Nordic Optical Telescope

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Mirror cleaning

The last mirror cleaning (in May) was less than satisfactory. It is clear that a wet wash is required ASAP and realuminisation will be necessary next summer.

Mirror Damping

A swedish undergraduate student, Anders Magnussen, joined NOT for two months to work on this project under Graham Cox's supervision. Graham reports:

The object of the project was to re-design the active primary mirror damping system for the NOT, in order to remove the significant oscillations measured at 12 and 14.5Hz. The signals from the load cells of the primary mirror are filtered, amplified, inverted and fed back using loudspeaker voice coils, mounted on the edge of the mirror.

An old mirror damping system using analogue filtering exists, but has not been operational on the telescope since the active optics upgrade. The new system uses a digital filter and a prototype was implemented on a Texas Instruments development board, the TMS320VC5402 EVM. The digital filter of type IIR band pass only passes the desired frequencies of interest and attenuates the unwanted noise.

Tests have demonstrated that this new filter works satisfactory though further work is required before the active damping system can be re-installed on the telescope.


Ingvar Svardh reports:

The new TCS will function as a server that performs all kinds of operations with the telescope. The goal for the new TCS (written in c, the old one in Pascal) is that the source code shall be very easy to understand for any professional real time programmer. I estimate a few minutes for most of the solutions, compared to many hours for the old system. Only simple solutions are used, all well explained. The size is expected to be a third of the old one with the same functionality. The switch from the old to the new system is expected to take place during a few hours in day time by moving about 25 connectors to a new mating contact. All functions will have been fully tested before this. A few hours night time adjustments will be needed for final servo and autoguiding adjustments. The I/O is arranged so that only one program controls an I/O section which speeds up and simplifies things. It is my intention that the new TCS should be as reliable as the old one immediately after commissioning.

32% done, finishing date stable at July 2003.

Programs done:

Master, initializes all data used in the system.
CPU load calculation.
Weather. Fully verified with the real weather station.
Building power.
Building servo.
Rotator power.
Rotator servo.
Support slow I/O (controls slow hardware).
AltAz power.
AltAz servo.
The calculation of the position using the coarse Stegmann and fine Inductosyn is done with a much better method, the old one was extremely difficult to understand.
Reference position calculation with a few statements instead of 20 A4 pages as in the old system. It should be noted that the old system was designed for unreliable communication between master and subunits.
Deceleration in advance to avoid overshoots has been made with a very elegant formula:
vRamp = c * abs(PositionError) where c = 2a/vMax
instead of a separate program as before.

GPS time client.

All programs have been tested in realistic simulation.

All server functions defined, amounted to 115. The definition file will be used by the GUI developers.

Small standalone GPS receiver installed for tests, had some faults but looks promising as a general time server placed in the service building.

Good progress has been reported by Carlos for the hardware part so we hope that tests on the telescope systems can be performed soon.


Project on hold.

Building crashes

Occasional unexplained building crashes (without telescope/building misalignment) suggest that all was still not well at the beginning of the reporting period. Eventually, they were found not to be building crashes at all, but arose from anomolous responses from the safety system, causing immediate power downs that appear like building crashes. The problem was traced and repaired. There have been no building crashes since.

next up previous contents
Next: Instruments Up: AiC Report to NOT Previous: Down Time

Tim Abbott, AiC

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