 24 PTCS Instrumentation Team Jason Ray: Temp sensor lead, GDAQ, electronics JD Nelson: QD lead, air temp sensor lead, electronics Randy McCullough: Electronics design Jeff Cromer: Mechanical Paul Marganian: Software John Shelton: Metrology