Thermal issues

Revised A.R. Walker July 14 2020

  •  Where to find useful logs?.Check in Tololo Environmental Web Page : Last seeing data ( Data Archive )  and Last weather data ( Weather Data Archive )
  • Memo describing the operation instructions at the 4m for image quality program (includes seeing measurements, thermal environment,...)
  • Is the mirror going to be wet? (check the risk of condensation)
  • Primary mirror cooling -NOT USED FROM 2019, INFORMATION FOR REFERENCE - (active only during day-time, at night time we simply reverse the system and extract air to prevent hot air bubles to form above the mirror). The 15 tons of Cervit have a large thermal inertia, but we can typically cool its surface by 0.75deg/hour by blowing 6deg cooler air around it. The control algorithm is rather simple as it is based on the fact that usually the dome temperature will reflect well the variations of the outside temperature, thus by keeping the mirror 2deg colder than the low dome during the day, we start the next night in optimum condition. The typical night time pattern is for the outside temperature to drop slowly and cross the mirror temperature at about 2/3 of the night to finish some 0.5deg colder at morning twilight. This graph shows statistics of the difference between mirror and low dome temperatures.
  • Temperature sensors (sensor list and some debugging hints for Temp4m)
  • Last improvements in the 4m dome for optimizing thermal environment:
    • The old console room walls were removed to open the direct pass of air flow blowing from the lateral doors into the dome (whenever the dome azimut is such that they are behind the console). These walls were 10m long. (March 2000)
    • The old mirror cover made of 24 petals opening up and forming a cylinder about 1.6m high (thus putting the mirror surface at the bottom of a 3.5m 'hole') was replaced by a 2-petal design (see picture 1 and picture 2) opening up on the west and east side (just in front of the top ends of the horseshoe). This leaves free path to the air flow along the north-south direction (at zenith) and provides better (closer) ventilation to the primary mirror. See picture. (August 2000)
    • The dome is covered with aluminium sticky foil (September-November 2000).