EMCCD Cold Finger Temperature Control System

The EMCCD is one of the most significant advances in the field of low light level imaging in this century. It has been used in several aspects of astronomical observations and revealed its value. The dark current of CCD is a key factor which affects the imaging quality of astronomical low light level observation. However it will be reduced with the temperature down. To reduce the dark current of EMCCD and improve the imaging quality, it is necessary to cool the CCD deeply and make its working temperature stable.Based on actual needs of an NSFC project (10978013) researched in out laboratory, this thesis studies some techniques and methods of temperature detection and control for an EMCCD cold finger which is cooled with LN2in a Dewar. A temperature control system for the cold finger is built. In the system a platinum resistor Pt1000is used as a temperature sensor, combined with three same5.1k Ω. resistors and a potentiometer to constitute a gauge bridge. An AD7705is used as an analog-to-digital converter. A REF192is designed to provide reference voltage for AD7705. And a microcontroller STC89C52is a master component to acquire the temperature data from the A/D convertor and to control the process of heating the cold finger. Temperature data are sampled and calibrated by the microcontroller, and displayed on an LCD in real-time when the system is working. At the same time, the temperature data can also be transmitted to a host PC for display and storage if necessary. In addition, to make the system more flexible, the baud rate and COM port settings can be configured in the PC, also the user can easy to change the settings according the field condition. In order to test the system, two experiments are conducted, in which two power supplies of20V and18.5V are used in the heating circuit respectively, and two groups of test data are collected, each has more than20000data points. A Matlab tool is used to analyze these temperature data. The statistic results show that the system can effectively control temperature of the EMCCD cold finger in the vicinity of a given low value, i.e.-100℃with the system error in less than0.0068℃and standard error in less than0.025.The research works of this thesis are supported by the Joint Fund of Astronomy of Natural Science Foundation of China (NSFC) and Chinese Academy of Sciences (CAS)(Grant No.10978013).