Install shutter control box (P-200 only)

 If the Fabry-Perot is being used on the 200-inch telescope with the F/9 guider base, the internal shutter should have already been installed in the instrument. Its control cable should be protruding from the small round hole in the side of the instrument near the camera lens plate. The shutter is controlled by a small silver electronics box, which is in turn operated by a standard shutter control line.

In principle, the silver shutter control box can be mounted anywhere in the Cassegrain cage. Given the light weight of the box, however, the easiest approach is to simply fasten it to the side of the instrument tube with tape (Figure 13). Fasten the box in a place where the shutter cable can be easily connected, using a liberal amount of glass tape. Make sure that the tape does not obstruct the movement of the camera focus arm plate. Connect the two-prong shutter cable to the appropriate socket on the shutter box. Use black tape to cover the hole in the instrument tube around the shutter control cable, to prevent light leaks.

  

Figure 13: The internal shutter control box taped to the side of the Fabry-Perot instrument tube.

The BNC connector on the side of the shutter box should be connected to a standard 200-inch shutter line, using a BNC extension cord from the astronomers' workshop. The Palomar staff can show you how this is done. Then be sure that the staff place the shutter polarity switch in the ``up'' position (i.e., opposite to that used for most other instruments), to ensure that the shutter opens and closes with the corresponding commands.

Finally, the shutter control box must be connected to a power outlet in the Cassegrain cage. However, due to a recent shutter failure and subsequent replacement, the standard line voltage is no longer sufficient to open the shutter. Therefore, power to the shutter control box should be filtered through a variable power supply from the electronics lab. Plug the shutter control box into the variable power supply; then plug the power supply into a plug bar in the Cassegrain cage. The scale on the variable power supply can be slightly confusing: The dot on the scale indicates the setting at which the power supply output matches the input line voltage. In order to actually fire the shutter, the dial on the power supply should be raised to a value of approximately 95. Do not set the voltage higher than this unless it is absolutely necessary to fire the shutter, as it may put undue stress on the shutter control box electronics. Fasten the variable power supply to the floor of the Cassegrain cage with a large amount of glass tape. Be sure that the power supply is firmly affixed to the cage, as it is quite heavy and capable of some damage should it come lose during the night.