Connect etalon to controller

  The controller is connected to the etalon by a black bundle of 5 small cables with silver LEMO connectors. There are two etalon controller cables, 6 and 39 feet in length. The choice of which to use depends primarily upon the telescope being used:

• 60-inch
  Experiments some time ago at the 60-inch telescope showed an oscillatory interference in the etalon plate separation when using the long (39-foot) cable, presumably from some portion of the telescope control or drive system. However, more recent measurements have found no such oscillation. It is therefore recommended that you use the long (39-foot) cable, unless you notice oscillations. The major problem with the use of the short (6-foot) cable is that the controller cart must be watched carefully over the course of the night, especially when the telescope is slewed, in order to ensure that the controller is not pulled from the cart, and that the cart is not struck by the moving telescope. In order to simplify operation and reduce such risks, the controller has occasionally been located on the floor under the telescope, rather than on a cart. The controller need only be moved then for telescope pointings at very large zenith angles. If you choose to exercise this option, you should probably not place the controller directly under the CCD dewar, to avoid liquid nitrogen draining directly onto the controller. In the future, these problems may be alleviated by mounting the controller directly on the side of the 60-inch telescope.

• 200-inch
  The choice of etalon cable at the 200-inch telescope is much simpler, motivated primarily by the scientific needs. Although the 6-foot etalon cable will barely reach from the controller to the instrument tube on the axis of the telescope, you may want to use the 39-foot cable if you anticipate rotating the Cassegrain ring to change the orientation of the instrument. Freedom to rotate the Cassegrain ring will give you the option of aligning the optical axis of the Fabry-Perot at a specific orientation. (Note: In practice, if you will be scanning the Fabry-Perot through an entire free spectral range to build up a complete velocity-sampled data cube, such orientation issues are irrelevant.)

Once you have selected an etalon cable, attach it to the connectors on the rear of the CS-100 controller (Figure 9c,d,e,f,i). The etalon cable connectors are fragile, and the components tend to loosen. Therefore, first carefully tighten the pieces of each connector by hand. Then plug the connectors into the controller. The largest two connectors are different on the two ends of the cable, so there is only one possible orientation. Be very careful to not confuse the three smallest connectors. They are labeled with small white bands; match X to X, Y to Y, and Z to Z. Note that the connectors on the controller and etalon are ordered X-Z-Y, not X-Y-Z. After they have been attached, the etalon cables should be arranged so that they are as far as possible from the RS-232 and power cords, in order to minimize electrical interference. You may want to tape the etalon control cable to the cart at the 60-inch telescope, so that the controller is not easily yanked off of the cart. At the 200-inch telescope, any excess cable should be coiled and taped to the bottom of the controller rack, or to the floor of the Cassegrain cage. This is done both to relieve strain on the cable connectors and to make sure nothing moves when the telescope is tipped.

Before attaching the etalon cable to the etalon itself, slip the cable boot box over the other end of the etalon cable. Also verify that the small anodized ring and rubber insert have been placed around the controller cable bundle on the etalon end of the cable. This ring will help keep a light-proof seal around the cables where they enter the boot box. You may need to move the ring from the other cable. Then plug the etalon connectors into the etalon, again being careful to match the labels on the cable connectors to the labels on the etalon connectors.