Guiding system

TV FOCUS AUTOMATIC OPTIMIZATION

A new feature for getting the TV focus adjusted either on request or after a preset is at the time of writing being tested on sky. After optimizing the TV focus servo to the capacity limit of the hardware the adjusting takes some 10 to 15 seconds. Seems to work as intended but will need some more tests and then adjustment of the involved parameters.

SCALINGS

To be sure all scales involved in object positioning were ok some tests were performed. The scales of the guide probe and autoguider were verified to be correct. Check was made of guide TV focus over the full ALFOSC field, no change in focus was found. The TV optics gives no change in FWHM of the guide star when moving the star along the TV optics radius and the alignment of the TV is within 0.1% wrt the directions of RA and DEC.

As reported earlier, the TCS occasionally looses count of the number of turns the guide-probe motors make and to minimise this problem the speed of the probe is limited. To not overload the TCS with this task, originally a hardware solution had been designed to do the turn counting. In the end it was decided to replace the encoders themselves with encoders that have the same mechanical properties as the existing ones, but that incorporate the multi-turn counting facility. These new encoders have arrived, and were successfully tested with the TCS development system. The new version of the adapter program is ready to be taken into use and will be executing at 10 Hz instead as of now with 100 Hz since guide probe turn counting will not be an issue. The speed of the guide probe can be maximised and several percent CPU load will be saved. The system will be installed as soon as possible. Some parameters will have to be adjusted to compensate for the lower frequency. With the new system, the speed of movement of the guide probe can be significantly increased.