The GenI CCD system uses the Generation I controller developed by San Diego State University (Leach group) and now managed under the company name of Astronomical Research Cameras, Inc. (ARC). The detector is an SI424A scientific grade CCD imager manufactured by Scientific Imaging Technologies, Inc. (SITe).
The SDSU controller is mounted directly on a CCD liquid nitrogen dewar with a serial fiber optic communications link leading from the controller housing to a PCI interface card in a Sun Ultra5 computer. For operation with the GenI controller, the toggle switch on the back panel of the computer should be set to ``GEN I''.
The power supply for the controller is a box mounted on the east side of the 40-in telescope tailpiece, and the box has a switch which must be turned on for the controller to operate. This power supply is plugged into an AC outlet on the tailpiece which receives power only when the CCD switch on the bottom rack panel in the control room is also turned on. The controller operates an electromechanical shutter mounted inside the tailpiece, either under software control or by way of a toggle switch on a black box near the controller power supply.
The Sun Ultra5 control computer is named crux and uses the Sun Solaris2.8 operating system with the CDE window system. The user interface to the CCD controller is the a program called Voodoo developed by SDSU, executed with the command juju, which runs a version of the program which has been modified locally for use with the GenI controller and CCD on the 40-in telescope at Fan Mountain. Images are stored on disk in FITS (*.fits) format and can be transferred from disk to magnetic tape (4mm DAT DDS4). A typical full frame requires 8.6MB of storage. Images can be displayed and analyzed using IRAF tasks. This manual does not explain the details of using IRAF, but IRAF has an extensive built-in help facility, and full documentation is available on the web at the IRAF Project Home Page.
Table 1 summarizes the current configuration of the CCD camera, chip, and dewar
Fig. 1 is a plot of quantum efficiency vs. wavelength for the CCD in the GENI camera.
The CCD is mounted on a cold finger in an evacuated chamber behind a fused silica window in a liquid nitrogen dewar and is cooled by direct contact of the cold finger with liquid nitrogen. The dewar, manufactured for ARC by Infrared Laboratories, Inc., has a capacity of 1 and a hold time of about 36 hours. The dewar is capable of cooling the CCD to a temperature as low as about C, but normally a heating resistor in the dewar is used to regulate the CCD temperature to some optimal working value between and C.
A small electric fan with a rotary on/off switch is mounted on the tailpiece of the 40-in telescope to blow warm air through a tube to a connector near the top of the CCD dewar to produce a continuous flow across the dewar window to prevent fogging. It should normally be left running constantly while the camera is mounted on the telescope.
As of January 2007 the GenI and GenII CCD dewars have new vacuum valves which share a single new gauge which can be connected to either dewar. The vacuum is good for several days without pumping as long as the dewar is not allowed to warm up. The LN2 hold time is about 24 hours.
As a routine, keep filling the dewar every 24 hours or so as long as the camera is in use on the telescope. Leave the camera control software up and running on crux to check the temperature, with temperature regulation set for C. For the GenI dewar be sure the defogging fan on the telescope tailpiece is running to keep frost from forming on the dewar window. This requires the CCD switch on the rack panel in the control room to be ON, to supply power to the camera controller and the defogging fan.
The equipment for reading the vacuum gauge can usually be found in the storeroom on the dome floor level, or in the spectrograph room. It consists of a power supply transformer wired up to a 9-pin D connector and a digital multimeter. The D connector should be plugged into the connector on the vacuum gauge (before plugging in the power supply). When the meter is switched on to the 2VDC scale the voltage should ideally read 1.000V, which translates to roughly 0.01 (0.01mTorr). Every increase of 1V is a factor of 10 in pressure, so 2V would be , 3V is , and 4V is . According to the dewar manual, problems (such as outgassing and difficuly holding LN2) set in when the pressure reaches 5, so for our purposes the vacuum is lost if the reading is over 4V. In practice, the dewar will probably not hold LN2 unless the reading is 2.5V or less.
To pump the dewar, connect the stainless steel hose from the vacuum pump to the dewar flange with a Quick Flange (QF) connector, but leave the dewar valve closed. The seal is made by compression of an O-ring between mating flanges by finger closure of a wingnut on a metal clamp, and the connectors on the dewar and the pump hose should be kept sealed with cover flanges when they are not connected to each other.
