The main vertical spectrograph at the McMath-Pierce solar telescope has been operated manually since its construction, making it necessary to look up the wavelength and order that the user wished to observe in tables, to find the corresponding value in encoder units. The grating turret could be moved by means of a DC slue motor to the general region of interest. For final positioning, it was necessary to move the grating by hand, with a crank, to position the spectral feature accurately. With a resolution of up to 500K, this could be a time-consuming task.
As a final phase of the spectrograph upgrade, the movement of the grating has now been placed under control of a DC slue motor for large movements, and a stepper for fine control. Both motors are controlled by a VME-based computer running VXworks. In addition, a new type of hand paddle has been developed that will eventually replace all of the old "dumb" hand paddles currently used at the McMath-Pierce complex. This new hand paddle features a backlit ASCII display for informational feedback to the user. Also, each button on the hand paddle employs a backlit 36 x 24 pixel display. The button display can be dynamically changed as its function changes. The backlit color can also be changed from continuous or flashed red, yellow, and green.
The hand paddle allows both manual and automatic movement of the grating. In manual mode, the user can select either slue or stepper motor control, as well as three pre-defined speeds. As the grating is moved, the ASCII display indicates the current grating angle. The wavelength at the exit port is also displayed, based on the grating order entered into the hand paddle, the angle, and the grating (visible or IR) in use. In the automatic mode, the user enters the desired wavelength, order, or grating angle, and presses "go." The software will then position the grating using the appropriate combination of slue and stepper motor motions. The spectral line will appear at the photoelectric port. For quick optical setups, there is also a zero order function. In both the auto and manual mode, the user may also enter an offset angle to shift the desired spectral feature to the photographic exit port.
The first phase of the spectrograph upgrade is primarily designed to allow the user to control the grating position from the hand paddle. The second phase will allow users alternate methods of control. A standard command language will allow users to control the grating over a RS232 serial port, an ethernet port, or remotely via a web GUI interface. The serial/ethernet access was implemented to allow users who bring their own computers and instrumentation to control the spectrograph directly. The GUI will allow users in the main observation room to run the grating without the hand paddle, as well as providing support personnel with a means to remotely troubleshoot the spectrograph operation. Phase 2 should be completed by the end of the calendar year.
Lonnie Cole, Dave Jaksha, Carole Leiker,
Jan Schwitters, Ed Stover