Configure the automatic stowing and unstowing of the telescope due to wind.

Optional Arguments:

Double stow_speed

The wind speed above which the telescope should automatically be stowed.

Double stow_gust

The gust wind speed above which the telescope should automatically be stowed.

Double unstow_speed

The wind speed below which it is okay to automatically unstow the telescope and resume observations.

Double unstow_gust

The gust wind speed below which it is okay to automatically unstow the telescope and resume observations.

Double hold_time

The minimum time that the telescope will be kept stowed after a wind instigated stow (hours).

Double hold_inc

After keeping the telescope stowed for the time specified by the hold_time argument, check whether the wind speed has reduced sufficiently to resume observing, and if not, extend the holding time by this interval (hours) before checking again.

Double update_timeout

Initiate a wind-stow if no usable weather update is received within this time, expressed in hours.

Double change_timeout

Initiate a wind-stow if neither the wind-speed nor the gust speed readouts change within this period, expressed in hours.

Boolean enable

This parameter determines whether or not the control system should stow the telescope during excessive winds or weather-station outages. If specified as false, then any existing wind-stow will be cancelled, and the control system will not subsequently stow the telescope if wind-speeds become excessive or the weather station stops responding.

Example:

The following example tells the control system that if the wind exceeds either an average wind-speed of 20 mph or a gust wind-speed of 25 mph, that it should automatically stow the telescope. It then says that after keeping the telescope stowed for at least 1 hour, if the average wind-speed has reduced below 18 mph and the gust wind-speed has gone below 22 mph, then it should unstow the telescope and resume observations. If the wind speed is still too high, then it should check again every 30 minutes. Finally, if the weather thread is unable to supply usable weather information from the weather station for more than 10 minutes, then a wind-stow should be initiated.

 wind stow_speed=20, stow_gust=25, unstow_speed=18, unstow_gust=22,
          hold_time=1:0:0, hold_inc=0:30:0, update_timeout=0:10:0,
          change_timeout=0:30:0, enable=true

Context:

To protect the telescope from high winds, it automatically stows whenever the average or gust wind speed exceeds thresholds that are specified by this command. For convenience it also un-stows the telescope and resumes observations if the wind speed later returns to specified lower speeds than it was stowed at. To prevent the telescope from stowing and unstowing very frequently, and wearing out the telescope drives, a minimum stow time is also specified with this command.

The un-stow speeds must be less than the stow speeds. If this isn't so, then the unstow speeds will be automatically decreased to 1mph less than the corresponding stow speeds.

Note that the wind-speed that is compared against stow_speed and unstow_speed, is the wind-speed averaged over 2 minutes. The wind-speed that is compared against stow_gust and unstow_gust, is the maximum wind-speed that was seen within the last hour.

If the weather station stops delivering usable information, then the control system has no way of knowing when dangerously high winds develop. So if no valid information is received from the weather station for more than the number of hours specified by the update_timeout argument, it initiates a wind-stow.

Similarly, a malfunction of the weather station wind-speed sensor can cause the wind-speed readouts to freeze, without any other indication that anything has gone wrong. So to handle this case, if neither the wind-speed nor the gust speed change for more than the number of hours specified by the change_timeout argument, then a wind-stow is initiated. Beware that especially during calm weather, it is possible for the true wind-speed to not change for long periods, within the coarse 1 mph resolution of the weather station. So the change timeout should generally be a longer duration than the update timeout, in order to avoid false positives that would needlessly stow the telescope during calm conditions. On the other hand, wind speeds can rise quite quickly to dangerous levels. So a shorter timeout will reduce the probability of the telescope operating during excessive winds when the sensor freezes. In practice, a change timeout of half an hour seems to be a good compromise with the current weather station. During the first 4 months of operation with the new control system and the current weather station, the wind speed reading legitimately stayed constant for more that half an hour only two times, whereas over the same period there were 6 times when it stayed constant for 25 minutes or more, and 24 times when it stayed constant for 20 minutes or more.

The wind-stow facility should usually be kept enabled, to ensure the safety of the telescope. However, just in case the weather station has to be taken off line for an extended period, the wind-stow facility can be disabled by setting the enable parameter to false. This will prevent the control system from holding the telescope wind-stowed during the outage, although during that time, it should only be operated while somebody is there to keep an eye on the weather.