Plug in the vacuum pump to a 220 VAC outlet, using the extension cord if necessary. Press the PUMPING button to turn it on. The vacuum pump is a two-stage pump system which includes a controller. The roughing pump operates by itself first. The turbopump should spin up automatically when the roughing pump has lowered the pressure far enough for the turbopump to safely operate. Allow the turbopump to evacuate the hose for at least 30 minutes. After that time, if the turbopump is spinning (check the speed indicator if you can't hear it), the pressure should be low enough to safely open the vacuum valve on the dewar. (If the turbopump is not spinning, do not open the dewar vacuum valve! If you cannot find a leak in the hose or fittings that you can repair, the pump may need maintenance.) If the dewar pressure reading is not less than 3V () after 3 hours, there is probably a leak of some kind which must be fixed before the camera can be used.
When the pressure reading has dropped to 2.5V, close the dewar valve, turn off the vacuum pump, and fill the dewar. Ideally, the dewar will fill completely and the pressure reading will drop to 1.0V (). If the dewar does not fill completely in less than 20 minutes, let it cool down for an hour or more, check to see that the pressure is still low and pump again if necessary, then try filling it again. As long as the dewar is kept filled and the pressure reading remains less than 2.5V the camera should work properly. When turning off the vacuum pump, wait until all rotor motion has stopped completely before unplugging the cord from the power outlet.
crux% mt -f /dev/rmt/0n status Sony 4mm DAT tape drive: sense key(0x6)= Unit Attention residual= 0 retries= 0 file no= 0 block no= 0
If you don't get the above message try power cycling the tape drive. Saving your data to tape is one of the last and most important things you'll do at the end of the night, so it's best to make sure this will go smoothly at the outset.
In addition to the Sun internal 19GB disk, there is also an external 34GB disk attached to crux which appears as a directory called /data. All raw image files should be stored in the subdirectory /data/genicam. In this directory (i.e. after entering cd /data/genicam), create a unique subdirectory for your images.
First start the DS9 image display program by entering ds9 & at the prompt in a terminal window. Then open an xgterm terminal by entering xgterm &. In the xgterm window, from directory /crux/genicam, enter cl to start IRAF. To see a help page for any IRAF task, enter help task at the cl> prompt. One way to run any IRAF task is to enter epar task, edit any parameters that you want to set or change, then type :go and hit RETURN. Tasks can also be run directly from the IRAF command line.
The filter wheels inside the telescope tailpiece above the CCD camera shutter can be operated from the filter control panel on the south face of the tailpiece when the switches are set to LOCAL or from the filter PC computer in the control room when the switches are set to REMOTE. Filter wheel A (the lower one, also known as filter wheel 1) has 4 openings spaced at 90 intervals and holds 6-in square filters. Filter wheel B (the upper one, also known as filter wheel 2) has 6 openings spaced at 60 intervals and holds 4-in square filters.
To load a filter into a filter wheel, first open the filter wheel access door (the rectangular panel above the filter control panel held shut by clamps) so you can see the filter wheels inside the tailpiece. Switch the filter wheel to LOCAL and use the SLEW button on the filter control panel to rotate it. Open the lock at the edge of the filter opening you select, slide the filter into the slot, then close and gently screw down the lock with your fingers. The filter opening in the telescope light path is the one diametrically opposite the one at the access door.
A Filter Control window (Fig. 7) has been added to Voodoo to provide an interface to the filter control system using a serial link between crux and the filter PC.
Assuming filter wheel positions 1,1 to start. If not, set positions on LOCAL ("GO HOME" buttons). Enter "Y" when ready to start.
If necessary, go upstairs to the dome and HOME both filter wheels under LOCAL control. This sets filter positions 1,1 (filter openings numbered ``1'' in the telescope light path). Then switch both wheels back to REMOTE and go back down to the control room.
A Scope Control window (Fig. 8) has been added to Voodoo to allow the user to load an object list and command the telescope to slew to a selected list object using the serial link to the telescope control PC.
An object list must be a simple text file with extension *.lst, with one line per object. The format of each object line is arbitrary and may include any number of fields of any reasonable length, except that each line must include the RA and DEC separated by whitespace (spaces or tabs) only, each in sexagesimal format with no whitespace padding.
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