Santa Barbara Instrument Group CCD Camera Operating Manual

Contents

Santa Barbara Instrument Group CCD Camera Operating Manual Manual pdf 12 page image

Section 2 - Introduction to CCD CamerasPage 8The CCD is cooled with a solid-state a thermoelectric (TE) cooler. The TE cooler pumps heatout of the CCD and dissipates it into a heat sink which forms part of the optical head'smechanical housing. In the ST-7E and ST-8E cameras this waste heat is dumped into the airusing passive radiators and a small fan, making the design and operation of the heads simpleand not inconvenienced by requirements for liquid recirculation cooling. The ST-9E and ST-10E include SBIG's secondary TE/Liquid cooling booster.Since the CCD is cooled below 0°C, some provision must be made to prevent frost fromforming on the CCD. The ST-7E, ST-8E, ST-9E, ST-10E and ST-1001E have the CCD/TE Coolermounted in a windowed hermetic chamber sealed with an O-Ring. The hermetic chamber doesnot need to be evacuated, another "ease of use" feature we employ in the design of ourcameras. Using a rechargeable desiccant in the chamber keeps the humidity low, forcing thedew point below the cold stage temperature.Other elements in the self contained ST-7E, ST-8E, ST-9E, ST-10E and ST-1001E includethe preamplifier and an electromechanical shutter. The shutter makes taking dark frames asimple matter of pushing a button on the computer and provides streak-free readout. Timingof exposures in ST-7E, ST-8E, ST-9E, ST-10E and ST-1001E cameras is controlled by this shutter.The Clock Drivers and Analog to Digital Converter interface to the CCD. The ClockDrivers convert the logic-level signals from the microcontroller to the voltage levels andsequences required by the CCD. Clocking the CCD transfers charge in the array and is used toclear the array or read it out. The Analog to Digital Converter (A/D) digitizes the data in theCCD for storage in the Host Computer.The microcontroller is used to regulate the CCD's temperature by varying the drive tothe TE cooler. The external Power Supply provides +5V and ±12V to the cameras. Finally, thecameras contain a TTL level telescope interface port to control the telescope and the optionalCFW-6A motorized color filter wheel.Although not part of the CCD Camera itself, the Host Computer and Software are anintegral part of the system. SBIG provides software for the ST-7E, ST-8E, ST-9E, ST-10E and ST-1001E cameras for the IBM PC and Compatible computers (all cameras, DOS and Windows)and the ST-7E/8E are also supported by the Macintosh. The software allows image acquisition,image processing, and auto guiding with ease of use and professional quality. Many man-yearsand much customer feedback have gone into the SBIG software and it is unmatched in itscapabilities.2.4. CCD Special RequirementsThis section describes the unique features of CCD cameras and the special requirements thatCCD systems impose.2.4.1. CoolingRandom readout noise and noise due to dark current combine to place a lower limit onthe ability of the CCD to detect faint light sources. SBIG has optimized the ST-7E, ST-8E, ST-9E, ST-10E and ST-1001E to achieve readout noises below 20 electrons rms for two reads (light -dark). This will not limit most users. The noise due to the dark current is equal to the squareroot of the number of electrons accumulated during the integration time. For these cameras,the dark current is not significant until it accumulates to more than 280 electrons. Dark currentis thermally generated in the device itself, and can be reduced by cooling. All CCDs have dark