Telescope drive

Similar to last summer we had some errors in the azimuth tracking. It is thought that the temperature difference between the cooling water of the cooling system, which goes through the center of the telescope fork, and the ambient temperature has some detrimental effect on the azimuth encoder system. Increasing the temperature of the cooling water of the cooling system remedies this. However, this has to be done manually and typically is only done after we detect some problems. To avoid this we want to make a system that sets the temperature of the cooling water at a value (a fixed offset) depending on the ambient temperature.

There were some problems with the altitude tracking where we had to replace some motor brushes, while we also have some issue with the azimuth tracking where as a precaution the brushes were replaced in one of the motors. The brushes have recently been checked and found to still be OK. Because of the changes we did not have any new brushes left and twenty new brushes were purchased. However, many of the brushes that we have changed in the past show little or no ware and can in principle be used.

We were informed by the manufactures of the altitude and azimuth motor amplifiers that they will be discontinued. We already have two spare units, but it was considered prudent to purchase two more amplifiers. These devices have been configured and are ready for use.

Some detailed monitoring and analysis has been made of stretches of tracking data to analysis the periodic errors in the tracking. The variations seem to be stable. When more data has been processed it should be possible to provide a simple array with a set of correction parameters as a function of position with sufficient resolution to correct for the variations while minimising the CPU load on the TCS.