Decreasing the humidity inside the telescope tube in order to prevent moisture condensation.
A silica gel package of high hygroscopic property is placed inside a steel container mounted on the telescope tube. The container is connected to the telescope tube via pipes and air valves. A low velocity air current in the telescope tube and the pipes is created by opening the air valves and turning on the fans, therefore the moisture inside the tube can be absorbed by the silica gel. The air valves, fans and the heating (if necessary) are controlled by the electronics based on the measurements of the temperature and humidity sensors placed inside the tube. The heating is turned on below 0 C, its heating point is 35 C. The regeneration and drying of the silica gel is not automatic. After opening the steel container, the device can be switched to drying mode. The air valves close, if the telescope tube is horizontal and pointing towards south, and the silica gel is heated to the temperature necessary for regeneration (approximately 120 C). The regeneration process takes a few hours. After that, the device can be used again. Both the air drying and regeneration modes can only be used while the telescope is powered down.
The device is ready for operation if the following conditions are met: the device is turned on, the switch labeled DEHUMI/DRYING is in position DEHUMI, the lid of the steel container is closed and the telescope is powered down. The small LCD on the container indicates the temperature and relative humidity value inside the telescope tube. In case the relative humidity exceeds a preset value, the device starts to operate. This is indicated by the green led on the device. If the humidity decreases below the preset values, the device goes into stand-by mode.
The status of the moisture absorbing silica gel has to be checked in every few weeks. If it turns green, it indicates that the gel is saturated and cannot absorbe more moisture. In this case, regeneration is necessary, which is done by heating the silica gel to approximately 120 C. This can be done by the following steps:
The silica gel should be replaced in every 1-2 years. For this, the device should be powered down by pulling it its plug out from the container. Two of the four stop-screws has to be loosened and the other two taken out. This way, the silica gel can be pulled out from the container. The rubber parts of the device should be treated with RUBOSIL 0-500 Metil silica oil in every year.