There are times when the azimuth coudé alignment needs to be checked and adjusted to establish better alignment of light to or from a telescope. One symptom of this misalignment is that the tiptilt lock position keeps moving in the ACQ window as the telescope moves with targets across the sky. If you do not have the chance due to time or technical problem to complete the necessary adjustment, please note during observing if a telescope needs the coudé alignment checked, and include this in the technical report.
To check the coudé alignment, the lab first needs to have the full alignment done for any scope being tested. If you do an alignment during or after observing, make sure the carts are at the back of the rails and that the M10 alignment is good. Also make sure the telescope is being tested on the beam for which it was aligned. When this is done, open the laser and visible shutters, open the M3, M5, and M7 covers, and put in the corner cube for each telescope you will test. Turn on the TV and put it in ACQ mode. Two laser spots should be visible in the ACQ window. Use the Laser Filter to select an appropriate brightness for the spots. Using the Adjust function of the tick marks on the telescope gui, move the marks to the location of the central spot. Use the Zoom function to see the cross hairs over the laser spot you are checking. Set step size to 1 to put the crosshair on the spot as precisely as possible. Write down the position of the crosshairs as displayed in the telescope server.
Turn on the power to the drives and enable the scopes. Rotate the telescope 180º in increasing azimuth by entering a new SET position (STOW+180º) in the AUTO tab on the Dome gui. Watch the spot position as the scope turns 180º. When it reaches the new position, move the crosshairs to the new position of the laser spot. Note its position in the telescope server as before. Ideally, the spot moves very little or in a circular arc. Sometimes it can move in a noncircular arc, an elliptical arc or even a partial figure 8.
Calculate the center position of the two points and move the crosshairs to this central position. This will be the new position of the laser spot when the coudé alignment is done. Open an engineering hut gui by typing hutgtk -E S1 & in a terminal window. Substitute each telescope in the example given for the other scopes. In the AOB ENG tab, find the M7_1 and M7_2 entries in the pull down menu next to the [ 100 ] displayed in the white field at the lower left. Select each one and hit the GET button to display the position of the M7 mirror actuators. The values will be centered around 3000000, but can range from 1000000 to 5000000. Write down the value of each actuator as a reference before making any adjustments. If the hut gui cannot connect to the hut server, error messages will be displayed. Try to restart the hut server to reestablish the connection. If that does not work, mention this in a tech report.
Using the yellow M7 buttons, move the mirror UP, DOWN, LEFT or RIGHT to move the spot to the center of the crosshairs. The default step size is 100000. This may show very small motions and a step size of 200000 can be used if it is moving too slowly. Note that if a large correction is required, for example, the laser spot has moved more than 20-25 pixels between the two positions, a manual adjustment may be needed to center it. The actuators may reach a limit if they are moved too far when trying to make a large correction. Be more cautious if the starting value is already close to one of the limits. The limits are 0 on one end and around 6000000 on the other limit. Once the laser spot has reached the crosshair, write down the new actuator positions for M7_1 and M7_2.
You may now watch the spot as the telescope is stowed to see if it holds in the new position. Ideally, it will not move, but this will not always be the case. Make sure to close all mirror covers and shutters as needed. Power off each scope when it has stowed. Report your findings and the positions of all spots and actuators to Judit via email when done.
Version 3, 1-5-18
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