Periodic Error Correction

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Periodic Error Correction

Opening the Dome

1. Turn off PEC in The SKy->Telescope->Options->More Settings by unchecking the "Apply PEC correction" box.


Figure 1: PEC window in The Sky. In More Settings window accessible from the Telescope->Options menu.

2. Open PEMPro. In the Setup tab (one of the lower tabs), connect to the scope and the camera. Switch to the Acquire Data tab, and set the exposure such that the bright star you are pointed at is bright but no saturated. Press Start to begin acquisition. Once Image is exposed. check Maxim DL to make sure it found the star, and not just a hot pixel. Acquire data for a large number of periods.

3. When you have enough periods, click Stop. Save the data, and you will be prompted to create a PE curve, which you should do (if for some reason you do not, at a later point you can load the data into the Analyze tab and click Create PEC Curve there.) Do not worry about any syncing messages. A separate Create PE Curve window will open, and a curve will be fitted automatically. Check to see if any frequencies need to be added; you can reference the Frequency Spectrum from the upper right pull down menu. The RMS error in the upper left window may be on interest. This window, along with the analyze data tab in the main window displaying the raw data collected with the correction off on 06/01/2010 are shown in figure 2. Save the curve by clicking the 'Create Paramount PEC curve' button (Note: throughout the procedure, save and open only text files). It will ask you if you want to open the curve data in a text file, which is unnecessary at this point. NOTE: if a this or any point it asks you to invert the curve, be careful. We determined that we do in fact need to invert the curve, but this is confusing (it is hard to tell exactly what each of the graphs represents: error, correction, telescope offset, star offset, etc.) and it is important to keep track of any inversions. You do not have to invert when prompted, since as we will see we can do it in the Refine window.


Figure 2: Raw data with correction off from 06-01-2010 in the analyze tab of the main menu, and the PEC curve creation window fitting a curve to the data.

4. Close the Create PE curve window. In the main PEMpro window, switch to the Refine tab and and load the curve data (not the original data) you just saved by clicking the 'Curve 1' button. Assuming the curve was not earlier inverted, click the Invert button next to where you loaded Curve 1. We determined (06/02/2010) that when we save a file here, and copy the data into the actual Periodic Error Correction window in The Sky (which does the actual correcting and actively follows the phase of the worm gear) there is a phase offset of 600 units (~66 seconds). On top of that, the zero phase point of the worm gear, as read from the The Sky window, corresponds to about the 15s phase point in PEMpro, requiring and additional 139 unit offset (the math: the worm gear cycle is divided into 1250 units, and has a period of 134.63 seconds. This corresponds to 9.3 units/second). Original offset was found by putting a spike in the The Sky correction curve, recording this spike in PEMpro, and then shifting the recorded curve fit and pasting it back into the sky until the spike's matched up. The 15s phase offset we notcied while Acquiring data, by seeing that the The Sky phase mark line passsed its zero point when in the PEMpro window the Current Worm Phase was at 15s. So the total offset we decide don is 740 units. So: using the Shift Curve section at the bottom of the window, shift the curve (make sure the pull down is on the correct curve) to an offset of +740 units (to the right. The maximum shift for each step is 50 units, so this will take some clicks. the recorder of the shift may wrap around to negative values, so you may have to keep track of how far you shifted to the right.) The curve fit from our 06/01/2010 data is shown in the Refine tab in Figure 3, along with its shifted and inverted version. Save teh curve from teh Save section , again selecting the right curve from the pull down. In the save window, select Paramount PEC files (*.txt) from the Save as type pull down.


Figure 2: Curve fit from 06/01/2010 in the refine window. Curve 1 is the original curve, Curve 2 is inverted and shifted +740 units (Note that the offset says -510; this is the wrap around).

Open Notepad, and open the file you just saved. copy the entire thing, and switch back to the The Sky PEC window. Here, click the past button. Your curve should appear in the table window. Click upload to save this curve. In the same window, switch to Powering up the Telescope

5. Remove the cover for the large mirror.

6. Turn ON the power on the black uninterrupted power supply (UPS) at the base of the telescope. The green power light will flash for a few seconds; wait until it glows steady green before proceeding.

7. Turn ON the power for the telescope on the black box in the base. Listen for 2 beeps.

Software Setup and Connections

If not already on, start up the PC that operates the telescope.

Log in to the PC as user "telescope".

13. Open TheSky6.

14. Establish link to telescope by clicking green telescope icon in the top shortcuts menu

15. Allow telescope to home if it wasn't done manually with the joystick. Listen for 3 beeps.

16. Open ddwcp.

17. Wait until program connects with the dome then check "Slave to Telescope." (Don't do this if you don't want the dome to move with the telescope, i.e. if you want to take dome flats.)

18. Open MaximDL Pro 5.

19. Click "Toggle Camera Control" (Ctrl + W) in the top shortcuts menu.

20. Camera 1 should read "Apogee U16M".

21. Select Camera 2 from Setup Camera, or "No Camera" if there isn't one connected.

22. Click "Connect."

23. Directly below "Connect", turn on Coolers. Set cooler set point with the Cooler button specific to each camera.

24. Click "Toggle Observatory Control" (Ctrl + T).

25. In the Setup Tab, check that under Telescope it reads "TheSky-controlled telescope" and that Focuser 1 reads "RCOS TCC".

26. Click "Connect All".

27. The telescope can be controlled under Observatory-Telescope (nudging or setting coordinates), set to specific objects through Observatory-Catalog, or moved through TheSky. Manual control of the telescope is possible with the joystick, but will confuse the dome.

Taking Images in MaxIm DL

1. Wait until sensor temperature reaches set point under Camera Control-Expose.

2. Under Camera Control-Expose, set exposure time and frame type for a single frame. Hit start. Single frames must be manually saved and will be deleted once the next image is taken.

3. Use Autosave to take multiple images. Enter an autosave file name. Use different Slots for images with different settings. Click slot number buttons, and select exposure type and a suffix to distinguish between multiple slots. The Repeat box controls the number of frames taken.

4. The image save path can be found under Options, on the right of the box. Images should be saved to the Z:\ drive, and Auto-Subfolder should be checked to save images by date taken.

5. Click Save and make sure to hit Start under the Expose tab.

6. If two cameras are connected, switch between them by selecting camera 1 or 2 next to the binning information.

Disconnecting and Shutting Down the Telescope


1. Under Observatory-Setup, click Disconnect All.

2. Under Camera Control-Setup, turn coolers OFF and Disconnect.

3. Close Maxim DL.

4. In TheSky, home the telescope under Telescope-Options-Find Home (or double click joystick) and then terminate the link with telescope by clicking the red telescope icon.

5. Make sure the dome is Homed, then exit DDW and hit close when the Pin settings window pops up.