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April 12, 2012

The FireNEX-800™ in a Sun Tracking System

Some pictures of the almost finished solar guider for the McMath solar telescope located on Kitt Peak, about 50 miles west of Tucson.

The guider stage consists of a platform cut from aluminum skinned, honeycomb. Two stepper motor controlled stages move orthogonally and carry the four cameras that sample the edge of the solar image at four locations located 90 degees apart around the parameter of the solar image.

There are four Point Grey firewire cameras connected serially and buss powered. The Firewire 800 output , 60 frames/sec, is connected through Newnex FireWire over optical repeaters (FireNEX-800™). The fiber travels through a cable wrap, under the floor, to a rack mounted control computer that displays the four images from the cameras and determines the solar images position on the cameras and provides feedback to the stepper controllers.

After some initial trouble shooting, and some help from Newnex, the system has run continually for weeks with no dropped frames.

Background on the application:

The Grasshopper cameras are taking several images of the limb of an image of the Sun ( one camera in each quadrant) projected onto a table. The image is about 0.8 m in diameter. The limb is the edge of the Sun. By taking an image of the limb in each quadrant it can determine how the image is moving and generate an error signal that is fed back to the telescope and allows it to move the image and correct the positional error. There are 4 Grasshopper cameras that are daisy chained together that compose the optical system. Since the system is imaging four areas on the Sun, it wants to grab the four locations at the same time. This is why the cameras are daisy chained, to take advantage of the automatic syncing of the cameras.

The FireNEX800™ correctly allowed the syncing of the cameras and the optical fiber was useful for avoiding noise generated by several stepper motors in the setup.

Information contributed by Dave Jaksha at the National Solar Observatory.