Peaking Up on the Secondary

This section will help you correctly align the beam of SC with the f/70 secondary. It requires that the dome be open, so wait until late in the afternoon to be sure sunlight will NOT fall on the telescope. Always check with the supervisor on call before opening the dome.

1. If necessary, refer to Sections Detector Electronics Checkout , Grating Scan Mechanism, and Final Cass Cage Checks to power up and initialize the SC-10 PC and electronics.

2. In the Cass cage, connect a scope to the detector output through the Utility Box:
   
   
   1. PClock Signal to Utility PClock Signal
   2. PClock Scope Trigger to Utility PClock Trigger
   3. Utility Scope Signal to Oscilloscope Chan 1
   4. Utility Scope Trigger to Oscilloscope Chan 2
   
   
   
   Settings for the Hitachi V-209 Oscilloscope:
   
   
   1. set the SWP VAR knob to the 2:30 position.
   2. set the LEVEL knob to (+).
   3. set the MODE lever to AUTO.
   4. set the SOURCE lever to CH2.
   5. set the INTEN knob to the 2:30 position.
   6. set the (left/right arrows) POSITION outer knob (black) to the 11:00 position.
   7. set the (left/right arrows) POSITION inner knob (red) to the 10:00 position.
   8. set the TIME/DIV knob to 10 ms. This can be varied later for easier viewing.

      For the CH1 or X side (lower left):

   9. set the input to AC.
   10. set the VAR VOLTS/DIV outer knob (black) to 10 mV.
   11. set the (up/down arrows) POSITION knob to the 1:00 position.
   12. set the MODE knob to CHOP.

       For the CH2 or Y side (lower right):

   13. the CH2 INV button should be out.
   14. set the (up/down arrows) POSITION knob to the 10:30 position.
   15. set the VAR VOLTS/DIV outer knob (black) to 5 mV.
   16. set the input to AC.

   
   

3. In the data room, turn the INTENSIFIER GAIN to zero on the Shepherd Autoguider. If using the Quantex video system, turn the SENSOR GAIN knob CCW until it stops.

4. Move the guider head away from the beam with the command

   M> og r 100 100

   from the SAM terminal.

5. Move the SC-10 flip mirror to the observe position. Check that its cover is off.

6. Check the outside conditions and if clear open the dome.

7. Open the mirror cover to about 180 inches.

8. Open the f/70 chopping secondary lid. Set the chopper to chop to N--S (rotation angle 0).

9. Set the SC control box to Fixed Chop Out, and turn the Gain up all the way. You should now have the chopper going 300'' p-p (7.5V p-p) at 10 Hz triangle wave on the data room scope.

10. From the Cass cage PC, check the following parameters and reset them as necessary:
    1. Instrument mode: Camera ( IM C )
    2. ROM table: 8 (RO 8)
    3. Chop Frequency: 5 Hz (CF 5)
    4. Filter: 8.8 um (MF 30)
    5. Slit: Open (MS 700)
    6. Integration Time: 2 sec (From Integration Parameters [IP] Menu, TI 2)
    7. Gain: 10 (GN 10 from IP)
    8. Bandwidth: 3000 (BW 3000 from IP)

11. Start Continuous Acquistion mode and move the GSM until the detector is evenly illuminated. Make sure the signal is betwen about 2000 and 12,000 mV.

12. Set the two Utility box toggle switches to the up position -- you are now seeing the normal signal from the detector. Look for a strong 5 to 10 V signal. If it seems too weak, change to one of the longer wavelength filters.

13. Log the tangent and west dewar micrometer readings (the east micrometer is almost unreadable).

14. Loosen the top inner bolts on the SC-10 dewar upper micarda blocks, and the bottom bolts on the lower blocks.

15. Loosen the micrometer on the east side by turning it CCW a few turns.

16. Set both toggle switches to the down position to see low-pass filtered signal and the data room triangle-wave trigger.

17. With luck the scope will show a 10 Hz trace. If not move the dewar and the flip mirror tangent arm around until the trace appears. Once you have found the 10 Hz wave, move the dewar in and out in the direction of the chop. As you move the dewar one of two things should happen:

    A. The 10 Hz signal dies away. You are going the wrong way!

    B. The 10 Hz wave gets distorted and eventually you reach a spot where it is replaced by a 20 Hz waveform. If you continue in the same direction past the 20 Hz waveform the 10 Hz signal will return with the opposite phase. Go back to the location which gives the purest 20 Hz signal.

18. Rotate the chop direction by 90 degrees and rotate the flip mirror tangent arm to change the E--W aim at the secondary. The same behavior as in 10 will be observed. Again locate the spot of purest 20 Hz.

19. Go back to N--S and re-adjust to purest 20 Hz.

20. Repeat this E-W and N-S cycle several times. Gradually tighten the micarda block bolts as you near perfect alignment (tightening the bolts may change the alignment slightly). Once you can go from N--S to E--W with the bolts tight and maintain a pure 20 Hz waveform you are lined up on the secondary. This is an extremely sensitive adjustment so it is unlikely you can get a perfect 20 Hz only alignment.

21. Set the East side micrometer tight against the Micarda block, then lock all the micrometers.

22. Exit Continuous Acq Mode and set the filter wheel to Block (10).

23. Turn off the GSM motor power, the detector power, and the stepper motor controller power as necessary.

24. Close the f/70 lid, the 200'' mirror cover, and the dome.

25. Set the SC-10 chop control box gain to about 60, and the mode to Adjustable Chop Out. Be sure the square waves are present on the scope. Do not leave the gain turned all the way up to avoid putting unnecessary stress on the chopping secondary system.

26. Remove the oscilloscope and the four Utility Box BNC cables installed for peak-up from the Cass. Cage.

27. During the night setup with camera mode on a bright calibrator. Drive the telescope out of focus a millimeter or two. You should see an out of focus ``donut.'' If not recheck the secondary alignment. Try going both inside and outside focus. Once properly aligned SC-10 should stay in alignment for the remainder of the run. However, it's a good idea to check it each night just to be sure.