UKIRT Auto-guider Performance

1. UKIRT Auto-guider Performance

2. UKIRT Servo Block Diagram

3. Auto-guider performance factors • Detector read noise • Detector efficiency • I.e.: (detected photons)/(incident photons) • Tip-Tilt system performance • Filtering and/or estimating • Total Loop Latency • Latency is a big problem since it introduces pure delay into the loop. Reducing the latency by a few ms, and is better than reducing the step response of the tip-tilt system by the same amount.

4. CCD Performance Factors • Readout noise • Similar between two chips given same DCS speed. • Effect flux detection efficiency (CCD Quantum efficiency, Optics efficiency, charge movement overheads). • Proposed CCD is a frame transfer chip so, even though it is larger, charge movement overheads is << total readout time so time lost to charge movement is probably fairly small. • Readout Latency • Large chip so must clock faster

5. Effect of read noise on guider error

6. Comparison of readout noise • Proposed chip (CCD47) and current chip (CCD39) have similar readout amplifiers so the read noise should be similar given similar DCS speed.

7. Readout overheads • Readout overheads are a combination of: • CCD clocking overheads • CCD readout time • CCD data transfer time • CPU processing within array controller

8. CCD Row Readout Timing Serial Clocks Read time per pixel (~25 s) Parallel Clocks

9. CCD Area Readout Timing Parallel clocks CCD read routine exits

10. Summary of CCD readout speeds • Bottom line is • Parallel clocks need to be ~ 100 times faster • Serial clocks probably have to be ~ 10 times faster • CCD is bigger so this has to be proven to work. • Not the same as UltraCam since you don’t have the entire integration period for readout.

11. Total loop latency • Combination of: • CCD overheads • Centroid processing • MCU data transfer time • MCU processing • Mirror movement overheads

12. Centroid processing CCD Read routine exits Centroiding Routine

13. MCU data transfer time MCU write routine Command Bytes Response bytes

14. Mirror Movement MCU Write Called Actual Mirror movement

15. Summarizing... • Loop latencies are a combination of: • CCD integration time • CCD readout overhead • CCD data transfer time • Centroid processing • Mirror Control Unit (MCU) data transfer time • MCU processing • Mirror movement time

16. Overall System Timing

17. Guide and Guide off power Ratio of on/off power Integrated power Performance Charts

18. HA Encoder ripple Dec 2 Hz resonance HA 4 Hz resonance

19. ~ 5 dB increase above 0 dB point at~ 1/10 loop frequency 20 dB/decade rejection below

20. Guide off power dominated by Freq < 1 Hz Guide on power down by ~ 40 (Amp ~ 6)

21. Big jump in power just below 0 dB point

23. Interfaces • EPICS external control I/F has 4 records • Guide on/off • X and Y guide centre (mm in focal plane). • EPICS external status I/F • Guide locked/unlocked. • Current, average and RMS Flux • Current, average and RMS X and Y. • Mount requires X and Y error voltage. • System should automatically acquire within a fairly large area.