The CHARA Array Wiki

The tiptilt server controls the CCD based tiptilt detection system.

Before you start the tiptilt server, you must ensure that the power to the cooling system and the CCD iteslf is on. It is extremely important that the cooler be running before you turn on the CCD and is only turned off if you are sure the CCD is NOT running. You can start the server from the X windows menu or with the command xtiptilt.

Note that there are background counts and read noise to deal with. Whenever you change the frame rate, please ensure that the bias frame is OK. The server will attempt to load an old bias frame that should work, but if things are not working, try making a new bias frame by ensuring that the detector is in the dark and typing “mkbias” into the tiptilt server.

In the tiptilt GUI windows, the white dots represent the starlight while the green dots represent the motion applied to telescope's secondary mirror to keep the starlight centered. When tiptilt is locked the white dots will be brought to the center of the tiptilt window. The green dots should be mostly centered also. W2 and E2 telescopes have a small oscillation that show as back and forth plots of the green dots.

Is the CCD turned on? When the tiptilt server starts up it tries no more than five times to communicate with the CCD. If they all fail, it will give up. If this happens, try cycling the power to the CCD and try again. If this fails, connect to the tiptilt machine and type the command rtccdAPIDemo, which should return with no errors. Try this command a few times, but if it still fails, there is a more serious problem. Turn off the CCD and reboot the tiptilt computer. If it still fails, I am afraid you are in more serious trouble.

Note that it is never a good idea to reboot machines unless you are very very sure it is necessary. The only reason to reboot tiptilt, other than a lock up of some kind, is that the clock interrupt has failed. You can test this by running the command “testclock” on a tiptilt command line. If this says the clock is working do not reboot the machine.

Also note that cycling the power on the CCD can cause harm so be sure you need to do it before trying it. Also, it is important to wait for at least 20 seconds after turning off the power before turning it on again.

Sometimes the telescope server will not show that TT is running. It will show 0Hz for a signal rate for TT. Running TIPTILT COMM will not get it started while other scopes do show it starting. Close and restart any telescope servers that won't connect after two tries of TIPTILT COMM.
Note: There is more info in the software manual on this topic, but I wasn't sure if it was still relevant.

First check whether the clock itself is running and the other machines receive the clock signal. Look at the clock cards at the back of other computers in the rack. The clock cards have three LEDs, one yellow and two greens. If the computer is receiving the clock signal properly all three LEDs should blink, but at a different rate. If the LEDs on all the clock cards are solid then reboot the GPS computer. When the GPS computer is down, it is best to cycle the power also on the box right above the GPS computer.

If the clock appears to be working properly on other machines and not on the tiptilt now it is time to reboot tiptilt.

[There is a bug in the real time part of the CCD code. It is caused by the clock in the tiptilt system either not running at all or having been set to a time very different from the last time the CCD ran.]

For the time being the only solution is to reboot tiptilt, but do so from the lab. Power OFF the CCD, then reboot the tiptilt machine and go into the BIOS. Make sure that interrupt 11 has been set to ISA legacy, save the BIOS and reboot. When the clock card LEDs in the tiptilt machine indicate proper clock signal, turn the CCD back on and start the tiptilt server.

Also, sometimes Serial Port 3 grabs IRQ 11 which stops the clock from running. Since there is no serial port 2 it's safe to disable this in the BIOS. This problem normally comes up when there has been a power outage.

Sometimes syncing the clock can also cause this problem, but that should be fixed soon. If it does, exit the tiptilt server, log in as root, and reload the tiptilt model using the following commands:
/sbin/rmmod tiptilt_rt
/sgin/insmod /usr/local/modules/tiptilt_rt.o

Note that it is never a good idea to reboot machines unless you are very very sure it is necessary. The only reason to reboot tiptilt, other than a lock up of some kind, is that the clock interrupt has failed. You can test this by running the command “testclock” on a tiptilt command line. If this says the clock is working do not reboot the machine.

• Are all the mirror covers open? [Note: W1 M7 cover sometimes needs two clicks to open, despite Scope-monitor indicates open.]
• Has TIPTILT COMM been run from Cosmic Debris?
• Check the ACQ alignment to make sure the tick marks are centered on the laser.
• If there is plenty of starlight getting into tiptilt, then try re-initializing by clicking [TIPTILT COMM] on Cosmic Debris.
• If there are a large number of background counts on TT, then close the M5 cover on the telescope, and click [DBIAS] on the TIPLTILT GUI to clear the background counts. Re-open the M5 cover.
• If a star drifts even with TT locked, there could be a bright sky or light from other beams getting into the affected telescope's beam. This will show in the TT server as much lower counts than the other locked stars, but still high enough to lock TT. Use the laser to find the correct position to lock TT.
• If TT unlocks and the star drifts, the TT servo may not have engaged. This is engaged with the TIPTILT button on the telescope gui. Clicking it may not start the servo the first time. Try it again if the green dots drift on the TT plot windows or if the Servo status in the telescope gui reads None instead of Wobb 1.
• Are the TIPTILT buttons turned on from the POWER GUI?

You will see the oscillation in the green dots of the tiptilt GUI windows. Sometimes you can also see the oscillation in the white starlight dots or as an elongation of the star when looking at the ACQ field while tiptilt is locked. Some scopes have an oscillation that has not yet been diagnosed. W2 is one that usually oscillates. A diagonal motion in the tiptilt box indicates an oscillation in one axis only, while a vertical/horizontal motion indicates an oscillation in both directions. Motion from the upper right to lower left corresponds to elevation axis while motion from the upper left to lower right corresponds to the azimuth axis. (I think you can check direction by typing sin into telescope server to send sine waves to the telescope.) There are a few ways you can try to correct the oscillation manually tuning the servo:

• Type “tune” into the tiptilt server. Select the appropriate telescope. Turning the gain down normally helps.
• Type “tune” into the appropriate telescope server. The default value for the proportional term is -0.5 and differential term is 0.0. Adjust these values between -0.2 to -1.0 for proportional and 0.0 to 0.2 for differential.
• Read section on adjusting the Telescope Tracking Gain using the Dome Server GUI (ref).

• Tiptilt saturates at ~ 200,000 counts. If you are near this limit, you can reduce the TT exposure time to lower the number of counts.
• Set the TT exposure time on Cosmic Debris in the box for “Tiptilt (mS)”. This will set the TT exposure time when slewing to a new target.
• To change the exposure when already at a target, then click the [EXP] button on the TipTilt GUI. This will bring up a dialog box where you can enter the new exposure time in msec. Check to make sure the tiptilt frequency (in Hz) changes on the tiptilt server after changing the exposure time. If the frame rate doesn't change, then set the exposure time back to the old value and try entering the new value again. You might have to do this a few times to actually get the frame rate to change.
• Frame rates for given exposure times:
  • ExpTime = 5 msec, Frame Rate = 157 Hz
  • ExpTime = 2 msec, Frame Rate = 299 Hz
  • ExpTime = 1 msec, Frame Rate = 427 Hz

Try using a slower frame rate or increasing the NSUM. Also ensure that the acquistion is properly aligned with the laser. To change the frame rate, click the [EXP] button on the tiptilt GUI and enter a longer integration time. Remember to change “Tiptilt (mS)” on Cosmic Debris to keep the same exposure time when slewing to the next target.

The bias frame is bad. Get a new one or turn it off.